engleski

Simulation of mechanical properties of forged and casted steel 42CrMo4 specimen

In this paper, the prediction of working stress of quenched and tempered shaft has been done. Prediction was done for two different manufacture processes. In the first manufacture process the shaft was made of steel and in second one the shaft was made of cast steel. The working stress was characterized by yield strength and impact toughness. The method of computer simulation of working stress was applied in workpiece of complex form. Hardness distribution of quenched and tempered workpiece of complex form was predicted by computer simulation of quenching using a finite volume method. Hardness of quenched and tempered steel can be expressed as function of maximal hardness of actual steel, hardness of steel with 50 % of martensite in microstructure, according to the time and temperature of tempering. The algorithm of estimation of yield strength and impact energy was based on hardness, HV. Starting point in studying of the mechanical properties of steel castings can be the fact that the mechanical properties of steel castings are derived from the mechanical properties of ordinary steel metal matrix reduced by the influence of the typical as-cast structure, i.e. casting defects on those properties. Hardness and yield strength will be unaffected by most defects. The only effect will be that due to the reduction in area. Coarse as-cast microstructure of cast steel lowers ductility and toughness. Impact energy of quenched and tempered cast steel was predicted based on pouring temperature, temperature of mould during the pouring and fact that steel castings are not subjected to different metallurgical and mechanical processes of microstructure improvement in so far as wrought steels. It can be concluded that working stress of quenched and tempered shaft can be successfully predicted by proposed method. The further experimental investigations are needed for final verification of established model. For efficient estimation of steel toughness from hardness, additional data about microstructure are needed. Estimation of hardness distribution can be based on time, relevant for structure transformation, i.e., time of cooling from 800 to 500 C (t8/5). The prediction of yield strength and toughness of steel can be based on steel hardness. The prediction of impact toughness of quenched and tempered cast steel can be based on impact toughness of quenched and tempered steel. Hardness distribution is predicted by involving the results of simple experimental test, i.e., Jominy-test in numerical modelling of steel quenching. Algorithm of estimation of hardness of quenched and tempered steel was improved. New algorithm of prediction of impact energy of quenched and tempered steel cast was found.

steel; cast steel; heat treatment; computer simulation; mechanical properties

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