Effects of Cr and Mo on Mechanical Properties of Hot-Forged Medium Carbon TRIP-Aided Bainitic Ferrite Steels

Koh-Ichi Sugimoto,Ashok Kumar Srivastava,Sho-Hei Sato,Junya Kobayashi

doi:10.3390/met9101066

Koh-Ichi Sugimoto, Ashok Kumar Srivastava + Show 2 more

Open Access

https://doi.org/10.3390/met9101066

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Journal: Metals	Publication Date: Sep 30, 2019
Citations: 16	License type: CC BY 4.0

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

Abstract

In this study, the effects of Cr and Mo additions on mechanical properties of hot-forged medium carbon TRIP-aided bainitic ferrite (TBF) steel were investigated. If 0.5%Cr was added to the base steel with a chemical composition of 0.4%C, 1.5%Si, 1.5%Mn, 0.5%Al, and 0.05%Nb in mass%, the developed steel achieved the best combination of strength and total elongation. The best combination of strength and impact toughness was attained by multiple additions of 0.5%Cr and 0.2%Mo to the base steel. The excellent combination of strength and impact toughness substantially exceeded those of quenched and tempered JIS-SCM420 and 440 steels, although it was as high as those of 0.2%C TBF steels with 1.0%Cr and 0.2%Mo. The good impact toughness was mainly caused by uniform fine bainitic ferrite matrix structure and a large amount of metastable retained austenite.

Highlights

In the past decades, first, second, and third-generation cold- and hot-rolled advanced high-strength steels (AHSSs) have been developed in the world [1,2]
Ferrite-martensite dual-phase steels, transformation-induced plasticity (TRIP)-aided steels with polygonal ferrite matrix structure, and complex steel are categorized as the first-generation AHSSs [1]
High-Mn twinning-induced plasticity (TWIP) steels are known as the typical second-generation AHSSs [2]

Summary

Introduction

First-, second-, and third-generation cold- and hot-rolled advanced high-strength steels (AHSSs) have been developed in the world [1,2]. Ferrite-martensite dual-phase steels, TRIP-aided steels with polygonal ferrite matrix structure, and complex steel are categorized as the first-generation AHSSs [1]. High-Mn twinning-induced plasticity (TWIP) steels are known as the typical second-generation AHSSs [2]. The typical third-generation AHSSs are transformation-induced plasticity (TRIP)-aided bainitic ferrite (TBF) [3], bainitic ferrite/martensite (TBM) and martensite (TM). Cold rolled AHSSs of 980−1180 MPa grade with excellent cold formability have already been applied to automotive body in white and seat frame in order to reduce the weight and enhance the crush safety [17,18,19]. 1180 MPa hot-rolled AHSS has been successfully applied in truck cylinders for concrete mixer [20]

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