冷却过程的动态特性与钢的实际淬火冷却

Dynamic Feature of Cooling Process and Actual Quenching for Steel

采用带中心电偶的钢探头在淬冷过程中产生的电势信号和信号处理技术获得了冷却过程的瞬时动态曲线。研究了不同尺寸探头和在不同淬火介质中的动态曲线,并与TTT和CCT曲线作了比较。结果表明,钢在具有物态变化的介质中淬火时,冷却速度剧烈波动主要出现在钢被浸入淬火剂的初始阶段,探头尺寸越小,冷却介质的冷却能力越强,冷却过程越不稳定;此外,冷却三阶段在动态曲线上没有明确的分界。在实际淬火操作中,宜选用特性点较高的淬火剂,以利于工件在动态特性变化大的范围内进行自适应调整。而在过冷奥氏体转变的快冷阶段,宜保持匀速冷却,以减少动态波动的干扰。动态波动程度低而又无物态变化的单一阶段冷却最有利于过程控制和减小工件畸变。

The transient dynamic curves in the cooling process of steel were established by means of a thermo-electrical potential of steel probe with thermocouple and a signal processing technology. The dynamic curves obtained by different sizes of probe and in diferent quenchants were investigated and compoared with the TTT and CCT diagrams. The experimental results indicate that when a steel is quenched into a quenchant the state of which will change,the violent fluctuation of cooling rate will mainly occur at the beginning of steel being immerged in quenchant, and that the smaller the diameter of probe and the stronger the cooling of quenchant, the more unstable the cooling process will be. Furthermore, there will be no distinct demarcation among three stages of cooling process. Those quenchants with higher upper characteristic point are to be chosen in the actual quenching in order to be advantageous to self-regulating workpiece in a wide dynamic characteristics change range and finally to reduce distortion of workpiece. In the rapid cooling stage in which the supercooled austenite will transform the cooling rate shall be uniform to avoid dynamic fluctuation. One-stage cooling with low dynamic fluctuation and without state change will be the most advanlagous to control cooling process and to reduce workpiece distortion.