In this paper, the mechanical properties and microstructure of hot-rolled low carbon steel containing Ti–Mg oxide inclusions as well as the effect of austenite grain size on acicular ferrite (AF) nucleation and the nucleation mechanism of AF were studied. The results indicated that the dominant inclusions in Ti–Mg deoxidized steel comprised Ti–Mg–Mn–O·MnS, which effectively promoted the nucleation of AF; thus, the microstructure after hot rolling consisted of fine AF and bainite (B). The variety of tensile property of Ti–Mg deoxidized steel was not obvious but the low-temperature impact toughness was significantly improved from 4 J to 126 J at −40 °C compared with Al deoxidized steel. Increasing the austenitizing temperature contributed to the nucleation of AF, and large amounts of fine AF formed in Ti–Mg deoxidized steel when the austenitizing temperature was 1250 °C with an average austenite grain size of ~92 μm. Two kinds of nucleation mechanisms of AF were elucidated: a Nishiyama-Wasserman (N–W) orientation relationship of (100)_ferrite‖(110)_oxide, [011]_ferrite‖[-111]_oxide between AF and Ti–Mg–Mn–O oxide, which caused low lattice disregistry, and a Mn-depleted zone (MDZ) around Ti–Mg–Mn–O·MnS inclusions. In order to investigate the reason for the formation of the MDZ, focused ion beam (FIB) was used to prepare the transmission electron microscope (TEM) sample containing a Ti–Mg–Mn–O·MnS inclusion, the specific orientation relationship of (-11-1)_MnS‖(11–1)_oxide, [-112]_MnS‖[011]_oxide between MnS and the Ti–Mg–Mn–O oxide was examined, and the atomic image of the Ti–Mg–Mn–O oxide was observed. The precipitation of MnS on the surface of Ti–Mg–Mn–O oxide followed by the absorption of Mn atoms by Ti–Mg–Mn–O oxide resulted in the formation of a MDZ around Ti–Mg–Mn–O·MnS inclusions.

本文研究了含Ti-Mg氧化物夹杂的热轧低碳钢的力学性能和显微组织，以及奥氏体晶粒尺寸对针状铁素体(AF)形核的影响和AF形核机制。结果表明，Ti-Mg脱氧钢中主要夹杂物为Ti-Mg-Mn-O·MnS，有效促进了AF的形核；因此，热轧后的显微组织由细小的 AF 和贝氏体 (B) 组成。Ti-Mg 脱氧钢的拉伸性能变化不明显，但与 Al 脱氧钢相比，-40 °C 时的低温冲击韧性从 4 J 显着提高到 126 J。提高奥氏体化温度有助于AF的形核，当奥氏体化温度为 1250 °C 时，Ti-Mg 脱氧钢中形成大量细小的 AF，平均奥氏体晶粒尺寸为~92 μm。阐明了 AF 的两种成核机制： (100) 的 Nishiyama-Wasserman (N-W) 取向关系AF 和 Ti-Mg-Mn-O_氧化物之间的_铁氧体‖(110)_氧化物，[011]_铁氧体‖[-111]_氧化物，导致低晶格失配，以及 Ti-Mg-Mn 周围的 Mn 耗尽区 (MDZ) –O·MnS 夹杂物。为了研究MDZ形成的原因，使用聚焦离子束（FIB）制备含有Ti-Mg-Mn-O·MnS夹杂物的透射电子显微镜（TEM）样品，（ -11-1) _MnS ‖(11-1)_氧化物, [-112] _MnS ‖[011]_氧化物检查了 MnS 和 Ti-Mg-Mn-O 氧化物之间的关系，并观察了 Ti-Mg-Mn-O 氧化物的原子图像。MnS 在 Ti-Mg-Mn-O 氧化物表面沉淀，随后 Ti-Mg-Mn-O 氧化物吸收 Mn 原子，导致在 Ti-Mg-Mn-O·MnS 夹杂物周围形成 MDZ .