Hardening and sensitization of conventional 316L stainless steel and Selective Laser Melted 316L stainless steel by cold rolling

Cold rolling can harden samples and cause them to exhibit different sensitization behaviors. The hardness of Selective Laser Melted (SLM) 316L stainless steel samples is much higher than that of solid solution 316L stainless steel samples. This could be attributed to small grain size, high geometric dislocation density, and optimized grain orientation of the former. A 75 % cold rolling treatment increased the hardness of both types of samples, with the substantial increase in the hardness of cold rolling solid solution 316L stainless steel being attributed to the transformation of austenitic to martensitic phase and grain refinement. Before 150 h, the Degree of Sensitization of 75 % cold rolled solid solution and SLM 316L stainless steels increased with the increase of sensitization time at 700 degrees C. However, it showed a downward trend at 200 h, at the same sensitization time, moreover, the sensitization degree of the former is higher than that of the latter, which may be attributed to the smaller grain size of SLM 316L stainless steel after cold rolling. For undeformed solid solution and SLM 316L stainless steels, the sensitization degree of the former was higher than that of the latter at 700 degrees C for 100 h and 200 h. The key factor is the inhibition effect of small grain size, high dislocation density, and low-angle grain boundary (LAGB) in SLM 316L stainless steel on sensitization. It was found that the cold rolling inhibited the sensitization for a short time (100 h), the sensitization degrees of the solid solution and SLM samples decreased by 7.0 and 9.4 times respectively; while it promote sensitization for a longer time (200 h), the sensitization degrees of the solid solution and SLM samples increased by 3.9 and 33.3 times respectively. The important reasons are the transformation of austenite to martensite phase induced by cold rolling, refined grain and stochastic grain orientation.