Q345钢焊接结构高温环境下拉伸形变PLC效应的声发射表征

The acoustic emission characterization of the PLC effect during tensile deformation of Q345 steel welded structure at high temperature

为进一步研究Q345钢焊接结构在高温下拉伸形变微观组织对声发射信号的影响,对Q345钢母材结构和焊接结构分别在20℃、200℃和250℃条件下进行拉伸形变测试,同时使用声发射手段进行监测。高温下焊接材料强度有所降低而塑性增强,在高温下拉伸的应力应变曲线硬化阶段出现同屈服阶段类似的锯齿波动即波特文-勒夏特利埃效应(Portevin-Le Chatelier简称PLC效应),在200℃和250℃条件下材料的屈服点较20℃有下降,且基本上无屈服平台。常温下母材试样硬化阶段声发射信号幅值大多集中在40~50 dB,而焊缝试样主要集中在50~70 d B其中个别信号超过80d B。200℃条件下弹性阶段在40~50 d B范围产生大量低幅值声发射信号,随着应变增大声发射信号幅值逐渐升高但总体处于60 dB以下。在硬化阶段对比200℃和250℃条件下声发射信号数量分布范围可见,温度升高后位错受溶质原子束缚小,位错运动活跃。

In order to study the microstructure effect on acoustic emission signal during the tensile deformation of the Q345 steel welded structure at high temperature, tensile deformation tests of base metal and welded structure of Q345 steel were carried out at 20, 200 and 250 C. Meanwhile, acoustic emission was used to monitor the deformation. At high temperatures, the strength of welded materials decreases while the plasticity increases. In the hardening stage of the tensile stress-strain curve at high temperature, a zigzag fluctuation similar to the yield stage occurs, that is the Portevin-Le Chatelier effect(PLC effect for short). The yield point of the material at 200 ~250 ℃ is lower than that at 20 ℃ and there is almost no yield platform. At room temperature, the amplitude of acoustic emission signals in hardening stage of base metal specimens is mostly concentrated in the range of 40~50 dB. The weld specimens are mainly concentrated in 50~70 dB, with individual signals exceeding 80 dB. A large number of low-amplitude acoustic emission signals are generated in the elastic stage at 200 C in the range of 40~50 dB. The amplitude of acoustic emission signals increases gradually with the increase of strain, and is generally below 60 dB. In the hardening stage, it can be inferred from the distribution range of acoustic emission signals at 200 and 250 C that dislocations are less bound by solute atoms and move actively when the temperature rises.