Analysis of the distribution of alloying elements in ultrafine-grained steel 05G2MFBT by atom-probe tomography

Abstract

It is shown that in low carbon steel, the structure after the controlled rolling comprises grains of ferrite and carbides. The average grain size of ferrite was 2.5 µm, the carbide size varied from 1 to 5 µm. Additional warm rolling led to the formation of a fibrous ultrafine-grained (UFG) structure with an average grain/subgrain size about 0.3 µm, the carbide size did not exceed 100 nm. The mechanical tests carried out under the uniaxial tension scheme at room temperature showed that the ultimate strength after the controlled rolling is 600-700 MPa, with a relative elongation of 21% while the impact strength at room temperature is 3.15 MJ/m2. In the state after warm rolling, the ultimate strength increased to 1000-1050 MPa, the elongation decreased from 21% to 17%, the impact strength at room temperature increased from 3.15 to 3.38 MJ/m2. One of the important factors leading to an increase in the mechanical properties of alloys is solid-solution hardening. To confirm this, a tomographic atomic-probe analysis of steel samples in both structural states was carried out, which made it possible to detect an increase in the concentration of carbon in steel ferrite by a factor of two in the state after warm rolling, compared with the state after the controlled rolling.