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在汽车零件热处理中,对形状复杂的工件,如被动螺旋锥齿轮和薄片形零件,若无专用齿轮淬火压床和特殊夹具,淬后平面翘曲都较大,难以达到图纸要求。据有关文献介绍,钢在热处理相变过程中,会出现短时间塑性偏高现象,即所谓“相变超塑性”效应。“相变超塑性”效应发生在奥氏体向马氏体转变过程中,只要适当改进工艺,例如采用分级淬火,即可利用这一效应达到减少热处理变形的目的。一、原理现以汽车齿轮常用的渗碳钢20CrMnTi为例,其渗碳层部位的M_s点约为140℃左右,未渗碳部位(心部)的M_s点约为365℃(图1)。将加热到淬火温度的钢快冷至210～220℃等温,由于该温度高于渗碳层的M_s
In the automotive parts heat treatment, the complex shape of the workpiece, such as passive spiral bevel gear and sheet-shaped parts, without special gear quenching press and special fixture, after quenching the plane warpage are large, it is difficult to meet the requirements of the drawings. According to the literature, steel in the heat treatment phase transition, there will be short-term plasticity phenomenon, the so-called “superplasticity” effect. The “phase transition superplasticity” effect occurs during the transformation from austenite to martensite, so long as the process is properly modified, for example, by using a fractional quenching, this effect can be utilized to reduce the heat treatment distortion. First, the principle Now commonly used car gear carburizing steel 20CrMnTi, for example, carburized layer of the M_s point is about 140 ℃, carburized site (heart) M_s point is about 365 ℃ (Figure 1). The steel heated to quenching temperature is rapidly cooled to 210 ~ 220 ℃ isothermal, the temperature is higher than carburized layer M_s