The Influence of Grade P6M5 Tool Steel Induction Nitriding Process Parameters on the Diffusion Layer Microhardness and Thickness

Abstract

The effect the inductor current and the duration of thermal exposure in a nitrogen medium have on the microhardness and depth of the diffusion layers formed in grade P6M5 steel is studied. The investigation was carried out on 5-mm-thick samples 10 mm in diameter that had not been subjected to preliminary heat treatment. The samples were nitrided in a specially designed chamber in the form of a sealed quartz vessel placed in an inductor. The steel samples were placed in the chamber at the inductor location level. After filling the chamber with nitrogen gas to a pressure of 0.2±0.05 MPa, the samples were subjected to high-frequency induction heating. The temperature of the samples was adjusted by changing the inductor current from 4.8 to 5.8 kA. It was found that at an inductor current of 4.8 kA, the sample was heated to a temperature above 800°C; with a further increase in the current, the sample temperature increased above 1000°C. As a result of nitriding with a duration of 300–1200 s at a temperature of 800–1000°C, a surface nitride layer with a thickness of up to 20 μm and a diffusion sublayer with a thickness of up to 200 μm were produced. The surface layers were characterized by a nitrogen content of up to 9 at % and microhardness of 1930–1950 HV (200 gf). The diffusion layers were characterized by a lower nitrogen content of up to 6 at %. and microhardness of 1450–1500 HV (100 gf). Based on the obtained experimental data, empirical models describing the effect of the inductor current and the duration of thermal exposure on the diffusion layer thickness and microhardness have been developed.