大壁厚Q345B钢板弯曲开裂原因分析及对策

Cause Analysis and Countermeasure of Bending Cracking of Large Wall Thickness Q345B Steel Plate

为了解决渣罐制造用大壁厚Q345B钢板弯曲过程中开裂的问题,采用化学分析、断口扫描分析、金相组织分析、显微硬度分析等手段,对渣罐卷筒开裂试样进行了试验研究。分析结果显示,钢板火切坡口面有清晰的火切沟槽;裂纹沿着火切坡口面启裂并快速扩展;裂纹面呈解理断裂,表现出脆性特征;火焰切割坡口上存在2~3 mm切硬组织,以板条马氏体为主,同时在表层存在大量魏氏体组织。研究表明,钢板火焰切割坡口存在大量的马氏体和魏氏体组织是开裂的主要原因。建议采取火切后打磨或火切前预热等手段,可以有效避免因火切硬化层和火切沟槽引起应力集中造成的弯曲开裂。

In order to solve the cracking of Q345B steel plate with large wall thickness for slag ladle manufacturing during bending process,the crack samples of slag ladle were studied by chemical analysis,fracture scanning analysis,metallographic structure analysis and microhardness analysis.The analysis results show that there are clear cannelures produced by flame cutting on the steel plate flame cutting groove surface.Cracks begin and propagate rapidly along the flame cutting groove surface.The crack surface presents a dissociation fracture and shows brittleness.There are 2~3 mm hard microstructure on the flame cutting groove,mainly lath martensite,and a large amount of widmanstatten microstructure on the surface.The results show that the large amount of martensite and widmanstatten in the flame cutting groove of steel plate is the main internal cause of crack.It is suggested to take means such as grinding after flame cutting or preheating before fire cut,which can effectively avoid bending crack by stress concentration caused by flame cutting hardened layer and flame cutting groove.