manganese-boron steels MBW ® . For ultrahigh strengths.

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Product information Manganese-boron steels Updated: September 2008 Page 1 of 11

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Hot press hardening

manganese-boron steels MBW ^® . For ultrahigh strengths.

Hot rolled Cold rolled

Applications

MBW^® manganese-boron steels are the 22MnB5 steels from ThyssenKrupp Steel. They offer ultrahigh strengths and good forming properties. By adding heat during the forming process and then cooling rapidly, the minimum tensile strengths of 500 MPa displayed by the material in the as-delivered condition can be increased to a maximum of 1650 MPa.

The hot stamping process significantly extends the possibilities for part production. Modification of process parameters allows the targeted control of part properties, such as strength or residual elongation, to provide e. g. optimized crash properties.

There are currently two common hot stamping methods: direct and indirect hot stamping. The one- stage direct hot stamping method is the most frequently used and is ideal for processing manganese boron steels with a hot-dip aluminized coating. The coating provides effective protection against scaling, which is a typical feature of the hot forming process, and thus increases the lifetimes of the forming dies.

0 10 20 30 40 50 60 70

200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 FB-W

CP-W DP-W

PAS DD

MHZ-W

MS-W

*MBW-W

**MBW-W

Tensile strength Rm (MPa)

Total elongation (%)

* As delivered ** Hot press hardened 0 10 20 30 40 50 60 70

200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 15001600 1700 Tensile strength Rm (MPa)

Total elongation (%)

* As delivered ** Hot press hardened CP-K

DP-K HX

WHZ

MHZ DC, DX

HSZ BHZ

**MBW-K

*MBW-K RA-K

20080919_ili_Manganese_boron_ste1 1

20080919_ili_Manganese_boron_ste1 1 08.10.2008 14:43:0908.10.2008 14:43:09

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The two-stage indirect hot stamping process allows the production of more complex-shaped parts, but is more complex and more cost-intensive due to the upstream cold stamping and subsequent hot stamping stages. Manganese-boron steels can be used with an x-tec(c) coating, which effectively avoids scaling and at the same time supports the hot and cold stamping processes through the use of suitable additives (see also p. 5).

Manganese-boron steels allow weight reductions when used for structural and safety components of specific strength in vehicle construction. Examples include bumper beams, side intrusion beams, pillars and body reinforcements, profile joints etc. For the applications-matched use of materials, manganese-boron steels can also be used as ThyssenKrupp Hotform Blanks (tailored blanks for hot stamping) to provide targeted part properties and reduce part weight.

Our offering is rounded out by our own test facility, with a mechanical press, furnace and heated die to simulate the die temperatures of 100-200 °C commonly used in volume production. As a partner for hot stamping, ThyssenKrupp Steel offers not only the suitable materials but also the facilities, for example to determine the optimum process parameters for hot stamping.

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Transformation behavior of manganese-boron steels

F = ferrite, P = pearlite, B = bainite, M = martensite, M = carbon enriched martensite

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Steel grade designation

Material characteristics

Manganese-boron steels are heat-treatable steels. They have a tailored chemical composition which allows hardening after hot stamping. Parts produced in this way display good ductility and strengths of up to 1650 MPa. Paint baking provides additional bake hardening potential with an average yield strength increase of approx. 100 MPa.

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50 μm 50 μm

Example of cold rolled manganese-boron steel microstructure in as-delivered condition.

Microstructure contrasting via Nital etching

Example of cold rolled manganese-boron steel microstructure in as-delivered condition.

Microstructure contrasting via Klemm color etching ThyssenKrupp Steel EN standard

MBW-W^®1500 based on EN 10083-3

MBW-K^®1500 based on EN 10083-3

MBW^® 1500 +AS based on EN 10083-3

Cold rolled Hot rolled

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Technical features

Chemical composition (ladle analysis in %)*

Manganese-boron steels are fully killed steels with a minimum aluminum content of 0.015 %.

Permissible deviations of the check analysis as per Table 4 in accordance with EN 10083-3.

Carbon equivalent in %: C_e = C + ≤ 0.54

Mechanical properties of transverse specimens in as-delivered condition*¹⁾

1) For direct hot forming, the mechanical properties of the initial condition are of lesser importance

2) W = hot rolled; K = cold rolled;

3) Thickness ≤ 3.0 mm; AS: hot-dip aluminized fal

* Unless otherwise agreed, the values indicated are binding upon order placement.

Re Rm A80 %³⁾

Condition Steel grade²⁾ MPa MPa min

uncoated MBW-W^® 1500 ≥ 320 >≥ 500 10

uncoated

recrystallization MBW-K^® 1500 310 - 400 480 - 560 20 annealed

AS-coated MBW^® 1500 +AS 360 - 500 550 - 700 12 Mn + Si

6

Steel grade C Si Mn P S Cr + Mo Ti B

max max max max max max max max

MBW-W^®1500

MBW-K^®1500 0.25 0.40 1.40 0.025 0.010 0.50 0.05 0.0050 MBW^® 1500 +AS

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Typical mechanical properties after heat treatment and rapid cooling⁴⁾

Surface treatment

Available finishes and coatings

Surface protection with x-tec^®

x-tec^® is a multi-functional paint system based on advanced nanotechnology which serves primarily as protection against scaling. With corresponding additives, x-tec^® also supports the cold and hot stamping processes and can thus contribute to longer die lifetimes. ThyssenKrupp Steel applies x-tec^® to manganese-boron steel for hot stamping by coil coating.

4) Austenitizing at 920 °C, subsequent water cooling

AS: hot-dip aluminized fal S: production supply

R_e R_m A₈₀%

Steel grade MPa MPa

MBW-W^®1500

MBW-K^®1500 1100 1650 5.0

MBW^® 1500 +AS

Steel grade uncoated AS x-tec^®

MBW-W^®1500 S — —

MBW-K^®1500 S — S

MBW^® 1500 +AS — S —

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Processing information Forming

Manganese-boron steels display outstanding hot stamping behavior. In the austenitizing temperature range, the formability of these grades is comparable with that of mild deep-drawing steels at room temperature.

Joining

Manganese-boron steels for hot stamping in both the as-delivered and the hot-stamped condition are suitable for welding with steels of the same or different grade on the condition that the welding parameters are matched to the material. Resistance spot welding, shield gas welding and laser beam welding are particularly suitable.

Resistance spot welding is the process of choice as it offers several advantages – it is easy to automate, delivers low component distortion and does not need weld fillers. In comparison with lower-strength steels, resistance spot welding of manganese-boron grades calls for higher electrode forces and longer welding times – optionally as multiple-pulse welding according to ISO 18278-2.

The welding ranges for both similar and dissimilar metal joints are wide for this strength class.

The spot welded joints are relatively ductile, i. e. despite the relatively high material strength and hardness of the weld joint, they generally suffer mixed mode fracture failure in the chisel test with a relatively high amount of nugget pull-out. Joint strengths follow the strengths of the base materials joined; in dissimilar joints, the joint strength is naturally influenced by the softer of the two materials.

The information sheet DVS 0938-2 “Arc brazing” describes the brazing of steels up to a tensile strength Rm of approximately 500 MPa. As the material here is above that strength, it is advisable to check suitability for brazing depending on the part.

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Results of resistance spot welding examinations (examples)

Thick- Thick- Force ts l min l max l Type of No. Material 1 ness 1 Material 2 ness 2 [kN] [Per] [kA] [kA] [kA] failure

1 MBW-K^® 1500 1.8 MBW-K^® 1500 1.8 4.5 20 6.5 10 3.5 M

2 RA-K^®42/80 +ZE 1.0 MBW-K^® 1500 1.8 4.5 20 6.1 9.7 3.6 N

3 MHZ 300 +Z 1.2 MBW-K^® 1500 1.8 4.5 20 6.7 11.2 3.5 N

M = Mixed mode N = Nugget

Example parameters for resistance spot welding

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Fatigue strength and energy absorption (crash performance)

Manganese-boron steels are offered specifically for hot stamping. Heat treatment in conjunction with hot stamping develops the material characteristics which go on to characterize the load bearing ability (strength, fatigue strength and crash properties). Due to the predominant effect of hot stamping (including heat treatment) on material properties, the description of material properties must be made by the component manufacturer. In general it can be said that due to their very high yield strength levels, these steels are used for components which are not intended to deform during a crash.

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Available shapes and sizes

Manganese-boron-steel MBW^® 1500 +AS, width < 900 mm available as slit strip. Higher thicknesses on request.

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Application examples

A manganese-boron steel tunnel with x-tec^® coating manufactured by indirect hot stamping

B pillar as ThyssenKrupp Hotform Blank made from hot-dip aluminized

manganese-boron steel and hot-dip aluminized microalloyed steel MHZ 340 +AS, sheet thicknesses: 1.55 mm and 1.55 m, manufactured by direct hot stamping

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Authorized users of our KISS customer information and service system can also access the latest product overview at http://kiss.thyssenkrupp-steel.com.

General Note:

All statements as to the properties or utilization of the materials and products mentioned in this brochure are for the purpose of description only.

Guarantees in respect of the existence of certain properties or utilization of the material mentioned valid are only if agreed upon in writing.

Subject to technical changes without notice. Reprints, even extracts, only with permission of ThyssenKrupp Steel AG.

ThyssenKrupp Steel AG

Kaiser-Wilhelm-Strasse 100, 47166 Duisburg Postal address: 47161 Duisburg

Telephone: +49 (0) 203 52-0, Telefax: +49 (0) 203 52-25102 E-Mail: info.steel@thyssenkrupp.com

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