Influence of Vacuum Heat Treatment and Salt-Bath Nitrocarburization on the Corrosion Behavior of JIS SKD61 and DH31S Hot Work Steels

The corrosion behavior of the nitrocarburized JIS SKD61 and DH31S hot work steels has been investigated. The as received JIS SKD61 and DH31S steel was quenched and tempered to obtain the tempered martensitic microstructure. The nitrocarburizing treatment was conducted in a 570°C salt bath for 40, 80, and 120 minutes, respectively. Treated specimens were characterized by means of microstructural analysis, microhardness measurements, X-ray diffraction analysis, glow discharge spectrometer analysis and electrochemical tests in a 3.5wt% NaCl aerated solution. The thickness of compound layer of nitrocarburized specimens was about 1-3μm, and the microhardness is in the range between 790 – 820 HV0.05. The compound layer of the nitrided specimen was consisted of e-phase (Fe2-3N) and the γ’-phase (Fe4N). The highest corrosion potential (Ecorr) in this study reached to -0.3 V for NC-S80 and NC-H80 specimen, it’s about 1.5 times higher than that of ferrite substrate. There is no evident difference on corrosion current density (Icorr) with prolonging nitrocarburizing treatment for both steels. Nevertheless, the corrosion properties were improved by nitrocarburizing process.