Dynamic compressive flow behaviour of S15C low carbon steel over wide temperature range

Abstract

The present study utilises the compressive split Hopkinson pressure bar to investigate the dynamic flow behaviour of S15C low carbon steel at temperatures ranging from 25 to 800uC. The effects of strain rate and temperature on the mechanical response and microstructure of the metal are evaluated. The flow stress of S15C low carbon steel is found to increase with increasing strain rate and to decrease with increasing temperature. Furthermore, the material temperature sensitivity is enhanced at higher strain rates. The study determines the strain rate sensitivity parameter and the activation volume under various strain rates and temperatures. It is found that the activation energy DG* varies as a function of strain rate and temperature and attains a maximum value of 62 kJ mol -1 under the current test conditions. A Zerilli-Armstrong bcc constitutive model is applied to describe the high strain rate plastic behaviour of S15C and is shown to produce acceptable results. Microstructural examination by TEM reveals that the dislocation density and degree of dislocation tangling both increase with increasing strain rate. Additionally, TEM observations indicate that a higher strain rate reduces the size of dislocation cells. Furthermore, it is shown that the annihilation of dislocations occurs more readily at elevated temperatures. The current results provide a valuable reference for the application of S15C low carbon steel in high speed plastic forming processes.