激光相变硬化残余应力研究

Research on Residual Stresses after Laser Trans formation Hardening LaSer Transtormation Hardening

本文主要采用X射线法对激光相变硬化处理后试样表面至内部的残余应力进行逐层测定。并辅以小孔应力释放法予以比较。结果表明:在通常激光相变硬化处理参数下,碳钢的残余应力按正弦波规津分布。表面为压应力,内部为拉应力。其幅值随激光参数减小而减小。二次激光相变硬化处理的残余应力为拉应力。本文对残余应力在激光相变硬化处理热循环过程中的形成进行了解释。在最初升温阶段,表面发生热塑性变形而形成少量压应变。在随后的冷却过程中产生拉应变。当发生奥氏体向马氏体组织转变时,又产生压应变。因此,最终残余应力状态是表面达到的温度,塑性屈服量,组织转变量等因素综合影响的结果。而与是终形成的组织,残余奥氏体量等没有对应关系。

Residual stresses from the surface to the interior of the samples after laser transtormation hardening have been studied by means of X-ray and compared with the way of stress release through drilling holes. The results show that the distribution of residual stresses follows the sine wave under the treatment with usual laser parameters. There are compressive stresses on the surface and tensile stresses in the interior of the samples, the peak value of the stress decreasing with the decrease of laser Prameters. The ensile residual stresses will be produced on the surface when the specimen is treated by laser beam for two times. In addition, the producing of residual stresses during the thermal cycle by laser beam has been explained. At the first stage of elevating temperature, the thermal plastic deformation on the surface takes place, leading to some compressive strains. At the subsequent cooling stage, when the austenite transforms into the martenite, the tensile stranis are produced. Therefore the ultimaet state of residual stresses has no corresponding relation with the final structure the amount of. the residual austenite and so on, but it is the' result of cooperating effects of some factors such as surface temperature, the amount of plastic yield and the amount of structure transformation.