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An application of Jominy test results in computer simulations of steel quenching

An application of Jominy test results in computer simulations of hardness and microstructure distribution in quenched steel specimen was studied. Hardness at different workpiece points can be estimated by the conversion of the cooling time t8/5 to the hardness. This conversion can be provided by the relation between the cooling time t8/5 and distance from the quenched end of the Jominy specimen (Fig. 1) [2]. To accept the assumption, that the equality of times of cooling t8/5 of several specimens, indicates equality in hardness of that specimens, the history of cooling of these specimens must be the same or similar, i.e. their cooling curves must be similar (Fig. 2). In many cases of quenching of steel this principle is not satisfied. In the developed numerical model, prediction of quenching results at specimen points are based on the equivalent cooling time from 800 to 500 ºC, t8/5e [1, 2]. Equivalent cooling time t8/5e is function of cooling time, t8/5 and history of cooling. In this way, prediction of as-quenched hardness was improved by using the equivalent cooling time t8/5e [4]. Since original Jominy test gives the cooling times t8/5 up to a maximum of 200 s (Fig. 1), the original Jominy test is not suitable for prediction of hardness of high-hardenability steel workpieces. The modified Jominy test (JMC) was designed for high-hardenability steels, i.e. steels for tools and dies [3]. In Fig. 3 the characteristic cooling curves of cylindrical specimen quenched in oil are compared to the cooling curves in different locations of JMC specimen. The cooling curves in Fig. 3 are enough similar to encourage the application of the JMC specimen in the estimation of hardness of quenched high- hardenability steel workpieces. Developed numerical model for computer simulation of quenching was also experimentally verified. Limitations of proposed numerical model were found out as well. Proposed numerical model can be successfully applied in computer simulation of quenching of tools and dies made of high- hardenability steel.

quenching ; computer simulation ; hardness ; high-hardenability steels

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