Plastic behavior and constitutive relations of DH-36 steel over a wide spectrum of strain rates and temperatures under tension

Abstract

To understand the plastic characteristics of DH-36 steel, uniaxial tensile tests have been performed on dog bone samples. The strain rate range is from 0.001 to 3000/s, and the initial specimen temperatures are 293–800K. To obtain the isothermal flow stress at high strain rates, dynamic recovery technique in Hopkinson Tension Bar has been used, and the interrupt and reloading tests have been performed. The value of strain rate sensitivity has been calculated based on the isothermal stresses at different strain rates. Similar to results from compressive tests, the dynamic strain aging has been observed under tension. Microstructure analysis of the samples after interrupt tests has been carried out by scanning electron microscopy (SEM). The results show that: (1) the strain rate sensitivity value is ∼0.0115 in terms of the isothermal flow stress (uncoupled with temperature) at a given strain, corresponding to 0.0045 coupled with temperature; (2) the 3rd dynamic strain aging (DSA) occurs at some relatively constant strain rates within certain temperature region under tension; DSA shifts to higher temperature or even disappears with increasing strain rates. Finally, in depth analysis of the data based on dislocation mechanisms, it leads to a physically based model which has taken into account the 3rd DSA effects. Good agreement between the theoretical prediction and experimental results has been obtained.