Effect of rare earths on mechanical properties of plasma nitrocarburized surface layer of 17-4PH steel

The aim of this investigation is to reveal the influence of rare earths (RE) addition on mechanical properties of plasma nitrocarburized 17-4PH steel. The nitrocarburized layers were characterized by optical microscope, scanning electron microscope equipped with energy dispersive X-ray analyzer, X-ray diffractometer, microhardness tester and pin-on-disc tribometer. The results showed that RE atoms could diffuse into the surface layer of 17-4PH steel plasma nitrocarburized at 500 °C for 4 h and did not change the phase structure of the surface layer. The presence of RE in the surface layer increased thickness, toughness, microhardness and wear resistance of the nitrocarburized layer. Additionally, grain boundary and micro-crack parallel to the surface have been depressed by plasma nitrocarburizing with RE addition. The severe plastic deformation, adhesion and abrasive wear produced during wear of the experimental steel could be changed into mild micro-abrasion and slight micro-crack wear by plasma nitrocarburizing without and with RE addition, respectively.