无取向电工钢线状表面缺陷分析

Study on Surface Linear Defects of Non-oriented Electrical Steel Strip

采用扫描电镜观察了W600冷轧无取向电工钢表面"黑线"和纵向发裂缺陷的形貌。成品带钢表面"黑线"缺陷的成因是连续退火炉均热段(SF段)内炉辊结瘤划伤带钢下表面,高温下异物嵌入划伤处,并被涂层覆盖;冷硬带钢和成品带钢纵向发裂缺陷则是连铸坯中的铝酸盐复合夹杂物在热轧、冷轧过程中由于变形而破碎并被压出至表面导致的。为了减少"黑线"缺陷,要定期更换碳套辊;将通入H2+N2+H2O湿混合气由原来的6段通入改为4段,并将各段的炉温上限调整为880℃。为减少纵向发裂缺陷,在精炼及连铸工序严格控制钢中夹杂物,保证结晶器内液面波动在±3 mm～±5 mm。

The surface ＂dark line＂ and longitudinal hair crack in W600 non-oriented electrical steel strip are observed by SEM.The cause of surface ＂dark line＂ defects found in the after coated strip is that foreign substances are embedded into the scratches of strip surface caused by the graphite bottom roll build-ups in the soaking furnace（SF） section of the continuous annealing line and then covered by the coating in the coating process;the cause of surface longitudinal hair crack defects found in both of the cold rolled strip and after coated strip is that the complex aluminate inclusions in the slab are broken due to deformation and then extruded out from the inside layer during hot and cold rolling processes.In order to eliminate the ＂ black line＂,the graphite bottom rolls should be changed or cleaned at regular intervals,and sections for feeding wet H2＋N2＋H2O gas should be reduced from the original 6 to 4 and the furnace temperature in these four sections should be controlled under 880 ℃.In order to eliminate the longitudinal crack,inclusions in steel should be strictly controlled in refining and continuous casting processes to ensure the liquid level fluctuation in crystallizer kept at ±3 mm-±5 mm.