摘要
本文主要研究50CrV钢中产生低温二次硬化现象的热处理工艺并通过实验分析第二相的形成特点说明微合金钢中产生低温二次硬化的前提条件和相应曲线的表现形式。
采用适当的热处理工艺，测绘不同回火温度下50CrV、9CrV、50Cr、GCr15等钢的回火硬度曲线后认为：对不同的钢种而言，低温二次硬化的低温是相对而言的，50CrV钢的相对最佳回火温度约在180～190℃左右。
为解释9CrV、50CrV钢中的低温二次硬化现象，通过对比实验和不同回火时间处试样的显微分析，本文认为第二相的沉淀析出、马氏体的回火分解、残余奥氏体的马氏体转变共同决定了微合金钢的最终硬化情况。特别是由于微合金元素的存在，促进了回火过程中第二相的弥散析出。如果工艺满足笫二相的沉淀强化大于回火中马氏体分解引起的软化效应，就会在硬度曲线中产生明显的二次硬化峰。最后，根据Orowan机制，选择Asbby—Orowan关系式对沉淀强化所产生的屈服强度增量σ_(PR)进行估算，与马氏体分解引起的强度降低比较，所得结果与实验测绘曲线大体相符。
由此得出结论：在一定的热处理工艺条件下，通过微合金化产生的弥散强化，可以弥补马氏体分解引起的硬度降低，从而使材料获得优良的综合力学性能即同时提高了材料的韧性和硬度。
The heat treatment technique which can result in secondary hardening phenomenon at low temperature tempering of 50CrV steel has been studied. And a series of experiments were designed to analyse the fonnation character of second phase particles which was formed during the temperring. From all of this analyses, we can obtain the necessary factors which may result in secondary hardening at low temperature and we also enumerated all kinds of curve shape that maybe exist.
From the graphs which we mensurated through special heat treatment technique, we can draw conclusions that to different materials 'the low temperature' is reletive, and the optimal temperature is at 180~ 190 C for 50CrV steel which the secondary hardening can be observed.
In order to explain the secondary hardening at low temperature which exists in the SOCrV, 9CrV steel .We designed the comparative experiment and observed the microstructure of the sample which has occurred the secondary hardening. The last experiment results were determined by three factors : the second phase precipitation, die decompound of martensite, martensitic transformation of remnant austenite. Especially, the microalloyed elements, which were made the second phase precipitation equally. There would be found distinct second hardening apex in the curve when .
In a brief, dirogh a special heat treatment technique die strcngdiening by precipition of microalloyed carbide can compensate die falling of hardening, so the optimal mechanical property of the steel was acquired .
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