电力机车连接螺栓断裂分析

采用宏观观察、金相检验、成分分析、力学性能检测及断口分析对断裂的连接螺栓进行分析。结果表明:螺栓呈现脆性断裂特征,裂纹源位于螺杆与六角头过渡处,源区微观特征为沿晶+准解理,晶面上存在孔洞及撕裂棱,具有氢脆断裂的特征,并且在螺杆与六角头过渡处存在过度腐蚀的特征;螺栓断裂的主要原因为酸洗过度导致过多的H渗入基体内,在扭转应力和拉伸应力共同作用下,发生氢致延迟断裂。

Fracture Analysis of Connecting Bolt of Electric Locomotive

Failure analysis on a connecting bolt of electric locomotive was carried out by macro and micro observation, chemical composition analysis, properties testing and microstructure examination. The results show that the bolt presented the feature of brittle fracture. The crack source was located at the transitional region between screw and hexagon head. Intergranular and quasi-cleavage fracture feature was found at the source region of the fracture surface, and there were some holes and tearing ridges at the grain boundary surface. These characteristics are the same as those of hydrogen brittleness fracture. In addition, there existed excessive corrosion at the transitional region between screw and hexagon head. Excessive acid pickling caused hydrogen to permeate into the matrix of the bolt. As a result, hydrogen induced delay rupture occurred to the bolt under the coeffect of torsion stress and tensile stress.