MICROSTRUCTURE OF DIFFUSION COATING ON STEEL 30XMA AFTER SIMULTANEOUS BORON-CHROMIUM-TITANATION UNDER VACUUM CONDITIONS
In this paper, a study was conducted of the process of surface diffusion saturation under vacuum conditions simultaneously with boron, chromium and titanium of low carbon 30XMA (AISI 4130) low alloy steel. Chemical-thermal treatment was carried out from a saturating daub in a vacuum oven. The saturation temperature was 950 ºС, the vacuum level was 0.1 Pa, the dwell time at the saturation temperature was 2 h. After the end of the exposure, the heating was turned off and the samples were kept in a furnace with the running pumping system to a temperature of 160 °C, after which the furnace was opened, the samples were removed and cooled in air to room temperature. After complete cooling, the samples were washed in a warm soap-soda solution. It is shown that the diffusion coating differs from the coating that forms under the conditions of the atmosphere - there is no needle-like structure characteristic of boride coatings. Durometric data indicate the formation of a diffusion coating with a thickness of up to 150 microns. The microhardness of the coating varies from 3250 HV0.1 on the surface to 1000 HV0.1 at 150 μm from the surface. The thickness of the borides, determined by metallographic, does not exceed the mark of 50 μm, its average microhardness is 2600 HV0.1. The transition zone located under the borides layer has a structure of martensite, the average microhardness of which is 1600 HV0.1. The base metal has a microstructure characteristic of this steel, which contains ferrite in an amount of about 35%, the rest is martensite. The microhardness of the ferrite is at the level of 190-210 HV0.1, martensite - 700-760 HV0.1.