非合金钢圆柱体的高速淬火壳层硬化

Shell Hardening of Unalloyed Steel Cylinders by High Speed Quenching

Kobasko等人率先指出,快速水淬可在零件近表面的部位产生压应力,从而大大提高疲劳极限(强烈淬火)。这种工艺能提高硬度,零件能被整体或壳层硬化,取决于零件的钢种和尺寸以及淬火烈度。较详细地研究了两种非合金钢圆柱体的壳层硬化工艺。研究的目的:一方面是弄清能使零件获得足够的表面硬度的同时又形成与之相匹配的硬化表层的必要条件;另一方面,在零件近表面的区域产生尽可能大的残余压应力,以便显著延长热处理零件的使用寿命。采用为高速淬火而研制的一种特殊装置进行试验,用自来水或10%盐水作淬火介质。研究表明,这种特殊的试验设备可获得高达50 000 W m^(-2)K^(-1)的热传递系数。在试验中,对材料为C35钢和C56E2钢、直径为25 mm和43 mm的圆柱体,以20 000~50 000 W m^(-2)K^(-1)的热传递系数进行了淬火。淬火后检测圆柱体的显微组织、硬度和残余应力。试验表明,圆柱体近表面区域的压应力达到了1 200 MPa。

Kobasko et al. have primarily shown that rapid water quenching can create compressive residual stresses near the surface and thereby a significant increase in the fatigue-limit （Intensive Quenching）. Such processes result in an increase in hardness. Depending on steel grade, dimensions of the component and quenching intensity through hardening or only shell hardening will result. In this work, shell hardening processes were investigated in a more detailed manner for cylinders made of two different unalloyed steels. The goal of the work was discovering the general requirements to reach, on the one hand, a sufficient surface hardness paired with a non-through hardened hardening profile. On the other hand, compressive residual stresses in the near surface area should be as high as possible to achieve huge lifetime cycles for the heat treated work pieces. The experiments were carried out with a device that was especially developed for high speed quenching. As a quenching medium only tap water or water with 10% salt were used. It was shown that with this equipment very high heat transfer coefficients up to 50 000 W · m^-2K^-1 can be reached. Within the experimental design, cylinder made out of C35 and C56E2 with diameters between 25 and 43 mm were quenched with heat transfer coefficients in the range of 20 000 to 50 000 W · m^-2 K^-1. The quenching results were characterised by measuring the mierostructure, the hardness and the residual stresses. The experiments show that compressive stresses in the near surface area of 1 200 MPa can be achieved.