风电机组用高强度螺栓断裂分析

风电机组用M39×315高强度螺栓在安装时断裂。通过化学成分分析,宏观和微观检验等方法对断裂原因进行分析。结果表明:螺栓断口为典型的在拉伸载荷作用下发生的混合型断裂,以脆性断裂为主,断口区域大小为400～550μm。螺栓心部存在少量沿晶分布的小块状铁素体,表明螺栓在热处理时加热不足。断裂螺栓钢中表面与心部非金属夹杂物无明显差别,D类环状氧化物夹杂物级别约为粗D2～D2.5级。断裂源区呈现的沿晶断裂和解理断口主要是螺栓热轧盘条存在不良组织缺陷所致。建议加强对螺栓B7钢原材料热轧态组织的进厂检验,分析其带状组织及热处理组织缺陷。对每批螺栓淬火后检查其淬透情况,以确保高强度螺栓心部马氏体组织体积分数达到90%。

Fracture analysis of high strength bolt for wind power unit

M39×315 high strength bolt for wind power unit cracked at installation.The fracture reason was analyzed through the method of chemical composition analysis,macro and micro examination.Results show that bolt fracture was typical mixed fracture occurring under tensile load,it is mainly brittle fracture,fracture area is 400～550 μm.Bolt central area exists intergranular little small ferrite,it shows that bolt is heated insufficiently.There is no obvious difference between surface and central non-metallic inclusion in fracture bolt steel,D type annular oxide inclusion grade is about coarse D2～D2.5.The intergranular fracture and cleavage fracture occurred in fracture source area are mainly caused by bad bolt hot rolled wire rod structure defects.It is suggested that incoming inspection of bolt B7 steel raw material hot rolled structure should be strengthened,its banded structure and heat treatment structure defects should be analyzed.The hardenability situation of every batch of bolt should be tested after hardened,it is ensured that high strength bolt central martensite structure volume fraction reaches about 90%.