Cold Formabilities of Martensite-Type Medium Mn Steel

Koh-Ichi Sugimoto,Junya Kobayashi,Hikaru Tanino

doi:10.3390/met11091371

Koh-Ichi Sugimoto, Junya Kobayashi + Show 1 more

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https://doi.org/10.3390/met11091371

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Journal: Metals	Publication Date: Aug 30, 2021
Citations: 2	License type: CC BY 4.0

Affiliation: Shinshu University, Ibaraki University, Hitachi (Japan)

Abstract

Cold stretch-formability and stretch-flangeability of 0.2%C-1.5%Si-5.0%Mn (in mass%) martensite-type medium Mn steel were investigated for automotive applications. High stretch-formability and stretch-flangeability were obtained in the steel subjected to an isothermal transformation process at temperatures between Ms and Mf − 100 °C. Both formabilities of the steel decreased compared with those of 0.2%C-1.5%Si-1.5Mn and -3Mn steels (equivalent to TRIP-aided martensitic steels), despite a larger or the same uniform and total elongations, especially in the stretch-flangeability. The decreases were mainly caused by the presence of a large amount of martensite/austenite phase, although a large amount of metastable retained austenite made a positive contribution to the formabilities. High Mn content contributed to increasing the stretch-formability.

Highlights

To date, the first, second and third-generation advanced ultrahigh- and high-strength sheet steels (AHSSs) have been developed for the weight reduction and high crush safety of automobiles [1,2,3,4]
The cold stretch-formability and stretch-flangeability of the martensite type 5Mn steel subjected to the isothermal transformation (IT) process at the temperatures from above Ms to below Mf were investigated and were related to the microstructural properties, as well as tensile ductility
The highest UEl and TEl were achieved in the 5Mn steel subjected to the IT process at temperatures between Ms and Mf − 100 ◦ C

Summary

Introduction

The first, second and third-generation advanced ultrahigh- and high-strength sheet steels (AHSSs) have been developed for the weight reduction and high crush safety of automobiles [1,2,3,4]. In most AHSSs, their ductility is enhanced by transformation-induced plasticity (TRIP) [5] and/or twinning-induced plasticity (TWIP) [6] of metastable retained austenite, reverted austenite, and austenite. These AHSSs are categorized as follows [4], Academic Editor: Beatriz López Soria. First-generation AHSS: ferrite-martensite dual-phase (DP) steel [2,3], TRIP-aided polygonal ferrite (TPF) steel [2], TRIP-aided annealed martensite (TAM) steel [7] and complex-phase (CP) steel [3], Second-generation AHSS: high-Mn TWIP and TWIP/TRIP steels [6], Third-generation AHSS (Type A): TRIP-aided bainitic ferrite (TBF) steel [3,8,9,10], onestep and two-step quenching and partitioning (Q&P) steels [3,11,12,13], carbide-free bainitic (CFB) steel [14,15,16], and duplex-type, laminate-type, and bainitic ferrite-type medium manganese (D–MMn [17,18,19,20,21,22], L-MMn [23,24,25], and BF-MMn [26]) steels, Third-generation AHSS (Type B): TRIP-aided martensitic (TM) steel [27,28,29] and martensite-type medium manganese (M–MMn) steel [30,31,32,33]

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