试制LNG2项目钢板边部微裂纹的分析与控制

Analysis and Control of Edge Microcracks of Trialed Plates for LNG2 Project

试制北极LNG 2项目用S 355 ML钢板,首批钢板下表面存在微裂纹,裂纹距钢板边部20~50 mm区间范围内,无明显规律。取厚度35 mm的S 355 ML头部边样,通过对其金相分析、扫描电镜及成分分析,发现裂纹深度集中在40~80μm,裂纹末端较钝,裂纹内部基体被氧化形成的氧化铁皮包裹,周边存在Si-Mn氧化物析出,认为连铸坯的角部横向裂纹是引发钢板微裂纹的起源。结合厚板连铸产线,严格控制过热度、拉坯速率及结晶器非正弦有序振动,并对连铸坯缓冷精整,保证连铸坯氧化铁皮及折叠处吹扫清理效果。采取相应措施后,有效避免角横裂纹的产生,确保了北极LNG2项目用S355ML钢板质量。

For the trialed S355 ML steel plates for Arctic LNG2 project,there were microcracks on the lower surface of the first batch of steel plates,within the range of 20~50 mm from the edge of the steel plates and without obvious regularity.The edge sample with microcracks was taken from S355 ML plate with thickness of 35 mm,and through metallographic analysis,SEM and composition analysis,it was found that,the crack depth is concentrated within 40~80μm,the crack end was blunt,the matrix inside cracks was covered by oxide scale formed by oxidation,and there was Si-Mn oxide precipitation around.And it can be considered that,the transverse cracks at the corner of continuous casting slabs is the beginning of microcracks of steel plates.Combined with the heavy plate continuous casting production line,a series of measures,including the strict control in superheat degree,casting speed,mold’s nonsinusoidal ordered vibration and the slabs’slow cooling and finishing to ensure the cleaning effect of their oxide scale and fold parts,were carried out.After the corresponding measures were taken,the generation of transverse cracks at the corner of slabs was effectively avoided,and then the quality of S355 ML steel plate for LNG2 project in the Arctic was ensured.