钢板表面网状裂纹的成因及演化研究

STUDY ON THE CAUSES AND EVOLUTION OF MESH CRACKS ON THE SURFACE OF STEEL PLATE

某钢厂生产的热轧钢板存在表面网状裂纹缺陷,利用金相显微镜、扫描电子显微镜以及能谱仪对其进行了宏观和微观综合分析。微区显微分析发现裂纹区域奥氏体粗大,裂纹附近存在大量的高温氧化原点,其金相组织呈现脱碳状态,且出现沿晶界向晶粒延伸的呈锯齿状的魏氏体组织。利用高温共聚焦显微镜对试样进行加热和降温过程分析,发现在升温过程中晶界处优先熔化,经过金相处理可以看到由于过热形成奥氏体边界氧化网络;在冷却过程中观察到锯齿状魏氏体从晶界处析出;晶内硬度比晶界大26HV0.2。综合分析表明铸坯在加热过程中因过热导致奥氏体组织粗大,晶界弱化,组织脱碳,在后续轧制过程中,形变应力使裂纹沿奥氏体扩展而形成网状裂纹。生产中将出炉温度由1150℃降低到1120℃,开轧温度由1120℃调整至1080℃,出口温度由830℃提高到860℃,卷取温度控制在610℃,钢板表面网状裂纹得到有效控制,缺陷率由3.98%降至0.81%,质量显著提升。

The hot-rolled steel plate produced by a steel mill had surface network crack defects,and the macroscopic and microscopic comprehensive analysis was carried out by metallographic microscope,scanning electron microscope and energy spectrometer.Microscopic analysis showed that the austenite in the crack area was course,there were a large number of high-temperature oxidation origins near the crack,and its metallographic structure showed a decarburized state,and a jagged Weistenite structure extending to the grain along the grain boundary appeared.The heating and cooling process of the specimen was analyzed by high-temperature confocal microscopy,and it was found that the grain boundary was preferentially melted during the heating process,and the austenite boundary oxidation network could be formed due to overheating after metallographic treatment;the serrated weinite precipitated from the grain boundary during the cooling process;the intracrystalline hardness was 26HV0.2 greater than the grain boundary.Comprehensive analysis shows that the overheating of the casting billet leads to coarse austenite structure,weakening grain boundary and microstructure decarburization during the heating process,and in the subsequent rolling process,the deformation stress causes the crack to expand along the austenite to form a network crack.In production,the furnace temperature is reduced from 1150℃to 1120℃,the rolling temperature is adjusted from 1120℃to 1080℃,the outlet temperature is increased from 830℃to 860℃,the coiling temperature is controlled at 610℃,the mesh crack on the surface of the steel plate is effectively controlled,the defect rate is reduced from 3.98%to 0.81%,and the quality is significantly improved.