Multiscale Analysis of the Microstructure and Stress Evolution in Cold Work Die Steel during Deep Cryogenic Treatment.

Junwan Li,Xin Cai,Xiaochun Wu,Yiwen Wang

doi:10.3390/ma11112122

Abstract

Through a combination of 3D representative volume element (RVE) and the metallo-thermo-mechanical coupling finite element (FE) analysis, a multiscale model was established to explore the localized characteristics of microstructure and stress evolution during deep cryogenic treatment (DCT). The results suggest that after cooling to near −160 °C, the largest intensity of martensite is formed, but the retained austenite cannot be eliminated completely until the end of DCT. The driving force for the precipitation of fine and uniform carbides during DCT is provided by the competition between the thermal and phase transformation stresses. Compared with the thermal stress, the phase transformation stress during DCT plays a more significant role. At the interface between retained austenite and martensite, a reduction of around 15.5% retained austenite even induces an obvious increase in the phase transformation stress about 1100 MPa. During DCT, the maximum effective stress in RVE even exceeds 1000 MPa, which may provide a required driving force for the precipitation of fine and homogeneously distributed carbide particles during DCT.

Highlights

As an extension of conventional heat treatment (CHT), deep cryogenic treatment (DCT) is widely accepted nowadays to enhance the physical and mechanical properties of materials [1,2].It has received considerable attention in the last decade and has been employed in a wide range of manufacturing industries [3], including measuring tools, precision instrument and automobile industry, to improve the wear resistance [4,5], toughness [6,7], dimensional stability [8], fatigue life [9]and favorable residual stress condition of metal materials [10]
It is known that the influencing factors of DCT are extremely complicated, such as the minimum
It is known that the influencing factors of DCT are extremely complicated, such as the minimum temperature, hold time, cooling and warming rate, which makes it very difficult to control in practice

Summary

Introduction

As an extension of conventional heat treatment (CHT), deep cryogenic treatment (DCT) is widely accepted nowadays to enhance the physical and mechanical properties of materials [1,2]. The multi-physical field coupled model can provide a reference for the optimization of DCT processes, it still cannot capture the physical detail of retained austenite and stress evolution in the realistic microstructure at the microscale To solve this problem, micro-to-macro modeling has become one of the most popular forms of methods, including the representative volume element (RVE) method [29]. Through a combination of RVE and the metallo-thermo-mechanical coupling finite element (FE) analysis, a multiscale numerical model with the incorporation of a realistic material microstructure was established to reproduce the DCT process, capture the actual localized characteristics and evolution regularity of microstructure and stress, and provide a necessary theoretical basis for some understanding of DCT effects

Experimental Procedures

Multiscale Numerical Procedure

Results and Discussion

Conclusions