Here we present a novel approach of intercritical heat treatment for microstructure tailoring, in which intercritical annealing is introduced between conventional quenching and tempering. This induced a heterogeneous microstructure consisting of soft intercritical ferrite and hard tempered martensite, resulting in a low yield ratio (YR) and high impact toughness in a high-strength low-alloy steel. The initial yielding and subsequent work hardening behavior of the steel during tensile deformation were modified by the presence of soft intercritical ferrite after intercritical annealing, in comparison to the steel with full martensitic microstructure. The increase in YR was related to the reduction in hardness difference between the soft and hard phases due to the precipitation of nano-carbides and the recovery of dislocations during tempering. The excellent low-temperature toughness was ascribed not only to the decrease in probability of microcrack initiation for the reduction of hardness difference between two phases, but also to the increase in resistance of microcrack propagation caused by the high density of high angle grain boundaries.

在这里，我们提出了一种用于显微组织剪裁的临界热处理的新方法，其中在常规淬火和回火之间引入了临界退火。这导致了由软的临界铁素体和回火的马氏体组成的异质组织，从而导致了高强度低合金钢的低屈服比（YR）和高冲击韧性。与具有完整的马氏体组织的钢相比，在进行临界退火后，由于存在软的临界铁素体，从而改变了钢在拉伸变形过程中的初始屈服和随后的工作硬化行为。YR的增加与由于硬质合金的析出和回火过程中位错的恢复而导致的软相和硬相之间的硬度差减小有关。