Ultrafine‐grained (UFG) dual‐phase (DP) AISI 5115 steel containing 0.12 wt% Ti is developed using thermomechanical treatment of cold rolling and intercritical annealing. The aim is to investigate the effect of intercritical annealing time on microstructural changes, mechanical properties, and fracture behavior. The results show that, with increasing intercritical annealing time up to 8 min, the martensite island size and the martensite volume fraction increase, whereas the ferrite grain size is not changed. Significant TiC precipitation is found inside the ferrite grains that retards grain growth during annealing. The yield strength (YS) and ultimate tensile strength (UTS) of the UFG DP steels are enhanced by increasing the martensite volume fraction, while slightly attenuated by enlarging the size of martensite islands. A suitable combination of strength and ductility is obtained in terms of the amount of energy absorbed for UFG DP steels (UTS × UE > 160 MPa%) compared with the coarse‐grained DP steel (≈100 MPa%). The fracture mechanism of the UFG DP steel is ductile in which increasing annealing time results in a smaller average diameter of the dimples.

中文翻译：

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临界退火对含钛超细晶双相低合金钢组织和拉伸性能的影响

含有0.12 wt％Ti的超细晶粒（UFG）双相（DP）AISI 5115钢是通过冷轧的热机械处理和临界退火工艺开发的。目的是研究临界退火时间对显微组织变化，力学性能和断裂行为的影响。结果表明，随着临界退火时间的增加，直至8 min，马氏体岛尺寸和马氏体体积分数均增加，而铁素体晶粒尺寸不变。在铁素体晶粒内部发现大量的TiC沉淀，这会阻碍退火过程中晶粒的生长。UFG DP钢的屈服强度（YS）和极限抗拉强度（UTS）通过增加马氏体体积分数来提高，而通过扩大马氏体岛的尺寸而略微减弱。根据UFG DP钢的吸收能量（UTS×UE> 160 MPa％）与粗粒DP钢（≈100MPa％）相比，可以得到强度和延展性的合适组合。UFG DP钢的断裂机理是延性的，其中增加的退火时间会导致凹坑的平均直径变小。