某企业700L钢制挂车车架大梁产品在较低服役寿命下出现开裂现象,对开裂大梁的断口形貌、化学成分、显微组织、力学性能、疲劳性能、服役性能等进行检验,并与未开裂大梁进行对比,分析大梁开裂的原因,并提出了相应的改进措施。结果表明:开裂700L钢制挂车车架大梁组织中存在一定的混晶现象,导致韧性和疲劳极限偏低,且在交变载荷的作用下,大梁板簧支架与梁下翼面加强板的位置及鞍板与梁连接处出现应力集中,微裂纹在应力集中位置萌生与扩展,最终导致车架大梁发生疲劳断裂;为降低开裂风险,应略微降低终轧温度,同时在大梁靠近鹅颈下翼面内侧增加C形加强板,减少大梁在服役条件下的应力集中现象。

700L steel trailer frame beam products in an enterprise under lower service lives cracked. The reason for cracking of the beam was analyzed by testing the fracture morphology, chemical composition, microstructure, mechanical properties, fatigue performance and service performance of the cracked beam, and comparing with those of the uncracked beam. The corresponding improvement was put forward. The results show that the structure of the cracked 700L steel trailer frame beam had mixed crystal phenomenon, led to low toughness and fatigue limit. Under the alternating load, stress concentration occurred at the position between the spring support and the reinforcing plate on the lower wing surface of the beam and the connection between the saddle plate and the beam. Microcracks initiated and growth at the stress concentration position, and eventually led to fatigue fracture of the frame beam. To reduce the risk of cracking, the final rolling temperature should be lowered slightly, and C-shaped reinforcing plate was placed near the inner side of the lower wing surface of the gooseneck to decrease stress concentration of the beam under service conditions.