正火工艺对冷轧态低合金低温钢组织及拉伸性能的影响

采用拉伸性能、显微硬度测试及OM、SEM、TEM等实验方法研究了正火工艺对冷轧态低合金低温钢板组织演变和拉伸性能的影响。结果表明,热处理温度为700℃时,冷轧试样仅处于回复阶段,铁素体基体内为严重的位错缠结组态和位错网格结构;正火温度升高至750℃和800℃时,冷轧组织再结晶及相变过程同时发生,以M/A小岛为特征的粒状组织出现;860℃完全正火组织为等轴铁素体和弥散珠光体,位错呈稀疏的位错墙组态。23%压下率冷轧试样经860℃正火后铁素体晶粒尺寸由10%压下率冷轧试样的12.0μm细化到10.2μm。正火温度为860℃时,冷轧试样达到最佳的强塑性配合,10%和23%压下率试样的强塑积分别为20 007 MPa%、17 850 MPa%。与700℃正火试样相比,860℃正火试样拉伸断口附近及颈缩区组织中微孔数量显著降低,拉伸变形能力改善。

Effect of Normalizing Process on Microstructure Evolution and Tensile Properties of Cold-rolled Low-alloy Cryogenic Steel

The effect of normalizing process on evolution of microstructures and tensile properties of cold-rolled low-alloy cryogenic steel plate was investigated by tensile test,microhardness test,OM,SEM and TEM.The results showed that the cold-rolled samples were in recovery when the heat treatment temperature was 700 ℃,and the dislocations in ferrite matrix featured severe tangles configuration or grid structure.As the normalizing temperature increased to 750 ℃ and 800 ℃,recrystallization and phase transformation processes occurred simultaneously,and formed granular structure characterized by M/A islands.The microstructure of 860 ℃ normalized sample was composed of equiaxed ferrite and dispersed pearlite,and dislocations were sparse dislocation wall configuration.The ferrite grain size of cold-rolled sample with 23％ reduction rate after 860 ℃ normalizing was refined to 10.2 μm,while that of cold-rolled sample with 10％ reduction rate was 12.0 μm.The optimal combination of strength and ductility was obtained at the normalizing temperature of 860 ℃,and the product of strength and ductility were 20 007 MPa％ and 17 850 MPa℃ for the cold-rolled samples with 10％ and 23％ reduction rate,respectively.Compared with that of 700 ℃ normalized sample,the number of microvoids near tensile fracture and necking zone in 860 ℃ normalized sample reduced significantly,indicating the improvement of tensile deformation ability.