Mathematical modelling and computer simulation of fatigue properties of quenched and tempered steel

The engineering and economical aspects of optimization of steel shaft quenching and tempering were investigated. The mathematical model and method of computer simulation for prediction of fatigue properties quenched and tempered steel has been developed. Computer simulation of fatigue properties quenched and tempered steel has been applied in optimization of quenching and tempering of steel shaft. Proper heat treatment process was accepted based on economical analyse. Fatigue properties of quenched and tempered steel have been predicted based on microstructure composition and yield strength. Microstructure composition and yield strength have been predicted based on as-quenched hardness. Distribution of as-quenched hardness in workpiece was predicted by computer simulation of steel quenching using a finite volume method. The as-quenched hardness is estimated based on time of cooling and on Jominy test results. It was taken into account that mechanical properties of quenched steel directly depend on hardness and degree of hardening and microstructural constituents. Using a numerical simulation of microstructure and mechanical properties, it was found out that best fatigue properties investigated shaft has if it was machined or formed on proper geometry before proper quenching and tempering. By economical analise of investigated shaft manufacturing was found out that most suitable shaft manufacture process is to manufacture the shaft from the quenched and tempered bar. But in this case, heterogeneous microstruture of ferrite, perlite, bainite and martensite, with very low fatigue limit could appeare at some critical locations.