Sunčana Smokvina Hanza

Computer Simulation of Quenched Steel Working Stress

The possibility of the application of a modified Jominy-test in the computer simulation of quenching of steels for tools and dies has been investigated. The performance of an investigated modified Jominy-test in the simulation of quenching of tools and dies was estimated by a comparison of the cooling curves of a modified Jominy-specimen (JMr ; -specimen) and a cylindrical specimen. The hardness distribution in a quenched specimen was estimated based on a relevant cooling time from 800 to 500°C, as well as on the results of a modified Jominy-test. The characteristic cooling time, relevant for the results of quenching, was predicted by the computer simulation of quenching of both the JMr ; -specimen and cylindrical specimen. Mechanical properties of quenched steel directly depend on the degree of quenched steel hardening. The algorithm of the estimation of yield strength and fracture toughness on the base of steel hardness is established in this paper. Using the established algorithm, the mechanical properties of quenched and tempered die steel were estimated by computer simulation. It was found that the modified Jominy-test can be applied in the simulation of quenching of high hardenability steel more successfully than by the original Jominy-test.

Mathematical Modeling and Computer Simulation of Steel Quenching

The purpose of this research is to upgrade the mathematical modeling and computer simulation of steel quenching. Based on theoretical analyses of physical processes that exist in quenching systems, the mathematical model for steel quenching is established and computer software is developed. The mathematical model of steel quenching is focused on physical phenomena, such as heat transfer, phase transformations, mechanical properties, and generation of stresses and distortions. The numerical procedure of computer simulation of steel quenching is divided into three parts: numerical calculation of transient temperature field, numerical calculation of phase change, and numerical calculation of the mechanical behaviors of steel during quenching. The numerical procedure is based on the finite volume method. Physical properties that were included in the model, such as heat conductivity coefficient, heat capacity, and surface heat transfer coefficient, were obtained by the inversion method based on the Jominy test results. By the completed algorithm, 3-D situation problems, such as the quenching of complex cylinders, cones, spheres, etc., can be simulated. The established model of steel quenching can be successfully applied in the practical usage of quenching.

Computer Simulations of Mechanical Properties of Steel Dies

The algorithm of estimation of yield strength and fracture toughness based on steel hardness HV has been made. The hardness distribution in a quenched die was estimated based on relevant time of cooling from 800–500°C, as well as on results of modified Jominy-test, which is designed for hardenability prediction of high-hardenability steels. The computer simulation of mechanical properties was made for steel 60WCrV7 (DIN). It can be concluded that, by the proposed method, mechanical properties of quenched and tempered steel dies can be successfully calculated.