Rapport 2013-009
HighT – Development of High Technology Castings
Swerea SWECAST AB Box 2033, 550 02 Jönköping Telefon 036 - 30 12 00 Telefax 036 - 16 68 66 swecast@swerea.se http://www.swereaswecast.se
I projektet har tre viktiga områden belysts; Högpresterande segjärn, lättviktskomponenter samt sammangjutna material.
Arbetet med högpresterande segjärn har resulterat i kunskap som möjliggör produktion av både tunn- och tjockväggigt lösningshärdat segjärnsgjutgods samt minskade egenskapsvariationer genom förbättrade sandformningsprocesser. Inom den del av projektet som behandlar lättviktskomponenter har man kartlagt mikrostrukturens och porhaltens koppling till hållfasthet och även beskrivit en metodik för restspänningsmodelleringar av aluminumgjutgods.
Med hjälp av simuleringar och gjutförsök har arbetet som behandlar nya teknologier tagit fram en metod för sammangjutning av olika material. Man har genom detta arbete tagit fram produkter med bättre nötningsegenskaper än vad som återfinns i dagens slitdelar.
Summary
Enhanced production and post production techniques and materials optimisation, performed in the project “HighT – Development of High-Technology Castings, have enabled production of cast components with improved mechanical and wear properties as well as lower weight and less variation in properties.
Within the project three important fields have been studied; High-Strength Cast Iron, Lightweight Components and Combining materials though casting.
The results from the work with High-Strength Cast Iron have enabled production of solution hardened castings with both thin and tick wall sections. By enhanced production of molds and cores, the spread in component properties has also been reduced.
Within the work regarding Lightweigt Components, the microstucure and pore content levels have been related to mechanical strength. Also, methods for modelling of residual stresses have been proposed.
By combining casting simulation and casting trials, the work related to New Technologies has resulted in an technoque for combining different materials thorugh casting. With this technique, it is possible to produce components with better wear properties than found in today’s wear parts.
4 GENOMFÖRANDE ... 2
4.1 BESKRIVNING AV ARBETSPAKETEN ... 2
4.1.1 WP1 – Samverkan, resultatspridning och projektledning ... 2
4.1.2 WP2 – Högpresterande segjärnskomponenter ... 3 4.1.3 WP3 – Lättviktskonstruktioner ... 3 4.1.4 WP4 – Nya teknologier ... 3 4.2 PROJEKTORGANISATION ... 3 4.3 PROJEKTFINANSIERING ... 5 5 RESULTAT ... 5
5.1 WP1–SAMVERKAN, RESULTATSPRIDNING OCH PROJEKTLEDNING ... 5
5.2 WP2–HÖGPRESTERANDE SEGJÄRNSKOMPONENTER ... 6 5.3 WP3–LÄTTVIKTSKONSTRUKTIONER ... 6 5.4 WP4–NYA TEKNOLOGIER ... 7 6 SLUTSATSER ... 8 6.1 UPPNÅDDA PROJEKTMÅL ... 8 6.2 INDUSTRIEFFEKTER ... 8 7 FORTSATT ARBETE ... 9
Bilageförteckning
Antal sidor Bilaga 1 WP2 – High-Strength Cast Iron 7 + bilagor Bilaga 2 WP3 – Light Weight Components 21 + bilagorProduktionen av gjutna komponenter och produkter är en stor och viktig del av svensk industri. Flera av Sveriges största exportbolag, såsom AB Volvo, Scania CV, Atlas Copco m.fl., är beroende av gjutna komponenter i sina produkter. Detta har inneburit att en stor gjuterinäring med uppemot 200 komponentgjuterier har vuxit fram i landet. På senare år har svensk gjuterinäring upplevt en allt större internationell konkurens och har genom Svenska Gjuteriföreningen identifierat att utvecklingen av gjutna komponenter genom forskning är ett viktigt medel för att möta konkurrensen från låglöneländer. Genom att förfina gjut- och efterbehandlingsprocesser samt genom att optimera material så var målsättningen med projektet att producera gjutna komponenter med högre prestanda och lägre vikt.
I HighT har tre viktiga områden belysts; Högpresterande segjärn, lättvikts-komponenter samt sammangjutna material. Dessa tre områden har behandlats i tre separata arbetspaket.
3 Syfte och mål
Huvudsyftet med projektet var att stärka svensk gjuteriindustri och svenska företag som är beroende av gjutna komponenter. Swerea SWECAST har tillsammans med projektets deltagande företag identifierat flera viktiga kunskapsområden och processer som projektet avsåg att stärka och förbättra. Genom ökad förståelse för fundamentala processer vid gjutning och efterberarbetning syftade projektet att öka prestandan för gjutna komponenter inom en rad olika applikationer. Arbetet har haft följande fokusområden:
1. Bättre och jämnare egenskaper för segjärnskomponenter genom bättre processkontroll och effektiva härdningsprocesser.
2. Effektivare produktion av aluminiumkomponenter med bättre och jämnare egenskaper för gjutna aluminiumdetaljer.
3. Robusta metoder för sammangjutning av metaller för bättre nötningsegenskaper hos slitdelar.
Genom effektivare produktion och ökad processkontroll och därigenom bättre komponentprestanda syftade projektet också att förbättra de ekonomiska förutsättningarna för gjutgodsproduktion i Sverige samt en mer hållbar produktion genom minskat resursutnyttjande både i produktionsfasen och i användningsfasen genom minskad vikt och längre komponentlivslängd.
Ytterligare ett syfte med projektet var att stärka Casting Innovation Centre i Jönköping genom samverkan med Tekniska Högskolan och Svenska Gjuteri-föreningen.
De tre fokusområdena utgjorde fokus för de tre arbetspaketen i projektet. Detaljerade målbeskrivningar för dessa återfinns i respektive rapport (bilagorna 1 – 3).
3.1 Vetenskapliga utmaningar
Arbetet i samtliga arbetspaket har förlitat sig mycket på simuleringar, vilket ställer stora krav på de använda programvarornas predikteringsförmåga. Oavsett simuleringsprogram kan en simulering aldrig prediktera verkligheten om de bakomliggande fysikaliska parmetrarna är felaktiga. I en del av projektet simulerades tunnväggigt gjutgods av lösningshärdat segjärn med hög kiselhalt, vilket utgjorde en stor utmaning i projektet då materialmodeller för detta material saknas. Ett liknande exempel kan återfinnas i den del av projektet som behandlar sammangjutning av metaller – där simuleringen på ett korrekt sätt måste beskriva fasomvandlingen från stelnat till flytande, vilket är tvärt emot vad de flesta simuleringsprogram är designade för.
Ytterligare en stor utmaning i projektet var att processparametrar och optimerade sammansättningar för de nya segjärnsmaterialen saknades vid projektets start. Detta utgjorde ett en stor utmaning för att nå projektmålen att framställa både tunnväggiga och tjockväggiga komponenter i dessa material.
4 Genomförande
I denna sektion återfinns en kort beskrivning av de fyra arbetspaket som utgör projektet. För en komplett beskrivning av projektgenomförande hänvisas till rapporterna från respektive arbetspaket.
4.1 Beskrivning av arbetspaketen
Projektet har delats in i fyra arbetspaket (WP) enligt nedan: - WP1 – Samverkan, resultatspridning, projektledning - WP2 – Högpresterande segjärnskomponenter
- WP3 – Lättviktskonstruktioner - WP4 – Nya teknologier
Nedan följer en kortfattad beskrivning av respektive arbetspaket.
4.1.1 WP1 – Samverkan, resultatspridning och projektledning
Arbetspaket 1 var ett administrativt arbetspaket där målen var en effektiv spridning av projektresultaten genom exempelvis konferenser och workshops.
mikrostrukturer och mekaniska egenskaper hos aluminiumgjutgods. Vid produktion av lättviktskomponenter med hög kvalitet krävs noggrann kontoll av smältans kvalitet, gjutprocess och komponentdesign. För att uppnå bättre gjutgodsegenskaper har fem olika delområden som starkt påverkar aluminium-gjutgods hållfasthet identifierats. Dessa delområden har även använts för att dela in arbetspaketet i fem olika delprojekt.
4.1.4 WP4 – Nya teknologier
Inom arbetspaket 4 ”New Technologies” har arbetet inriktats på att utveckla robusta metoder för att gjuta samman olika material. Genom att gjuta samman material är det möjligt att, i en och samma komponent, kombinera egenskaperna från olika material. Exempelvis är det möjligt att kombinera hög duktilitet med hög nötningsbeständighet. I arbetspaketet har man utvecklat metoder för sammangjutning av vitjärn och stål samt manganstål och verktygsstål.
4.2 Projektorganisation
I Figur 1 illustreas projektets organisation. Projektet har delats in i tre vetenskapliga arbetspaket, WP2 – WP4 som motsvarar projektets tre fokusområden. Aktiviteter relaterade till projektledning och resultatspridning har samlats i WP1. I projektets syrgrupp sitter företag från samtliga fokusområden. Huvudprojektledare för projektet var Anders Gotte som också var samman-kallande i styrgruppen. Styrgruppen har sammanträtt 1 gång per kvartal.
Varje arbetspaket har haft en projektgrupp knuten till sig bestående av företagsrepresentanter från projektdeltagarna. WP-ledarna för respektive arbetspaket har varit sammankallande för projektgrupperna. Arbetspaketen har i sin tur delats in i delprojekt där grupperingar av intresserade företag från projektgrupperna har deltagit i aktivitetsrelaterade möten. I Tabell 1 beskrivs projektgruppernas och styrgruppen sammansättning. Interna projektorganisationer i delprojekten beskrivs i WP-rapporterna (bilagorna 1 – 3).
Tabell 1. Projektorganisation och projektgrupper
WP1 WP2 WP3 WP4 Projektledare: Anders Gotte WP-ledare: Henrik Svensson WP-ledare: Salem Seifeddine WP-ledare: Stefan Fredriksson Delprojektledare: Henrik Svensson Ulf Gottharsson Delprojektledare: Salem Seifeddine Håkan Svensson Styrgrupp: Torbörn Rudqvist, Vestascastings Guldsmesdhyttan Bo Mattsson, Fundo Components Richard Larker, Indexator Mathias König, Scania CV Per Quarfordt, Combi Wear Parts
Projektgrupp: Håkan Andersson, Atlas Copco Jonas Hjortmark, Componenta Richard Larker, Indexator Rototilt Systems Joakim Jakobsson,
Nya Arvika Gjuteri Sune Jansson, Nya Arvika Gjuteri
Nulifer Ipek, Scania CV
Björn Israelsson, SKF Mekan AB Per Jennfors, Volvo Lastvagnar , Volvo Group Trucks Technology Rolf Andersson, Nya Arvika Gjuteri AB
Per Carlin, Vestas Castings AB Projektgrupp: Tomas Tegnemo, Mönsterås Metall AB Jörgen Henriksson, Finnveden Gjutal AB Hans Brantemo, Metall Fabriken Ljunghäll AB Cecilia Bergquist, Scania CV AB Tomas Liljenfors, Stena Aluminium AB
Niklas Köppen and Madeleine Blad, Volvo Group Truck Corporation Bo Mattsson, Fundo Components Håkan Fransson, Novacast Systems AB
Tomas Mangs and Mats Nordin,Ostnor AB Projektgrupp: Mehdi Aram, Sandvik SRP Svedala Per Quarfordt, Combi Wear Parts
Håkan Porthén, Combi Wear Parts
Erik Stark, Österby Gjuteri
Marcel Gustafsson, Österby Gjuteri
Naturainsatser från
industrin - 7,7 Mkr 3,2 Mkr 2,7 Mkr 13,6 Mkr
5 Resultat
5.1 WP1 – Samverkan, resultatspridning och projektledning
Inom WP1 har resultat från projektet förmedlats via ett flertal nationella och internationella workshops, konferenser och publikationer. Nedan följer en sammanställning av informationsspridningsaktiviteterna i projektet.- Mars 2011: M. Holmgren, föredrag, Norsk industri, Oslo
- Mars 2011: M. Holmgren, föredrag, Svenska Gjuteriföreningens FoU-dag - Maj 2011: M. Holmgren, föredrag, Svenska Gjuteriföreningens
årskonferens, Jönköping
- Juni 2011: M. Holmgren, föredrag, CAEFs generalförsamling, Storbritanien
- Augusti 2011: M. Gutegård - ´Lätta komponenter väger tungt hos Swerea SWECAST´, Gjuteriet 5/2011.
- September 2011: M. Holmgren, Föredrag, Sveriges Gjuteritekniska Förenings årskonferens, Nyköping
- Oktober 2011: S. Farre, seminarie för gjutgodskunder, Jönköping - Oktober 2011: S. Farre, seminarie för gjutgodskunder, Göteborg
- December 2011: M. Holmgren, Föredrag, CAEF Management Meeting, Frankrike
- September 2012: A Gotte, ´High-strength Cast Irons Process, properties and applications´, CIC Conference - Cost efficient cast components - September 2012: M. Gutegård, ´Casting Optimisation for Lightweight
Designs´, CIC Conference - Cost efficient cast components.
- September 2012: S. Fredriksson, ´Optimised wear properties by compound casting´, CIC Conference - Cost efficient cast components.
- September 2012: S. Seifeddine, ´The response of Mg and Cu on strength of cast aluminium components´, CIC Conference - Cost efficient cast components.
- September 2012: B. Israelsson, H. Svensson, ´Si-legerade segjärn´, Svenska Gjuteriföreningens höstkonferens, Västerås.
- December 2012: A. Gotte - ´Gjutjärn, ett modern material för framtida utmaningar´, Gjuteriet 9/2012
- December 2012: H. Borgström - ´Processutmaningar kan ge mer chunkygrafit i segjärn´, Gjuteriet 9/2012
- Mars 2013: S. Fredriksson – ’Det bästa av två världar’, Gjuteriet 2/2013 Vid sidan av informationsspridningsverksamheten har aktiviteterna inom WP1 stärkt samarbetet inom Casting Innovation Centre.
5.2 WP2 – Högpresterande segjärnskomponenter
I den del av projektet som behandlar högpresterande segjärnskomponenter har man lyckats omvandla en svetsad komponent till en gjuten komponent med lägre vikt och samtidigt bibehållna mekaniska egenskaper. Genom att optimera ingjutsystemet, har man lyckats att gjuta tunnväggit gods (≥ 4 mm) utan imperfektioner, vilket var ett av de mål som sattes upp för projektets start.
Vidare har man i projektet gjutit komponenter med höga mekaniska egenskaper i dimensioner upp till 100 mm godstjocklek i kisellegerat segjärn och kisellegerat ausferritiskt ADI (SiSSADI), vilket också var uppsatt som ett projektmål.
Utmattningsegenskaper för ADI, både provstavar och även verkliga komponenter, testades i riggprover. Undersökningen visar tydligt att en bearbetad och polerad yta med efterföljande kulblästring ger de bästa utmattningsegenskaperna, vilket ger en förklaring till varför ADI-komponenter inte har uppnått förvändande utmattningsegenskaper i ”as-cast”-tillstånd
Härdbarhetseffekten av legeringsämnen i ADI material har också undersökts. Resultaten visar att nickel förbättrar härdbarheten mer än kisel, förmodligen på grund av det faktum att en ökning av Si reducerar kolets löslighet i austeniten, vilket kräver högre austenitiseringstemperatur för att uppnå samma härdbarhetsbidrag från kol.
Inom delprojektet som behandlade sandgjutningsprocessen utarbetades metoder för att nå en robustare process, både för coldbox- och furanbindemedel. Detta gör det möjligt för gjuterier att minska på processrelaterade egenskapsvariationer.
5.3 WP3 – Lättviktskonstruktioner
Inom den del av arbetspaketet som behadlade inverkan av porers form, typer och storlekar på de mekaniska egenskaperna visade resultaten att grov mikrostruktur inverkade negativt på de mekaniska egenskaperna, samt att en ökad porandel
realisera en 50-procentig förbättring av sträckgränsen för AlSi9Cu3 (Fe).
I delprojektet modellering av restspänning i aluminiumgjutgods utvärderades olika metoder för mätningar av restspänningar. Olika mätmetoder visade samma trender för restspänningar, även om absolutvärdena inte blev desamma. Vidare visade man att simuleringar kan användas för att, inom 25 % felmarginal, bestämma restspänningarna om inte spänningsgradienterna är för stora. I arbete konstaterades att en högupplöst modell för den yttersta millimetern och det initiala värmeövergångstalet h0 är viktiga för en korrekt beskrivning av restspänningarna
vid simuleringar av pressgjutgods.
Fullständiga resultatsammanställning från WP3 återfinns i Bilaga 2.
5.4 WP4 – Nya teknologier
Inom projektet har provgjutningar för att gjuta samman manganstål och verktygsstål utförts vid Swerea SWECAST pilotgjuteri. Försöken visade att beroende på verktygsstålets temperaturhistoria vid gjutningen kan olika effekter uppnås, alltifrån en struktur identisk med det kallbearbetade utgångsmaterialet till ett kraftigt påverkat material om temperaturpåverkan från smältan varit stor. Där omsmältning skett i gränszonen mellan det två materialen bildas en metallisk bindning. I andra fall är vidhäftningen sämre vilket kan dock kan kompenseras med mekanisk fixering av insatserna.
En annan del av projektet inriktades på sammangjutning av vitjärn och stål. En speciell utformning på en vitjärnsdetalj togs fram som göts in i en grävtand. Såväl detaljens geometri som vitjärnets sammansättning optimerades iterativt för att uppnå optimala förhållanden för omsmältning under gjutprocessen. Ett antal varianter av vitjärnsdetaljen tillverkades av Österby Gjuteri och färdiga tänder göts av Combi Wear Parts. Även här uppnåddes en god metallisk bindning mellan materialen. Överensstämmelse med datorsimuleringarna var god med avseende på geometrins betydelse för graden av omsmältning och kvalitén på den metalliska bindningen mellan materialen. Vissa förändringar uppträdde i vitjärnets mikro-struktur vilket främst antogs göra materialet sprödare. Hårdheten var dock oförändrad varför materialets goda slitegenskaper bör kvarstå.
Deltagande företag var nöjda med resultaten av projektet och båda studierna kommer att leda till modifiering av existerande respektive framtagning av nya kommersiella produkter.
6 Slutsatser
I samtliga arbetspaket inom projektet har resultat tagits fram som är till nytta både för akademi/institut och för de deltagande företagen. Projektet har resulterat i omkonstruktion av flera komponenter vilket har reducerat tillverkningskostnaden för dessa. Vidare har projektet presenterat en metod för att gjuta samman material och simulera sammangjutningsprocessen. Detta gör det möjligt att tillvarata olika materials egenskaper i en och samma komponent. Detta projektresultat kommer att leda till att det lanseras komponenter med längre livslängs än vad som tidigare har varit möjligt. Vidare har projektet visat att systematiskt arbete med sand/bindemedelssystemet leder till bättre kontroll av gjutprocessen, vilket i sin tur gör det möjligt att uppnå bättre och jämnare komponentegenskaper samt möjliggör att drastiskt minska kassationsgraden.
6.1 Uppnådda projektmål
I arbetspaketet angående höghållfasta segjärnskomponenter sattes mål upp att genom projektet lösa problemen relaterade till att gjuta tunn- och tjockväggigt gods. Dessa mål har uppåts. Vidare har två deltagande gjuterier genom projektet fått kunskaper i hur man framställer Si-legerat segjärn av hög kvalitet, lämpligt för efterföljande ADI-behandling. I samma arbetspaket uppnådde ett deltagande gjuteri det uppsatta målet att minska kassationgraden med 50 % för en utvald komponent genom systematiska studier av avgasning av kärnbindemedel.
I arbetet med lättviktskomponenter har man för de flesta fall nått det uppsatta målet med att beskriva restspänningar inom 25 % felmarginal. Det är fortfarande inte möjligt med en noggrann beskrivning av restspänningar i fall med mycket stora spänningsgradienter. Målet som var uppsatt angående 50 % minskning av restspänningar i befintlig komponent har inte varit möjligt att följa upp, då ingen komponent har omkonstruerats i projektet. Detsamma gäller därför också målet om minskning av komponentvikt.
Genom ett iterativt arbete med simuleringar och gjutförsök har man i arbetspaketet om nya teknologier nått de mål som var uppsatta i projektet. I projektets början hade man satt upp ett mål angående minskning av komponentvikt, men detta mål bedömdes vara sekundärt i förhållande till komponentlivslängd.
6.2 Industrieffekter
Genom en kombination av lyckosamma fundamentala studier av processparametrar vid produktion av komponeter i segjärn, aluminium och blandade material och ett stort företagsengagemang från projektdeltagarna har projektet resulterat i industrinytta i form av minskade produktionskostnader, minskade kassationer och jämnare kvalitet, nya typer av slitdelar i blandmaterial som vid projektets slut ska genomgå fälttester inför en förmodad lansering, samt en ny och innovativ produktionsprocess för tunnväggigt segjärnsgjutgods. Vidare har projektet bidragit till att kartlägga och fastställa lämpliga produktions- och värmebehandlingsparametrar för segjärnskomponenter med stora
sektions-för ett fortsättningsprojekt samt vilka frågor som bör behandlas i en eventuell fortsättning. De flesta företagen önskade att projektet forsätter. Merparten av företagen ansåg att ett fortsättningsprojekt ska behandla liknande frågor som nuvarande projekt, men att fokus bör vara att arbeta med processfrågor för att göra det möjligt att med robusta metoder framställa material med höga mekaniska egenskaper med hjälp av gjutning. Arbetet inkluderar bland annat bättre kontroll av ingångsråvaror till processen samt ytterligare insatser för en stabilare formningsprocess.
2013-009 – Appendix 1
HighT, WP2 – High-Strength Cast Iron
Swerea SWECAST AB PO Box 2033, SE-550 02 Jönköping
Phone 036 - 30 12 00 swecast@swerea.se http://www.swereaswecast.se
Author Report No. Date
Henrik Svensson 2013-009_ 2013-06-30
Summary in Swedish
Denna rapport sammanfattar två delprojekt i ett större projekt ”Development of High Technology Castings” (HighT).
I det ena delprojektet (WP2.1) har fokus varit på kisellegerade segjärn och värmebehandling av dessa till så kallade SiSSADI, men även konventionella segjärn och ausferritiska segjärn (ADI) har behandlats.
Resultaten har varit positiva och flera av de medverkande företagen kommer att ändra material i sina produkter och övergå till kisellegerade segjärn eller SiSSADI istället för det tidigare materialvalet. Även en tidigare (sjudelad) svetsad stålkonstruktion kommer att ändras till en gjuten konstruktion.
Det främsta syftet inom den andra delprojektet (WP2.2) var att minska gasrelaterade gjutdefekter från formar och kärnor så att gjuteriet kan producera höghållfasta material med jämna mekaniska egenskaper.
Arbetet fokuserade på furan och coldbox: en metod för att bestämma och optimera produktionsparametrar för ett syrahärdande furansystem utvärderades med gott resultat. Sammansättningen och avgången av gas från flera kärnmassor i coldbox bestämdes genom en kombination av termogravimetrisk analys och masspektroskopi. Ett gjuteri minskade sin kassation på en specifik komponent med mer än 50 % inom ramen för projektet.
Summary
This report summarizes two projects of a larger project "Development of High Technology Castings" (HighT).
One of the sub-project (WP2.1) has focused on silicon solution strengthened ductile iron and their heattreatment to the so-called SiSSADI, but also conventional ductile and ausferritic ductile iron (ADI).
The results have been so positive that several of the participating companies will change the materials in their products and switch to silicon ductile iron or SiSSADI instead of the earlier material selection. Also a previous (seven pieces) welded steel construction will be changed to a cast construction.
The primary purpose of the second sub-project (WP2.2) was to reduce gas-related casting defects from molds and cores, so that the foundry can produce high-strength materials with even mechanical properties.
The work focused on furan and coldbox: a method to determine and optimize the production parameters of an acid curing furan system was evaluated with good
Index
1 INTRODUCTION ... 1
2 WORKPACKAGE DESCRIPTION ... 1
2.1 GOALS AND OBJECTIVES ... 1
2.2 SCIENTIFIC CHALLENGES ... 2
2.3 INDUSTRIAL CHALLANGES AND BENEFITS ... 3
3 IMPLEMENTATION ... 3
3.1 PROJECT ORGANISATION ... 4
3.2 SUB-PROJECTS ... 5
3.2.1 WP 2.1 - Development of High-Strength ductile iron ... 5
3.2.2 WP 2.2 – Gases during castings ... 5
4 RESULTS ... 6
4.1 DEVELOPMENT OF HIGH-STRENGTH DUCTILE IRON ... 6
4.2 GASES DURING CASTINGS ... 6
5 ACHIEVED GOALS... 6
6 CONCLUSIONS ... 7
7 FUTURE WORK ... 7
List of appendices
Appendix 1.1 Henrik Svensson and Henrik Borgström, Sub-project report – HighT, WP2.1 - Development of High Strength Ductile Iron Appendix 1.2 Ulf Gotthardsson, Sub-project report – HighT, WP2.2 – Gases
1 Introduction
Cast ductile irons (DI) are widely used in a variety of components where both high ductility and high ultimate tensile strength (UTS) are necessary. Lately “new” (silicon solution strengthened) DI have been developed and standardized in Europe. These have much higher ductility, with maintained strength, than the other DIs. Since these materials are very new there is a lack of e.g. cast simulation data, which makes it more difficult to produce them with appropriate properties and without any casting defects.
Heat treatment of DI, during very controlled conditions, can achieve very high strength DI, so-called ausferritic DI (ADI). These materials have also a high wear resistance, and at the same time rather good ductility. To achieve these excellent mechanical properties, the heat treatment must be performed accurately at different steps. However, also the alloying elements must be added carefully and correctly. This is even more important for thick components, since the correct material structure must develop during the complete wall thickness of the cast component; otherwise the mechanical properties are decreased significantly. In many applications the fatigue limit is the critical value for the component. The fatigue properties are dependent of many factors, especially the surface roughness. The surface of cast component can be controlled and modified by different pre- or post-processes.
In the first project the above subjects have been illustrated and several practical tests have been performed in order to elucidate the problems.
Some variations in mechanical properties that occur in castings, have their origins in gases from moulds and cores. The binders used for bonding the sand grains together, and the adhesive that is used to join pieces of cores into one core package, often consist of organic substances. In contact with the hot molten metal, these organics are downgraded into relatively large amounts of gas. Some of these gases become solved in the metal and may, at the solidification, cause porosities inside the finished component. The amount of pores, and their position in the component, varies between casting occasions. They lead to inferior mechanical properties as well as an increasing variation in those properties.
2 Workpackage description
2.1 Goals and objectives
• The goal in WP 2.1 was to cast silicon solution strengthened ductile iron with thin (≤4 mm) and thick (≥100 mm) wall sections, without
The main objective of WP2.2 was to reduce gas related casting defects to be able to produce high strength materials with consistent and unimpaired mechanical properties. Gas related defects are an important source of quality related costs for the foundries and increased knowledge on how to avoid gas porosities in castings is therefore of great value to the industry. Higher mechanical properties due to the absence of porosities also make it feasible to produce more weight-efficient cast components.
The detailed short-term goals for WP2.2 were:
• To achieve 50 % decrease in scrap rate for the chosen component at Arvika Foundry
• To have a tool for selecting suitable binder systems for different components to minimise the risk of gas related defects
• To define chemical fingerprints of gases and condensates from different binders
• To gain experimental data to serve as input for simulations • To make reliable simulations of gas evolution and gas transport
2.2 Scientific challenges
Lack of casting simulation data for silicon solution strengthened ductile iron causes problem with e.g. shrinkage porosity and other possible casting defects. The high silicon content in these materials may also affect the graphite structure negatively. Therefore, it is very important to have control of the alloying elements, especially trace elements.
Swerea SWECAST, JTH and the Swedish foundry companies have been working with gas evolution matters for some time, and it is obvious that the major influencing factors are quite well-known by now. There are still many details left to investigate. The fact that the mould and core always releases gas is probably one important factor for the formation of defects, but it may not be the most important one. Impurities, like oxides, within the molten metal or air entrapped because of turbulence are also probable factors for gas porosities.
There are definitely a lot more detailed studies to make before a reliable simulation of gas evolution and upcoming gas defects can be used to secure the properties of castings.
2.3 Industrial challanges and benefits
To limit the extent of casting process adaptation required to incorporate silicon solution strengthened ductile iron in production and ensure freedom from imperfections like unwanted graphite formation and other defects.
Increased knowledge on how various mould-making and after-treatment of the casting surface parameters affects the fatigue properties of ausferritic ductile iron (ADI).
To bridge the knowledge gap in hardenability alloying for ADI, in order to secure a fully hardened structure through the whole component.
It is usually difficult to predict how a change somewhere in an industrial process affects the product or process. This makes the implementation of good research results take long time. Sometimes a change in process parameters is positive on one level, but negative on another. In this project, we encountered difficulties when the foundry tried to exchange their standard core binder to another one with less gas evolution. The total emission of gas was lowered, but the core binder’s other properties and content gave unexpected problems within the coreboxes, nossles and at the final air cleaning process.
3 Implementation
In order to clarify and solve the arisen problems, people from several foundries and also users of cast components were gathered in this project. Together with researchers at Swerea SWECAST AB this project named “High Strength Cast Iron” (WP2) was established. WP2 was divided into two sub-projects; “Development of High-Strength Ductile Iron (WP2.1) and “Gases during castings” (WP2.2). Companies and people in the group, as well as the organisation, are described in 3.1 below.
WP 2.1 – Development of High-Strength Ductile Iron WP 2.2 – Gases during castings
Participants in the project: WP 2.1
Håkan Andersson Atlas Copco AB Jonas Hjortmark Componenta
Richard Larker Indexator Rototilt Systems AB Joakim Jakobsson Nya Arvika Gjuteri AB
Sune Jansson Nya Arvika Gjuteri AB Nulifer Ipek Scania CV AB
Björn Israelsson SKF Mekan AB
Per Jennfors Volvo Lastvagnar AB, Volvo Group Trucks Technology Henrik Borgström Swerea SWECAST AB
Henrik Svensson Swerea SWECAST AB Karl-Olof Björhall Swerea SWECAST AB WP 2.2
Rolf Andersson Nya Arvika Gjuteri AB Sune Jansson Nya Arvika Gjuteri AB
Per Carlin Vestas Castings AB Henrik Borgström Swerea SWECAST AB Anders Gotte Swerea SWECAST AB Ulf Gotthardsson Swerea SWECAST AB
3.2 Sub-projects
3.2.1 WP 2.1 - Development of High-Strength ductile iron
WP2.1 was divided in further sub-projects, as following;
1. Hydraulic cover – for casting thin sections in silicon solution strengthened ductile iron.
2. Geared component for load bearing application – for casting thick sections in silicon solution strengthened ductile iron.
3. Tool holder for hammering machines – for casting ADI
4. Chassis component – for casting conventional DI, silicon solution strengthened DI and ADI. Commercial components were cast in these three materials and tested in rig tests.
5. Fatigue test – test rods cast in ADI (and one reference in DI) for investigate the influence of the surface roughness on the fatigue properties.
6. Hardenability – for investigate the influence of alloying element on the hardenability in cylinders, cast in ADI.
3.2.2 WP 2.2 – Gases during castings
The project ran with three sub-projects:
• To achieve 50 % decrease in scrap rate for the chosen component at Arvika Gjuteri
• Tool for selecting suitable binder and curing agent levels to minimise the risk of gas related defects in an acid-cured furan system
• Chemical fingerprints of gases from downbreaking cores bonded with PU coldbox
elements (including RE-metals) and other casting parameters. If these are not optimised the cast component may contain porosities, low nodularity and inclusions, which all will affect the mechanical properties negatively.
The hardenability experiments show the high influence of nickel on the hardening effect. The volume dilatation was measured and resulted in both expansion and shrinkage from the origin geometry, depending on the amount of alloying elements.
4.2 Gases during castings
The sub-projects focused on furan and coldbox: a method for determining and optimising production parameters for an acid catalyst furan system was evaluated with god results. The composition and evolution of gas from several coldbox core formulations was determined by combining thermogravimetric analysis and mass spectroscopy. A foundry succeeded to lower the scrap rate on one specified component with more than 50 % within in the frame of this project.
5 Achieved goals
Cast thin (4 mm) and thick (100 mm) walled components in silicon solution strengthened ductile iron. Thin walled casting in ductile iron is attributed to mould filling problems and thick wall casting is often related to problems with the shape of the graphite nodules.
Production of components and test rods in ADI in conventional and silicon solution strengthened ADI (SiSSADI).
Evaluation of how the casting surface affects the fatigue properties in ADI cast components.
Investigated how alloying elements affect the hardenability in ADI.
A method for evaluating factors that affect the final bond strength for a foundry’s sand process was achieved. The method uses standard measuring equipment and is immediately available for any foundry using at least the acid curing furan system. For future work, the data of thermal breakdown of coldbox cores can be used in modelling and simulating gas evolution from cores, in order to prevent gas
porosity defects. The data was, within this project, also used by Arvika to compare some technical and environmental aspects of different core binders and formulations. The proposed decreasing of scrap rate for a specific component was also achieved, even though some technical drawbacks made the gas evolution data less important, at least for the time being.
6 Conclusions
Within the first sub-project we have successfully converted a welded component into a cast component with reduced weight and maintained mechanical properties. By optimizing the ingatesystem, thin walled (≤4 mm) sections were achieved without imperfections.
Silicon solution strengthened DI and ADI components with high mechanical properties were cast in dimensions up to 100 mm wall thickness.
Fatigue properties for both flat test rods and also real components were performed in rig tests. Presence of minor casting defects resulted in some scattering of the obtained fatigue limits. However, the investigation clearly shows that a machined and polished surface with subsequently shot peening gives the best fatigue mean limit.
The hardenability effect of alloying elements in ADI materials has been investigated. Here Ni improved hardenability more that Si. Furthermore, ausferritic patches were seen in high Si alloys, which mean that the true potential for SiSSADI needs to be investigated further.
7 Future work
Silicon solution strengthened DI and ADI are material with superior properties and can be a good alternative to cast steels. This project has clearly shows that it is possible to cast components with high complexity, but still achieve advantageous properties in the final product. The intention is to encourage the Swedish foundries to adopt these materials in their production and thereby be more competitive on the global market.
The scattering from the fatigue test will be investigated further. Fracture surfaces from the rods will be characterised in detail and will hopefully give insight to some outstanding issues.
Concerning the hardenability of ADI materials there is still much to investigate, in order to elucidate all combination effects from different alloying elements, but above all in combination to various combinations of process temperatures and dwell times.
2013-009 – Appendix 1.1
HighT, WP2.1 – Development of High Strength Ductile
Iron
Henrik Svensson and Henrik BorgströmSwerea SWECAST AB PO Box 2033, SE-550 02 Jönköping
Phone 036 - 30 12 00 swecast@swerea.se http://www.swereaswecast.se
ausferritiska segjärn (ADI) har behandlats.
I sex olika delprojekt har kommersiella komponenter eller provkroppas gjutits av medverkand gjuterier. Många detaljer har riggtestats och huvuddelen av allt gods har analyserats ingående för att se hur mikrostrukturen, legeringsämnen, defekter m.m. påverkar de mekaniska egenskaperna.
Resultaten har varit så positiva att flera av de medverkande företagen kommer att ändra material i sina produkter och övergå till lösningshärdade segjärn eller SiSSADI istället för det tidigare materialvalet. Även en tidigare stålkonstruktion (svetsad av sju delar) kommer att ändras till en gjuten konstruktion.
Summary
This report concerns a subproject in the larger project "Development of High Technology Castings" (HighT).
In this subproject the focus has been on solution strengthened ductile irons and their heat treatment to the so-called SiSSADI, but also on conventional ductile and ausferritic ductile iron (ADI).
In six themes constituting the whole sub-project commercial components or cast test pieces have been cast by the participating foundries. Many castings have been rig tested and most of all castings have been characterized in detail to see how the microstructure, alloying, defects etc. affect the mechanical properties.
The results have been so positive that several of the participating companies will change the materials in their products and switch to solution strengthened ductile iron or SiSSADI instead of the earlier material selection. Also a previous design (welded out of seven pieces) will be changed to a cast design.
3 IMPLEMENTATION ... 2
3.1 PROJECT ORGANISATION ... 3 3.2 SUB-PROJECTS IN WP2.1 ... 4
4 RESULTS ... 4
4.1 DEVELOPMENT OF HIGH-STRENGTH DUCTILE IRON –WP2.1 ... 4
4.1.1 Hydraulic cover ... 4 4.1.2 Gear component for load bearing application ... 6 4.1.3 Tool holder for hammering machines ... 12 4.1.4 Chassis component ... 18 4.1.5 Fatigue tests ... 22 4.1.6 Hardenability tests ... 29 5 ACHIEVED GOALS... 40 6 CONCLUSIONS ... 40 7 FUTURE WORK ... 40
very high strength DI, so-called ausferritic DI (ADI). These materials have also a high wear resistance, and at the same time rather good ductility. To achieve these excellent mechanical properties, the heat treatment must be performed accurately at different steps. However, also the alloying elements must be added carefully and correctly. This is even more important for thick components, since the correct material structure must develop during the complete wall thickness of the cast component; otherwise the mechanical properties are decreased significantly. In many applications the fatigue limit is the critical value for the component. The fatigue properties are dependent of many factors, especially the surface roughness. The surface of cast component can be controlled and modified by different pre- or post-processes.
In this project the above subjects have been illustrated and several practical tests have been performed in order to elucidate the challenges.
2 Workpackage description
The industrial partners have cast ductile iron components and test rods in different ductile iron materials. Some materials have also been heat treated to ausferritic ductile iron (ADI). Thin (≤ 4 mm) and thick (≥ 100 mm) walled casting components are produced in silicon solution strengthened ductile iron with high mechanical properties. Fatigue tests have been performed on ADI test rods, in order to evaluate the influence of the surface roughness on the fatigue properties. Real components, cast in different ductile iron materials, have also been fatigue tested and compared to each other. Influence of alloying elements on the hardenability in ADI castings was also investigated.
2.1 Goals and objectives
To cast silicon solution strengthened ductile iron with thin (≥4 mm) and thick (≤100 mm) wall sections, without imperfections. This will result in more homogeneous and ductile material, and also the machinability is improved. To convert a welded steel component into a cast ductile iron component with reduced weight and maintained mechanical properties. This will reduce e.g. energy consumption, cost and lead-time.
Investigate how different surfaces affect the fatigue properties in ausferritic ductile iron (ADI). This is important for optimizing the production parameters connected to fatigue fractures.
Due to lack and inconsequent information of how different alloying elements affect the hardenability in ADI, this was investigated for the most interesting elements.
2.2 Scientific challenges
Lack of casting simulation data for silicon solution strengthened ductile iron causes problem with e.g. shrinkage porosity and other possible casting defects. The high silicon content in these materials may also affect the graphite structure negatively. Therefore, it is very important to have control of the alloying elements, especially trace elements.
2.3 Industrial challanges and benefits
To limit the extent of casting process adaptation required to incorporate solution strengthened ductile iron in production and ensure freedom from imperfections like unwanted graphite formation and other imperfections.
To increase knowledge on how various parameters in mould-making and after-treatment of the casting surface affect the fatigue properties of ausferritic ductile iron (ADI).
To bridge the knowledge gap in hardenability alloying for ADI, in order to secure a fully hardened structure through the whole component.
3 Implementation
In order to clarify and solve the arisen challenges, people from several foundries and users of cast components were gathered in this project. Together with researchers at Swerea SWECAST AB this sub-project named “Development of High-Strength ductile iron” (WP2.1) was established. Companies and people in the group, as well as the organisation, are described in 3.1 below.
WP 2.1 – Development of High-Strength ductile iron WP 2.2 – Gases during castings
Participants in the project: WP 2.1
Håkan Andersson Atlas Copco AB Jonas Hjortmark Componenta
Richard Larker Indexator Rototilt Systems AB Joakim Jakobsson Nya Arvika Gjuteri AB
Sune Jansson Nya Arvika Gjuteri AB Nulifer Ipek Scania CV AB
Björn Israelsson SKF Mekan AB
Per Jennfors Volvo Lastvagnar AB, Volvo Group Trucks Technology Henrik Borgström Swerea SWECAST AB
Henrik Svensson Swerea SWECAST AB Karl-Olof Björhall Swerea SWECAST AB
3.2 Sub-projects in WP2.1
WP2.1 was divided in further sub-projects, as follows;
1. Hydraulic cover – for casting thin sections in silicon solution strengthened ductile iron.
2. Gear component for load bearing application – for casting and austempering thick sections in silicon solution strengthened ductile iron into alloyed SiSSADI. 3. Tool holder for hammering machines – for casting silicon solution strengthened DI and austempering into unalloyed SiSSADI
4. Chassis component – for casting conventional DI, solution strengthened DI and conventional ADI. Commercial components were cast in these three materials and tested in rig tests.
5. Fatigue test – test rods cast in conventional ADI (and one reference in DI) for investigate the influence of the surface roughness on the fatigue properties.
6. Hardenability – to investigate the influence of alloying element on the hardenability in cylinders, cast in ADI and SiSSADI.
4 Results
4.1 Development of High-Strength ductile iron – WP2.1
4.1.1 Hydraulic cover
The hydraulic cover, currently a welded steel component, was engineered into a one piece cast component (Figure 1). Earlier seven steel sections were welded together to the final component. With the new design a minor weight reduction was achieved, but the overriding benefit is the huge reduction in production cost and component lead-time.
Table 2. Mechanical properties from separately cast sample (Y-Block). Material Rp0,2 [MPa] Rm [MPa] A5 [%] HBW
EN-GJS-600-10 519 626 16,1 226
In order to see how the wall thickness affects the microstructure, the microstructure was analysed at different positions, with different thickness (4 mm, 7 mm and 20 mm). Images from the polished and etched (Nital 2%) microstructure are shown for 4, 7 and 20 mm wall thickness in Figure 2, Figure 3 and Figure 4 respectively.
Figure 2. Microstructure at 4 mm wall thickness (magnification 100x and 200x).
Figure 4. Microstructure at 20 mm wall thickness (magnification 100x and 200x).
Image analysis was performed on the three samples with a Leica MEF4A microscope and the Leica QWin V3 software, according to SS-EN ISO 945-1:2008. The results are presented in Table 3.
Table 3. Results from image analysis at different wall thicknesses. Sample Nodularity [%] Nodule count [nod/mm2] Size Pearlite [%] 4 mm 83 558 7/8 <1 7 mm 89 555 7 <1 20 mm 79 250 6/7 <1
As expected, the nodule count is higher at the thinner sections compared to the thicker one. Since thinner wall thickness solidifies fast, the nucleated nodules do not have time to grow to as big nodules as in the thicker sections.
The main challenge in casting components with thin sections is the mould filling. Since the melt is exposed to high cooling during mould filling in the thin sections, there is a big risk for cold shuts or uncompleted mould filling. Usually there is also risk for nucleation of carbides, but in this material with high silicon content this risk is highly reduced, since silicon promotes graphite nucleation instead of carbides.
A lot of casting simulations were performed at Swerea SWECAST to optimise the mould filling and solidification. The ingate system was modified several times to improve the filling rate and to reduce shrinkage porosity. The porosities could not be eliminated completely, but they were intentionally controlled to non-critical volumes, which are supposed to be drilled away at a later stage.
4.1.2 Gear component for load bearing application
Figure 5. Tensile properties of as-cast SiSSADI (solution strengthened by Si + Ni).
The major sub-project challenges have been to optimize the mould filling and solidification to avoid solidification stress that can impart negatively to the roundness of the gear component as well as adapting the composition to avoid unwanted graphite structures. Extensive casting simulations with the software Magma were performed at Componenta Weert to optimise the mould filling and solidification for the geared component. The positioning and geometry of the feeder was modified several times to improve roundness but also to reduce shrinkage porosity. It is in the scope for this report impossible to give all details on the extent of the simulations owing to the risk of exposing propriety strategies for mould filling and other competitive advantages like the placement of the ingate system and feeders. Unfortunately the reporting for the simulation work will confined to presenting the select simulation images for the displacement and stress in Trial 1 in Figure 6.
Figure 6. Key Magma simulation results in the casting designs optimized by Componenta Weert.
In order to counteract the risk of unwanted graphite morphologies in the microstructure due to the size of the component, extensive light optical microstructural, LOM verification was performed by Componenta Weert and select scanning electron microscopy performed by Swerea SWECAST AB. In order to see how the wall thickness affects the microstructure, the microstructure was analysed at select locations of the component’s rotation symmetric cross-section. To gain an understanding for how difficult it is to accurately depict unwanted morphologies like chunky graphite, images from the polished and etched (Nital 2%) microstructure for exterior and interior sections are shown in Figure 7. Here chunky graphite containing microstructures with >85% nodularity according to Table 4, are shown on the right, which only have marginally larger graphite nodules and possibly some more pearlite compared to the nodular counter parts on the left. One is pushed hard to see Chunky graphite in the bottom right image in Figure 7. Similar small distinctions are found in the bottom left image that only has a marginally larger grain size compared to the other <90% nodular microstructures, despite of being located in the direct vicinity of a feeder.
To investigate the issues surrounding the chunky graphite morphologies in Figure 8, SEM analyses on polished and fractured samples were conducted. From EDX area analysis of the polished image EDS spectra indicating Mg inclusions are seen, where MgS is seen in the middle EDS and MgO with RE contributions is seen in the bottom EDS. To facilitate more accurate EDX spot analysis a sample was thoroughly cleaned and fractured prior to SEM. This resulted in the top right image with Cu rosettes in the EDS spectrum in the middle, which can be compared to the bottom right nodular spectra. Finding Cu with Chunky is somewhat of a novelty.
Figure 8. SEM and SEM-EDX images of chunky graphite in polished and fractured samples from Trial 1.
In the LOM microstructure for Trial 2 it can be seen that the pearlite content is <2% from the typical casting on the left in Figure 9. On the right the microstructure in the direct vicinity of the feeder shows that <4% pearlite is present along with some not shown porosity. Therefore, the porosity was characterised separately with SEM and EDX. From Figure 10 Mg, O, P and RE is seen, which is typical of Mg-inclusions.
Figure 9. 100x magnifications of the generalized (left) and feeder (right) microstructure in Trial 2.
should be optimized to avoid dross.
4.1.3 Tool holder for hammering machines
The component in Figure 12, used as a tool holder for tools in hammering machines, has been investigated in this sub project. The as-cast material produced by SKF Mekan AB in Figure 12 is an EN-GJS-600-10, ferritic ductile iron solution strengthened with silicon without addition of other alloying components, as seen in Table 5. To cope with the load in the intended application as-cast material has been heat treated by Atlas Copco AB to SiSSADI with a hardness of 480 HB and with tensile properties seen evaluated at Swerea SWECAST AB in Table 6. The component is rough machined by Atlas Copco AB before austempering with 0.5 mm radial allowance and then finished with CBN inserts to a surface roughness of Ra ~ 0:32 after ADI heat treatment.
The largest through-hardened material wall was 17.5 mm (possible with unalloyed SiSSADI due to Si contribution, but not with conventional unalloyed ADI) and the measured shape dilation +0.08 mm and +0.05 mm for the outer and inner diameters and +0.06 mm for the length measurement. After ADI heat treatment and final machining, the component was subjected to a long term rig test for striking machines. Testing by Atlas Copco AB was carried out in several stages, with inspection between each, where steps 1-2 were performed under normal load and steps 3-5 with overload
Figure 12. As-cast condition (left). Machined tool holder (right).
Table 5. How the composition (weight-%) of the casting at SKF Mekan evolved through the trials.
ID C Si Si
Grav
Cequ Mn P S Cr Cu Mg Ce
ICP
Figure 13. The initial (left) and final (right) casting designs optimized by SKF.
To conveniently evaluate each casting trial, 7 mm tensile test bars were extracted and evaluated by Swerea SWECAST AB. Four tensile test bars were taken from coarse and thin section of the component as seen in Figure 14. Here the relative variation in tensile properties for each section is elucidated. Samples positioned in coarse sections close to the inlet and feeder has reduced tensile properties. In Figure 15 the effect of silicon to substitutionally strengthen ferritic ductile iron is clearly seen as a concurrent increase in elongation and decrease in ultimate tensile strength, when Si decreases from 4.70 via 4.46 to 4.24 wt% in trials 1 to 3, respectively.
Figure 14. The extraction position for the coarse tensile bars (left) and the tensile properties for all Trials and sections (right).
Figure 15. The tensile properties for as-cast (left) and SiSSADI austempered to 480 HBW (right). Samples next to feeders/ingate are removed in the figures.
Table 6. Image analysis results for Trial 1 and 3 (Trial 2 omitted due to Chunky Graphite). Sample Nodularity [%] Nodule count [nod/mm2] Trial 1 92 176 Trial 3 84 164
Figure 17. SEM images of Trial 1 voids (Top), feeder voids (Middle) and best fracture (Bottom) in Trial 3.
To further analyse the issues identifies during LOM, a number of SEM investiga-tions were conducted on fracture surfaces from tensile bars. From Figure 17 the size of the voids from Trial 1 in Figure 16 were confirmed to be around 0.5 mm. Additionally to their size, it can be seen that their nature is essentially dendritic, which is usually related to mould filling. Therefore SKF revised the geometry of the feeder and inlet for the casting before Trials 2 and 3. Before Trial 3 the Mg-treatment was made Ce-free to avoid unwanted graphite morphologies. From Figure 17 voids could be seen in a region directly below the feeder, which is not an issue owing to minimal loading there. Finally, the best tensile sample from Trial 3 was analysed in SEM to display at bottom in Figure 17 the appearance of a successful fracture surface. A number of fracture surfaces for different tensile strengths were analysed at the same time, but since it is very difficult to see that the lesser performing samples have more cleavage and less dimple fractures than the best, their images are not depicted here.
Figure 18. Polished and etched (Nital 2%) microstructure for SiSSADI at
magnification 220x (Top), 550x (Middle and bottom left) and 1100x (Bottom right).
From Figure 18 images from polished and etched (Nital 2%) microstructures for SiSSADI show that the acicular phases are even, well dispersed and exceptionally fine. If one has to complain only a very slight decoration of the nodules with pro-eutectoid ferrite can be seen. This did however not degrade the hardenability due to the rapid quenching of the relatively thin sections.
To finalise the subproject component rig testing was employed to verify the true performance for the potential application. To initiate the testing the component was tested in the as-cast state, where the failure seen in Figure 19 occurred early during Step 2 of the rig test and could thus directly be rejected. From selected wear on component surfaces in Figure 20 after rig testing only minor differences in wear was observed on SiSSADI material compared to standard material, low alloyed case hardening steel. Consequently, it is considered that the new material possess a reasonable potential to achieve the ultimate life requirement for normal work at the customer.
Figure 19. Failure of as-cast component.
Figure 20. Significant wear regions for SISSADI (left) vs. standard material, low alloyed case hardening steel (right).
4.1.4 Chassis component
Earlier the chassis component was produced in conventional ferritic-pearlitic EN-GJS-500-7. However, owing to increased component load a change in material was necessary. Therefore, the chassis component was cast in two different silicon solution strengthened ductile irons, EN-GJS-500-14 and EN-GJS-600-10 according to SS-EN 1563:2012 and in one conventional ADI. The ADI components were by Nya Arvika Gjuteri cast simultaneously with the fatigue rods in chapter 4.1.5. The cast component is shown in Figure 21 and the chemical compositions are shown in Table 7, Table 8 and Table 9, respectively.
The ADI components were heat treated and quenched in salt bath at Atlas Copco with the following time and temperatures:
Austenitation at 930 °C for 90 minutes. Austempering at 360 °C for 3 hours.
Figure 21. Chassis component cast in silicon solution strengthened ductile irons and in conventional ADI.
Table 7. Chemical composition in weight-% for the EN-GJS-500-14 material.
C Si Mn P S Mg Cu Cr Cequ
3,19 3,85 0,13 0,013 0,012 0,043 0,027 0,033 4,16
Table 8. Chemical composition in weight-% for the EN-GJS-600-10 material.
C Si Mn P S Mg Cu Cr Cequ
3,11 4,24 0,17 0,012 0,011 0,043 0,052 0,028 4,17
Table 9. Chemical composition in weight-% for the ADI material.
C Si Mn P S Mg Cu Cr Ni
3,66 3,01 0,18 0,043 0,014 0,047 0,81 0,03 0,95
Mo Ti Sn N Cequ
0,14 0,010 0,007 0,021 4,43
Tensile tests were made from separately cast samples and performed according to EN ISO 6892-1:2009 A224 and the hardness test performed according to SS-EN ISO 6506:1:2008 (HBW 10/3000). The results are presented in Table 10.
Table 10. Mechanical properties for the castings. (Results from separately cast samples.)
Material Rp0,2 [MPa] Rm [MPa] A5 [%] HBW
EN-GJS-500-14 477 552 19,5 208
EN-GJS-600-10 539 620 15,6 219
DI before heat treatment 573 845 5,1 287
Results from the rig tests are visualised in Figure 22, Figure 23, Figure 24 and Figure 25.
Figure 22. Result from the fatigue rig test with the chassis component cast in conventional ferritic-pearlitic EN-GJS-500-7 material. H and R is the fracture position described in Figure 26. At the 170 MPa stress level one component run out (did not break).
Figure 23. Result from the fatigue rig test with the chassis component cast in solution strengthened ferritic EN-GJS-500-14 material. H and R is the fracture position described in Figure 26. At the 213 MPa stress level one component run out (did not break).
Figure 24. Result from the fatigue rig test with the chassis component cast in solution strengthened ferritic EN-GJS-600-10 material. H and R is the fracture position described in Figure 26.
Figure 25. Result from the fatigue rig test with the chassis component cast in conventional ADI material. R is the fracture position described in Figure 26.
As seen in the graphs, there are big scattering in the results. The ADI components is the only material that show rather homogeneous results and this also breaks were it was intend to do (position R). The ADI material contains intercellular phases (MgO). These derive from the magnesium treatment and will affect the fatigue properties negatively. However, the measured nodularity is really high (>90%), which is very good for ADI material and affects the fatigue in a positive way.
The silicon solution strengthened materials showed a slightly low nodularity (70-80%) and also some intercellular phases. There is a correlation between low nodularity, amount of intercellular phases and low fatigue properties. However, lower nodularity in silicon solution strengthened DI should not be as critical as in ferritic/pearlitic DI for the mechanical properties, at least for static loads.
4.1.5 Fatigue tests
In order to investigate the influence of the surface roughness on the fatigue properties, flat rods were cast in ductile iron (DI) and heat treated to ADI. The geometry of the cast samples is shown in Figure 27.
Figure 27. Geometry of the cast bars.
The samples were cast in moulds with two different sand grain size, blacking or not, shot peened or not, all visualized in Table 11. The chemical composition of the fatigue tested bars is shown in Table 12.
Table 11. Variation in production parameter for the fatigue test rods. Serie Sand Blacking Shot peening Machined Polished
1 0,14 Yes Yes No No
2 0,14 Yes No No No
3 0,14 No No No No
4 0,25 No Yes No No
5 0,25 No No No No
Table 13. Mechanical properties before and after heat treatment. (Results from separately cast samples, data taken from Table 10.)
Material Rp0,2 [MPa] Rm [MPa] A5 [%] HBW
DI before heat treatment 573 845 5,1 287
ADI after heat treatment 786 1072 5,9 342
The microstructure was analysed before and after the heat treatment. Figure 28 and Figure 29 show the microstructure before the heat treatment in polished and etched condition, respectively. The micro structure was measured, before and after heat treatment, with image analysis program at the cross section of “the head” of the test rods. The obtained result is shown in Table 14.
Table 14. Results from image analyses from the cross-section of “the head” of the test rods. Material Nodularity [%] Pearlite content [%] Nodule count [Nod/mm2]
DI before heat treatment 94 80 526
ADI after heat treatment 90 - 507
Figure 28. Polished microstructure before heat treatment (magnification 100x and 200x).
Figure 29. Polished and etched (Nital 2%) microstructure before heat treatment (magnification 100x and 200x).
The DI bars were ADI heat treated and quenched in salt bath with the following time and temperatures:
Austenization at 930°C for 90 minutes. Austempering at 360 °C for 3 hours. The long austempering time (3h) was chosen since other commercial components were simultaneously heat treated with the bars. For the bars only 1-2 h of austempering would be enough. The polished microstructure after ADI heat treatment is shown in Figure 30 and the etched (Nital 2 %) in Figure 31 and Figure 32.
Figure 30. Polished microstructure after heat treatment (magnification 100x and 200x).
Figure 32. Polished and etched (Nital 2%) microstructure after heat treatment (magnification 500x and 1000x) showing blocky austenite regions.
The amount of austenite (white in the images) was analysed with image analysis program to about 20 %, while the rest is acicular ausferrite.
4.1.5.1 Results from the fatigue tests
The obtained mean fatigue limit values are presented in Table 15 and in Figure 33.
Table 15. The obtained fatigue limit values, i.e. the flat line from the Wöhler curves. Series Sand Blacking Shot
peening
Machined Polished Mean Fatigue limit [MPa] 1 0,14 Yes Yes No No 214 2 0,14 Yes No No No 205 3 0,14 No No No No 183 4 0,25 No Yes No No 186 5 0,25 No No No No 178
6 0,25 Yes No Yes Yes 195
7 0,25 Yes Yes Yes Yes 239
8* 0,25 Yes No Yes Yes 204
Figure 33. Stress amplitude results from the High Cycle Fatigue bending. The Limit Life was set to 106 cycles, R= -1 and runout was defined as a survivor at 3M cycles (with the exception of series 7 where runout was defined at 7M cycles). Upper and lower fatigue limit encloses the true mean with a probability of 80%.
Effect of sand size:
The smaller grain size of the sand gave a slightly higher fatigue limit (see series 3 and 5).
Effect of blacking:
Comparing series 2 and 3 it looks like blacking of the moulding sand has increased the fatigue limit about 20 MPa.
Effect of shot peening:
By comparing series 4 and 5, which are in as-cast condition, the shot peening has increased the mean fatigue limit about 10 MPa. The same result was obtained with the blacking surface (series 1 and 2). With machined surface (series 6 and 7) the fatigue limit is enhanced more than 40 MPa.
Effect of combined finer sand, black and shot peening:
By comparing series 1 and 4, the mean fatigue limit increased about 28 MPa. Effect of machining and polishing:
Machining and polishing of the cast surface (series 5 and 6), increased the mean fatigue properties almost 20 MPa.
Effect of heat treatment:
