Study of structure and properties of surface layer of 38Cr2MoA steel after ion-plasma nitriding and

In the article the results of study of the structure and micro-hardness of the surface layer of 38Cr2MoAl steel after volumetric quenching and high tempering, followed by ion-plasma nitriding, in comparison with electromechanical surface hardening (EMSH) are presented. Experimentally confirmed, that after the EMSH of 38Cr2MoAl steel, a gradient microstructure of finely dispersed martensite, bainite and austenite with a residual hardness of up to 8100 HV MPa and a depth of up to 0.8 mm is formed in the surface layer. At the same time, the maximum microhardness of the surface layer is not on the surface, but at a depth of 0.1 mm. The EMSH is formed by gradient surface layers of metal of high hardness on the surface of products. For a wide range of machine parts, EMSH can be used as a finishing treatment, since it is not accompanied by the presence of defects in the decarburization of the surface layer and deterioration of roughness. After ion-plasma nitriding for 8 hours, the microhardness of the surface layer of 38X2MYA steel was 9030 HV MPa at a depth of 0.1 mm and 8650 HV MPa at a depth of 0.2 mm. At a depth of 0.3 mm, the microhardness of the surface after nitriding and EMP are almost equal, respectively 7230 and 7170 HV MPa. The results of wear tests according to the “rubber roller — fixed sample” scheme and the American Society for Testing and Materials (ASTM G65) “Standard Method for Measuring Abrasive Abrasion using the “Dry Sand” Installation/Rubber wheel” showed high wear resistance of nitrided samples. However, with the continuation of the tests, due to the shallow depth of the nitrided layer (up to 0.3 mm), the wear resistance of the nitrided and hardened samples is leveled. The practical significance of the study is associated with the possibility of reducing the cost of manufacturing parts from nitrided steels by hardening the executive surfaces of the products of the EMSH. In addition, the EMSH allows steel 38Cr2MoAl for surface hardening and subsequent finishing by finishing turning on metal-cutting machines.