Dario Iljkić

An analysis of application of modified Jominy-test in simulation of cold work tool steels quenching

The possibility of application of modified Jominy-test in computer simulation of quenching of cold work tool steels has been investigated. Because of high hardenability of cold work tool steels there are limits in application of original Jominy-specimen in simulation of quenching of steels. The modified Jominy-test was designed for prediction of hardenability of cold work tool steels. The characteristic cooling time, relevant for results of quenching, was predicted by computer simulation of quenching of both of JM ® -specimen and of cylindrical specimen. Modified Jominy-test can be applied in simulation of quenching of high hardenability steel more successfully than by original Jominy-test.

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

A mathematical model and method of computer simulation for the prediction of mechanical properties of quenched and tempered steel were developed. Numerical modelling of hardness distribution in as-quenched steel components was performed based on experimental results of Jominy test. Modified Jominy test was designed for hardenability prediction of high-hardenability steels. Hardness of quenched and tempered steel was expressed as a function of maximal hardness of actual steel and representatives of chemical diffusivity of steel according to the time and temperature of tempering. Yield strength and fracture toughness distributions were estimated using the Hahn−Rosenfield approach. Fatigue resistance was estimated based on predicted microstructure and hardness. Distribution of other relevant mechanical properties was found out based on predicted as-quenched and tempered hardness of steel. Experimental investigation was performed on high-hardenability steel for tools and dies. The established procedure was applied in computer simulation of mechanical properties of a quenched and tempered steel workpiece.

Mathematical Modeling and Computer Simulation of Fatigue Properties of Quenched and Tempered Steel

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

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.

Evaluation of Steel Hardenability by JM® -test

The modified Jominy-test was designed for prediction of hardenability of high-hardenability tool steels and possibility of application of modified Jominy-test in computer simulation of quenching of high-hardenability tool steels has been investigated. Because of high hardenability there are limits in application of original Jominy-specimen in simulation of quenching of steels. The performance of investigated modified Jominy-test in simulation of quenching of high-hardenability tool steels was estimated by comparison of cooling curves of modified Jominy-specimen (JM®-specimen) and cylindrical specimen. The influence of dimension of JM®-specimen on cooling curves has been investigated. The time of cooling, t8/5 relevant for results of quenching was predicted. Modified Jominy-test can be applied in simulation of quenching of steel with higher hardenability rather than 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.

Mathematical Modelling of Steel Quenching

Mathematical modelling of phase transformations and hardness distribution in non-monotonic quenched steel specimen was developed based on the results of simple experimental test i.e. Jominy test. The hardness in specimen points was estimated by the conversion of cooling time results to hardness by using both, the relation between cooling time and distance from the quenched end of Jominy specimen, and by using the Jominy hardenability curve. The cooling curve at the specimen point was predicted by numerical modelling of cooling by using the finite volume method. Developed numerical model for computer simulation of quenching was also experimentally verified. Limitations of proposed numerical model were found out as well. It has been shown that proposed numerical model can be successfully applied for purposes of simulation of continuous and interrupted quenching of carbon and low alloyed steel specimens.

Computer simulation of hardness and microstructure of casted steel 100Cr6

The research purpose is to upgrade the mathematical modelling and computer simulation of casting of steel. Based on theoretical analyses of physical processes which exist in casting systems the proper mathematical model is established and computer software is developed. On the basis of control volume method, the algorithm for prediction of mechanical properties and microstructure distribution in steel casting has been developed. The computer simulation of casting of steel is consisted of two parts: numerical calculation of transient temperature field in process of solidification and cooling of casting to the final temperature, and of numerical calculation of mechanical properties. The hardness and microstructures of casting has been predicted based on CCT diagrams. 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. The algorithm is completed to solve 3-D situation problems such as the casting of complex cylinders, cones, spheres, etc. The established model of steel casting can be successfully applied in the practice of casting.

Adhesivity of electroless Ni-P layer on austenitic stainless steel

Purpose: Optimization of testing of adhesivity of electroless deposited nickel-phosphorous coatings on austenitic stainless steel substrate. Design/methodology/approach: The main study has been focused on comparison of testing methods of adhesivity of electroless nickel- phosphorous coatings and analyses of influence of heat treatment on adhesivity of electroless nickel- phosphorous. Findings: It was found out that adhesivity of electroless nickel- phosphorous coatings can be successfully characterized by Vickers hardness tester. Research limitations/implications: The study was not extended to other types of deposited layers in order to be able to bring a general decision about applicability of this method in the testing of adhesivity of deposited layers. Practical implications: Based on experimental results it was found out that heat treated nickel-phosphorous coating have higher microhardness than non-heat treated electroless nickel-phosphorous coatings. High microhardness of heat treated nickel-phosphorous coating is connected with formation of Ni3P phase. Moreover, better adhesivity can be achieved by application of proper activation process before electroless coating. Originality/value: Standard Vickers hardness method was successfully applied in testing of adhesivity of electroless nickel- phosphorous coatings on austenitic stainless steel substrate.

Computer modelling of as–quenched hardness and microstructure composition of steel

Industry needs to control and to optimise the process parameters of the steel quenching can be accomplished by considering achievement of desired mechanical properties and microstructure distribution. A joined thermometallurgical approach is applied to complete the numerical model of phenomena of steel quenching. Because of wide range of applicability and ease of use of finite volume method (FVM), this numerical method was suitable to create integrated computer program for simulation of transient temperature field, microstructure transformations and mechanical properties during a quenching of steel components. The computer model of steel quenching has been applied for simulation of quenching of steel die components of complex form. By experimental verification of the computer simulation results, it has been found out that phenomena of steel quenching could be successfully described by the proposed computer model.