剧烈扭转压缩轧制45钢超细晶棒组织演变机理

Microstructure Evolution Mechanism of Ultrafine Grained Bar of 45 Steel Rolled by Severe Torsional Compression

基于自主研制的剧烈扭转压缩轧制技术,以45钢为研究对象,在750℃下采用48%径缩率经一次轧制成形,获得了直径为25 mm的超细晶棒。借助扫描电子显微镜(SEM)、电子背散射衍射(EBSD)和透射电子显微镜(TEM)分析了微观组织演变规律及晶粒细化机理,并对力学性能进行了测定分析。结果表明,心部扭转压缩程度相对边部略弱,晶粒沿轴向具有取向性,晶粒尺寸细化至2.3μm;边部扭转压缩程度剧烈,晶粒取向分布均匀且细化显著,晶粒尺寸为1.7μm;晶粒主要细化机理:因剧烈扭转压缩形变诱导了奥氏体向铁素体的转变,以及发生了充分的连续动态回复再结晶过程;轧后棒材屈服强度、抗拉强度及延伸率分别为402.5 MPa、643.5 MPa及25.7%,较轧制前分别提升24%、5.6%及14.7%。

Based on the self-developed severe torsional compression rolling method,taking 45 steel as the research object,the ultrafine-grained bar with a diameter of 25 mm was obtained by single pass rolling at 750℃with a diameter reduction rate of 48%.The microstructure evolution and grain refinement mechanism were analyzed by scanning electron microscopy(SEM),electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM),and the mechanical properties were measured and analyzed.The results show thatthe degree of torsional compression in the center of the bar was slightly weaker than that of the edge,the grains were oriented along the axial direction and the grain size was refined to 2.3μm.In contrast,the edge region experienced intense torsional compression,resulting in a uniform distribution of grain orientation and significant grain size refinement to 1.7μm.The main refinement mechanism of grain:the transformation from austenite to ferrite induced by severe torsional compression deformation,as well as the occurrence of a sufficient continuous dynamic recovery and dynamic recrystallization process.After rolling,the yield strength,tensile strength and elongation of the steel bar were 402.5 MPa,643.5 MPa and 25.7%,respectively,representing a 24%,5.6%,and 14.7%increase compared to the pre-rolling values.