Плазменная поверхностная цементация с использованием графитового покрытия

Abstract

This paper is considered a new technology of plasma surface carburization using graphite pastes made from liquid glass and graphite. The use of this type of coating together with a new composition of the plasma-forming gas (a mixture of argon and carbon dioxide) makes it possible to saturate the metal surface with carbon without surface melting. It is established that during the time of plasma action 0.1-1с the surface layer is saturated to the level of white iron concentration. The main parameters of the cemented layer are determined: the depth of the cemented layer is 35-250 μm with microhardness of up to 12000 MPa. Depending on the composition of the coating and the cooling rate, γ → α - the conversion may result in the formation of a wide range of structural components. The morphological composition obtained in the process of plasma surface carburization is very diverse and specific, which is due to the distribution of carbon in the volume of material in the plasma treatment zone, the speed parameters of heating and cooling, and the composition of the graphite coating. Each phase and structure in the hardened layer (retained austenite, cementite, martensite, ledeburite) has its own varieties. The cemented layer consists of two zones, the first zone with significant carbon supersaturation (white iron structure) is formed due to frontal diffusion of carbon (ledeburite,retained austenite, martensite). And the second zone is formed due to intensive or reactive diffusion, in this zone the carbon concentration gradually approaches the initial one.