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弯曲疲劳试验表明:低碳钢经软氮化后的疲劳强度比退火材料提高140%。通过 X射线及电子显微镜研究证明:在扩散层最外边的400微米区域中发生了细微程度的沉积析出。在此层下面,氮和碳基本上处于固溶体中。当软氮化材料经受疲劳时,可观察到明显的循环硬化。外应力越大,则硬化层深度越大。在大的应力下,硬化深度伸展超过了扩散层,深入到材料的心部。在疲劳中可观察到表面应力发生衰退。然而在材料的整个寿命中,次表面层的压应力始终存在。在小的外应力下,软氮化材料的次表面层产生塑性形变。在长疲劳寿命情况下,引起软氮化材料断裂所需的整体塑性形变量比退火材料的要大得多。但在低寿命时,可观察到相反的情况。
Bending fatigue tests show that the fatigue strength of mild steel after nitrocarburizing is 140% higher than that of annealed materials. X-ray and electron microscopy studies have shown that a slight degree of precipitation occurs in the 400 μm outermost region of the diffusion layer. Below this layer, the nitrogen and carbon are essentially in solid solution. When the nitrocarburized material is subject to fatigue, significant cyclic hardening can be observed. The greater the external stress, the greater the depth of the hardened layer. Under large stress, the depth of hardening extends beyond the diffusion layer, deep into the core of the material. In the fatigue can be observed in the surface stress decline. However, throughout the life of the material, compressive stresses in the subsurface layer are always present. Under small external stresses, the sub-surface layer of the nitrocarburized material undergoes plastic deformation. In the case of long fatigue life, the overall amount of plastic deformation required to cause the soft nitrided material to break is much greater than that of the annealed material. However, at low life, the opposite is observed.