Mechanical and Wear Properties of 42CrMo Steel by Plasma Nitriding assisted Hollow Cathode Ion Source

F.S Zhao,Y.Q Zhao,Y.J Bi,Z.W Wang,X.G Xu,Z.H Zhang,Y Li,M.H Shao,Y.Y He,H.H Li

doi:10.1590/1980-5373-mr-2021-0137

Abstract

Plasma nitriding is a plasma-activated thermochemical method widely used to increase the fatigue strength, hardness and wear resistance of low-alloy steels. In this work, a new structure consisting of a hollow cathode metal plate can produce a hollow cathode discharge and heat the workpiece by radiation. This principle is used to perform hollow cathode source plasma nitriding (HCSPN). Herein, 42CrMo steels were treated by conventional plasma nitriding (CPN) and HCSPN treatments. The 42CrMo steels were nitrided at 525 °C for 6 h in NH3 atmosphere. The mechanical and dry wear properties were measured by nano-indentation, Vickers micro-indentation and ball-on-disk tribometer, respectively. The H3/E⁎2 ratio was 0.0274 GPa (H=11.51 GPa and E⁎=235.84 GPa) for the CPN sample and 0.0276 GPa (H=10.87 GPa and E⁎=215.54 GPa) for the HCSPN sample. Compared with the untreated 42CrMn steel, all the nitrided samples possess increased fracture toughness. Because the workpiece was not used as a discharge cathode, this HCSPN treatment overcame the disadvantages of the conventional CPN treatment. Additionally, results showed that the surface of the HCSPN sample was smoother than that of the CPN sample, and its tribological performance was better.

Highlights

42CrMo steel is often used as the material of hydraulic piston
No edge effect is found on the surface of the hollow cathode source plasma nitriding (HCSPN) samples
Plasma forms on the screen instead of plasma forming on the sample. This device can heat the workpiece as a high-efficiency heat source and generate plasma distributed in the discharge space and around the workpiece through diffusion and convection[28]

Summary

Introduction

Due to the high load and high impact working environment of the hydraulic system, the surface of the plunger is required to have high hardness, good wear resistance and fatigue strength[1,2,3]. Plasma nitriding is one of the most widely used surface modification methods to improve the surface hardness and wear resistance of various engineering materials[4,5,6,7]. In the Fe-N system[8,9], nitriding low alloy steels may produce the following phases: γ’-Fe4N (fcc), ε-Fe2-3N (hcp) and a nitrogen solid solution in an α-Fe phase. The alloying elements (Cr, V, and Mo) usually dissolve in these nitrides. Some special workpieces need auxiliary heating system to reach the required processing temperature[10]

Methods

Results

Conclusion