Low Temperature Deformation Induced Microstructure Refinement and Consequent Ultrahigh Toughness of a 20Mn2SiCrNi Bainitic Steel

Yu Tian,Bingzhe Bai,Zhunli Tan,Bo Gao,Min Zhang,Ji Li

doi:10.3390/met10010019

Abstract

In this paper, we have studied the influence of deformation on the microstructure and mechanical properties of 20Mn2SiCrNi bainitic high strength steel processed through a hot rolling route. Simulation of different temperatures and degrees of deformation was carried out via Gleeble-1500. The study suggested that grain size is refined when the deformation is carried out at lower temperature (> Ac3). When the degree of deformation was increased from 20% to 60%, grain size and microstructure were both refined and the size of retained austenite was reduced. The tensile strength increased from 1345 MPa to 1432 MPa. The impact toughness increased from 115 J/cm2 to 210 J/cm2 at room temperature, from 63 J/cm2 to 142 J/cm2 at −40 °C. Furthermore, it was observed that the microstructure after air cooling was composed of granular bainite (GB), lath bainite (LB) and martensite/austenite (MA) island for different deformation conditions. The study reveals that the impact toughness of 20Mn2SiCrNi bainitic high strength steel can be increased by increasing the degree of deformation.

Highlights

In recent years, with the rapid development of industry, traditional structural steels cannot completely meet development needs
High strength low alloy (HSLA) steels with high toughness and good weldability are widely used in construction machinery, petroleum industry, transportation and other fields [1,2,3]
High strength and toughness can be obtained by air cooling after fully austenitizing, followed by low temperature tempering of Mn-Si-Cr bainitic low alloy steels [4,5,6,7,8]

Summary

Introduction

With the rapid development of industry, traditional structural steels cannot completely meet development needs. There are many ways to refine grain size including alloying, cyclic quenching and thermomechanical controlled process (TMCP). Microalloying, with their precipitation phenomenon in steels, is crucial for the design of alloys in order to achieve the ideal mechanical strength during the TMCP [10,11]. Rational heat treatment such as cyclic quenching used for 1.24 wt.% carbon steel and hypereutectoid steel reaches more uniformly dispersed finer cementite particles in the austenite matrix [12,13].

Methods

Results

Discussion

Conclusion