Effect of liquid nitriding at 400-670 ℃ on microstructure and properties of C110 Steel

Liquid nitriding of C110 steel was conducted in a wide range of temperatures (400-570 ℃) using a kind of chemical heat-treatments,and the hardness,mechanical and corrosion properties of the nitrided surface were evaluated.Experimental results revealed that the microstmcture and phase constituents of the nitrided surface alloy are highly depended on the processing condition.When C110 steel was subjected to liquid nitriding at 430 ℃,the nitrided layer was almost composed of a thin ε-Fe2-3N layer.When C 110 steel was subjected to liquid nitriding at 640 ℃,the phase composition of the nitrided layer was greatly changed.The nitrided layer depth increased significantly with increasing the treating temperature.The liquid nitriding effectively improved the surface hardness.After liquid nitriding,the absorption energy of the treated sample decreased and the tensile strength increased by Charpy V-notch (CVN) test.But the elongation of treated sample decreased.The reason is that the nitrided layer of sample is hardened and there is brittlement by diffusion of nitrogen atom.Despite of treatment temperature,the liquid nitriding can improve the corrosion.After being nitrided at 430 ℃,the nitrided layer of the C 110 steel was mainly composed by ε-Fe2-3N,which has excellent corrosion resistance and high microhardness,the nitrided sample has the best corrosion resistance.After nitriding temperature over 580 ℃,especially at 680 ℃,the sample's surface was covered by the thick oxide layer,which has very low hardness and corrosion resistance.So,the corrosion resistance of samples is severely compromised.