钢热处理的新工艺

New Processes for Steel Heat Treatment*

钢经热处理后保存残余奥氏体可以改善钢件的塑性和韧性。在20世纪,我们在热处理中应用奥氏体热稳定化,有效地减小淬火(高速钢回火)时钢件的畸变。本文介绍Speer等近年来发展的钢热处理新工艺—淬火和分配(Q&P)处理,即含Si或A l的Q-P钢经淬火至Ms-Mf间一定的温度(QT)后,再在一定温度(PT,在淬火温度或者高于Ms)停留,使碳由马氏体扩散(分配)至残余奥氏体,使其稳定化,增加最后淬至室温的奥氏体含量,改善钢件的强、韧混合性质。示例说明,钢经Q-P处理后显示良好的力学性质。实验表明,Q-P热力学模型“限制条件碳准平衡”(CPE,CCE)的限制假设条件常不存在。认为:在Q-P处理,尤其在较高温度、作较长时间分配处理时,宜以稳态平衡为理论基准,并计算各类可能相变的△G值,以预测可能发生的相变,包括碳化物的析出,γ→α,以及M(α)→γ。碳原子可能按扩散动力学在马氏体和奥氏体两相间分配。以Q-P处理为基础,本文作者提出淬火-分配-回火(Q-P-T)工艺,钢件局域的渗碳,以及高强度钢经碳分配等热处理新工艺。

The retention of austenite after heat treatment may 20th century, we applied the thermal stabilization of austenite improve the ductility and toughness of steel parts. In in order to reduce the deformation during quenching for steel parts（during tempering for high speed steel）. This article introduces the new process （quenching and partitioning process） for steel heat treatment developed by J. Speer et al, i. e, quenching at a temperature between Ms -Mr, followed by partitioning treatment either at initial quenching temperature or above Ms, designed to enrich the remaining untransformed austenite with carbon, escaping from the martensite, thereby stabilizing retained austenite for Q-P steel containing Si and（or） Al, increasing the amount of retaining austenite after last quenching at room temperature and improving the combination of strength and toughness of steel parts. Some examples are taken to illustrate that steels show good mechanical properties after treated with Q-P process. Experiments have shown that the assumed constrained conditions for thermodynamical model of constrained carbon equilibrium（ CPE, CEE）often not exist during the partitioning. It is suggested that orthoequilibrium should be a theoretical base for partitioning, especially at higher partitioning temperature for longer time. The A G values for different probable transformations should be calculated in order to predict the transformations which may occur, including the precipitation of carbides, γ-α and M（α） →γ, during the partitioning. Extent of carbon partition between martensite and austenite may proceed according to diffusion kinetics. Based on the Q＆P process, new heat treatment processes, such as quenching-partitioning-tempering （Q-P-T）, local carburization of steel parts as well as partitioning treatment for high strength steel are suggested.