QPQ Nitriding Process Parameters Of 42CrMo Piston Rod

In the actual production of continuous casting production line,the mould vibrating cylinder works at the frequency of 2-4Hz,which causes serious wear on the piston rod surface of the vibrating cylinder,and SO2,H2 S,CO2 and other gases in the air etch the piston rod surface.Under the interaction of wear and corrosion,the wear on the piston rod surface is intensified,resulting in the leakage of hydraulic working medium or even the abnormal operation.In order to solve this problem,QPQ(quench Polish quench)salt bath nitriding process was used to nitride the surface of 42 Cr Mo steel piston rod,and the QPQ(quench Polish quench)salt bath nitriding process parameters were found to improve the wear resistance and corrosion resistance of 42 Cr Mo steel.Under the conditions of cyanate concentration(28 ? 32)%,nitriding temperature(550 ? 590)?,nitriding time(90 ? 150)min,oxidation temperature(360 ? 380)? and oxidation time(15 ? 25)min,the QPQ salt bath nitriding treatment of 42 Cr Mo steel was carried out.The results showed that the thickness and surface of the nitriding layer of 42 Cr Mo steel were affected by the three process parameters of cyanate concentration,nitriding temperature and nitriding time The surface hardness has a great influence.In this paper,the 42 Cr Mo steel was treated with QPQ salt bath nitriding by orthogonal test.Through XRD and SEM experiments,it was found that the compound composition of the nitriding layer was mainly composed of Fe3O4,Fe2 N,Fe3N,Fe4 N and ?-Fe.These new phases refined the grains and improved the surface hardness,wear resistance and corrosion resistance of the material.The nitriding layer of the test piece showed a layered structure,covering the nitride layer of iron A layer of passivated Fe3O4 is added,which greatly prolongs the anti-corrosion time and improves the wear resistance and corrosion resistance of the material.The optimum QPQ salt bath nitriding process parameters of 42 Cr Mo steel piston rod are A3B2C2,that is,the concentration of cyanate,nitriding temperature,nitriding time are 32%,570 ? and 120 min respectively.The surface hardness of the sample is increased from 270 HV to 800 HV,which is higher than that of the base material Nearly three times,the friction coefficient is reduced by about 0.1,Tafel slope is increased by 2?4 times,corrosion current density is reduced by 2?3 orders of magnitude,which greatly improves the wear resistance and corrosion resistance,and meets the requirements of piston rod of vibration cylinder for surface hardness(520HV ? 700HV);the optimal influence degree of factors is C > B > A,that is,nitriding time > nitriding temperature > cyanate concentration.