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Rapid heating is a promising technique for achieving excellent mechanical properties. This study innovatively applies rapid heating to a novel Ti–Mo martensite steel through in-situ observation experiments. By comparing the microstructure evolutions at heating rates of 1 and 30 °C/s, the relationship between microstructure and property evolution was elucidated. The results indicate that the refined austenite grains resulting from rapid heating stem from enhanced grain nucleation, accumulated dislocations, and the increased formation of new carbides under the large superheat. Furthermore, carbide maturation predominates during the slow heating process, while rapid heating accelerates new carbide precipitation with limited carbide maturation. Moreover, during rapid heating, both coherent and non-coherent relationships were observed between the (Ti, Mo, Fe)C particles and the martensite matrix, demonstrating a remarkable pinning effect on grain boundary migration. Nevertheless, during slow heating, large-sized (Ti, Mo)C carbides were formed, presenting a non-coherent relationship with the martensite matrix. Additionally, the primary differences in strength caused by rapid heating compared to slow heating include grain refinement, dislocation, and precipitation strengthenings, with dislocation strengthening playing the dominant role.

The rapid heating treatment with different tempering temperatures of 160, 200 and 320 °C was innovatively applied in one developed martensitic wear-resistant steel. The elaborate characterization on the evolution of microstructure-mechanical properties including the wear performance in different tempering temperatures were compared. Results manifested that the rapid heating treatment yielded a peak performance in the martensitic wear-resistant steel when tempered at 200 °C, by which the tensile strength and elongation were 1762.46 MPa and 13.13%, respectively, accompanied by the highest product of strength and elongation of 23.14 GPa·%. The enhanced work hardening contribution caused by the refined martensitic laths and carbides, as well as the appropriate recovery leaded to the peak performance at 200 °C. However, the mechanical properties both deteriorated by tempering at 160 and 320 °C subjecting to either the stress concentration or the coarsen carbides. Besides, the Baker–Nutting relationship between carbides and the matrix was established and furtherly proved the coarsen carbides resulted in the worst elongation by tempering at 320 °C. In addition, the main strength differences caused by different tempering temperatures were the grain refinement strengthening, dislocation strengthening, and precipitation strengthening, in which the grain refinement and precipitation strengthening played the dominating role. The current findings provide foundation for the industrial application of rapid heating techniques on the high-performance martensitic wear-resistant steels.

Rapid heat treatment is an important method to improve the properties of steel. Moreover, the study of the phase transformation process plays an important role in the formulation of rapid heat treatment. This paper investigates phase transformation behavior and microstructure evolution of ultrafine bainite at varying heating rates, and reveals the influence mechanism of retained austenite on austenitizing. Results showed that the decomposition of retained austenite was influenced by the diffusion of Si element. Therefore, the decomposition temperature of retained austenite is severely affected by the heating rate. Retained austenite completely transformed into cementite and ferrite when heating rate was below 5 °C/s. A small amount of retained austenite was kept when the heating rate was higher than 5 °C/s. The kept austenite effectively suppressed the hysteresis of Ac1 and resulted in a unique mechanism of austenite grain formation. When the heating rate range was 5–10 °C/s, some new austenite skipped the nucleation process and grew directly on the kept austenite, forming the large austenite grains. And other new austenite was obtained via nucleation and growth process. Thus, the grain size of bimodal distribution is formed. This leads to the phenomenon of austenite memory effect. When the heating rate was increased to 50 °C/s and higher, the austenite grain size was less than 14 μm. Therefore, rapid heating makes the phase transition lag. When the heating rate is high enough, part of the austenite is kept, which has an important influence on austenitizing process of the steel.

The present study aims to clarify the possibility of rapid heating in the preparation of low-carbon ultrafine (UFG) steel. The effects of heating rate on the phase transformation, microstructure and precipitation of a low-carbon microalloyed steel were elaborately investigated. The results manifest that rapid heating potentially provides a simple and innovative process for the preparation of UFG steels just by increasing the heating rate. The parent austenite grains were refined due to the more reserved (Nb, Ti, V)C precipitates and dislocations within a short heating process by rapid heating. However, an effective holding time was proposed in the rapid heating to ensure the refined austenite grains. Moreover, the synthetic influences of initial increased grain boundaries and redissolved (Nb, Ti, V)C carbides provoked the abnormal grains with weakened thermostability. Redissolution of (Nb, Ti, V)C carbides were apparent during austenite nucleation at a slow heating rate, and it was verified during the isothermal holding stage by rapid heating. In addition, the austenitic phase transition occurred at higher temperature with the increase of heating rate, by which the transformation rate was accelerated.