Tempered medium carbon steel with poor low-temperature toughness always limits its practical applications, while temper forming process can realize the strengthening-toughening aim by changing the microstructure. In this work, a grade 45 medium carbon steel was deformed with different rolling reduction ratios of 28%, 52%, 78%, and 82% by caliber rolling at the temperature of 500^oC, respectively. The texture intensity, high angle boundaries density, and elongated fibrous grains are gradually increased, as well as the tensile strength, fracture elongation, and low-temperature impact toughness are also improved with the increase of caliber rolling reduction ratio, and strengthening-toughening aim of 45-grade steel has been realized at high caliber rolling reduction ratio. Fibrous grains, <110>//RD texture, grain boundaries type, and carbides bimodal distribution resulted in the formation of crack bifurcation and delamination cracks during the tensile testing and impact testing, which can obviously decrease the ductile-brittle transition temperature and improve the low-temperature impact toughness. The caliber rolled 45 steel at the rolling reduction ratio of 82% obtains superior mechanical properties with the tensile strength of 964MPa, uniform elongation of 0.18, and low-temperature impact toughness of 176J at −40^oC, which can effectively extend the practical low-temperature service range of 45-grade steel.

低温韧性差的回火中碳钢始终限制了其实际应用，而回火成形工艺可以通过改变组织来实现强韧化的目的。在这项工作中，通过在500 ^{o C}的温度下进行口径轧制，使45级中碳钢以28％，52％，78％和82％的不同轧制压下率变形^。C分别。随着口径轧制压下率的增加和增强增韧的目的，织构强度，高角度边界密度和伸长的纤维晶粒逐渐增加，抗拉强度，断裂伸长率和低温冲击韧性也得到改善。以高口径轧制率实现了45级钢的轧制。纤维状晶粒，<110> // RD织构，晶界类型和碳化物双峰分布导致在拉伸试验和冲击试验中形成裂纹分叉和分层裂纹，这可以明显降低延性-脆性转变温度并提高韧性。低温冲击韧性。^o C，可以有效地扩展45级钢的实际低温使用范围。