550 MPa级中厚板矫直过程中表面凹坑缺陷的成因与对策

针对550 MPa级高强中厚板在矫直过程中极易出现氧化铁皮压入凹坑缺陷的问题，根据现场矫直工艺，研究了在不同温度下进行热变形时试样表面和横截面的形貌，钢基体与氧化铁皮界面处平直度的变化规律。结果表明，热变形温度为450 ℃时，表面氧化铁皮开始出现裂纹，且随着变形温度的降低，裂纹的数量逐渐增加；此外，氧化铁皮与钢基体之间的界面长度随变形温度的降低而呈直线增加，表明氧化铁皮与钢基体界面平直度随着热变形温度的降低越发粗糙、易脱落而形成凹坑缺陷。为此，应适当提高终轧温度以确保矫直时钢板表面温度大于450 ℃，同时提高钢板的运行速率，防止氧化铁皮在低温变形发生破碎和脱落的同时降低氧化铁皮厚度，从而减小因氧化铁皮脱落而造成凹坑缺陷的发生几率。

Causes and countermeasures of pit defect on the surface of 550 MPa grade plate during straightening process

Aiming at the pit defect formed on the surface of 550 MPa grade plate during straightening process,the morphologies of surface and cross section of samples and the regularity of the flatness at the interface between the steel substrate and the scale under different deformation temperature were studied based actual straightening process.The results show that when the thermal deformation temperature is 450 ℃,cracks begin to appear on the surface oxide scale,and as the deformation temperature decreases,the number of cracks gradually increases.In addition,the interface length between the oxide scale and the steel substrate increases linearly with the decrease of the deformation temperature,indicating that the flatness of the interface between the scale and the steel substrate becomes rougher and scale easier to fall off to form pit defect with the decrease of the thermal deformation temperature.To this end,the finishing rolling temperature should be appropriately increased to ensure that the surface temperature of the plate is above 450 ℃ during straightening,and at the same time to increase the running speed of the plate to prevent the scale from breaking and falling,and reduce the thickness of the scale,thereby reducing occurrence of pit defect caused by scale fall off.