厚壁管表面感应淬火时内应力和畸变的演变

Evolution of Stress and Distortion During Induction Case Hardening of Thick-walled Tube

由于感应淬火是局部加热,温度梯度大,工件中产生的应力比炉内加热时的复杂。同时,表面淬火有可能在工件中获得最佳的残余应力状态。感应淬火时的应力和畸变从最初即上世纪30年代中期开始应用该工艺时就是人们的研究课题[1-2]。此后对这一问题进行了大量的试验研究[3-11]。业已确定,感应表面淬火会在马氏体层产生很大的压应力,能提高零件的抗弯强度和耐磨性,改善零件的使用性能[12]。但是在某些情况下也会产生拉应力,恶化零件的使用性能,甚至产生显微或宏观裂纹。过大的残余应力也能引起零件尺寸的变化,即导致零件发生畸变。通常都不希望零件发生畸变,但有时也可以对畸变进行有效的利用。譬如,用感应加热对某些零件进行热压配合或矫正,包括大型轴承圈及舰船的壳体等[2]。

The stress produced in workpiece is more complicate during induction heating than during furnace heating owing to steep temperature gradient caused by partial heating .At the same time , it is possible to offer the optimum residual stress condition in workpiece due to surface hardening .The stress and distortion during induction hardening has been investigated in the 1930 s when the induction hardening was just adopted , and a great number of research on this problem has been performed ever since .It has been clarified that the very great compressive stress will produce in martensite case during induction case hardening , which can increase bending strength and wearability of part and improve on its serviceability .In certain cases , however , the tensile stress will occur , consequently the serviceability of part will worsen and even the micro or macro crack will offer in part .Excessively great residual stress will cause part dimension to change , i.e.cause part to distort .In general, the distortion of part is unwanted , but may be utilized effectively at times , for example , thermo-compression assembling or leveling of certain parts with induction heating , including large-size bearing race , housing of warships , etc.