临界淬火工艺处理高强结构钢Q690GJ的韧化机理

Fracture resistance mechanism of high strength structural steel Q690GJ treated by intercritical quenching process

研究了QT(淬火+回火)和QLT(淬火+临界淬火+回火)热处理对高强结构钢Q690GJ微观组织及低温韧性的影响。通过金相、扫描电镜等方法,对低温冲击试样、无塑性转变试样进行了微观分析。结果表明:QLT工艺处理的Q690GJ钢低温韧性明显优于QT工艺。微观组织分析表明:QLT工艺处理试验钢组织为板条马氏体+残留奥氏体,临界淬火工艺形成了更多数量的、且较为稳定的残留奥氏体软相,提高了起裂前的塑性变形能力;同时形成更多取向混乱的马氏体板条束,有效阻碍了裂纹的扩展,从而提高低温韧性、降低无塑性转变温度。

Effects of QT(quenching+tempering) and QLT(quenching+intercritical quenching+tempering) process on microstructure and low temperature toughness of high strength structural steel Q690 GJ were investigated. The microstructure of the low temperature impact specimen and the NDT(nil-ductility transition) specimen was analyzed by means of optical microscopy and scanning electronic microscopy. The results show that the low temperature toughness of the steel treated by QLT process is obviously better than that treated by QT process. The microstructure obtained by QLT process is lath martensite+retained austenite. More stable retained austenite that responsible for the enhanced plastic formability before crack initiation is transformed through intercritical quenching. While, chaotic martensite lath bundles formed by QLT process effectively prevent crack propagation. Then the low temperature toughness and NDT temperature of the steel is improved and reduced, respectively by QLT process.