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通过拉伸、系列冲击以及NDT落锤试验,采用SEM、TEM及EBSD技术手段,研究了轧后空冷+离线淬火+回火(QT)与轧后在线淬火+回火(DQT)工艺对620 MPa级高强钢组织及力学性能的影响。结果表明,调质后组织均为回火索氏体,但DQT工艺下组织粗大、扁平化且板条更加细长;淬火后试样在回火过程中,随着回火温度的升高,强度降低,塑性升高,且在线淬火试样纵向强度高于横向;在相同的回火工艺下,经DQT工艺处理的试样强度高于QT工艺处理的试样,但QT工艺下的调质钢断后伸长率、韧脆转变温度(FATT)及无塑性转变温度(NDTT)高于DQT工艺处理的试样。离线淬火工艺下的调质钢位错密度低、马氏体板条块尺寸小、残留奥氏体及大角度晶界含量高,该工艺处理后试样具有较低的韧脆转变温度和良好的止裂性能。
By means of tensile test, series impact test and NDT drop test, the effects of post-rolling air cooling + off-line quenching + tempering (QT) and on-line quenching and tempering (DQT) Grade High Strength Steel Structure and Mechanical Properties. The results showed that all the tempered tissues were tempered sorbite. However, the structure of the quenched and tempered sorbite was coarse and flat, and the slender slats were more elongated. During the tempering process of the quenched samples, with the increase of tempering temperature, Strength and plasticity increased, and the longitudinal strength of the sample quenched in-line was higher than that in the transverse direction. The strength of the sample treated by the DQT process was higher than that of the QT process under the same tempering process. However, The elongation at break, ductile-brittle transition temperature (FATT) and ductile-free transition temperature (NDTT) of the steel are higher than those of the DQT process. Off-line quenching process quenched and tempered steel low dislocation density, martensite lath size, residual austenite and high-angle grain boundary, the sample after treatment has a lower ductile-brittle transition temperature and good Stop-crack performance.