• No results found

Application of the low-blow impact test to the study of weldments

N/A
N/A
Protected

Academic year: 2021

Share "Application of the low-blow impact test to the study of weldments"

Copied!
117
0
0

Loading.... (view fulltext now)

Full text

(1)

T-1754

APPLICATION OP THE LOW-BLOW IMPACT TEST

TO THE STUDY OP WELDMENTS

By

(2)

ProQuest N um ber: 10781979

All rights reserved

INFORMATION TO ALL USERS

The qu ality of this repro d u ctio n is d e p e n d e n t upon the q u ality of the copy subm itted.

In the unlikely e v e n t that the a u th o r did not send a c o m p le te m anuscript and there are missing pages, these will be note d . Also, if m aterial had to be rem oved,

a n o te will in d ica te the deletion.

uest

ProQuest 10781979

Published by ProQuest LLC(2018). C op yrig ht of the Dissertation is held by the Author.

All rights reserved.

This work is protected against unauthorized copying under Title 17, United States C o d e M icroform Edition © ProQuest LLC.

ProQuest LLC.

789 East Eisenhower Parkway P.O. Box 1346

(3)

T-1754

A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial ful­ fillment of the requirements for the degree of Master of Science, Metallurgical Engineering.

Signed; ,r ,

Juan An-BoHrcT Fuentes Montemay"tr Student Golden, Colorado April 3 , 1975 Approved; /z -t'vr Dr. David K. Matlock Thesis advisor

Dr. William M. MUeller, Head Department of Metallurgical Engineering

Golden, Colorado April 3 , 1975

(4)

T-1754

ABSTRACT

A discussion is presented of the standard impact test in terms of ductility transition temperature and of fracture transition temperature, which have been associated respec­ tively with crack-initiation and crack-propagation. These two transition temperatures have been determined by means of different levels of energy absorbed, and/or # shear, and/or lateral contraction or expansion. The results have been con­ fusing in terms of which of these levels are really measuring the ductility and the fracture transition temperature.

The low-blow impact test seems to offer a solution to such arbitrary determination of the 2 transition tempera­ tures by uniquely determining 2 transition temperatures, one for crack-initiation and another for crack-propagation. The survey of such possibility has been made in this thesis using a mild-steel weldment. Weldments are particularly difficult to be studied with the standard impact test because of the relatively large scatter obtained in the results.

The low-blow impact test was able to determine, for the weld and base metal, the transition temperatures for crack initiation and for crack propagation. These transition

o o

temperatures were respectively -30 C and 10 C for weld

o o

(5)

T-1754

for the base metal in the as-hot-rolled condition. Further­ more, these transition temperatures were easier to determine in the weld metal than in the base metal. This experimental outcome was contrary to expectations of finding the weld metal more difficult to study than the base metal. The ex­ planation was found by comparing the low-blow impact test results with the total energy absorbed and the fracture surface of samples broken with the standard impact test. The weld metal showed a crack-initiation transition range at the end of a crack-propagation transition range while in the base metal the crack-initiation transition range occurred in the middle of the crack-propagation transition range. The transition temperatures for crack initiation and for crack propagation are easier to measure in the weld metal than in the base metal because the respective transi­ tion ranges are separated from each other in the weld metal but overlap each other in the base metal.

The appearance of the crack-initiation transition range at the end of the crack-propagation transition range explains why some steels show 2 transition curves (2-transi­ tion steels) in the whole transition temperature range. Furthermore, some steels can also show 3 transition ranges (3-transition steels) in the whole transition temperature range when the crack-initiation transition range appears in the middle of the crack-propagation transition range.

(6)

a?-i

754-t a b l e OF CONTENTS Page A B S T R A C T ... iii TABLE OF CONTENTS... . . . v LIST OF F I G U R E S ... viii LIST OF T A B L E S ... xi ACKNOWLEDGEMENTS... xii D E D I C A T I O N ...xiii Chapter I. INTRODUCTION ... 1 A. Main P u r p o s e ... 1

B. Description of the Low-Blow impact T e s t ... 1

C. Application of Low-Blow Impact Test to the Study of Impact Toughness • 2 D. Correlation of Low-Blow Impact Test and Design and Fracture Mechanics • 3 E. Application of the Low-Blow Impact Test to the Study of the Impact Toughness of Weldments ... . .

4-II. LITERATURE SURVEY ... 6

A. Introduction ... 6

B. Description of Impact Testing for Fracture Analysis 6 1. Standard Impact Test 6 2. Possible Disadvantages of Standard Impact Test 16 3. Motivation for the Low-Blow Impact T e s t ... 17

(7)

T-1754-Table of Contents (continued)

Chapter Page

II 4-. The Low-Blow Impact T e s t ... 19 C. Applications of the Charpy Impact Test 25 D. Relationship between the Impact Test

and Fracture Mechanics • 26 E. Applications of Low-Blow Impact Test

to the Study of Impact Toughness of

Weldments • • • • • 27 III MATERIALS AND EXPERIMENTAL PROCEDURE . . . 29 A. Materials • . . . . . 29 B. Welding Procedure • 31 C. Machining of Specimens • 31 D. Heat Treatments • 34-E. Impact Tester 34-F. Cooling and Heating of Specimens . . . 35 G. Testing Procedure 36 1. Low-Blow Impact Test 36 2. Standard Impact Test 37 3. Sample Analysis • 38 IV RESULTS AND A N A L Y S I S ... 39 A. Introduction 39 B. Low-Blow Impact Test 39 1. Crack Initiation 39 2. Crack P r o p a g a t i o n ... 50 C. Correlation Between the Low-Blow and

Standard Impact Tests . 55 1. Crack-initiation vs. Crack-Propagation

Behavior . . . 55 2. Standard Impact Test Results . . . 57

(8)

T-1754-Table of Contents (continued)

Chapter Page IV 3. Weld M e t a l ... 60 4. Base metal • • ... 62 D. General Discussion 67 1. Crack-initiation Energy 67 2. Crack-initiation Transition Temperature • • ... • 67 3. Crack-Propagation Transition Temperature • 69 4-. Concept of Steels with various

Transition Ranges. 69 V SUMMARY AND CONCLUSIONS... 73 A. Low-Blow Impact Test... . 73 B. Standard Impact Test. 74-C. The Low-Blow Impact Test and the Impact

Toughness of Weldments • 75

VI FURTHER S T U D Y... 77

APPENDIX : Tabulations of Experimental Results. • 81 LITERATURE CITED ... 92

(9)

T-1754-LIST OF FIGURES

Figure

No. Title Page

II-1 Description of fracture appearance in a Charpy sample broken in the transi­

tion temperature range • 8 II-2 Transition curves representing the

transition of metals from ductile to

brittle behavior • 10 II-3 Relationship between Ductility Transi­

tion Temperature (DTT) and Fracture

Transition Temperature (FTT) and Fracture

Behavior • 13 II-4- Concept of double transition temperature

range and its correlation with Ductility Transition Temperature (DTT) and Fracture

Transition Temperature (FTT) • 13 II-5 The fracture behavior of a steel cannot

be represented by DTT alone 15 II-6 Effect of temperature oh crack-initiation

energy and determination of crack-

initiation transition temperature (CITT) . 22 II-7 Effect of temperature on crack-propa­

gation energy (CPE) and determination of crack-propagation transition

temperature • • 22

III-1 Geometry and dimensions of base plate

and machined groove 30

(10)

T-1754-List of Figures (continued) Figure

No. Title Page

III-2 Disposition of b e a d s ... • 32 III-3 Standard Charpy V-notch specimen • 32 III-4* Orientation of specimen axis and notch . . 33 IV-1 Effect of initial low-blow energy and

temperature on depth of initial crack . 4*1 IV-2 Determination of crack-initiation energy

(CIE) and of crack-initiation transition

temperature (CITT) • 4-2 IV-3 Effect of temperature on depth of initial

crack for a constant low-blow • 4-5 IV-4 Effect of temperature on crack-initiation

energy and determination of crack-

initiation transition temperature (CITT) . 4-7 IV-5 Effect of temperature on crack-propagation

energy and determination of crack-

propagation transition temperature (CPTT) . 52 IV-6 Standard impact test results. Weld metal,

as-welded • 58 IV-7 Standard impact test results. Base metal,

as-hot-rolled. Average one transition

curve 59

IV-8 Standard impact test results, base metal, as-hot-rolled. 3 transition ranges

curve ... 61

IV-9 Relationship between standard test and low-blow impact test results. Weld metal

as-welded. 63 ix

(11)

T-1754

List of Figures (continued) Figure

No. Title

IV-^10 Relationship between standard impact test and low-blow impact test results. Base metal, as-hot-rolled • .

Page

66

(12)

T-1754

LIST OF TABLES Table

No. Title Page

IV-1 Low-blow impact test parameters for

weld and base metals • 44 APPENDIX

1 Low-blow impact test results. Weld

metal, as-welded. 81 2 Low-blow impact test results. Weld

metal, 700 °C, 1 h.,F. C ... 83 3 Low-blow impact test results. Weld

metal, 800 °C, 4 h., F. C ... 84 4 Low-blow impact test results. Weld

metal, 1000 °C, 4 h., F. C ... 85 5 Standard impact test results. Weld

metal, a s - w e l d e d ... ... 86 6 Low-blow impact test results. Base

metal, as-hot-rolled. 87 7 Low-blow impact test results. Base

metal, 700 °C, 1 h., F. C. . . . . . . 88 8 Low-blow impact test results. Base

metal, 800 °C, 4 h., F. C ... 89 9 Low-blow impact test results. Base

metal, 1000 °C, 4 h., F. C ... 90 10 Standard impact test results. Base

metal, as-hot-rolled • • ... 91

(13)

T-1754-ACKNOWLEDGMENTS

The author wants to thank his principal advisor Dr. David K. Matlock, and his graduate committee members: Drs. Walter L. Bradley and David L. Olson for the invaluable advice and help given during the course of this research.

Thanks are also due Dr. William M. Mtteller, Head of the Department of Metallurgical Engineering, Dr. William D. Copeland, Dean of the Graduate School, and the Colorado School of Mines for their encouragement and financial aid.

Mr. and Mrs. Glen Marica from Denver, Dr. Cyril Schieltz from Golden, and Don Luis Elizondo from Monterrey, N. L.,

Mexico, also contributed to the completion of this thesis with their encouragement and economic help. Thanks to all of them.

The author also wants to thank the Hobart Bros. Company for the donation to the Department of Metallurgy of the

welding equipment and filler wire used in this thesis.

Further thanks are due the Latin-American Scholarship Program of American Universities and the Conseco Nacional of Ciencia y Tecnologia (Mexico) for their respective scholarships.

(14)

T-1754

DEDICATORIA

Dedico el logro de 6sta meta con todo carino a mi Senora Esposa Luz Marla, y con todo el carino y el res- peto a mis Padres Juan Antonio Fuentes y Esperanza Gua­ dalupe Montemayor, as! como a todos mis hermanos por haberme brindado todo su apoyo y haber permanecido siem pre unidos en busca de mejores horizontes. Que el logro de 6sta meta sirva para unirnos adn mds y para acelerar nuestros progresos hacia una vida mejor

(15)

T-1754 1.

CHAPTER I

lf ' ' ^a r y

INTRODUCTION Cq iQ}-: °-l M m Bs

^ 80401

I-A MAIN PURPOSE

The main purpose of this thesis is to survey the ap­ plicability of the low-blow impact test to the study of the impact-toughness of weldments. The determination of transi­ tion temperatures is particularly difficult in weld-metals because of the scatter in the experimental results. The low-blow impact test seems to be able to detect the transi­ tion temperatures better than the standard impact test but weld-metals have not been studied so far with the low-blow impact test.

I-B DESCRIPTION OF THE LOW-BLOW IMPACT TEST

The low-blow impact test is a modification of the standard impact test and has the purpose of extending the usefulness of the Charpy impact test (Orner, 1959* P* 3^5s) from simple tool in quality control and steel selection to applications in the accurate study of impact-toughness, cor­ relation with service failures, correlation with fracture mechanics, etc. The way the low-blow impact test is expected to extend the usefulness of the impact test is by dividing

(16)

T-1754 2.

the fracturing process into crack-initiation and crack- propagation stages, i. e., nucleation and growth stages of the fracture. The low-blow impact test gives for each

testing temperature the energy spent in crack initiation and the energy spent in crack propagation. These 2 ener­ gies yield 2 graphs, one for crack-initiation energy vs. temperature and other for crack-propagation energy vs. temperature, instead of the single graph for total energy absorbed vs. temperature yielded by the standard impact test. The crack-initiation transition temperature is the temperature at which the crack-initiation behavior changes from ductile to brittle and it is determined from the graph of crack-initiation energy vs. temperature. The crack-propa­ gation transition temperature is the temperature at which the crack-propagation behavior changes from ductile to brit­ tle sind it is determined from the graph of crack-propagation energy vs. temperature. The crack-initiation energy, crack- propagation energy, crack-initiation transition temperature and crack-propagation transition temperature will be called the low-blow impact test parameters in this thesis.

I-C APPLICATION OP LOW-BLOW IMPACT TEST TO THE STUDY OP IMPACT TOUGHNESS.

The low-blow impact test parameters indicate not only which steel has a lower crack-initiation and/or crack-prop­ agation transition temperatures but also which steel has a

(17)

T-1754 3

higher crack-initiation energy, i. e., higher resistance to crack initiation. This means that two different heat treatments may produce no appreciable change in the transi­ tion temperatures while producing a significant change in the crack-initiation energy. In this case the standard im­ pact test will not detect any change in the impact-toughness of the steel while the low-blow impact test will detect the change in crack-initiation impact toughness. In other words, with the low-blow impact test, the impact toughness of a

steel at a certain temperature can be expressed not in terms of total energy absorbed but in terms of crack-initiation energy and crack-propagation energy, i. e., crack-initiation impact toughness and crack-propagation impact toughness.

I-D CORRELATION OR LOW-BLOW IMPACT TEST AND DESIGN AND PRACTURE MECHANICS.

The low-blow impact test, if instrumented, can yield the load required to initiate the crack. This load could help to determine the ability of the material to withstand dynamic loads in bending without initiating a crack. Cor­ relation of fracture mechanics can be made with the propa­ gation process during which the plastic deformation asso­ ciated with the extension of the crack is confined to a thin layer around the tip of the crack (Dvorak and Vrtel, 1966, p. 272s). The load required to propagate the crack can be determined by instrumentation and be used in fracture

(18)

me-T-1754 4

chanics calculations.

I-E APPLICATION OF THE LOW-BLOW IMPACT TEST TO THE STUDY OF THE IMPACT TOUGHNESS OF WELDMENTS.

Despite of the advantages of the low-blow impact test it has been applied a few times to hot-rolled steels but not to weldments. The low-blow impact test is especially appealing to the study of weld-metals because they show a large scatter in the energy absorbed and the detection of the transition temperatures with the standard impact test is more difficult than in the hot-rolled steels. If the scatter in weld-metal results does not permit the accurate determination of the low-blow impact test parameters, then the low-blow impact test cannot be used in the study of weld-metals. Furthermore, these parameters must respond to heat treatments so that the low-blow impact test can be used to study the effect of heat treatments in the impact- toughness of weldments.

The applicability of the low-blow impact test to the study of weldments will be studied in this thesis using mild steel base and filler metals welded with a gas metal- arc welding process. Mild steel was selected for this thesis because they show a well defined ductile-brittle transition and because they are of interest to a wide range of applica­ tions. The low-blow impact test will be applied to specimens

(19)

T-1754 5

in the as-hot-rolled, as-welded, and as-heat-treated condi­ tions to determine the low-blow impact test parameters. The parameters corresponding to the as-hot-rolled and as-welded conditions will be compared with the standard impact test results for the as-hot-rolled and as-welded specimens in an attempt to determine whether the transition temperatures for crack initiation and for crack propagation correlate with the ductility transition temperature and the fracture appearance transition temperature respectively, yielded by the standard impact test.

(20)

t-1754 6

CHAPTER II

LITERATURE SURVEY

II-A INTRODUCTION

This chapter discusses the impact test, its signifi­ cance, its limitations, and how it may be improved,, Eirst, the standard impact test is discussed as well as the cri­ teria used to measure the impact-toughness of steels. Sec­ ond, the low-blow impact test is discussed in terms of the improvements it offers to the standard impact test. Third, a review is given of the applications of the impact test, followed by a discussion of the relationship between the impact test and fracture mechanics. This chapter is finished with a discussion of the application of the low-blow impact test to the study of impact-toughness of weldments.

II-B DESCRIPTION OE IMPACT TESTING FOR FRACTURE ANALYSIS 1. Standard-Impact Test

The standard impact test uses mainly Charpy V-notch spec­ imens (Eelbeck, 1958, p. 267s; Linnert, 1967, p. 585; Stout and Doty, 1971, P« 175; United States Steel, 1971, P« 1242; Zar and Goedjen, 1961, p. 372s) to determine the temperature range in which the material shows a transition from ductile

(21)

T-1754 7.

to brittle failure (ductile-brittle transition) under impact loading. Fracture appearance characteristics change in this transition temperature range and are indicative of the duc­ tile-brittle transition which is therefore usually measured by one or more of the following (Colangelo and Heiser, 1974, p. 21; Doty, 1965, p. 300s-301s, 304s; Linnert, 1965, p.

290-292, 1967, P. 586; Norris and Wylie, 1970, p. 208; Rolfe, Haak, and Gross, 1965, p« 43s; Rosenstein and Lubahn, 1967, p. 482s; United States Steel, 1971, P- 1242):

i) The decrease in potential energy of the impacting hammer is measured and equated to the energy ab­ sorbed by the sample during fracture. In the USA this value is expressed in Ft-lbs (Doyle, Keyser, Leach, Schrader, and Singer, 1969, P« 41).

ii) The decrease in lateral contraction (necking) is measured as the initial dimension minus the final dimension under the notch root and it is called just lateral contraction. It is measured in mils and it is clearly indicated in Figure II-1a where a schematic drawing of a typical Charpy V-notch fracture surface is presented,

iii) The decrease in lateral expansion is measured as the final dimension minus the initial dimension at the back of the sample and it is called lateral expansion which is also indicated in Figure II-1a.

(22)

a?-i?54 8 Lateral contraction Lateral expansion 10

mm-WZZ7Z7ZZZ&?

f?

Original notch [77., Ductile Ov a thumbnail Shear lips Ductile hinge Brittle gran­ ular zone (a) 0>)

Figure II-1: Description of fracture appearance in a Charpy sample broken in the transition temperature range, (a) ideal representa­ tion showing the different regions asso­ ciated with fracture; (b) example of broken specimen.

(23)

T-1754 9

iv) The decrease in shear fracture is measured as the percentage of shear fracture on the total fracture surface and it is called % shear.

When the energy absorbed, $ shear, and lateral contrac­ tion or expansion are plotted vs. temperature the decrease in these parameters with a decrease in temperature produ­ ces a transition curve as shown in Figure II-2 (Stout and Doty, 1971, p. 276; Swift and Rogers, 1973, p. 150s; Weston and McKean, 1974, p. 9-3).

The transition from ductile to brittle behavior is not specified in terms of the whole transition temperature

range but rather in terms of a certain temperature within this transition temperature range as shown in Figure II-2

(Reed-Hill, 1964, p. 551; United States Steel, 19719 p. 1240). This temperature is called the transition temperature and

it is arbitrarly taken either at a certain level of energy absorbed, for example at 10 Ft-lbs, 15 Ft-lbs, 40 Ft-lbs, etc. (Czyzewski, 1975, p. W10; Strunk and Stout, 1972, p. 513s, 516s), or at a certain level of % shear, for ex­ ample 10$, 30$, 80$, etc. (Kerr, 1962, p. 263s; Roper, Koschnitzke, and Stout, 1967* p. 255s, 257s), or at a cer­ tain amount of lateral expansion or contraction, for example, 10 mis, 15 nils, etc. (Gross, 1970, p. 34; Swift and Rogers, 1971, P. 360s).

The several transition temperatures just described are generally included in 2 types of transition temperature

(24)

L A T E R A L E X P A N S I O N E N E R G Y A B S O R B E D OR C O N T R A C T I O N ( m i l s ) * S H E A R (Ft-lb s) T-1754- 10 Curve A TT 10 Curve B 80 TT TT 80 Curve C TT. TT 10 T E M P E R A T U R E

Figure II-2: Transition curves representing the tran­ sition of metals from ductile to brittle behavior as temperature is lowered, in terms of energy absorbed, Curve A; of

% shear, Curve B; and of lateral expansion or contraction, Curve C. The different tran sition temperatures are also shown in this figure.

(25)

T-1754 1 1.

given as follows (Colangelo and Reiser, 1974, p. 24; United States Steel, 1971 , 1241):

Fracture Transition Temperature (FTT) also called Fracture Appearance Transition Temperature (FATT) which is intended to mark the upper end of the transition range and the beginning of the upper shelf. FTT is taken within the temperature range in which the fracture appearance

changes from 100 % shear to about 50 % shear (Tanaka, Tani, and Ouchi, 1975, P* 20-21). FTT is considered to be asso­ ciated with crack propagation because at this temperature the crack begins in a shear manner as indicated by the shear thumbnail (Newhouse, 1963) but then changes and propagates in a brittle manner as represented in Figure II-1a (Linnert, 1965, P- 292-293; Dieter, 1961, p. 379). FTT represents therefore the change in the propagation be­ havior of the crack from relatively tough to relatively brittle (Linnert, 1965, p. 291)*

Ductility Transition Temperature (DTT) which is inten­ ded to mark the lower end of the transition temperature

range and the beginning of the lower shelf. DTT is therefore the temperature at and below which the fracture is essen­ tially brittle and the energy absorbed and the lateral con­ traction and expansion are very small. DTT is therefore taken at low values of energy absorbed and of lateral con­ traction or expansion like 10 or 15 Ft-lbs and/or 10 or 15 mils. DTT is considered to be associated with crack initia­

(26)

T-1754 12.

tion because the crack begins in a brittle manner as indi­ cated by the absence of shear thumbnail and it should there­ fore be the temperature at which the crack initiation changes from ductile (i. e., shear thumbnail) to brittle (Linnert, 1965, p. 291; Linnert, 1967, p. 588; McNicol, 1965, p* 385s; Dieter, 1961, p. 380). DTT is usxially taken at a fixed

value of energy absorbed, lateral contraction or expansion, or % shear, but it should not be so because DTT may change from steel to steel (Puzak, Babecki, and Pellini, 1958, p. 407s; Tetelman and McEvily, 1967, P* 118).

Since PTT marks the onset of easy crack propagation while DTT marks the onset of easy crack initiation, the whole transition temperature range can be represented as in Figure II-3 which is described as follows (Colangelo and Heiser, 1974, p. 24; Dieter, 1961, p. 379; Tetelman and McEvily, 1967, P* 117)• above FTT the fracture is dif­ ficult to initiate and difficult to propagate; between DTT and FTT the fracture is difficult to initiate and easy to propagate and the total energy absorbed decreases; below DTT the fracture is easy to initiate and easy to propagate and the total energy absorbed remains mainly constant with temperature.

Dieter (1961, p. 379) states that theoretically DTT and FTT correspond to 2 distinct transition temperatures ranges as shown in Figure II-4, but that real materials

(27)

E N E R G Y A B S O R B E D (F t -l b s) T-1754 13. Brittle fracture -*■ Ductile ■►fracture Easy crack initiation and-<. propagation Difficult crack initiation and propagation Brittle failure in service ---Ductile behavior in service T E M P E R A T U R E

Figure II-3: Relationship between Ductility Transition Temperature (DTT) and Fracture Transition Temperature (FTT) and fracture behavior. (Colangelo and Heiser, 1974, p* 24)

(28)

T-1754 14.

must be taken respectively, at a certain low and high level of either energy absorbed, % shear, or lateral con­ traction or expansion as shown in Figure II-2. Neverthe­ less, there is ample experimental evidence that real ma­ terials do show the 2 transition temperature ranges shown in Figure IV-4 (Armstrong and Warner, 1950, p. 297s-301s; Cowan, Fearnehough, and Nichols, 19679 p. 102s; Doty,

1955) P* 428s; Ford, Radon, and Turner, 1967» p. 857;

Griffin and Emmanuel, 1961, p. 395s; Gross and Stout, 1958 p. 151s, 153s; Grotke, 1964, p. 270s; Heuschkel, 1964, p. 377s; Johnson and Stout, 1960, p. 499s; McGeady, 1958, p. 550s; McGeady, 1968, p. 123s; McNicol, 1965* p* 387s, 388s, 390s; Nippes and Sibley, 1956, p. 476s-477s; Nippes, Savage, and Paez, 1960, p. 333s-336s; Puzak, Babecki, and Pellini, 1956, p. 404s; Savage and Owczarski, 1966, p. 58s Sibley, 1963* p. 225s, 230s-231s; Stout, Machmeir, and Quattrone, 1970, p. 524s; Suh and Turner, 1975* P* 442; Wessel and Hays, 1964, p. 223s, 228s-229s)

The fact that FTT and DTT are related to crack pro­ pagation and to crack initiation respectively, indicates that the several arbitrary transition temperatures men­ tioned previously may be reduced to 2 transition tempera­ ture, a transition temperature for crack propagation and another for crack initiation. Furthermore, these 2 tran­ sition temperatures can be determined based only on energy

(29)

E N E R G Y A B S O R B E D (Ft -lb s ) T-1754- 15 FTT S

s

§ g DTT T E M P E R A T U R E

Figure II-4-: Concept of double transition temperature range and its correlation with Ductility transition temperature (DTT) and fracture transition temperature (FTT) (Dieter, 1961, p. 379)

2 1

Figure II-5: The fracture behavior of the steel cannot be represented by DTT alone•

(30)

T-1754- 16

absorbed because the energy absorbed is directly related to, and it is easier to measure than lateral expansion or contraction and fracture appearance (Hartbower, 1954-, p. 929; Harsem and Wintermark, 1970, p. 67; Newhouse, 1963, p. 106s; Orner, 1958, p. 201s-202s; Reed-Hill, 1964, p. 549; Tetelman and McEvily, 1967, p. 117; United States Steel, 1971, p. 1243).

2. Possible Disadvantages of Standard Impact Test a) One of the limitations of the standard impact test is the lack of correlation between the different transi­ tion temperatures (Parker, 1957, P* 163; Pellini, 1956; Vanderbeck and Gensamer, 1950, p. 38s) that exist when DTT or FTT are taken arbitrarily at different levels of energy absorbed, lateral expansion or contraction, or % shear. For example, there may be no correlation between the DTT at 10 Ft-lbs and the DTT at 10 mis, resulting in

that sometimes the transition temperatures found by different investigators for the same steel do not correlate (Enzian and Salvaggio, 1950, p. 543s).

b) The scatter in the transition range produces curves that if drawn through a few points may be to the right or to the left of the real curve (Vanderbeck and Gensamer,

1950; Harris, Rinebolt and Raring, 1951, p. 4-17s), producing contradicting results (McGeady and Stout, 1950, p.246s).

(31)

T-1754- 17

c) Despite the fact that FTT and DTT are associated with crack propagation and crack initiation respectively, the standard impact test has been unable to determine in­ dependently the energies absorbed in crack initiation and in crack propagation (Judy, Puzak, and Lange, 1970, p* 201s- 203s, 205s; Linnert, 1967, p« 588) because the nature of the test allows for determination only of the total energy absorbed.

d) Even when two steels may have the same DTT, the propagation behavior or FTT may be different as shown she- matically in Figure II-5 (Armstrong and Warner, 1950, p. 297s-301s; Chin, 1969, p. 291s; Connor, Rathbone, and Gross, 1967, p. 230s).

3. Motivation for the Low-Blow Impact Test

The problems concerning the use of the standard impact test could probably be diminished or solved if the total energy absorbed in the fracturing process is divided into the energy spent in initiating the crack and energy spent in propagating it. The low-blow impact test, which has been called low-blow technique or low-blow test in the past

(Orner, 1959, P* 322s; Hatch, 1961, p. 26s; Hatch and Hartbower, 1958, p. 4-56s), seems to be able to achieve such a separa­

tion and gives a transition temperature for crack initia­ tion and another for crack propagation that correspond to very specific inflections in the transition curves eliminating

(32)

T-1754 18

thus the arbitrary determination of transition temperatures at different levels of energy absorbed, % shear, or lateral expansion or contraction.

The energy required for crack propagation can also be measured by initiating the crack by fatigue and then propa­ gating it in impact. This fatigue precracking does not deter­ mine the energy required for crack initiation, but it is felt that resistance to crack propagation is the material property of importance instead of crack initiation resis­ tance because cracks may be already present in a structure, mainly in welded structures (Linnert, 1967* P« 588). Never­ theless, the impact test results from steel plates that failed in service indicate that the temperature of service failure has been so far found equal to or lower than the DTT which corresponds to crack initiation (Dieter, 1961, p. 380; Gross and Stout, 1958, p. 151s; Harris, Rinebolt, and Raring, 1951; Williams, 1958, p. 453s). Therefore, not only resistance to crack propagation but also resistance to crack initiation should be determined, and this requires the separation of the energy for crack initiation from the energy required for crack propagation. Such separation can be done either with the low-blow impact test or with the instrumented impact test. Nevertheless this latter test,

besides requiring more equipment and a more elaborate testing procedure does not separate the crack initiation process

(33)

de-t-1754 19.

termine the 2 transition temperatures, one for crack ini­ tiation and another for crack propagation. This leaves the low-blow impact test as the most promising test not only for correlation with service failures but also for studies of impact toughness.

4. The Low-Blow Impact Test a) Procedure.

The low-blow impact test (LBIT) is the same as the standard impact test (SIT) in that it uses Charpy specimens and the same impact tester, but the LBIT instead of breaking the samples in a single blow as in the SIT, initiates first the crack by applying a low-energy blow enough to produce a small crack at the root of the Charpy notch. This initial crack is then propagated to full fracture by a full capa­ city blow. For the purposes of this thesis, the initial crack shall be taken as a crack that is approximately 0.7 mm deep. The depth has been determined by staining the initial crack before propagation with a solution of india ink plus 10 to 20fVJ of Kodak phot of lo solution as wetting agent (Orner and Hartbower, 1958). This same procedure will be followed in this thesis to detect the initial crack. It

should be noted that the initial crack is not the same as the thumbnail. The initial crack has a constant depth while the thumbnail decreases with temperature until disappearing at crack-initiation transition temperature.

(34)

t-1754 20.

The energy required to initiate the crack will be called crack-initiation energy (CIE) in this thesis while the energy required to propagate it to full fracture will be called

crack propagation energy (CPE).

V/hen the initial and propagating blows are applied at several temperatures within the transition temperature range, the LBIT produces data of CIE and CPE vs. temperature. This data is analyzed in the following sections b and c.

b) Crack Initiation.

Crack-initiation energy (CIE) is considered in this thesis as the energy of the blow that produces a crack of about 0.7 mm depth. Any small variation in depth of the initial crack is suppossed to have a negligible effect on CIE since most of CIE is spent in plastically deforming the

specimen during the bending that preceeds crack initiation (Orner and Hartbower, 1957* V * 526s; Orner and Hartbower, 1958, p. 637; Linnert, 1967* P* 588; Orner, 1958, p. 205s). Therefore CIE represents the plastic deformation that takes place during the bending of the sample and not during the separation of the surfaces of the small initial crack. What this means is that CIE is not affected by the heterogeneities of the material at the notch root.

The CIE is determined by applying different blows to various specimens at a single temperature in the upper zone

(35)

T-1754 21

breaking 3 or 4- samples and observing the fracture appearance. When this procedure is performed at several temperatures

within the transition range CIE is found to be the same (Hartbower, 1956, p. 523), probably because in this small transition temperature range the plasticity of the samples does not change. Thus the degree of bending required to

initiate the crack at different temperatures remains constant producing a constant CIE. Therefore, the procedure to find CIE vs. temperature data followed in this thesis and in previous works (Orner, 1959) is to find CIE-level blow and then apply this same blow at other temperatures within the transition range. Upon decreasing the temperature a temperature is reached at which the CIE-blow not only ini­

tiates the crack but propagates it either to full or partial depth. At this temperature, CIE suffers a transition to a lower value which is found by applying different capacity blows to various specimens until obtaining the small crack at the notch root.

The temperature of the transition of CIE to a lower value will be called in this thesis crack-initiation tran­

sition temperature (CITT) and it is graphically represented in Figure II-6 , where CIE is plotted vs. temperature. Below CITT crack initiation constitutes failure as plasticity effects are not available to halt the initiated brittle crack.

(36)

T-1754 22 d 0 •rl -P (A •P •H d *H 1 M O a u o w H O OJ W H O CITT T E M P E R A T U R E Figure II-6 s Effect of temperature on crack-initiation

energy(CIE) and determination of crack- initiation transition temperature (CITT).

60

CPTT TEMPERATURE

Figure II-7: Effect of temperature on crack-propagation energy (CPE) and determination of crack- propagation transition temperature (CPTT)*

(37)

T-1754 23

c) Crack Propagation.

The initial crack is propagated by a full capacity blow and the machine reads the energy absorbed which will be called in this thesis crack-propagation energy (CPE). This CPE is associated mainly with plastic deformation at the fracture surfaces and not with plastic deformation in the bulk which is instead associated with CIE. Over a cer­ tain transition range the CPE decreases at a fast rate cor­ responding to a decrease in the amount of ductile areas on the surface, until a temperature is reached at which such rate becomes slower producing an inflection in the absorbed energy vs. temperature as shown shematically in Pigure II-7« At this temperature most of the fracture surface is brittle with exception of the small thumbnail, shear lips and hinge (Orner and Hartbower, 1958, p. 629). Below this temperature the crack propagation is mainly brittle and absorbs very little energy, above it the crack propagation becomes more and more ductile producing a relatively rapid increase in crack-propagation energy. Therefore, this temperature marks the onset of easy propagation of a natural crack (Orner and Hartbower, 1958, p. 629) and it has been called upper tran­

sition temperature (Harris, Rinebolt, and Raring, 1951) and. low-blow transition temperature (Orner, 1959)• However in this thesis it will be called crack-propagation transition temperature (CPTT) to differentiate it from crack-initiation

(38)

T-1754-

24-transition temperature (CITT).

CPTT has been found to be independent of notch geometry because propagation takes place not from the original notch but from the initiated ductile natural crack which is the

one that depends on notch geometry (Orner, 1959,p. 315s; Orner and Hartbower, 1961, p. 467s; Parker, 1957, P« 16; Vanderbeck and Gensamer, 1950, p. 38s). CPTT has also been found experimentally to be independent of specimen dimensions as long as the thickness (width of the specimen across the notch) is larger than 0.2 in. (Orner and Hartbower, 1957; Orner and Hartbower, 1958; Orner, 1959) and CPTT is there­ fore considered to be the same for any thickness greater than 0.2 in. because any thickness larger than 0.2 in. seems to produce enough plastic constraint to produce a self-prop­ agating brittle crack in the bulk of the material. Since this plastic constraint increases with increasing sample dimen­ sions CPTT is considered to correspond to a plate of infinite dimensions, even when CPS is a function of sample size. CPTT on the other hand decreases for decreasing thicknesses below 0.2 in. (McNicol. 1965, p. 387s-390s; Orner and Hartbower, 1957, P. 521s, 525s).

CPTT has been found to correspond to PTT (Orner, 1958) which is expected to be so since CPTT and PTT correspond to crack propagation characteristics (Linnert, 1967, P* 588). Also, STT and CPTT have been found to be independent of

(39)

T-1754 25.

specimen geometry, notch sharpness, and rate of loading (Dieter, 1961, p. 380; Doyle, Keyser, Leach, Schrader, and Singer, 1969, p. 41)*

II-C APPLICATIONS OF THE CHARPY-IMPACT TEST.

Because of its small size and rapid testing procedure, the Charpy V-notch impact test is extensively used not only in the study of the influence of processing and metallur­ gical variables on impact-toughness of steel (Witt and Berggren, 1971; Bruscato, 1970; Chun, 1972; Doyle, Keyser, Leach, Schrader, and Singer, 1969, p. 4-1; Mints and Coch­ rane, 1973; Rosenstein, 1970; Swift and Rogers, 1973), but also in the selection of steels by determining which steels are tougher at the lowest service temperature, under impact loads and in the presence of stress raisers (Judy, Puzak and Lange, 1970, p. 201s; Matthews, 1970, p. 18). The study of the effect of notches, temperature and sudden loads on the fracture behavior of steels is necessary because no matter how good the design or how thorough the inspection, the service structures always contain stress raisers and are subjected to accidental impact loads and sudden decreases in temperature (Jonassen, 1952, p. 317s; Smith, 197^, P* ^5 Tipper, 1950, p. 51s).

The Charpy V-notch impact test has been also applied to correlation with service failures (Parker, 1957, P* 294*) because it has been found that temperatures corresponding

(40)

T-1754 26.

to energy values of 10 Ft-lbs or less, i. e., temperatures equal to or lower than DTT in the Charpy V-notch impact test, have given better correlation with the temperatures of service failures than any transition temperature based on energy absorbed, fracture appearance, or lateral expansion or contraction, either from the Charpy Key-notch, Schnadt, or wide plate tests (Dieter, 1961, p. 380; Gross and Stout, 1958, p. 151s; Harris, Rinebolt, and Raring, 1951; McNicol, 1965* p. 385s; Newhouse, 1963* P* 105s; Puzak and Pellini, 1954; Stout and KcGeady, 1949; Tetelman and McEvily, 1967* P* 118; Vanderbeck and Gensamer, 1950; Williams, 1958, p. 453s).

II-D RELATIONSHIP BETWEEN THE IMPACT TEST AND FRACTURE MECHANIC'S.

The standard impact test yields energy vs. temperature data that has been used mainly in quality control, compar­ ison of the suitability of various steels in a given appli­ cation, and in the study of the effect of processing and metallurgical variables on impact toughness (Karsem and Wintermark, 1970, p. 55; Matthews, 1970, p. 18; Tetelman

and McEvily, 1967* p. 113; United States Steel, 197^* P* 1242). The impact test has not been used in fracture mechanics or

in mechanic design equations because it requires to determine the load applied during impact fracture. This determination has been extensively done only since the 1960*s by instru­

(41)

T-1754 27

mentation of the impact tester (Wullaert, 1970; Turner, 1970) to obtain load vs. time data. This data has been translated into energy absorbed data which has correlated well with the energy absorbed given by the machine dial (Fearnehough and Hoy, 1964, p. 916; Turner, 1970, p. 97)* Furthermore, by comparison of the instrumented impact test results with

the results from the slow-bend test, it has been possible to differentiate between crack-initiation and crack-prop­ agation energies (Wullaert, 1970, p. 151; Kobayashi, Takai, and Maniwa, 1967), but no determination has been done so far of transition temperatures based on crack initiation and on crack propagation (Fearnehough and Hoy, 1964). Con­ sequently the instrumented impact test adds little to the study of impact-toughness acting mainly as a link between impact test and design and fracture mechanics equations by determining load information.

The energy vs. temperature data needed for impact- toughness studies can be readily obtained with the standard or with the low-blow impact test without the additional cost and experimental complications of instrumentation. II-E APPLICATIONS OF LOW-BLOW IMPACT TEST TO THE STUDY

OF IMPACT-TOUGHNESS OF WELDMSNTS.

The study of impact-toughness of weldments is difficult because the heterogeneities of the weld metal increases the

(42)

T-1754 28

samples is required to test if relatively accurate transi­ tion temperatures are to be obtained (Hawthorne, 1972, p. 37^s-375s; Judy, Puzak, and Lange, 1970, p. 203s-205s; Lange and Loss, 1970, p. 25s; Nordell and Hall, 1965, p. 130s-131s; Pellini, 1956, p. 226s, 229s, 230s; Swift and Rogers, 1971, P* 358s; Venne, 1974-, P* 1-3)- Since the low-blow impact test produces two distinct transition tem­ peratures, one for crack initiation and another for crack propagation, its application to the study of weld metal may yield more accurate transition temperatures using fewer

(43)

T-1754

CHAPTER III

MATERIALS AND EXPERIMENTAL PROCEDURE

III-A MATERIALS

The filler and base metals used in the experiments were mild steels having the following designations and nominal compositions;

Filler metal: Hobart HB-25 (AWS E70S-3) Base metal : AISI-SAE 1019

Filler metalx Base metal3^

C 0,11 0.15-0.20

Mn 1.20 0.70-1.00

Si 0.50

P 0.020 0.04-0 max.

S 0.019 0.050 max.

^Hobart Brothers Company, 1973t p. 68 ^^Hnited States Steel, 1971» P* 1118

The base metal plate had the dimensions shown in Figure III-1. The surface to be welded was ground prior to welding to eliminate oxidation as much as possible.

(44)

t-1754 30

16

2 ~

>

15”

Figure III-1: Geometry and dimensions of base plate and machined groove.

(45)

T-1754 31.

III-B WELDING PROCEDURE

A gas metal-arc welding process was used with a con­ stant voltage rectifier welder model Hobart RC-500 coupled to an automatic wire feeder model Hobart 1044. The welding parameters and characteristics were as follows:

Polarity Protective atmosphere Gas flow Average voltage Average current Peed rate Travel speed

Average heat input Interpass temperature Reverse 98% Ar-2% 02 36 fph 27.8 v 297*8 amps 1.86 ips 15.25 ipm (0.254 ips) 32.59 Kj 250 °F

Seven beads, positioned as shown in Pigure III-2, were used to fill the groove. The average current and voltage remained almost constant between beads.

III-C MACHINING OP SPECIMENS

The specimens used were standard Charpy V-notch spec­ imens shown in Pigure III-3, and were machined from the welded plate as shown in Pigure III-4. All heat-treatment was performed on Charpy blanks before machinning the notches.

(46)

T-1754 32.

Pigure III-2: Disposition of beads

T

27.5 mm

8 mm

55 mm

10 mm

(47)

T-1754 33

Figure III-4: Orientation of specimen axis and notch

(48)

T-1754 34

III-D HEAT-TREATMENTS

The ductility of the steel is improved by annealing treatments (ASM Handbook, v. 2, 197^» P* 3* 4), There­ fore 3 annealing treatments were performed to see whether they improve the impact-toughness of the weldment. These treatments were a full-annealing at 1000 °C for 4 h, a stress-relief-annealing at 700 °C for 1 h, and an inter­ mediate annealing at 800 °C for 4 h.

The specimens were annealed in a small Marshall elec­ tric furnace model 1144 that has an accuracy of - 1 °C. An atmosphere of 8 5 % Ng-15# H 2 was used to prevent oxida­ tion on the specimens which were furnace cooled after per­ forming the various annealing treatments.

Ill—E IMPACT TESTER

The impact tester used was a Tinius Olsen Universal impact tester built to ASTM Designation E-23, with Change- O-Matic head and with the following characteristics:

Capacity : 120 Ft-lbs and 264 Ft-lbs Impact velocity : 16.5 fps at 240 Ft-lbs and

11.0 fps at 120 Ft-lbs Hammer weight at

striking edge : 60 lbs

Length of hammer : 900 mm (35.43 in.) from center of suspension to center of

(49)

T-1754 35.

percussion.

Anvil span : 40 mm (1.574 in.)

The various blows used had the following characteris­ tics:

P(Ft-lbs) 10 15 20 30 35 264

H(in.) 2 3 4 6 7 52.8

V(fps) 3.28 4.01 4.6 5.67 6.13 16.83 Where:

P: Potential energy at height of releasing of pendulum.

H: Height of releasing of pendulum from the center of strike in the positioned spec­ imen to the center of percussion in ham­ mer.

V: Velocity of pendulum at moment of strik­ ing the specimen.

The various heights H were indicated on a board at­ tached conveniently to the impact tester which was cali­ brated to ASTM designation E-23 prior to testing.

III-F COOLING AND HEATING OF SPECIMENS

Dry ice and acetone or water and ice were used to cool the specimens which were held for at least 5 minutes at about 3 °C below testing temperature. An electric heater and water were used to heat the samples which were held

(50)

T-1754 36.

for at least 5 minutes at about 5 °C above test temperature. When breaking specimens at temperatures higher than 50 °C, the bath was allowed to reach the testing temperature be­ fore placing the samples in it so as not to have the sam­ ples at high temperature for a time so long as to produce microstructural changes. A bulb thermometer was used to measure the temperature. During either heating or cooling, the samples were placed at about 1 in. below the bath sur­ face and about 1 in. above the bath bottom. A jig was used to center the samples in the anvil span as fast and accurately as possible after removing them from the bath.

III-G TESTING PROCEDURE 1. Low-Blow Impact Test

The crack-initiation energy was determined by taking 4 or 5 samples and, at the same temperature, applying to

each sample a low-blow of different energy. The average low- blow energy that produced an initial crack of about 0.7 mm depth was taken as the crack-initiation energy. To determine whether this average initial energy was constant in the

temperature transition range, the above procedure was ap­ plied at 3 different temperatures, one a little above CITT, other at the upper end of the transition range, and the third one in the middle of such range. The crack-initiating

(51)

T-1754 37.

blow was then applied at decreasing temperatures until reaching the CITT at which the crack propagated to the depth. After initiated, the crack was stainned with a solu­ tion of india ink containing approximately 20$ by volume of Kodak photoflo solution as a wetting agent. The samples were dried at room temperature for about 15 hours before applying the full capacity (264 Ft-lbs) crack-propagating blows. The data recorded for each specimen broken was

crack-initiation energy (-CIE) in Ft-lbs, crack-propagation energy (CPE) in Ft-lbs, initial crack depth in mm, and temperature in °C.

13 weld-metal samples jammed the pendulum when tested at temperatures below -43 °C. The results from such samples were not included in the analyzed data as recommended by ASTM Designation E-23 (ASTM, 1973, v. 31, p. 283). Such jamming occurs when the specimen halves rebound from the anvil supports into the striking pendulum (Orner, 1958, p. 202s; Fahey, 1970, p. 79).

2. Standard Impact Test

The samples were broken with a full capacity (264 Ft- Ibs) blow at the proper temperatures. The energy absorbed in each sample was compared with its fracture appearance in order to detect the effect of temperature on the thumb­ nail, shear lips, and hinge, and consequently in the energy

(52)

T-1754 38

absorbed.

3. Sample Analysis

The impact-toughness was approached in this thesis through the determination of the transition temperatures and ranges corresponding to crack-initiation and to crack- propagation, and required as only sample analysis the ob­

servation of the fracture surface to detect changes in the size of the ductile patches visible to the naked eye. There fore, no metallographic work, hardness analysis, or other tests were deemed necessary.

(53)

T-1754 39

CHAPTER IV

RESULTS AND DISCUSSION

IV-A INTRODUCTION

This chapter presents the analysis of the experimental results produced by the low-blow and standard impact tests for the weld and base metals. The analysis is made in terms of crack-initiation energy and crack-propagation energy and includes, for the low-blow impact test, determination of the transition temperatures corresponding to crack-initiation and to crack-propagation. In addition, the standard impact test is analyzed by correlating fracture appearance with the standard energy absorbed versus temperature data, with the purpose of looking for correlations between the results from the low-blow impact test and those from the standard impact test.

IV-B LOW-BLOW IMPACT TEST (LBIT) 1. Crack Initiation

a) Crack Initiation energy (CIE)

The low-blow energy that produces an initial crack of about 0.7 nim depth is considered in this thesis as the

(54)

T-1754 40

crack-initiation energy. However, for both the weld and base metals, a crack of about 0.7 mm depth was produced, at a single temperature, by blows that differed in energy by as much as 6 Ft-lbs. For the case of the weld metal in the as-welded condition, such initial blows ranged from 27 Ft-lbs to about 33 Ft-lbs and produced the same crack depth of about 0.7 mm at temperatures of -20 °C, 10 °C, and 50 °C as it is shown in Figure IV-1. Figure IV-1 shows the initial crack as the ink-stainned zone (i. e., black lip) on the fracture surface. After initiation these samples were failed by a full capacity (264 Ft-lbs) blow and thus these fracture surfaces show also the effects of the second impact. Therefore the crack-initiation energy for the weld metal was taken at 30 Ft-lbs. Furthermore, preliminary tests with the standard impact test showed that the tempe­ rature range from -20 °C to 50 °C (i. e., Figure IV-1) was the transition range for weld metal. This was evidenced by the change in the appearance of the fracture surface which was completely brittle at -20 °G and completely ductile at 50 °C. Consequently the crack-initiation energy of 30 Ft- lbs for the weld metal was considered constant at all tem­ peratures within the transition temperature range, which are above the crack-initiation transition temperature, as it is shown in Figure IV-2. Figure IV-2 shows schematically that the crack-initiation energy falls within an energy

References

Related documents

Generally, a transition from primary raw materials to recycled materials, along with a change to renewable energy, are the most important actions to reduce greenhouse gas emissions

Both Brazil and Sweden have made bilateral cooperation in areas of technology and innovation a top priority. It has been formalized in a series of agreements and made explicit

För att uppskatta den totala effekten av reformerna måste dock hänsyn tas till såväl samt- liga priseffekter som sammansättningseffekter, till följd av ökad försäljningsandel

The increasing availability of data and attention to services has increased the understanding of the contribution of services to innovation and productivity in

Av tabellen framgår att det behövs utförlig information om de projekt som genomförs vid instituten. Då Tillväxtanalys ska föreslå en metod som kan visa hur institutens verksamhet

Generella styrmedel kan ha varit mindre verksamma än man har trott De generella styrmedlen, till skillnad från de specifika styrmedlen, har kommit att användas i större

Närmare 90 procent av de statliga medlen (intäkter och utgifter) för näringslivets klimatomställning går till generella styrmedel, det vill säga styrmedel som påverkar

På många små orter i gles- och landsbygder, där varken några nya apotek eller försälj- ningsställen för receptfria läkemedel har tillkommit, är nätet av