Modeling of Reversed Austenite Formation and Its Effect on Performance of Stainless Steel Components

Sadie Louise Green,Hemantha Kumar Yeddu

doi:10.1115/1.4050134

Abstract

Abstract The kinetics of reversed austenite formation in 301 stainless steel and its effect on the deformation of an automobile front bumper beam are studied by using modeling approaches at different length scales. The diffusion-controlled reversed austenite formation is studied by using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model, based on the experimental data. The model can be used to predict the volume fraction of reversed austenite in a temperature range of 650–750 °C. A three-dimensional elastoplastic phase-field model is used to study the diffusionless shear-type reversed austenite formation in 301 steel at 760 °C. The phase-field simulations show that reversion initiates at martensite lath boundaries and proceeds inwards of laths due to the high driving force at such high temperature. The effect of reversed austenite (RA) and martensite on the deformation of a bumper beam subjected to front and side impacts is studied by using finite element (FE) analysis. The FE simulations show that the presence of reversed austenite and martensite increased the critical speed at which the beam yielded and failed. RA fraction also affects the performance of the bumper beam.

Highlights

Steels are widely used in the automotive industry
In order to model the effect of annealing temperature and time on the reversed austenite formation, experimental data of the volume fraction of martensite reverted to austenite in 301 steels annealed at 650 ◦C, 700 ◦C and 750 ◦C was obtained from Ref. [6]
JMAK model is developed to study the kinetics of diffusional reversion of martensite, based on the experimental data

Summary

Introduction

Steels are widely used in the automotive industry. The main reason for its use is the range of yield strengths that the different grades of steel provide and their ability to absorb energy during impact. In order to model the effect of annealing temperature and time on the reversed austenite formation, experimental data of the volume fraction of martensite reverted to austenite in 301 steels annealed at 650 ◦C, 700 ◦C and 750 ◦C was obtained from Ref. Another study by Lee et al [15] confirmed the diffusional reversion mechanism in this transformation temperature range as they found reversed austenite, with a film-like structure and with a thickness of 1 μm, had formed along the martensite lath boundaries. Microstructure obtained at higher transformation temperatures, such as 7501000 ◦C, is believed to consist of granular reversed austenite structure which existed inside the martensite laths as well as the film-like reversed austenite at the lath boundaries [15] This can be attributed to the rapid grain growth which occurs due to the large amount of grain boundaries and there is a large driving force for grain growth to occur [34]

Phase-field model

Macroscopic FEA

Findings

Conclusions