工程机械用800MPa低合金高强度钢焊接热影响区断裂韧性评价

随着工程机械的大型化,需要采用800MPa低合金高强度钢结构。为了保证焊接接头具有良好的韧性,必须合理控制焊接热作用,避免焊接接头脆化。本研究采用热模拟试件,研究了焊接冷却时间及加热温度对800MPa低合金高强度钢焊接热影响区(HAZ)断裂韧性的影响及其显微组织特征。发现在t8/5为18s时,HAZ具有最好的断裂韧性。随着t8/5的增加,奥氏体晶粒逐渐长大,马氏体的体积分数逐渐降低,粒状贝氏体的数量不断增加,断裂韧性逐渐下降。t8/5大于45s,LT方向试件出现脆性失稳现象。焊接接头各区的韧性分布是,过热区的断裂韧性最好,两相区的断裂韧性最差,粗晶区的韧性优于细晶区。影响HAZ韧性的主要因素是贝氏体的形态和分布。研究结果为制定合理的焊接工艺和大型工程机械的断裂安全评定奠定基础。

Evaluation of HAZ Fracture Toughness for 800MPa Grade HSLA Used for Construction Machinery

As construction machinery is large scaling, application of 800MPa grade high strength low alloy (HSLA) steels is essential. In order to obtain good toughness of welded joints, rational control of welding heat input is needed to avoid brittleness of welded joints.The effects of welding cooling time and heat temperature on fracture toughness and microstructure feature for an 800MPa grade HSLA steel and heat affected zone(HAZ) were investigate using thermal simulation specimens.It is found that the fracture toughness of the simulated HAZ is the best when the cooling time of t8/5 is 18s. With gradually increase in t8/5, austenite grain size grows, fraction of martensite volume decreases, quantity of grain bainite increases, and fracture toughness decreases. If t8/5 is larger than 45s, brittle instability occurs for the LT specimens. Among the toughness distribution of various zones of HAZ, the fracture toughness of overheat zone is the best, that of dual phase zone is the lowest. In addition the toughness of coarse grain zone is better than that of fine grain zone. The main factor affecting toughness of HAZ is the configuration and distribution of bainite. The results will be valuable for determination of welding procedure and fracture evaluation of large scale construction machinery.