Study of Crack Sensitivity of Peritectic Steels

By comprehensively considering both the high temperature mechanical properties and peritectic transformation during peritectic steel solidification, the strain εCth is proposed to evaluate the crack sensitivity of peritectic steels produced in the brittle temperature range in the present work. The zero ductility temperature (ZDT) and the zero strength temperature (ZST) of Fe–C–0.32Si–1.6Mn–0.01P–0.015S steel under nonequilibrium conditions by taking the effect of the peritectic transformation on the solute segregation into account were calculated by the CK microsegregation model (Clyne–Kurz model) and were compared with the measured data. The comparison results show that this model can well simulate the nonequilibrium solidification process of peritectic steel. Then, based on the calculation of the CK microsegregation model, the strain during the peritectic phase transformation in the brittle temperature range (ZDT < TB < LIT) was calculated under nonequilibrium conditions. The results show that the calculated strain is in good agreement with the actual statistical longitudinal crack data indicating that the strain can therefore be used to predict the crack sensitivity of peritectic steels effectively.

Analysis of the causes and conditions for the formation of surface defects on hot‑rolled products from peritectic steel grades obtained under the conditions OJSC “BSW – Management Company of the Holding “BMC”

OJSC “BSW – Management Company of the Holding “BMC” produces a wide range of carbon, high‑quality, alloyed and high‑carbon steel grades, among which a signifi ant share is peritectic grade steels. Basically, the steel of this group is used to produce rolled products intended for the manufacture of components for the automotive industry. The process of production and casting of these steels is characterized by the greatest instability and is often accompanied by rejects and forced sorting of products. This situation is typical for other metallurgical enterprises. Therefore, the search for technological solutions that ensure an increase in the yield while maintaining the existing productivity of metallurgical units is an urgent aspect of improving the technology of continuous casting of peritectic grade steels. At the same time, the main scientific and technical task is to obtain a stable quality of continuously cast billets, aimed at preventing and eliminating the formation of a number of characteristic defects, primarily cracks on the surface of continuously cast billets and rolled products. The search for methods and technological solutions to improve the quality of products made of peritectic grade steel is the goal of the ongoing research.

Effect of Magnesium Treatment on the Hot Ductility of Ti-Bearing Peritectic Steel

Surface cracking is a major defect in the production of continuous casting slabs of peritectic steel. The difference in crystal structure between δ phase (before peritectic transformation of steel) and γ phase (after peritectic transformation) results in volume contraction, which leads to uneven cooling of mold and thus forming slab shells with different thicknesses. Then, coupled with the concentration of local stress, surface cracking occurs on slabs. In this paper, the effect of magnesium treatment on the hot ductility of Ti-bearing peritectic steel was studied, and the characteristics of solidification structure and TiN particles were analyzed. Magnesium treatment for Ti-bearing peritectic steel could significantly improve the hot ductility of continuous casting slabs by refining the original austenite structure. After the magnesium treatment, the average grain size of the original austenite of peritectic steel decreased by about 18.7%, and the size of Mg-rich TiN particles decreased by about 41%. In addition, the minimum reduction of area at the third brittle zone after the magnesium treatment was higher than 60%, and the fracture appearance changed from intergranular fracture to ductile fracture after the treatment. The contents of Mg, Ti, O, and N in peritectic steel and the cooling conditions were adjusted reasonably to promote the formation of highly dispersed Mg-rich TiN particles with a sufficient number density and a proper size in the initial solidification stage of peritectic steel, so as to induce the high-temperature δ-ferrite nucleation. Based on the fine δ structure formed by peritectic transformation, through the use of structure heredity and the pinning effect of secondary-precipitated nano TiN particles on the austenite grain boundary, a fine and dense original austenite structure could be obtained to improve the hot ductility of peritectic steel. Industrial tests showed that through the magnesium treatment, the surface cracks of Ti-bearing peritectic steel were effectively restrained, and the corner cracks of slabs were basically eliminated.