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Computer simulation of working stress of heat treated steel specimen

Smoljan B., Iljkic D., Smokvina Hanza S.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 34, nr 2

152-156

EN

Purpose: In this paper, the prediction of working stress of quenched and tempered steel has been done. The working stress was characterized by yield strength and fracture toughness. The method of computer simulation of working stress was applied in workpiece of complex form. Design/methodology/approach: Hardness distribution of quenched and tempered workpiece of complex form was predicted by computer simulation of steel quenching using a finite volume method. The algorithm of estimation of yield strength and fracture toughness was based on steel hardness, HV. Yield strength and fracture toughness distributions have been predicted using the Hahn-Rosenfield approach. Findings:It can be concluded that working stress of quenched and tempered steel can be successfully predicted by proposed method. The further experimental investigations are needed for final verification of established model. Research limitations/implications: For efficient estimation of fracture toughness from hardness, additional data about microstructure are needed. Practical implications: Estimation of hardness distribution can be based on time, relevant for structure transformation, i.e., time of cooling from 800 to 500 şC (t8/5). The prediction of distribution of microstructure composition, yield strength, and fracture toughness, can be based on steel hardness. Originality/value: Hardness distribution is predicted by involving the results of simple experimental test, i.e., Jominy-test in numerical modelling of steel quenching.

2

An analysis of modified Jominy-test (JMC®-test)

Smoljan B., Iljkić D., Smokvina Hanza S., Traven F.

Archives of Computational Materials Science and Surface Engineering

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2009

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Vol. 1, nr 2

120-124

EN

Purpose: The performance and possibilities of application of modified Jominy-test (JMC®-test) in computer simulation of high-hardenability steel quenching were investigated. JMC®-specimen and cylindrical specimen has similar cooling curves if the cylindrical specimen has been quenched in oil or cooled in air. Design/methodology/approach: The performances of investigated JMC®-test have been estimated by comparison of cooling curves of JMC®-specimen and cylindrical one cooled in different quenchants. Findings: Based on the sufficiency of both, time of cooling and similarity of cooling curves of investigated workpieces and JMC®-specimen it can be concluded that JMC®-test can be accepted as very useful test for estimation of the hardness of quenched workpieces made of high-hardenability steels. Research limitations/implications: The cooling curves of JMC®-specimen and the cooling curves of cylindrical specimens have been given by computer simulation and more experimental researches are advisable. Practical implications: The simulation of quenching based on modified Jominy-test can be applied for steels with high hardenability. This method of simulation is especially suitable for tools and dies steels. Originality/value: Using the results of simple modified Jominy-test (JMC®-test) in numerical modeling of steel quenching it is possible to simulate hardness in quenched specimen of high-hardenability steel.

3

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.