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  • Automotive Worldwide

    Bake hardening steels

    Extract from the product catalogue -European edition

    Note: Information contained in this catalogue is subject to change.Please contact our sales team whenever you place an order to ensure that your requirements are fully met.

    Please contact us if you have a specific requirement that is not included in the range of products and services covered by this catalogue.We are also reachable by the e-mail address automotive.request@arcelormittal.com.

    http://fce.arcelormittal.com/saturnus/tmp/../sheets/images/large/_STR3654.jpghttp://fce.arcelormittal.com/saturnus/tmp/../sheets/images/large/Porte%20260%20BH.jpghttp://fce.arcelormittal.com/saturnus/tmp/../sheets/images/large/Longeron%20300%20BH.jpghttp://fce.arcelormittal.com/saturnus/tmp/../sheets/images/large/Mecanisme%20BH%20_%20UK.jpghttp://fce.arcelormittal.com/saturnus/tmp/../sheets/images/large/Microstructure%20180%20BH.jpghttp://fce.arcelormittal.com/saturnus/tmp/../sheets/images/large/Courbes%20formage%20BH_UK.jpghttp://fce.arcelormittal.com/saturnus/tmp/../sheets/images/large/Courbe%20Wohler%20180%20BH%20260%20BH_UK.jpg

  • We are also reachable by the e-mail address automotive.request@arcelormittal.com.

    Bake hardening steels High yield and tensile strengthsteels

    Description

    The composition and processing of these steels are designed to promote a significant increase in yield strength during low-temperature heat treatment, particularly paint curing.ArcelorMittal Bake hardening steels can thus achieve higher strength in the finished part while retaining good forming performance. The gain in yield strength through the "bake hardening" (BH) effect is generally greater than 40 MPa. Thanks to this BH effect, ArcelorMittal steels offer two advantages compared to conventional drawing quality steels:

    Improved dent resistance in all finished parts in the case of low forming strains (hood, roof, doors and wings);Substantial weight reduction potential at equivalent dent resistance (the decrease in thickness is offset by increased yield strength resulting from the heat treatment process).

    Bake hardening steels thus offer a suitable response to automotive bodywork requirements. By providing an excellent drawability-dent resistance combination, they enhance vehicle weight reduction and aesthetics.

    Applications

    Steels in the BH range are designed for visible (door, hood, tailgate, front wing, roof) and structural (underbody, reinforcement, cross member, lining) parts.

    Hood in 180 BH

    Door in 260 BH

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  • Front longitudinal beam in 300 BH

    Designation and standard

    Euronorms VDA 239-100

    180 BHHC180B (+ZE) /HX180BD (+Z, +ZF,

    +ZM) CR180BH (-UNC,-EG,-GI,-GA,-ZM)

    195 BH

    220 BHHC220B (+ZE) /HX220BD (+Z, +ZF,

    +ZM) CR210BH (-UNC,-EG,-GI,-GA,-ZM)

    260 BH HC260B (+ZE) /HX260BD (+Z, +ZM) CR240BH (-UNC,-EG,-GI,-ZM) 300 BH HC300B (+ZE) /HX300BD (+Z) CR270BH (-UNC,-EG,-GI)

    Euronorms Uncoated ( EN 10268: 2006+A1: 2013): Steel grade nameElectrogalvanized (EN 10268 :2006+A1: 2013 + EN 10152 :2017): Steel grade name +ZEGalvannealed (EN 10346 :2015): Steel grade name +ZFExtragal/Ultragal for visible parts (EN 10346 :2015): Steel grade name +ZZagnelis (EN 10346 :2015): Steel grade name +ZM

    VDA 239-100 Uncoated: Steel grade name-UNCElectrogalvanized: Steel grade name-EGGalvannealed: Steel grade name-GAExtragal/Ultragal for visible parts: Steel grade name-GIZagnelis: Steel grade name-ZM

    Hot rolled Cold rolled

    While the ArcelorMittal grades conform perfectly well to the indicated EN standards, ArcelorMittal grades generally offer tighter mechanical properties (see table below).The above indicative table summarizes the European and VDA standards corresponding to the ArcelorMittal product range.

    The 195 BH grade corresponds to Japanese standards.

    Guaranteed for ISO 20X80 test specimen in the transverse direction

    YS (MPa) UTS (MPa)ef (%)

    L0 = 80 mmth < 3 mm

    r n BH2 (MPa)

    180 BH 180 -230 300 -360 34 1,6 0,17 35195 BH 195 -270 340 -400 32 1,3 0,16 35220 BH 220 -270 340 -400 32 1,5 0,16 35260 BH 260 -300 370 -430 30 0,15 35300 BH 300 -360 420 -480 28 0,14 40

    Hot rolled Cold rolled

    Chemical composition (%)

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  • Chemical composition (%)

    C Mn Si Max Max Max

    180 BH 0,04 0,70 0,50 195 BH 0,06 0,70 0,50 220 BH 0,06 0,70 0,50 260 BH 0,08 0,80 0,50 300 BH 0,10 0,70 0,50

    Hot rolled Cold rolled

    Definition of BH2

    "Bake hardening" is a controlled aging phenomenon related to the presence ofcarbon and/or nitrogen in solid solutionin the steel. The BH2 parameter is used to evaluate the resulting increase in dent resistance. It is given by: BH2 = LYS -2% PS, in which LYS is the lower yield stress measured after heat treatment and PS is the yield stress after initial 2% plastic pre-strain. BH2 measurement is a reliable and reproducible way to quantify the metal's ability to harden during cataphoresis.

    The diagram below illustrates the Bake hardening mechanism and shows the displacement of carbon atoms in solution during heat treatment-typically 20 minutes at 170C to block the dislocations generated by forming. This ultimately increases the metal's yield strength.

    BH effect

    Available coatings and Worldwide availability

    Uncoated Electrogalvanized Extragal Ultragal Galvannealed Zagnelis

    EUR NAM SAM RSA CHI EUR NAM SAM RSA CHI EUR NAM SAM RSA CHI EUR NAM SAM RSA CHI EUR NAM SAM RSA CHI EUR NAM SAM RSA CHI

    180 BH

    195 BH

    220 BH

    260 BH

    300 BH

    Hot rolled Cold rolled

    Available in non-visible part quality Undergoing customer testing Under development Available in visible and non-visible part quality (Z)

    EUR : Europe Region -NAM : North America Region -SAM : South America Region -RSA : South Africa Region -CHI : China

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  • For additional information about the availability of thin organic coatings for the ArcelorMittal range of BH steels, please refer to the coating technical sheets. Curing of these organic coatings may lead to changes in mechanical properties.

    Microstructure of grade 180 BH

    Recommendations for use and secondary processing

    FormingThe bake hardening family of steels exhibits good drawability in all strain modes; its drawability is essentially equivalent to that of IF (interstitial-free) steels of similar yield strength.

    The figure below shows examples of forming limit curves for the bake hardening family of steels in a thickness of 1.0 mm.

    Forming limit curves for the bake hardening family of steels (thickness: 1.0 mm)

    ArcelorMittal has a database on the forming of BH grade steels. To integrate these steels at the design stage, a team of experts is available to perform specific studies based on modeling or shop-floor experience.

    Welding

    Weldability is determined by means of the method set out in the ISO 18278-2 standard.

    Examples of resistance spot welding parameters for the bake hardening range of products:

    Welding range (kA)

    180 BH Ez (thickness: 0.75 mm) 1,6

    180 BH nu (thickness: 0.75 mm) 1,4

    Hot rolled Cold rolled

    Due to their low alloy content, bake hardening steels can be readily welded by all conventional welding processes.ArcelorMittal can provide technical support in adjusting the welding parameters for any other product in its Bake Hardening range.

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