45钢零件盐浴加热淬火常出现黑班软点。本文通过试验及光学和电子金相分析发现黑斑表层有深度0.3毫米左右的贝氏体组织,其余部分是马氏体组织,所以黑斑处硬度低。试验证实黑斑不是腐蚀痕。笔者认为黑斑软点是淬火加热时零件出炉瞬间盐浴中某些粘稠悬浮物附着在零件表面,使淬火冷却时冷速降低而形成“逆淬”现象。黑班是附着痕 45 steel parts salt bath quenching often appear black shift soft spot. This article through experiments and optical and electronic metallographic analysis found that the surface of the dark spot has a depth of about 0.3 mm bainite, the rest is martensite, so the dark spots at low hardness. Test confirmed that dark spots are not corrosion marks. The author believes that the dark spot is the soft spot quenching heating parts instantaneous salt bath in some viscous suspended matter attached to the surface of the part, so that the cooling rate of cooling down to form a “reverse quenching” phenomenon. Black class is attached marks