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1

Computer simulation of hardness and microstructure of casted steel 100Cr6

Smoljan B., Iljkić D., Maretić M.

Archives of Materials Science and Engineering

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2016

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Vol. 78, nr 1

23--28

EN

Purpose: The research purpose is to upgrade the mathematical modelling and computer simulation of casting of steel. Design/methodology/approach: Based on theoretical analyses of physical processes which exist in casting systems the proper mathematical model is established and computer software is developed. Findings: On the basis of control volume method, the algorithm for prediction of mechanical properties and microstructure distribution in steel casting has been developed. Research limitations/implications: 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. Practical implications: 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. Originality/value: 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

2

Adhesivity of electroless Ni-P layer on austenitic stainless steel

Smoljan B., Iljkić D., Maretić M.

Archives of Materials Science and Engineering

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2016

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Vol. 80, nr 2

53--58

EN

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.

3

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.

4

Computer simulation of microstructure of quenched moulding die

Smoljan B., Iljkić D., Tomasic N.

Archives of Materials Science and Engineering

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2014

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Vol. 68, nr 2

81--86

EN

Purpose: The research purpose is to upgrade the mathematical modelling and computer simulation of quenching of steel. Design/methodology/approach: The computer simulation of steel hardening is consisted of numerical calculation of transient temperature field in process of cooling, and of numerical calculation of mechanical properties. The hardness has been predicted by the conversion of calculated time of cooling from 800 to 500°C at specimen points to the hardness. The algorithm is completed to solve 3-D situation problems such as the quenching of complex cylinders, cones, spheres, etc. Findings: On the basis of control volume method, the algorithm for prediction of mechanical properties and microstructure distribution in quenched steel specimens with complex geometries has been developed. The established relations were applied in computer simulation of mechanical properties and microstructure distribution of forged steel centrifugal casting pipe mould. The investigated model of steel quenching can be successfully applied in the practice of heat treatment. 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 algorithms can be used in heat treating practice. Originality/value: Microstructure distribution is estimated based on time relevant for structure transformation, i.e., the cooling time from 800 to 500°C, t8/5.

5

Input physical properties in mathematical model of steel quenching

Smoljan B., Iljkić D., Pomenić L

Journal of Achievements in Materials and Manufacturing Engineering

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2013

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Vol. 58, nr 2

81--86

EN

Purpose: Developing of new methods for input data of mathematical model is established. Design/methodology/approach: Temperature dependency of both, heat transfer for quenchant with Grossmann severity of quenching H=0.35, which are adequate for oil and heat conductivity coefficients has been calibrated on the base of Crafts-Lamont diagrams. Findings: Evaluation of physical properties such as specific heat capacity, c, heat conductivity coefficient, λ, density, ρ, heat transfer coefficient, α involved in mathematical model of transient temperature field was done by the inversion method, or by calibrations. Research limitations/implications: In the future this investigation should be broaden on investigation of more quechants. Practical implications: By proper input data of mathematical model of steel quenching, correct computer simulation can be performed. Originality/value: New inverse method of input data such as specific heat capacity, c, heat conductivity coefficient, λ, density, ρ, heat transfer coefficient, α, which is based just on achieved distributions of mechanical properties in Crafts-Lamont diagrams.

6

Prediction of quenched and tempered steel and cast steel properties

Smoljan B.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 49, nr 2

369--374

EN

Purpose: The influence of processing parameters, such as pouring temperature and cooling rate during the casting, as well as application of hot working and pre-heat treatment, on strength and toughness of quenched and tempered steel was investigated. Design/methodology/approach: Strength and toughness were presented by yield strength and Charpy-V notch toughness, respectively. Experimental procedure of material properties optimization was done using the 25-2 factor experiment. Findings: It was found out that yield strength is insensitive on differences between applied manufacturing processes, but by application of hot working and with appropriate pouring temperature the Charpy-V notch toughness is increased. Also, Charpy-V notch toughness is increased by interactive effect of the appropriate cooling rate during the casting and application of hot working. Research limitations/implications: The research was focused mainly on Charpy-V notch toughness of carbon and low alloyed heat treatable steels. Practical implications: The established algorithms can be used for prediction of tensile strength, yield strength and Charpy-V notch toughness in heat treating practice. Originality/value: Original relation for prediction of quenched and tempered steel and cast steel Charpy-V notch toughness are developed.

7

Computer simulation of quenched and tempered steel properties

Smoljan B., Iljkić D., Novakova H

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 46, nr 2

175--181

EN

Purpose: The algorithm of estimation of mechanical properties based on steel hardness has been established. Design/methodology/approach: Numerical modelling of hardness distribution in as-quenched steel specimen was performed by involving the results of simple experimental test, i.e., Jominy-test. Hardness of quenched and tempered steel has been expressed as function of maximal hardness of actual steel and hardness of actual steel with 50% of martensite in microstructure, according to the time and temperature of tempering. After that distribution of other relevant mechanical properties was predicted based on predicted as-quenched and tempered hardness of steel. Experimental investigation has been performed on low alloy steel. The established procedure for estimation of quenched and tempered properties of steel has been applied in computer simulation of mechanical properties of quenched and tempered steel workpiece of complex form. Findings: Algorithm of estimation of hardness of quenched and tempered steel was improved. It can be concluded that working stress of quenched and tempered shaft can be successfully predicted by proposed method. The proposed computer simulation method could be applied in failure prevention. Research limitations/implications: The research was focused only on carbon and low alloyed heat treatable steels. Practical implications: The established algorithms can be used for prediction of mechanical properties in heat treating practice. Estimation of as-quenched hardness distribution is based on time, relevant for structure transformation, i.e., time of cooling from 800 to 500°C (tg/5). The hardness in the quenched and tempered state is estimated from the as-quenched hardness. The prediction of yield strength and toughness of steel is 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.

8

Simulation of mechanical properties of forged and casted steel 42CrMo4 specimen

Smoljan B., Iljkić D.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 43, nr 2

597--602

EN

Purpose: In this paper, the prediction of working stress of quenched and tempered shaft has been done. Prediction was done for two different manufacture processes. In the first manufacture process the shaft was made of steel and in second one the shaft was made of cast steel. The working stress was characterized by yield strength and impact 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 quenching using a finite volume method. Hardness of quenched and tempered steel can be expressed as function of maximal hardness of actual steel, hardness of steel with 50% of martensite in microstructure, according to the time and temperature of tempering. The algorithm of estimation of yield strength and impact energy was based on hardness, HV. Starting point in studying of the mechanical properties of steel castings can be the fact that the mechanical properties of steel castings are derived from the mechanical properties of ordinary steel metal matrix reduced by the influence of the typical as-cast structure, i.e. casting defects on those properties. Hardness and yield strength will be unaffected by most defects. The only effect will be that due to the reduction in area. Coarse as-cast microstructure of cast steel lowers ductility and toughness. Impact energy of quenched and tempered cast steel was predicted based on pouring temperature, temperature of mould during the pouring and fact that steel castings are not subjected to different metallurgical and mechanical processes of microstructure improvement in so far as wrought steels. Findings: It can be concluded that working stress of quenched and tempered shaft can be successfully predicted by proposed method. Practical implications: Estimation of hardness distribution can be based on time, relevant for structure transformation, i.e., time of cooling from 800 to 500°C (t8/5). The prediction of yield strength and toughness of steel can be based on steel hardness. The prediction of impact toughness of quenched and tempered cast steel can be based on impact toughness of quenched and tempered steel. Originality/value: Hardness distribution is predicted by involving the results of simple experimental test, i.e., Jominy-test in numerical modelling of steel quenching. Algorithm of estimation of hardness of quenched and tempered steel was improved. New algorithm of prediction of impact energy of quenched and tempered steel cast was found.

9

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.

10

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.

11

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.

12

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.

13

An analysing of heat treatment process planning

Smoljan B.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 20, nr 1-2

563-566

EN

Purpose: Process planning of heat treatment has been investigated. The established approach of heat treating process planning is suitable for effective integration of heat treatment in computer added manufacturing. Design/methodology/approach: Process plan of heat treating process has been established based on fundamental process planning principals. The heat treatment was treated in the same as other manufacture processes. Findings: The general approach for process planning of heat treatment processes has been established. Heat treatment processes have to be designed into operations and sub-operations with the same principles that are also valid for other manufacturing processes. Research limitations/implications: The further research should be focused on development of methods for the better application of achieved results. Practical implications: This way of heat treatment process planning is more appropriate for integral trends of manufacturing, i.e., with the trend of introducing the modern systems in all parts of industrial manufacturing. Originality/value: The global approach of process planning of heat treatment processes was established and better unification with other manufacturing processes was achieved.

14

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.