OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 1 2025 As a continuation of this study, the effect of normalizing temperature on the microstructure and mechanical properties of hot-rolled Steel 10 sheets produced both by the conventional industrial mode and with the application of DTCT was investigated. The experiments were conducted across a range of normalizing temperatures from 600 to 1,000 °C, with a holding time of 10 hours at each temperature. This extended holding time ensured the attainment of thermodynamic equilibrium at the specified temperature. The results of the study showed that altering the normalizing temperature significantly affects the steel’s microstructure [2], with increasing temperature having the most pronounced effect. It was found that increasing the normalizing temperature up to 900 °C leads to a noticeable refinement of pearlite colonies within the steel’s microstructure. This, in turn, affects the mechanical properties, necessitating further investigation of the correlations between the temperature and time parameters of normalizing and changes in strength and ductility. Additional studies will enable the optimization of the technological process to achieve the maximum benefit from the application of DTCT and subsequent normalizing. The process of structural changes in steel during normalizing proceeds with varying intensity depending on the pretreatment. It was found that steel subjected to pre-forging exhibits more active structural rearrangements during normalizing than steel that has not undergone forging. This is attributed to the higher dislocation density and higher strain energy accumulated in the steel structure after forging. These structural defects act as nucleation sites for the formation of new grains at high normalizing temperatures. Increasing the normalizing temperature up to 1,000 °C results in an increase in grain size and, consequently, coarsening of the steel structure, regardless of whether a prior DTCT was applied. This is caused by recrystallization and grain growth processes at high temperatures. The coarsening of the structure is accompanied by a decrease in strength properties and an increase in the ductility of the material. Therefore, an optimal normalizing temperature exists at which the best combination of strength and ductility is achieved. Analysis of the results obtained (Fig. 2, a, b), demonstrating the influence of normalizing temperature on the properties of hot-rolled Steel 10, revealed an optimal normalizing temperature of 900 °C. At this temperature, the most favorable combination of strength and ductility is achieved, both for steel produced by conventional technology and for steel pre-treated by deformation thermocycling (DTCT). Notably, the application of DTCT does not result in a substantial increase in strength properties compared to conventionally hot-rolled steel. However, a significant increase in ductility is observed. Specifically, an increase in relative elongation of approximately 15 % and a relative reduction in area of 11 % are observed with the use of DTCT. These considerable improvements in ductility clearly demonstrate the potential of DTCT as a method for enhancing the ductility of steel without significant strength degradation. This is a critical result, as many processes, such as cold forming or deep drawing, demand high ductility without a significant reduction in strength. The data suggest that DTCT modifies the steel microstructure in a manner that enhances its ability to undergo plastic deformation. This is probably due to the reduction of internal stresses and the redistribution of steel phase composition, leading to a more uniform distribution of deformation throughout the material volume. Overall, the results of the study confirm the feasibility of using DTCT in conjunction with normalizing to produce sheet Steel 10 with an improved balance of strength and ductility, particularly if the final product requires high ductility. Subsequent normalizing of DTCT-pretreated steel induces significant changes in its properties. A reduction in strength of approximately 15 % is observed, indicating a decrease in deformation resistance. Concurrently, the ductility of the steel increases significantly — by more than 50 % compared to the initial hot-rolled state. This change in properties is attributed to microstructural rearrangements occurring during normalizing following DTCT. The secondary heat treatment further refines the crystalline structure, which, in turn, reduces strength but significantly increases ductility. Furthermore, the normalizing process effectively relieves residual stresses accumulated in the steel during DTCT. The release of these stresses contributes to improved ductility, making the material more amenable to further forming operations. Thus, the combined effects of DTCT and normalizing produce a highly ductile material, which can be particularly valuable in the production of parts requiring substantial plastic deformation. This significant increase in ductility
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