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Mathematical modelling of hardness of quenched and tempered steel

Smoljan B., Iljkić D., Tomašić N.

Archives of Materials Science and Engineering

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2015

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Vol. 74, nr 2

85--93

EN

Purpose: In this paper a new mathematical model and expressions for prediction of hardness of quenched and tempered steel was established. Design/methodology/approach: Novel mathematical expression for prediction of hardness of quenched and tempered steel was established. This expression includes tempering temperature, hardenability properties and degree of hardening. By experimental work it was found out that results of quenching and tempering are related to hardenability properties of steel. Findings: Based on experimental work it was found out that prediction of hardness of quenched and tempered steel is more precise by novel mathematical expression than by relation according to the German standard DIN 17021, or than by relation established by Just, E. Research limitations/implications: By taking into account the hardenability properties of steels, influence of diffusivity on kinetic of tempering processes is indirectly taken into account in the mathematical modeling of tempering processes without using the chemical composition of steel. Practical implications: The established relations were applied in mathematical modeling and computer simulation of quenching and tempering of shaft made of low alloyed steel. It was found out that hardness of quenched and tempered steel workpieces can be successfully calculated by the proposed method. Originality/value: Hardenability properties of steel are included in the established relation to achieve more precise prediction of quenched and tempered steel hardness. The influence of diffusivity on kinetic of tempering processes is indirectly taken into account in the mathematical modeling of tempering processes without using the chemical composition of steel.

2

Computer simulation of mechanical properties of quenched and tempered steel specimen

Smoljan B., Iljkić D., Tomašić N.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 40, nr 2

155-159

EN

Purpose: The computer simulation of mechanical properties of quenched and tempered steel was investigated. The established method of computer simulation was applied in prediction of mechanical properties of workpiece with complex form. Design/methodology/approach: The method of computer simulation of mechanical properties of quenched and tempered steel was established by theoretical analysis of relevant properties which have influence on hardness of quenched and tempered steel, and by regression analysis based on experimental results. Findings: The new method of prediction of mechanical properties of quenched and tempered steel was established. Proposed method of computer simulation of mechanical properties of quenched and tempered steel is based on predicted steel hardness. Hardness distribution of quenched and tempered workpiece of complex form was predicted by computer simulation of steel quenching using a finite volume method. It was found out that mechanical properties of quenched and tempered steel can be successfully predicted by proposed method. Research limitations/implications: The investigation was done on carbon and low alloyed steel. The further experimental investigations are needed for final verification of established model. Practical implications: The established method could be applied in industrial practice. Originality/value: As-quenched hardness distribution is predicted by involving the results of simple Jominy-test in numerical modelling of steel quenching. Estimation of hardness distribution is based on time, relevant for structure transforma- tion, i.e., time of cooling from 800 to 500°C (t8/5). The distribution of mechanical properties in quenched and tempered steel workpiece is estimated based on as-quenched steel hardness, tempering temperature and Jominy-test results.

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Computer simulation of microstructure transformation in heat treatment processes

Smoljan B., Smokvina Hanza S., Tomašić N., Iljkić D.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 24, nr 1

275-282

EN

Purpose: Most often used methods for prediction of austenite decomposition are described and analysed. Design/methodology/approach: The austenite decomposition prediction is usually based on continuous cooling transformation (CCT) diagrams. The next method is based on semi-empirical approach based on the Scheil's additivity rule. The third method is based on time, t8/5, relevant for microstructure transformation measured on Jominy-specimen. Very good results are obtained by artificial neural network (ANN) with learning rule based on the error backpropagation algorithm. Findings: By the comparison of application ability of investigated methods in mathematical modelling and computer simulation of austenite decomposition during the cooling of low-alloyed steel, it can be concluded that everyone method gives different results, and minimum variation in elemental composition and history of cooling may produce extremely different results in microstructure portion. Very good results were achieved by the method, which applies the Jominy-test results. In this method the additivity rule and specific performance of Jominy-test has been combined. Research limitations/implications: The investigation was performed on low-alloyed steels. Practical implications: The results of prediction of microstructure transformations could be used for prediction of mechanical properties after a heat treatment and of generation of stresses and strains during a heat treatment. Originality/value: The ability and applicability of potential methods of austenite decomposition prediction in general mathematical modelling of heat treatment of steel are carried out. The finding of this paper will be so useful in development new algorithms in mathematical modelling and computer simulation of heat treatment of low-alloyed steels.

4

Application of JM®-Test in 3D simulation of quenching

Smoljan B., Tomašić N., Iljkić D., Felde I., Reti T.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 17, nr 1-2

281--284

EN

Purpose: Simulation of hardness distribution in quenched steel specimen has been investigated using 3D numerical formulation. Structural mesh has been used in numerical simulation. Numerical calculations of hardness distribution in specimen made of high hardenability steel have been performed in order to define appropriate steel for manufacturing of machine part. Possibility of application of numerical model based on experimental results in steel quenching has been investigated. Design/methodology/approach: Numerical simulation of the steel quenching is consisted of computation of cooling curve during the quenching and prediction of hardness at specimen points after the quenching. Hardness at specimen points is estimated by the conversion of cooling time results to hardness. Conversion is provided by the relation between cooling time and distance from the quenched end of Jominy-specimen. In this way the numerical simulation has been combined with experimental Jominy-test. Findings: Structure transformation and hardness distribution can be successfully estimated based on time, relevant to structure transformation. Relevant time for quenching results for most structural steels is cooling time from 800 to 500 ̊C (t8/5). Research limitations/implications: Since high hardenability of investigated steel there are limits in application of original Jominy-specimen in simulation of quenching of steels. The modified Jominy-test enables cooling time, t8/5 higher than Jominy-test. Practical implications: The simulation of quenching based on modified Jominy-test can be applied for steels with higher hardenability. This method of simulation is especially suitable for tools and dies steels. 3D numerical simulation of quenching is more confident in practical implementation and provides more information than 2D formulation. Originality/value: Using the results of simple experimental test, i.e., modified Jominy-test in numerical modeling of steel quenching it is possible to achieve better results of hardness simulation.