Abstract
Refined microstructures achieved by cyclic heat treatment significantly contribute to improving the wear resistance of steels. To acquire the refined microstructures of 65Mn low-alloy steel, first, the specimens were solid solution-treated; then, they were subjected to cyclic heat treatment at cyclic quenching temperatures of 790–870 °C and quenching times of 1–4 with a fixed holding time of 5 min. The mechanical properties of 65Mn low-alloy steel in terms of hardness, tensile strength, elongation and wear resistance were characterized. Afterwards, the effect of cyclic heat treatment on microstructure evolution and the relationships between grain refinement and mechanical properties’ improvement were discussed. The results show that the average grain size firstly decreased and then increased with the increase in the quenching temperature. Hardness increased with grain refinement when the temperature was lower than 830 °C. Once the temperature exceeded 830 °C, hardness increased with the temperature increase owing to the enrichment of carbon content in the martensite. With the increase in cyclic quenching times, hardness continuously increased with grain refinement strengthening. In addition, both tensile strength and elongation could be significantly improved through grain refinement. The relationships among wear loss, hardness and average grain size showed that wear resistance was affected by the synthesis reaction of grain refinement and hardness. Higher hardness and refined grain size contributed to improving the wear resistance of 65Mn low-alloy steel.
Highlights
A typical spring steel, 65Mn low-alloy steel possesses dual mechanical properties of high-carbon steel and low-alloy steel involving high strength and hardness, excellent elasticity and hardenability, and superior wear resistance [1,2,3]
It is necessary to explore the microstructure evolution with cyclic heat treatment parameters and further uncover the relationships among wear resistance, hardness and grain refinement
That, with the increase in cycle quenching times, the hardness increased continuously with the decrease Materials 2021, 14, x FOR PEER REVIEinWaverage grain size. This is mainly due to the fact that, at the same optimal cyclic quenching temperature, grain refinement was prominently increased with the increase in cyclic quenching times
Summary
A typical spring steel, 65Mn low-alloy steel possesses dual mechanical properties of high-carbon steel and low-alloy steel involving high strength and hardness, excellent elasticity and hardenability, and superior wear resistance [1,2,3]. Preparing refined microstructures of 65Mn low-alloy steel is critical to improving the wear resistance and service performances of such components. Cyclic heat treatment has been applied to many steels and alloys to refine grain size and further enhance their mechanical performance without thermo-mechanical treatment or adding alloying elements This technique involves repeated heating and quenching processes. The crucial cyclic heat treatment parameters, including temperature, holding time, quenching rate and cycles, directly influence the final microstructure morphology and grain refinement effect, thereby determining the mechanical properties of steels. It is necessary to explore the microstructure evolution with cyclic heat treatment parameters and further uncover the relationships among wear resistance, hardness and grain refinement These will provide significant guidance for improving the wear resistance of 65Mn low-alloy steel through adjusting grain refinement by cyclic heat treatment. The relationships among wear loss, hardness and grain refinement were uncovered
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