1000MPa级高强度结构钢板焊接热影响区组织和性能演变规律研究

Study on Evolution Law of Microstructure and Mechanical Properties at Welding HAZ for 1000 MPa Grade High Strength Structural Steel Plate

针对屈服强度1000 MPa级工程机械用高强度结构钢板的焊接热影响区组织和性能展开研究,同时分析模拟焊接环境热影响区在不同冷速下获得的组织和硬度,绘制出实验钢热影响区连续冷却转变曲线(SH-CCT)。结果表明,实验钢母材组织为细小回火索氏体,并含有较多的5~10 nm微小析出物;随着焊接热输入量的增加,焊后冷却速度由慢变快,实验钢热影响区粗晶区发生B、M+B和M等3种不同类型的组织转变;实验钢热影响区最高硬度值达到HV454。为减小淬硬倾向和冷裂纹敏感性,以小热输入量进行极限条件焊接时,应采用焊前预热或焊后缓冷等特殊措施,避免淬硬组织和冷裂纹的产生。

The study is carried out on the microstructure and mechanical properties at welding HAZ of 1000 MPa yield strength grade high strength structural steel plate for construction machinery,the analysis is performed on the micrcostructure and hardness of simulated welding heat affected zone determined at different cooling rates,the SH-CCT curve is plotted for the experimental steel.The results show that base material microstructure of experimental steel consists of fine tempered sorbite with a large amount of nano-precipitates sizing from 5 nm to 10 nm.With increase of welding heat input,the cooling rate after welding increases from slow to fast,and three types of microstructure transformation such as bainite,martensite+bainite and martensite happen at CGHAZ of experimental steel,where the max.hardness value reaches to HV454.In order to reduce the hardening tendency and cold cracking sensitivity,special measures of preheating before welding or slow cooling after welding are taken when welding under limiting conditions with small heat input,thus hardening microstructure and cold cracking are prevented.