Saturation of complex shaped parts with thermal chromizing

Abstract

The paper proposes the composition of the saturating powder mixture and the method of thermal diffusion chromium plating using cumulative gratings, which ensures reliable production of an increased diffusion layer of chromium on the internal parts of the parts. The paper presents the results of saturation of bushings made of steel 40NiCrMo4KD at a temperature of 1000 °C for 24 hours using a nickel cumulative grating with a perforation density of 1 hole by 2 mm2. The control of the elemental composition of the diffusion layer was carried out on transverse sections in the direction from the saturating surface to the base metal of the sample using a JEOL JSM-6460 LV universal scanning (scanning) electron microscope. X-ray phase analysis (XPA) was carried out on an Ultima IV diffractometer, the radiation used was Cu Kα. The microhardness of the coatings was measured using an FM-800 microhardness tester. The use of a cumulative grating for the inner surface of the sleeve provided an increase in the depth of the chromium diffusion layer by 20 %. It is also shown that the use of a cumulative grating provides additional nickel alloying of both the surface of the saturating metal itself and the emerging outer diffusion layer, which leads to an increase in their hardness by 100...200 HV compared to similar areas saturated without the use of a cumulative grating.