Simulation of Structure Formation in Shaped Rolled Steel in the Process of Its Heat Treatment

We present the results of development of the technology of thermal hardening and thermal straightening of shaped rolled St3 steel (structural angles) based on the mathematical and physical simulation of the process of heat transfer with accelerated water cooling of the metal. For this purpose, we used the DEFORM 3D + HEAT TREATMENT software environment of the finite-element method and carried out laboratory experiments in three furnaces for different temperatures and holding times varying within broad ranges in order to simulate the modes of accelerated water cooling of shaped rolled products. The characteristics of mathematical simulation of the technology of thermal treatment of equal-section rolled structural angles 63 × 63 × 4 mm in size made of St3sp steel are presented with an aim to evaluate the structure and mechanical properties of the rolled metal. It is confirmed that the diffusion phase transformation is accompanied by the heat release (the so-called phenomenon of recalescence). We also present the temperature distributions over the sections and areas of the rolled steel showing that the less massive areas of the profile (edges of the structural angles) are cooled much more intensely than the massive sections (the top of the profile angle). However, the areas accumulating more heat transfer their heat to less massive and hardened areas. As a result, we observe the self-tempering of the martensitic areas accompanied by the formation of tempering pearlitic structure quite efficient for the purposes of operation. The laboratory investigations were carried out on three shaped profiles (equal-leg structural angles 40 × 40 × 4 and 75 × 75 × 8 mm in sizes and channel No. 5). The efficiency of thermal treatment was proved for shaped profiles made of unalloyed ordinary St3sp steel hardened within the range of tempering temperatures 200–650°C, with attainment of the hardening coefficient within the range 1.4–2.6 (according to the temporal rupture resistance). This guarantees the possibility of the production of angled rolled products of elevated strength classes within the range 440–1130 MPa instead of the original hot-rolled strength class of 320 MPa (by the yield strength). The obtained results of modeling of the technology of thermal treatment of structural angles made of St3sp steel can be extended (after the required experiments) to other types of steel (e.g., 09G2, 09G2S, 10KhSND, etc.) with the exception of expensive microalloying with vanadium, niobium, titanium, and other elements.