Structure of the surface layer of cast iron after heat treatment by electric arc

Abstract

The influence of the parameters of the mode of the electric arc heat treatment of the surface layer of cast iron with spherical graphite on the structure, microhardness of the structural components and the depth of the hardening zone was studied. It is shown that electric arc heat treatment of the surface makes it possible to obtain a ledeburite structure at a depth of up to 0.4 mm with a concentration of residual austenite variable depending on the effective thermal power of the arc. In subsurface areas, a martensitic-austenitic structure with a microhardness of 8000–10000 MPa is formed in place of perlite. It includes graphite and cementite, sequentially enclosed in ledeburite and austenitic-martensitic shells. Carbon-saturated austenite is formed around partially dissolved carbon phases. It is possible to isolate dispersed inclusions of cementite in it. At the same time, the microhardness of this structural component increases. The dispersion of the components of the martensitic-austenitic structure decreases as it approaches the sample surface. The formation of ledeburite-martensitic or austenite-martensitic structures in a heat-treated electric arc working layer of cast iron with spherical graphite allows to increase the hardness. The presence of residual austenite provides additional surface hardening under conditions of dynamic contact friction. The combination of these factors provides an increase in the operational resistance of cast iron rolls with spherical graphite.