Improvement of erosion and erosion-corrosion resistance of 2Cr13 stainless steel by low temperature plasma nitriding

The erosion and erosion-corrosion behavior of 2Cr13 stainless steel influenced by nitriding treatment at 350°C low temperature and 550°C high temperature was studied using solid particle erosion tester and slurry erosion-corrosion apparatus. The mechanisms of erosion and erosion-corrosion resistance improvement by low temperature nitriding were investigated on the basis of microstructure analyzing, hardness testing and electrochemical impedance spectroscopy measurement. The results show that plasma nitriding treatment at both 350°C and 550°C can improve the erosion resistance of 2Cr13 stainless steel in the condition of dry erosion with small angle. Furthermore, the anti-erosion property of the steel nitrided by 350°C low temperature is much more perfect than that by 550°C nitriding. The erosion-corrosion rate of 2Cr13 stainless steel in 5% NaCl solution with 10% quartz sand was reduced by 96.7% in neutral environment and 87.4% in acidic environment by low temperature plasma nitriding, while the erosion-corrosion rate was increased 4.13 times in neutral environment and 0.49 times in acidic environment by normal nitriding. The 350°C nitrided surface was dominated by both ε-Fe₃N and a supersaturated nitrogen solid solution α_N phases which had good chemical stability and high hardness properties. Therefore the corrosion, erosion and erosion-corrosion resistances of 2Cr13 martensitic stainless steel were considerably improved by the 350°C nitriding treatment. When the nitriding temperature was above 550°C, the α_N phase decomposed into a and CrN. The Cr composition in the nitrided surface was reduced and the corrosion resistance was decreased. In addition, because of the surface hardness of normal plasma nitriding was lower than that of low temperature nitriding, so the erosion resistance of the former was inferior to that of the latter and the erosion-corrosion properties was also poorer than the latter.