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The main goal of this paper is mathematical modelling and computer simulation of isothermal decomposition of austenite in steel. Mathematical modelling and computer simulation of isothermal decomposition of austenite nowadays is becoming an indispensable tool for the prediction of isothermal heat treatment results of steel. Besides that, the prediction of isothermal decomposition of austenite can be applied for understanding, optimization and control of microstructure composition and mechanical properties of steel. Isothermal decomposition of austenite is physically one of the most complex engineering processes. In this paper, methods for setting the kinetic expressions for prediction of isothermal decomposition of austenite into ferrite, pearlite or bainite were proposed. After that, based on the chemical composition of hypoeutectoid steels, the quantification of the parameters involved in kinetic expressions was performed. The established kinetic equations were applied in the prediction of microstructure composition of hypoeutectoid steels.

A novel, simple, low-cost, and user-friendly potentiometric surfactant sensor based on the new 1,3-dihexadecyl−1H-benzo[d]imidazol−3-ium-tetraphenylborate (DHBI–TPB) ion-pair for the detection of cationic surfactants in personal care products and disinfectants is presented here. The new cationic surfactant DHBI-Br was successfully synthesized and characterized by nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectrometry, liquid chromatography–mass spectrometry (LC–MS) and elemental analysis and was further employed for DHBI–TPB ion-pair preparation. The sensor gave excellent response characteristics for CTAB, CPC and Hyamine with a Nernstian slope (57.1 to 59.1 mV/decade) whereas the lowest limit of detection (LOD) value was measured for CTAB (0.3 × 10−6 M). The sensor exhibited a fast dynamic response to dodecyl sulfate (DDS) and TPB. High sensor performances stayed intact regardless of the employment of inorganic and organic cations and in a broad pH range (2−11). Titration of cationic and etoxylated (EO)-nonionic surfactant (NSs) (in Ba2+) mixtures with TPB revealed the first inflexion point for a cationic surfactant and the second for an EO-nonionic surfactant. The increased concentration of EO-nonionic surfactants and the number of EO groups had a negative influence on titration curves and signal change. The sensor was successfully applied for the quantification of technical-grade cationic surfactants and in 12 personal care products and disinfectants. The results showed good agreement with the measurements obtained by a commercial surfactant sensor and by a two-phase titration. A good recovery for the standard addition method (98–102%) was observed.

An increase in technical requirements related to the prediction of mechanical properties of steel engineering components requires a deep understanding of relations which exist between microstructure, chemical composition and mechanical properties. This paper is dedicated to the research of the relation between steel hardness with the microstructure, chemical composition and temperature of isothermal decomposition of austenite. When setting the equations for predicting the hardness of microstructure constituents, it was assumed that: (1) The pearlite hardness depends on the carbon content in a steel and on the undercooling below the critical temperature, (2) the martensite hardness depends primarily on its carbon content, (3) the hardness of bainite can be between that of untempered martensite and pearlite in the same steel. The equations for estimation of microstructure constituents&rsquo, hardness after the isothermal decomposition of austenite have been proposed. By the comparison of predicted hardness using a mathematical model with experimental results, it can be concluded that hardness of considered low-alloy steels could be successfully predicted by the proposed model.

The paper presents a review of the methods of modelling the hardness and hardenability of steel. Among the various numerical methods there were presented method of multiple regression, artificial neural networks, fuzzy systems genetic programming and Finite Element Method. In the case of regression analysis, it has been only mentioned well-known methods and models proposed in the literature. While for the other three computational tools the results of own work indicating the possibility of their use for hardenability modelling were presented. The developed neural network model can also be employed for simulations of the relationship between hardness at a given distance from the Jominy specimen face and the chemical composition of steel. This can be done in the entire range of concentrations of the main alloying elements occurring in constructional alloy steels. The fuzzy system deals very well with data on which it was created - in cases outside the scope of the model results were very different. The systems are a good tool to approximate inference what is possible because of previously created if-then rules, which describe the phenomenon that is otherwise hard to describe. This computer tool, which was used in materials science for structural steels for quenching and tempering, could be successfully used for other materials and their properties. The results of calculations obtained using genetic programming looks very promising, considering, that the loaded set of data ignored other alloying elements that have influence on hardness of steel. Genetic programming is a very useful tool for solving problems like that. This problem is particularly important when there are more factors affecting the investigated phenomenon. What is the main advantage of genetic programming is to release the investigator from the problem of predicting the correct form of a model describing the phenomenon investigated. GP method accomplishes this task autonomously. The established FEM models can be applied in mathematical modelling of microstructure transformations and hardness distribution, as well as, stress and strain generaton. One of the most important factors for efficient simulation of hardening is the proper selection and use of representative cooling phenomena that is relevant for microstructure transformation. The structure transformations and hardness distribution can be estimated based on time relevant for structure transformation. Hardness at different location of quenched steel specimen can be estimated by the conversion of the calculated cooling time t8/5 to the hardness. It can be done by using both, the relation between cooling time, t8/5 and Jominy distance and the Jominy hardenability curve

A 1,3-dihexadecyl-1H-benzo[d]imidazol-3-ium-tetraphenylborate (DHBI-TPB) ion-pair implemented in DHBI-TPB surfactant sensor was used for the potentiometric quantification of anionic surfactants in detergents and commercial household care products. The DHBI-TPB ion-pair was characterized by FTIR spectroscopy and computational analysis which revealed a crucial contribution of the C–H∙∙∙π contacts for the optimal complex formation. The DHBI-TPB sensor potentiometric response showed excellent analytical properties and Nernstian slope for SDS (60.1 mV/decade) with LOD 3.2 × 10−7 M, and DBS (58.4 mV/decade) with LOD 6.1 × 10−7 M was obtained. The sensor possesses exceptional resistance to different organic and inorganic interferences in broad pH (2–10) range. DMIC used as a titrant demonstrated superior analytical performances for potentiometric titrations of SDS, compared to other tested cationic surfactants (DMIC &gt, CTAB &gt, CPC &gt, Hyamine 1622). The combination of DHBI-TPB sensor and DMIC was successfully employed to perform titrations of the highly soluble alkane sulfonate homologues. Nonionic surfactants (increased concentration and number of EO groups) had a negative impact on anionic surfactant titration curves and a signal change. The DHBI-TPB sensor was effectively employed for the determination of technical grade anionic surfactants presenting the recoveries from 99.5 to 101.3%. The sensor was applied on twelve powered samples as well as liquid-gel and handwashing home care detergents containing anionic surfactants. The obtained results showed good agreement compared to the outcomes measured by ISE surfactant sensor and a two-phase titration method. The developed DHBI-TPB surfactant sensor could be used for quality control in industry and has great potential in environmental monitoring.

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.

The technology of High Pressure Gas Quenching (HPGQ) in modern vacuum furnaces has already reached the level of 20 to 25 bar pressure and up to 80 m/s gas flow velocity. By using primarily nitrogen (N2) it is possible to quench also low-alloyed steels, and to compete, in some cases successfully, with oil quenching. This depends basically on the hardenability of the steel and on the cross-section thickness of the quenched workpiece. The present work explains experimental testing of steels' hardenability when gas quenching is applied. For determination and vizualization of the hardening capacity of steels quenched by HPGQ, a computer aided method has been developed for axially symmetric workpieces of any complex shape, to show at a glance the complete hardness distribution on longitudinal section. An included database of relevant steel grades and possible gas quenching parameters enables to choose another steel grade and/or other quenching parameters, and see on the display another relevant hardness distribution, without performing additional experiments.

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.

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.

Development and application of reusable industrial packages, which can be used in assembly line has been investigated. The reusable industrial packages are often called reusable crates and totes or reusable/returnable packaging containers. The trend of development of reusable packaging systems has been facilitated by the plastics industry developing lightweight rugged crates and totes, which can be used in storages and manufacturing lines. Sizes range of these kind packages is from handled totes to pallet-load sized intermediate bulk containers for manufacturing. Possibility that each component reaches the manufacture at the right time, in the right sequence, and in the appropriate version, referred as Just-In-Sequence was analysed. An automotive supply chain characteristics and scheme of component suppliers’ structure in Just-In-Sequence way was illustrated. Materials properties of reusable packaging was studied. The most important packaging performance factors are durability, flammability, sanitation and ergonomics of packaging, which affect the cost, and operations of a reusable packaging system. Since the importance of industrial reusable packaging is growing up, the new sophisticated test method for transport packages are needed by which vulnerabilities and exposures in the application of reusable industrial containers will be taken into account.

The review of the numerical modelling of casting and welding of steel workpieces was studied. The contemporary industry needs tools to optimize and control parameters of processes by considering the favourite chemical composition of steel. In recent time, very efficient tool for optimizing and controlling of the process parameters is numerical modelling of engineering processes. At casting and welding numerical modelling is focused on optimization of distribution of microstructure contents, mechanical and physical properties distribution and tolerated distortions and residual stresses. Mechanical properties and prevention of distortion and cracking can be accomplished by prediction and control of residual stresses and microstructure distribution. The numerical modelling of thermal processing of metals consists of the research of multi-scale processes and multi-physics processes, such as phase transformations, heat transfer and mechanics of materials, and research of numerical methods for computer interpretation of the problem. By means of the numerical modelling and computer simulation of thermal processing should calculate the transient temperature field, melting and solidification processes, as well as, to calculate distribution of mechanical and physical properties and microstructure composition. In this work, the numerical models of studied thermal processes are based on the finite volume method. Values of surface heat transfer coefficient, heat capacity and heat conductivity coefficient were obtained by the inversion method. The microstructures composition has been predicted by CCT diagrams and additionally improved by the kinetic equations. The mathematical model has accomplished to solve thermal processing of 3-D axially symmetric specimens.

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.

The research main stream in this paper is to upgrade the mathematical modelling and computer simulation of quenching of steel. Based on theoretical analyse of physical processes which exist in quenching systems of steel workpieces, the mathematical model for computer simulation mechanical properties and distortions during the quenching has been 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. Because of that the numerical procedure of computer simulation of steel quenching is divided in three parts: numerical calculation of transient temperature field, numerical calculation of phase change and numerical calculation mechanical behaviours of steel. The numerical procedure is based on control volume method. Relevant physical properties about which cooling rate depends are specific heat capacity of steel, heat conductivity coefficient of steel, steel density, linear thermal expansion, transformation expansion, and heat transfer coefficient of quenchant. Also, the transformation plasticity has been included in the model. Physical and mechanical properties that were included in such model have been predicted by taking into account their temperature dependences. In the developed computer program for simulation quenching the hardness at different workpiece points is estimated by the conversion of the calculated cooling time from 800 to 500 °C, t8/5 to the hardness by using both, the relation between cooling time, t8/5 and Jominy distance and the Jominy hardenability curve. Other properties of steel have been estimated based on as quenched hardness of steel. Based on the developed algorithm, computer software is developed for simulation of 3D situation problems, such as the quenching of complex cylinders, cones, spheres, etc., can be simulated. The established numerical model and computer softwaire for simulation of steel quenching can be successfully applied in the practical usage of quenching.

The research purpose is to upgrade the mathematical modelling and computer simulation of quenching of steel. Based on theoretical analyze of physical processes which 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. 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 Jominy test results. The numerical procedure is based on finite volume method. By the developed algorithm, 3D 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.

Properties of electroless deposited nickel - phosphorous coatings on austenitic stainless steel substrate were investigated. The main study has been focused on influence of heat treatment on microhardness and microstructure analysis of electroless Ni-P coatings. Nickel - phosphorous coatings was deposited without nickel strike pre- coating treatment. The electroless Ni-P layer has been deposited on stainless steel as substrate. The sodium hypophosphite has been used as reducing agent. Microstructure and morphology of the electroless treated specimens were analyzed by optical and scanning electron microscopy. Adhesivity was estimated by Vickers indenter. Based on experimental results, it can be concluded that heat treated electroless nickel - phosphorous coatings have higher microhardness than non-heat treated electroless nickel - phosphorous coatings. Analyze of Vickers indentation results showed that proposed electroless process gives satisfied results.

Numerical model of controlled cooling in the production of steel hot rolled bars was developed. The numerical model and algorithm are completed to solve problems in controlled cooling of hot rolled bars in cooling beds. The controlled cooling is performed by special placement of hot rolled bars on cooling beds. By numerical model of controlled cooling is possible to predict a transient temperature field, microstructure evolution and hardness of round steel bars during their cooling in cooling beds. The numerical model of transient temperature field is based on control volume method. The hardness and microstructure distribution in steel bars has predicted by using equations of austenite decomposition kinetic. The algorithm for prediction is based the real chemical composition. Numerical model and computer program were experimentally verified by experimental work in a real industrial production of low-alloyed steel bars. The verification of developed numerical model was performed by comparison of simulated with experimentally evaluated results hardness and cooling curve.

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.

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.

The computer simulation of electromagnetic, thermodynamic and microstructural transformations in the treated workpiece is usually recommended for the exact definition of working parameters in process planning of the induction hardening processes. A special simulation program has been developed for the axially symmetric workpieces. The simulation program performance has been tested by the simulation of one case of induction hardening of cylindrical workpiece made from the 42CrMo4 steel grade. The measured values of surface hardness and hardening depths have been compared with the specified values and the good conformity of the simulated values with the experimental ones values has been observed.

Brittle material behavior and mode of failure are contrasted with those characteristics of ductile materials. The stochastic nature of brittle fracture, which results from the random occurrence of fracture-initiating microstructural imperfections, necessitates a probabilistic fracture mechanics approach to design with brittle materials. It is also clearly shown which main properties of brittle materials have to be optimized to improve the reliability of mechanically loaded components made of brittle materials. Important features of designing with brittle materials are elucidated and illustrated by an exemplary design calculation of a ceramic disc spring. It is shown how even environmentally induced subcritical crack growth, characteristic of ceramic materials, can be adequately accounted for in the assessment of reliability.

A mathematical model and expressions for hardness prediction were established, where quenched and tempered steel hardness is predicted based on as-quenched hardness of steel. Hardenability properties of steel are included in the model to achieve a more precise prediction of quenched and tempered steel hardness. Prediction of the as-quenched hardness of steel is based on the relationship between as-quenched hardness and the characteristic cooling time from 1073 K to 773 K (800 °C to 500 °C) (t 8/5). The model was used to simulate the hardness of a quenched and tempered steel workpieces.

Achievements of the induction hardening of ferritic ductile iron were investigated. Ductile iron is not advisable for use in induction hardening because of the small carbon content in the metal matrix of ferritic ductile iron. The carbon content in the metal matrix of ductile iron can be increased by additional preparation of metal matrix before final induction heat hardening. Wear resistance of the induction hardened ferritic ductile iron can increase as result of increased carbon content of the metal matrix and higher hardness after induction hardening. Some heat pretreatments for metal matrix preparation were applied before the induction hardening of ferritic ductile iron. The process parameters of the induction hardening heat pretreatment were analyzed and optimized. According to recommended elemental composition of ferritic ductile iron and required mechanical properties, the process parameters of the investigated induction heat pretreatment were optimized. The efficiency of pretreatment processes of induction hardening was analyzed. Applicability and manufacture ability of engineering components by proposed heat pretreatments were investigated. The limitations of the investigated heat pretreatment applications were estimated by the comparison of mechanical properties of heat-treated specimens.

The algorithm and computer program are completed to simulate the quenching of complex cylinders, cones, spheres, etc. Numerical simulation of steel quenching is a complex problem, dealing with estimation of microstructure and hardness distribution, and also dealing with evaluation of residual stresses and distortions after quenching. The nonlinear finite volume method has been used in numerical simulation. By the established computer program, mechanical properties and residual stresses and strains distributions in the quenched specimen can be given at every moment of quenching.

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.

New mathematical expressions for the prediction of hardness, yield strength and Charpy-V notch toughness of quenched and tempered steel were established. Quenched and tempered steel’s hardness is predicted based on as quenched hardness of steel. In the relation to hardness between quenched and tempered steel and as quenched steel, the hardenability of steel is taken in account. The mathematical model of hardness of steel is similar to the relationship established by Just. Yield strength and Charpy-V notch toughness of steel are predicted using the hardness of the quenched and tempered steel. Charpy-V notch toughness of cast steel is predicted using the Charpy-V notch toughness of steel with a same chemical composition. The mathematical expressions established were applied in computer simulation of mechanical properties of shafts made of quenched and tempered steel which the very well known relationship between hardness of as quenched steel and characteristic cooling time from 800 to 500uC (t8/5) during the quenching is used.

Achievements of professor Liščić in heat treatment and surface engineering of metals have been described.

Unsuitable mechanical behaviour of cast steel GS-42CrMo4 (EN) was investigated. In this paper the influence of inclusions and pouring temperature on mechanical properties of arm of carrying jaw made of cast steel GS-42CrMo4 (EN) was investigated. It was found that a high content of aluminium caused the formation of aluminium nitride, AlN which significantly decreased the strength of casting. In the process of solidification, enrichment of lamellas of AlN nitride arise on the grain boundaries. Because of low deformability of AlN nitride, initiation of fracture was possible at minimal deformation. The strength of the casting was not being raised by subsequent heat treatment. High pouring temperature and low cooling rates resulted in coarse-grained microstructure of steel casting. Coarse microstructure was not reduced by subsequent heat treatment., Istraživano je nepovoljno mehaničko ponašanje čeličnog lijeva GS-42CrMo4 (EN). U radu je prikazan utjecaj uključaka i temperature lijevanja na mehanička svojstva poluge kliješta izrađenih od čeličnog lijeva GS-42CrMo4 (EN). Visok sadržaj aluminija uzrokovao je tvorbu aluminijevog nitrida AlN, kojim se bitno umanjila čvrstoća odljevka. Za vrijeme skrućivanja slitine došlo je do obogaćivanja lamela AlN nitrida na granicama kristalnih zrna. Zbog male deformabilnosti AlN nitrida, do iniciranja prijeloma došlo je već kod minimalne deformacije. Čvrstoća odljevka nije se povećala naknadnom toplinskom obradom. Visoka temperatura ulijevanja prouzrokovala je grubozrnatu strukturu. Grubozrnata struktura nije se usitnila naknadnom toplinskom obradom.

A quench probe, based on the Temperature Gradient method was used to measure and record cooling curves when quenching real axially symmetric workpieces of any complex shape in liquid quenchants. Calculation of relevant heat transfer coefficients is based on the cooling curve measured just below surface of the cylindrical probe of 50-mm diameter. A two-dimensional computer program, based on the cooling time from 800°C to 500°C (t8/5), and the Jominy hardenability curve of the steel grade in question, is used to predict the hardness distribution within the whole volume of the workpiece, all at once, which is a unique feature of this method.

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.

Influence of microstructure on mechanical behavior of hot-work steels is analyzed on submicro, micro, and macro scale. Except for suitable microstructure, phase distribution, and microstructure refinement, proper alloy chemistry and melting practice are important for hot-work steel properties. Methods of determination of working stress of hot-work steels have been presented. In optimization and selection of hot-work steels, proper failure criteria are based on predicted specific failure micromechanism of tools and dies in application. Failure micromechanisms have to be modeled and numerically defined in terms of time and temperature. Hot-work steel development has to be based on simultaneous optimization of materials properties and tool performance. In modern optimization and selection of hot-work steels, proper failure criteria have to be recognized based on probable failure micromechanisms in tool or die applications.

A novel numerical approach for testing and evaluation of quenching media and quenching systems is outlined. The technique proposed is based on determination of heat transfer coefficient from temperature signals recorded and applying it as input for simulation of quenching process. The evaluation method is based on the calculated microstructural and mechanical properties of cylindrical samples.

Sažetak Honanje ili vlačno glačanje je postupak kojim obrađujemo najfinije površine metala radi postizanja zahtijevane točnosti i kvalitete obrađenih površina. Samo honanje kao i procesi struganja, glodanja, brušenja, tj. rezno uobličavanje metalnih materijala u svom se djelovanju ograničava na relativno tanak površinski sloj izratka i uglavnom izaziva hladnu plastičnu deformaciju, ali ne utječe dalekosežno na strukturu i svojstva materijala. Pri izvođenju procesa honanja vrlo je bitno da se radna površina oplahuje znatnim količinama sredstava za hlađenje i podmazivanje. Radnu površinu valja hladiti da ne bi došlo do promjene strukture zbog procesa rekristalizacije i otpuštanja. Osim toga, ispiranjem se odvodi metalna prašina nastala honanjem te iščupana zrnca s bruseva. Danas su istraživanja na ovom području usmjerena na primjenu novih sredstava za hlađenje i podmazivanje. Na temelju ekonomske i ekološke analize i analize kvalitete postupka honanja pri primjeni sredstava za hlađenje i podmazivanje na osnovi mineralnih ulja i uz sadržaj različitih tipova aditiva, u radu je ispitivana mogućnost primjene novih ulja pri honanju košuljica cilindara., Honing is a procedure treating the finest metal surfaces in order to achieve the required precision and quality of treated surfaces. Honing itself, as well as proceses of grating, milling, grinding, i.e. using cutting for the shaping of metal materials, is in its activity limited to a relatively thin surface layer of the workpiece, mostly causing cold plastic deformation, without any long-term impacts on either the structure or properties of the material. When performing the process of honing, it is extremely important that the working surface be washed by considerable volumes of the cooling and lubrication agents. The working surface needs to be cooled, so as not to cause any structural change due to the processes of recrystallization and release. Apart from that, rinsing takes away the metal dust generated by honing, as well as the pulled out grinding wheel grains. Research in this area is today oriented towards applying new cooling and lubricating agents. Based on economic and environmental analysis, as well as that of the quality of honing procedure when applying cooling and lubricating agents based on mineral oils, containing various types of additives, the paper also considers the possibility of applying new oils for the honing of cylinder bores.

A numerical simulation of steel quenching has been developed to predict the distribution of mechanical properties of quenched and tempered specimen with complex form. The numerical simulation is based on the finite volume method, and consists of numerical calculation of temperature fields in process of cooling and simulation of mechanical properties, i.e., hardness, strength and toughness. Hardness in specimen points was estimated on the basis of time of quenching from 800  C to 500  C, i.e., by the conversion of mentioned specific time to hardness results. The time of quenching from 800  C to 500  C steel specimens was estimated by using the calibrated values of heat transfer coefficient for used quenchant. Strength and toughness properties distribution were estimated on the base of predicted steel hardness (HV) distribution. The established model has been successfully applied in computer simulation of mechanical properties of the quenched and tempered truck shaft with complex form made of two different kind of steels.

The strengthening of AISI 4140 steel by cyclic heat treatment has been investigated. The applied cyclic heat treatment was consisted of both, temperature cycling with diffusional transformation and double quenching with diffusionless transformation. Both, temperature cycling and second quenching increase yield strength and Charpy-V toughness as measures of steel strength and toughness. The increase of yield strength and Charpy-V notch toughness are directly in relation of structure fineness. Much better mechanical properties are obtained by the appropriate cyclic heat treatment than by the quenching and tempering of steel AISI 4140.

On the basis of the control volume method the algorithm and computer program for prediction of the hardness distribution in quenched steel specimens with complex geometries have been developed. The algorithm and computer program are designed to solve 2D situation problems such as the quenching of complex cylinders, cones, spheres, etc. The computer program consists of three parts: automatic computation of domain and grid generation, computation of cooling curve in grid-points, and computation of hardness in grid-points. The mathematical model has been tested experimentally. The test showed that the model describes the hardness distribution in a quenched steel specimen of a complex form, with quite satisfactory accuracy. © 1998 John Wiley & Sons, Ltd.

The cost aspect of heat treatment quality management has been presented. Quality management cannot be successful without quality cost management. The activity of heat treatment quality system as cost centers have been defined. The heat treatment quality costs have been classified in categories.

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.

In contrast with small laboratory probes developed to check the sample of a quenchant, the new Liščić /Petrofer probe is designed to measure and record the quenching intensity in real industrial conditions. The probe is a cylinder of 50 mm diameter and 200 mm length, made of INCONEL 600, and instrumented with 3 thermo-couples on the same radius of the cross- section at the middle of the length. The outer thermocouple measures the temperature at 1 mm below surface ; the second thermocouple is located at 4.5 mm below the surface, and the third thermocouple is located at the center of the probe. The working principle of the probe is the measurement of the dynamics of heat extraction which is best represented by the change of temperature gradients. The results of each test with this probe are presented in the form of 4 diagrams: 1.) The recorded cooling curves ; 2.) The calculated heat transfer coefficient (α) as function of time ; 3.) The calculated α as function of surface temperature ; and 4.) The calculated surface temperature with characteristic points on the temperature and on the time scale. For impartial and precise evaluation of a test, 6 characteristic criteria from these diagrams are applied.The series of 26 tests recently performed with this probe at the Quenching Research Centre (QRC) of the Faculty for Mechanical Engineering, University of Zagreb, Croatia has shown that by using this probe, distinctive differences canola oil and a petroleum oil quenchant are easily characterized. Final conclusions of this series of tests confirm that: a)The information provided, which is valuable for the practical use of a quenchant, is not obtainable from any of the small laboratory probes that are currently standardized (ISO 9950, ASTM D6200 and JIS K2242 ; b)The probe and the evaluation method are sufficiently sensitive to clearly differentiate the results with changes of quenching conditions ; c)The Liščić /Petrofer probe can be used for different types of liquid quenchants under different quenching conditions and it is a unique device to evaluate and compare their quenching intensity in industrial practice.

The quenching oils contain base oil and different types of additives according to application requirements and also safety impact to the workers or environment. High-performance quenching oils must have very high oxidation and thermal resistance, high flash point, low sludge formation and acceptable heat-transfer characteristics. That can be achieve by proper components selection, both base oils and additives. Adequate selection of quenching media decreases the risk of tensile stresses, cracking and workpiece distortion, and imparts cleanliness to metal parts. There are numerous compounds available for formulate quenching oils: as base oil are mineral, synthetic and natural oils, used separately or in combination, as additives are used different rust and oxidation preventives, accelerators, busters and others. Mineral base oils are widely used because of their advantages with respect to stability in comparison to natural oils, or lower prices in comparison to synthetic oils. In this work are presented the results of laboratory investigation of physical and chemical properties of new quenching oils based on several types of mineral oils and proper additives at different treat levels. Cooling characteristics of oils are determined at three temperatures according to ISO 9950 standard.

Hot rolling of CuZn27Al4 shape memory alloy results in the forming of defects in austenitic crystals. The defects such as dislocation and deformed boundaries of austenitic grains affect both “ classical” material properties and the specific properties related to shape memory. Rolled and quenched alloy (ausforming treatment) shows hardening proportional to the value of introduced deformation. By increasing the level of true plastic deformation not only the yield stress and tensile strength are increased but also the pseudo yield stress thus making the mechanically induced martensitic transformation more difficult. Besides, the ausforming treatment reduces all the transformation temperatures of the austenitic-martensitic reaction, thus expanding the temperature field of pseudo-elasticity. In spite of the hardening, the thermo-mechanically treated CuZn27Al4 alloy retains the pseudo-elastic shape memory so that favourable combination of strength and transformation behaviour can be achieved by the ausforming treatment, which is required in the majority of applications of these alloys.