engleski

Prediction of Mechanical Properties of Quenched and Tempered Steel Die

The algorithms of the estimation of yield strength, fracture toughness and fatigue resistance on the base of steel hardness are investigated in this paper. Mechanical properties of quenched and tempered steel directly depend on the degree of steel hardening. The algorithms of estimation of yield strength and fracture toughness were based on steel hardness, HV. Numerical modelling of the hardness distribution in quenched and tempered steel die has been performed based on time of cooling from 800 °C to 500 °C (t8/5) and by involving the results of modified Jominy test (JMC® test). The time of cooling at workpiece points was predicted by numerical simulation using the finite volume method. JMC® test is designed for hardenability prediction of high-hardenability steels. Since the critical cooling rate of martensite transformation of high-hardenability steels is less then maximal cooling rate of Jominy specimen the application of the original Jominy test in computer simulation is limited. Yield strength and fracture toughness distributions have been estimated using the Hahn-Rosenfield approach. Fatigue resistance was estimated based on predicted microstructure and hardness. Mathematical model of microstructure composition in quenched steel has been based on cooling time, t8/5 during the quenching. Using the established algorithm, the mechanical properties of quenched and tempered die steel were estimated by computer simulation. The computer simulation of mechanical properties has been made for steel 60WCrV7 (EN). It was found out, that mechanical properties of quenched and tempered steel dies can be successfully calculated by the proposed method. The modified Jominy test, which is a good potential test for estimation of hardenability of steel with higher hardenability, can be successfully applied for simulation of quenching of this kind of steels.

tool steel; quenching; tempering; mechanical properties; microstructure

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