Decarburization and hardness changes of Fe-C-Cr-Mn-Si steels caused by high temperature oxidation in ambient air

In the present paper the investigation of carbon diffusion and hardness cha nges in Fe-C-Cr-Mn-Si steels initiated by surface oxidation are reported. T he oxidation anneals were carried out in ambient air. The measurements of c arbon concentration and the metallographic investigation have shown that th e steels decarburize expressively in the course of the oxidation process. T he evaluation of the carbon concentration curves N-c(x, t) yielded diffusio n coefficients D-c of carbon in the given steels. The dependence of D-c on the concentration N-i of alloying elements i is expressed by the use of dif fusion interaction coefficients beta(c)(i). The decrease of carbon concentr ation caused the increase of grain size in subsurface layers and the decrea se of hardness HV. The dependence of HV(x, t) on Nc(x, t) is expressed by t he general parabolic relationship y(t)= k t(m).