Tensile properties and strain hardening mechanism of Cr-Mn-Si-Ni alloyed ultra-strength steel at different temperatures and strain rates

Abstract

To reveal the relationship between the microstructural morphologies, tensile behaviors, and strain hardening mechanism of Cr-Mn-Si-Ni alloyed ultra-strength steel, uniaxial tensile tests of a Cr-Mn-Si-Ni alloyed steel were conducted at room temperature (RT) and elevated temperatures with different strain rates in this study. When the tensile test was carried out at RT, increased strain rate led to increased dislocation density of the tensed Cr-Mn-Si-Ni alloyed steel specimen and resulted in increased value of yield strength. Because the dislocation entanglement and strain hardening of tensed Cr-Mn-Si-Ni alloyed steel were inhibited by increased strain rate, decreased value of ultimate strength was measured. During tensile test at RT, the dislocations rearranged and transformed to low-angle grain boundaries and high-angle grain boundaries sequentially. Above microstructural evolution resulted in microstructural refinement of Cr-Mn-Si-Ni alloyed steel. The strain hardening of Cr-Mn-Si-Ni alloyed steel during tensile test at RT was divided into four stages according to the calculated values of strain hardening rate. The microstructural evolution behaviors including accumulation of dislocations, generation and transformation of slips took place in different stages of strain hardening were affected significantly by the strain rate. Based on the true stress-true strain curves, the effects of the tensile temperature and strain rate on the values of the yield strain, fracture strain, yield strength, and ultimate strength of Cr-Mn-Si-Ni alloyed steel tensed under different experimental conditions were studied. A two-stage constitutive model of Cr-Mn-Si-Ni alloyed steel associated with dislocation density was established based on the experimental results.