“两步法”制备等温淬火球铁的研究

An Investigation on Using Two-Step Austempering Process to Obtain ADI

由于单一温度下的等温淬火工艺不能同时达到高硬度和高韧性,开发了两步法等温淬火热处理工艺。其原理是:工件经奥氏体化后,先在低温盐浴保温一段时间,使其基体在过冷度较大时大量形核,然后再经高温保温使基体组织转变成具有含碳量较高的残余奥氏体,细化组织,进而提高力学性能。通过在低温不同保温时间下的组织对比,确定较佳的低温盐浴保温时间;然后进行单一温度下等温淬火和两步法热处理工艺试验。将两种工艺的结果进行对比,发现两步法等温淬火工艺得到的组织和性能介于单一温度等温淬火工艺的低温和高温之间。

Since high hardness and high toughness couldn＇t be obtained simultaneously by normal single-step austempering treatment in which the isothermally quenching is conducted only one time and at a single temperature, a two-step austempering process was developed. The principle of the new process is as follows： at first hold the austenited workpiece in a low temperature salt bath for some time to promote the matrix nucleus to be formed in a large quantity under the deep supercooling condition of low temperature, and then hold the workpiece in a high temperature salt bath to make the matrix structure to be transformed into the retained austenite with relatively high carbon content so that the structure would become more fine and the mechanical properties could be increased. By comparing the structures obtained after holding at low temperature and for different time durations, the optimum low temperature bath holding time was determined, then both the single-step isothermally quenching and two-step iso-quenching process tests were conducted. It was found by comparing the test results of two processes that the structure and mechanical properties obtained with two-step process were intervenient between those obtained by single step process with low and high quenching temperature respectively.