Abstract:

Microstructure of QPQ treated 40Cr alloy steel under different nitriding temperature was observed and analyzed by means of optical microscopy (OM), Vickers hardness test and pin-disc friction and wear test, the hardness gradient and wear weight loss of the carburized layer were carried out, and the morphologies of the worn surface was observed and analyzedby using SEM. The results show that after QPQ treatment at different nitriding temperatures, a surface layer consisting of oxide film, compound layer and diffusion layer is formed on the surface of 40Cr steel. However, with the increase of nitriding temperature, the thickness of nitriding layer increases first and then decreases, and the effective depth of nitriding layer reaches 0.14, 0.20, 0.29 and 0.26 mm when thenitriding temperatures are 580, 600, 620 and 640 ℃, respectively. With the increased of nitriding temperature, the wear loss decreases first and then increases, which reaches the lowest value at 620 ℃. The wear forms are all mainly abrasive wear and adhesive wear under those four nitriding temperatures, but with the increase of nitriding temperature which changes the thickness and hardness of the nitrided layer, the wear degree shows a gradual decreasing trend.

Key words: nitriding temperature, QPQ process, microstructure, microhardness, wear resistance