Evolution of Dynamic Recrystallization in 5CrNiMoV Steel during Hot Forming

Zhiqiang Hu,Kaikun Wang

doi:10.1155/2020/4732683

Abstract

The dynamic recrystallization (DRX) behavior of 5CrNiMoV steel was investigated through hot compression at temperatures of 830–1230°C and strain rates of 0.001–10 s−1. From the experimental results, most true stress-strain curves showed the typical nature of DRX that a single peak was reached at low strains followed by a decrease of stress and a steady state finally at relatively high strains. The constitutive behavior of 5CrNiMoV steel was analyzed to deduce the operative deformation mechanisms, and the correlation between flow stress, temperature, and strain rate was expressed as a sine hyperbolic type constitutive equation. Based on the study of characteristic stresses and strains on the true stress-strain curves, a DRX kinetics model was constructed to characterize the influence of true strain, temperature, and strain rate on DRX evolution, which revealed that higher temperatures and lower strain rates had a favorable influence on improving the DRX volume fraction at the same true strain. Microstructure observations indicated that DRX was the main mechanism and austenite grains could be greatly refined by reducing the temperature of hot deformation or increasing the strain rate when complete recrystallization occurred. Furthermore, a DRX grain size model of 5CrNiMoV was obtained to predict the average DRX grain size during hot forming.

Highlights

Hot work die steel is a kind of metal material widely used for forging dies, hot extrusion dies, and die-casting dies, which makes the metal heated above the recrystallization temperature or the liquid metal into a workpiece
When the metal is subjected to plastic deformation at high temperature larger than half melting temperature, dynamic recrystallization (DRX) is the main approach of microstructure control and mechanical property improvement [1,2,3,4]. erefore, detailed research on the DRX behavior of metals during hot working is essential to optimizing processing parameters
Considerable investigations have been done on DRX kinetics, and those research studies concentrate on revealing the relationships between the deformation conditions and the microstructures by analyzing the true strain-stress curves obtained from hot compression tests

Summary

Introduction

Hot work die steel is a kind of metal material widely used for forging dies, hot extrusion dies, and die-casting dies, which makes the metal heated above the recrystallization temperature or the liquid metal into a workpiece. In order to get the optimum microstructure in terms of properties, such as strength, ductility, impact toughness, and thermal stability, the deformation process parameters such as temperature, strain per pass, strain rate, and initial grain size must be well selected. Erefore, detailed research on the DRX behavior of metals during hot working is essential to optimizing processing parameters. Considerable investigations have been done on DRX kinetics, and those research studies concentrate on revealing the relationships between the deformation conditions and the microstructures by analyzing the true strain-stress curves obtained from hot compression tests. Recrystallization models were constructed based on the hot compression tests with wide temperature and strain rate ranges to predict DRX evolution [5,6,7,8]. Gan et al [13] structured the kinetics equations of DRX and a constitutive model to predict the flow stress behavior, of which fifth order

Methods

Discussion

Conclusion