Numerical modeling of the dynamic strain aging in steels at high strain rates and high temperatures

R A Rubio,M Hokka,F Gálvez Díaz-Rubio,D.A Cendón Franco

doi:10.1051/epjconf/202125002023

Abstract

Carbon steels can be heat treated to produce different microstructural variations and mechanical properties. At high temperatures the material plasticity and strength can be influenced by diffusional effects like the Portevin-Le Chatelier effect, leading to a commonly observed increased strength at elevated temperatures. The diffusional effects are influenced by the chemical composition, but also the heat treatment history that affects the local composition and especially the concentrations of free solute atoms. In this work, a numerical approach was implemented to reproduce the thermomechanical behaviour of two different microstructural variants of steel grade C45. The experimental data used to calibrate the model includes information of the plastic behaviour of material subjected to dynamic compression loading at a wide range of temperatures. Special emphasis was focused to describe the effects of the dynamic strain aging (DSA) on the flow stress. A strategy based on machine learning was implemented to obtain a model that reproduces the strengthening of the material due to diffusional effects. Cubic Support Vector Machine models were trained for both microstructure variants of the steel and different surfaces were obtained to describe the topology of the flow stress as function of temperature and strain rate. The model predictions were compared to the behaviour described by the Johnson-Cook model to estimate the influence of the DSA effect on the strength of the material at high strain rates and temperatures. Furthermore, the model quantifies how the microstructure affects the strength of the material and the strength of the DSA-hardening.

Highlights

It is well known that the plastic behaviour of metallic materials depends on temperature and strain rate
It is possible to see that the Johnson-Cook Model (JCM) does not account for the rise of the flow stress at high temperature due to the dislocation pinning by solutes atoms, while the Support Vector Machine (SVM) model can reproduce the material strengthening with increasing temperature
Even though the absolute value of the Dynamic Strain Aging (DSA) contribution to the flow stress is slightly higher in the reference microstructure, the relative contributions of the DSA on the total flow stress for the two structures are 33% for the reference structure and 42% for the globular pearlite

Summary

Introduction

It is well known that the plastic behaviour of metallic materials depends on temperature and strain rate. There are models that are widely accepted and used in the industry to predict the dependence of the flow strength on applied strain, temperature, and strain rate, such as the Johnson-Cook Model (JCM) [1]. One good example is the diffusional process of solute atoms to the cores of dislocations pinning them and leading to an increase of strength. This is widely known as Dynamic Strain Aging (DSA) or Portevin Le-Chatelier effect [2]

Methods

Results

Conclusion