Microstructure of chrome-vanadium cast iron formed during plasma surfaces treatment and subsequent heat treatment

The article presents the results of the study of Cr-V spheroidal vanadium carbides cast iron subjected to plasma surface heating. The cast iron contains 3,10% C; 1,05% Si; 3,99% Mn; 9,49% V; 9,10% Cr; 1,71% Ni; Fe being the basic metal. In as-cast state its structure consists of austenite, M7C3- and VC-based eutectics, and spheroidized VC carbides. Plasma treatment was conducted using the plasmatron of indirect action with argon being plasma-making gas. Plasma heating resulted in surface temperature increase up to 1500-1550°С which was followed by partial surface melting, the melted layer being of 160 mm depth. The initial eutectic colonies have become the melted areas; the primary austenite dendrites and spheroidal carbides did not melt. New dispersive eutectic carbides and new primary austenite dendrites developed in the melted layer under superfast crystallization after plasma heating. Thus it was concluded that plasma treatment resulted in modification effect that is a sharp decrease in the size of eutectic colonies, eutectic carbides and austenite dendrites. Subsequent heating in the furnace at 950°C leads to the decomposition of eutectic austenite with the precipitation of the secondary acicular or granular carbides which increases the microhardness of the eutectics by 60 HV as compared with the melted state