Effect of shot peening and treatment temperature on wear and corrosion resistance of sequentially plasma treated AISI 316L steel

Abstract

Austenitic stainless steels exhibit excellent corrosion resistance but relatively poor wear resistance. Previous investigations have demonstrated that surface treatments consisting of plasma carburizing and plasma nitriding were able to successfully increase the wear resistance of austenitic stainless steels. In this work, the effect of a prior shot peening (SP) process on wear and corrosion resistance of sequentially plasma carburized and plasma nitrided AISI 316L austenitic stainless steel was investigated. Triode plasma carburizing (TPC) and triode plasma nitriding (TPN) were sequentially carried out at two temperatures: 400°C and 475°C. SP processing prior to sequential plasma treatments led to a significant increase in the near-surface hardness. The sequential plasma treatment at 475°C in combination with a SP pre-treatment promoted a further increase in thicknesses of carburized and nitrided layers, leading to a greater hardening depth. The best wear resistance exhibited by austenitic AISI 316L samples subjected to SP and sequential plasma processing at higher temperature could be attributed to their high surface hardness and greater treatment depth. However, this treatment at higher temperature yielded CrN precipitates that impaired the corrosion resistance in aerated 0.5M H2SO4 aqueous solution. Electrochemical tests also revealed that the use of shoot peening prior to sequential plasma treatments at 475°C could partially counteract the deleterious reduction in corrosion resistance promoted by chromium nitride precipitation at this higher processing temperature. Although the precipitation of chromium nitrides at higher plasma processing temperatures promoted a reduction in corrosion resistance in such acidic environment, results indicate that austenitic stainless steels modified by shot peening (SP) followed by sequential plasma treatments at high processing temperatures could be potentially used in applications where high wear resistance and moderate corrosion resistance in specific environments are required.