终轧温度对600 MPa级高钛高成型性铁素体-珠光体酸洗带钢组织与织构的影响

利用扫描电子显微镜(SEM)与电子背散射衍射技术(EBSD)研究了高Ti高成型性铁素体-珠光体型热轧酸洗带钢不同终轧温度下的组织与织构特征.研究结果表明, 终轧温度对显微组织的演变影响较小, 但却引起了大角晶界密度的升高.不同终轧温度时形成的组织均以铁素体为主, 少量的珠光体弥散分布在铁素体基体之间.终轧温度的提高引起了织构类型的显著改变, 随着终轧温度的升高, 织构强度整体增强, 并形成了明显的对冲压成型性有利的近γ织构.当终轧温度为850℃时, 近α织构与γ织构强度均较弱, 此时的织构类型主要为{001}[110]、{113}[471]、{114}[110]和{223}[110]成型不利织构, 成型不利织构强度更高; 当终轧温度升高至875℃时, 织构类型主要为近γ织构和{001}[110]旋转立方织构, 近γ织构体积分数由19.9%升高至41%, 成型有利织构强度显著增强. 

Effect of FDT on microstructure and crystallographic texture of 600 MPa grade high-titanium high-formability ferrite-pearlite pickling steel

Obtaining a near-γ texture that parallels that of a rolling plane enhances the r value of steel, thereby improving its formability. A high-angle grain boundary with a misorientation greater than 45 degrees is another crucial factor contributing to the formability of steel. Steel's crack arrest capability is dramatically improved by increasing the density of the high-angle grain boundary. The primary factors associated with texture evolution include chemical composition, finishing delivery temperature (FDT), rolling speed, and cooling rate after final rolling, of which the FDT is the most critical. Previous studies, which emphasized only pipelines and interstitial-free steels, have suggested that there is a discrepancy in the relationship between FDT and texture, and this relationship remains unclear with respect to high-titanium high-formability ferrite-pearlite steel. In this study, the microstructure and crystallographic texture of a 600 MPa grade high-titanium high-formability ferrite-pearlite steel with differential FDT were investigated by scanning electron microscopy and electron backscatter diffraction techniques. The results reveal that its microstructure comprises ferrite and pearlite irrespective of FDT, but increases in the FTD cause an increase in the high-angle grain-boundary density. The primary microstructure is ferrite in both these samples, with a small amount of pearlite dispersed between the ferrite grains. The texture dramatically changes with elevated FDT. The intensity of all the textures significantly increases as the FDT increases from 850℃ to 875℃, with the transformation of a large amount of apparent near-γ textures, which is beneficial to formability. The intensities of near-α texture and γ texture are low in the sample with an FDT of 850℃, wherein the primary textures include {001}[110], {113}[471], {114}[110], and {223}[110]. The intensity of the textures disadvantageous for formability is stronger than that of the advantageous textures in the sample with a lower FDT, which constrains formability and should be avoided. A positive change was observed in the textures as the FDT increased to 875℃. A strong near-γ texture was transformed in the steel that was finally rolled at 875℃, and its fraction increased to 41% from 19.9% at 850℃. A strong {001}[110] rotated cubic texture also occurred in the 875℃ finally rolled steel, which is bad for formability. However, superior formability can be guaranteed in general as the transformation of more advantageous textures than disadvantageous textures was observed.