Corrosion behavior of 17-4 PH stainless steel manufactured by laser powder bed fusion: Effect of graphene coating and heat-treatment

The purpose of the study is to understand the effect of heat treatment and protective coating of graphene on the corrosion behavior of additive manufactured 17-4 PH steels. The metastable phases such as retained austenite introduced during laser powder bed fusion can be removed through appropriate heat treatments. Studies reported in literature on additive manufactured 17-4 PH steels have only focused on standard heat treatment involving solutionizing at 1040 degrees C and aging at 480-500 degrees C. The novelty of this work is that we investigate the effect of intermediate temperature heat treatment at 650 C-degrees for 2 h on the corrosion behavior and hardness of LPBF 17-4 PH steel and the same is compared to conventional 17-4 PH steel. The heat treatment temperature was arrived at from DSC studies. The microhardness of conventional 17-4 PH steel, LPBF 17-4 PH steel and its heat-treated counterpart was found to be 4.73, 3.98 and 2.82 GPa respectively. Corrosion tests in 3.5 wt% NaCl solution revealed the icorr of the conventional, LPBF and heat treated 17-4 PH steel to be 44.8, 425 and 4.8 mu A/ cm2 respectively. Although heat treatment enhanced the corrosion resistance, it caused a reduction in hardness. Hence an alternate approach involving the use of a protective graphene coating on the LPBF 17-4 PH steel was employed and this resulted in an icorr value of 14.1 mu A/cm2 which is a 96 % improvement over the uncoated material.