700MPa级热轧高强钢在剪切加工过程中分层开裂的原因

Reason for Lamellar Cracking of 700 MPa Grade Hot-Rolled High Strength Steel during Shearing Process

700MPa级热轧高强钢板在剪切加工过程中于剪切断面出现分层开裂现象,采用形貌和显微组织观察、化学成分分析、微区成分分析、拉伸性能测试等方法,对分层开裂的原因进行分析。结果表明:高强钢中由成分偏析造成的严重的铁素体-珠光体带状组织是出现分层开裂的直接原因,在裂纹尖端变形区域中大尺寸第二相粒子或夹杂物附近的微小孔洞的长大加剧了裂纹的扩展;通过控制连铸机起车速度、稳定浇铸速度,调整扇形段辊缝的精度,采取各种提高钢液洁净度的措施后,该高强钢在剪切加工过程中未再出现分层开裂现象。

During shear process,lamellar cracking appeared on the shear section of 700 MPa grade hot-rolled high strength steel plate.The causes of lamellar cracking were analyzed by means of morphology and microstructure observation,chemical composition analysis,micro area composition analysis and tensile property testing.The results show that the serious ferrite-pearlite banded structure caused by composition segregation in the high strength steel was the direct cause of lamellar cracking,and the growth of small holes near the large-sized second phase particles or inclusions in the deformation area at crack tip aggravated the crack growth.By controlling the starting speed and stable casting speed of the continuous caster,adjusting the precision of the roller gap in the sector section,and taking various measures to improve the purity of liquid steel,there was no lamellar cracking in the high strength steel during shear process.