Tensile properties and microstructural aspects of 304L stainless steel weldments as a function of strain rate and temperature

This paper presents an investigation into the effects of loading rate and temperature on the tensile properties and microstructural evolution of 304L stainless steel weldments. The stress-strain behaviour during tension was determined by loading specimens in a material testing system at strain rates ranging from 10(-3) to 10(-1) s(-1) and temperatures between -100 and 500 degrees C. Extensive quantitative microstructural examinations were performed to identify the correlation between the tensile response and the substructure of dislocations and alpha martensite. It was found that the tensile flow stress increased with increasing strain rate, but decreased with increasing temperature. For a test conducted below room temperature, a negative strain rate sensitivity was apparent at strains exceeding 0.3. Fracture feature examination revealed that an enhanced fracture resistance was evident in the base metal at low temperatures, whereas it is evident in the weld metal at high temperatures owing to their different hardening rates and microstructural states. Microstructural analysis revealed that both the dislocation density and the alpha' martensite volume fraction increased with increasing strain rate, but decreased as the temperature was increased. In the range of -100-25 degrees C' both dislocations and alpha' martensite enhanced the strength of the tested weldment. However, between 300 and 500 degrees C, the strengthening effect was dominated only by dislocation mechanisms. For a given strain rate and temperature, a higher dislocation density existed in the weld metal, whereas a larger volume fraction of alpha' martensite was present in the base metal. Both increased dislocations and volume fractions of alpha' martensite yielded a greater work-hardening stress.