Corrosion behaviours of additively manufactured nitrided 17-4 PH steels in different environments

Abstract

The destructive effects of corrosion on structural materials can never underestimated. These challenges depend on the constituents of engineering materials, their manufacturing techniques and working environments. Application, functionality and durability/life span of materials can be reduced, due to the attack of corrosion on them. In an attempt to further understand and reduce this problem, the corrosion behaviours of additively manufactured nitrided 17-4 PH steels in different environments were experimentally investigated. The influence of nitriding on corrosion resistance of 3.5 wt.% of sodium chloride (NaCl) and 0.5 M of sodium sulphate (Na2SO4) environments was investigated. The salt bath nitriding process was carried out on the 17-4 PH steels at three different temperatures of 530, 560 and 580 oC for 2 hours, separately. The corrosion test was conducted using electrochemical test. From the results obtained, it was evident that the as-built specimens exhibited corrosion in form of pits in both environments. From energy dispersive X-ray spectroscopy (EDS) analysis, the pit region showed the presence of manganese (Mn), sulphur (S), copper (Cu) and oxygen (O). The nitrided 17-4 PH at 580 oC produced the best/optimum corrosion resistance property when compared with as-built and other nitrided steels in both environmental conditions. The improved corrosion resistance can be attributed to the presence of homogeneous distribution of chromium (Cr) and nitrogen (N) on the surface along with other compounds. Summarily, these information or results can help to guide the choice of these engineering materials especially in thermal applications, harsh conditions and chemical/nuclear sector.