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Recrystallization kinetics and two critical temperatures—the non-recrystallization temperature TNR and the static recrystallization critical temperature TSRCT—of five Nb, Ti, and V microalloyed steel grades are evaluated. The experimental examination is realized by employing isothermal double-hit compression tests and continuous hot torsion tests, both performed on a Gleeble® 3800 thermo-mechanical simulator. The experimental results are used for the critical assessment of predicted TNR using four empirical equations from the literature, and for the validation of simulated TNR and TSRCT. The thermokinetic computer simulations are realized using the mean-field microstructure modeling software MatCalc. Analysis shows that higher microalloying contents increase both critical temperatures, TNR and TSRCT, whereby the effect of recrystallization retardation of Nb is more pronounced than that of Ti or V. The most accurate reproduction of the experimental recrystallization behavior of the five examined steel grades is realized by the employed physics-based simulation approach.

This article deals with the problem of cavitation damage of hydraulic parts of centrifugal pumps. It is known that cavitation erosion can occur when the stage of fully-developed cavitation is reached, which results to failure of hydraulic parts. Based on many years of experience in combating the negative effects of cavitation erosion, specialists of JSC "VNIIAEN" have concluded that the most effective way to increase the cavitation performance of centrifugal pump hydraulic parts is to use an inducer upstream of the first stage impeller. Based on this, the properties of cavitation-resistant steels were studied for inducers fitted upstream of the first stage impellers of centrifugal pumps, which, operating under fully-developed cavitation, are most susceptible to cavitation wear. The article presents the results of study carried out on bench-scale test stand and the interrelation of chemical and mechanical properties of steels resistant to cavitation., У роботі розглянута проблема руйнування робочих органів відцентрових насосів, що виникає внаслідок впливу кавітації. Як відомо, під час досягнення рівня розвитої кавітації виникає явище кавітаційної ерозії, внаслідок дії якої руйнуються елементи проточної частини. Спираючись на багаторічний досвід боротьби з негативними наслідками кавітаційної ерозії, спеціалісти АТ«ВНДІАЕН» прийшли до висновків, що найбільш ефективним способом підвищення кавітаційних властивостей проточних частин відцентрових насосів є застосування першого шнековідцентрового ступеня. Виходячи з цього, дослідження якостей кавітаційно-стійких сталей проводилося саме для передвключених коліс перших ступенів відцентрових насосів, які працюючи в режимі розвиненою кавітації, найбільше піддаються кавітаційному зношуванню. Наводяться результати досліджень на експериментальних модельних стендах та показано взаємозв'язок хімічних і механічних властивостей сталей з опором кавітаційному впливу.

This study presents a possibility to predict the connection between the cooling regime and the properties of steel. An important factor to enhance the properties of steel is the speed of the cooling regime. To be in accordance with the experimental results, this study considered a correlation between the speed of cooling for laminated steel with a low carbon content and other properties of steel. It is important to choose the optimal cooling regime because the steel was laminated at high temperature.

Results of experimental investigations concerning a quantitative assessment of the influence of corrosion intensity in sheets applied to side surface of tanks for liquid fuels on values of mechanical properties of steel they have been made from, have been presented and analysed. Noticeable reduction of steel yield point as well as growth of its brittleness have been observed mainly in sheet zones with not uniform and pitting corrosion. The reason for such an occurrence is associated to impairment of cementite skeleton of steel, as well as to accumulation of micro‐damages and micro‐notches, both inside of material structure and on its surface, what resulted in local stress concentrations. Santrauka Pateikti ir aptarti eksperimentinių tyrimų, susijusių su lakštų, naudotų skystojo kuro talpyklų išoriniams paviršiams, rūdijimo intensyvumo poveikio į plieno, iš kurio jie buvo pagaminti, mechaninių savybių skaitiniu įvertinimu, rezultatai. Vertas dėmesio plieno takumo ribos sumažėjimas, taip pat jo trapumo padidėjimas, buvo pastebėti lakštų srityse, pakenktose tolygiojo ir taškinio rūdijimo. Tokio atvejo priežastis siejama su plieno cementito griaučių gadinimu, taip pat su mikropažaidų ir mikrogriovelių sankaupa, abiems esant medžiagos sandaroje ir ant jos paviršiaus. Tai sukėlė vietinių įtempių santalką. First Published Online: 14 Oct 2010 Reikšminiai žodžiai: rūdijimas, plieninės skysčių talpyklos, plieno savybės, tempiamasis stipris, smūginė laikomoji galia, trapumas, mikrogrioveliai.

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.

Yüksek Lisans Tezi Kimyasal bileşim ve ısıl işlemler çeliğin fiziksel, kimyasal ve mekaniksel özellikleri üzerinde etkilidir. Bu husus çeliğe uygulanacak kaynak tipleri ile doğrudan ilişkilidir. Kaynak çelik köprülerin en önemli unsurlarından biridir. Çelik köprülere standartlara uygun kaynak tiplerini, uygulama yöntem ve tekniklerini uygulamak önemlidir. Çelik köprülerin çok çeşitleri vardır. Basınç, çekme, dinamik kuvvetler ve dış tesirler gibi fiziksel ve mekaniksel zorlamalara maruz çelik köprüler için en uygun malzeme seçimi, kaynak teknikleri ve kaynak testleri önemlidir. Bu çalışmada, çelik köprülerde kullanılacak malzemelerin özellikleri, sınıfları, şartnameleri, imalat -kaynak standart tanımlamaları ve testlerine yer verilmiş, çelik köprülerin inşasında kullanılacak ASTM-A709 50W(345W) çeliğinin özellikleri ve bu çeliğin kaynak performansını incelemek adına numune parça kaynatılarak tahribatlı ve tahribatsız testler yapılmış ve test sonuçları değerlendirilmiştir. Çelik malzemelerin seçimi ve uygulanmasında Avrupa'da (EN) ve Amerika Birleşik Devletleri'nde (ASTM) normları esas alınmıştır.Anahtar Kelimeler : Köprüler, Çelikler, Çelik Özellikleri, Kaynaklar, Kaynak Özellikleri, Kaynak Testleri Abstract Chemical composition and heat treatments are effective on the physical, chemical and mechanical properties of the steels. This matter is directly related with the welding types to be applied. Welding is one of the most important component of steel bridges. It is very important to perform approriate welding type, welding method and technic. There are many types of steel bridges. It is very critical to choose most appropriate material, welding types and their tests for the steel bridges which are under mechanical and physical stresses like compression, tension, dynamic forces and other exterior effects. In this study, types, properties and specifications, manufacturing - welding standard identification and tests of the materials, which are used in steel bridges, have been explained, and in order to investigate the welding performance of "ASTM A709 50W(345W)" steel, which is used in the construction of the steel bridges, a sample has been prepared, welded and destructive and non-destructive tests has been performed on it. Steel choosing and application reference codes are EN in Europe and ASTM in USA. Key Words:Bridge, Steel, Welding, Welding Properties, Steel Properties

Yüksek Lisans Tezi Kimyasal bileşim ve ısıl işlemler çeliğin fiziksel, kimyasal ve mekaniksel özellikleri üzerinde etkilidir. Bu husus çeliğe uygulanacak kaynak tipleri ile doğrudan ilişkilidir. Kaynak çelik köprülerin en önemli unsurlarından biridir. Çelik köprülere standartlara uygun kaynak tiplerini, uygulama yöntem ve tekniklerini uygulamak önemlidir. Çelik köprülerin çok çeşitleri vardır. Basınç, çekme, dinamik kuvvetler ve dış tesirler gibi fiziksel ve mekaniksel zorlamalara maruz çelik köprüler için en uygun malzeme seçimi, kaynak teknikleri ve kaynak testleri önemlidir. Bu çalışmada, çelik köprülerde kullanılacak malzemelerin özellikleri, sınıfları, şartnameleri, imalat -kaynak standart tanımlamaları ve testlerine yer verilmiş, çelik köprülerin inşasında kullanılacak ASTM-A709 50W(345W) çeliğinin özellikleri ve bu çeliğin kaynak performansını incelemek adına numune parça kaynatılarak tahribatlı ve tahribatsız testler yapılmış ve test sonuçları değerlendirilmiştir. Çelik malzemelerin seçimi ve uygulanmasında Avrupa'da (EN) ve Amerika Birleşik Devletleri'nde (ASTM) normları esas alınmıştır.Anahtar Kelimeler : Köprüler, Çelikler, Çelik Özellikleri, Kaynaklar, Kaynak Özellikleri, Kaynak Testleri Abstract Chemical composition and heat treatments are effective on the physical, chemical and mechanical properties of the steels. This matter is directly related with the welding types to be applied. Welding is one of the most important component of steel bridges. It is very important to perform approriate welding type, welding method and technic. There are many types of steel bridges. It is very critical to choose most appropriate material, welding types and their tests for the steel bridges which are under mechanical and physical stresses like compression, tension, dynamic forces and other exterior effects. In this study, types, properties and specifications, manufacturing - welding standard identification and tests of the materials, which are used in steel bridges, have been explained, and in order to investigate the welding performance of "ASTM A709 50W(345W)" steel, which is used in the construction of the steel bridges, a sample has been prepared, welded and destructive and non-destructive tests has been performed on it. Steel choosing and application reference codes are EN in Europe and ASTM in USA. Key Words:Bridge, Steel, Welding, Welding Properties, Steel Properties

Mathematical expressions for prediction of hardness, yield strength and Charpy-V notch toughness of quenched and tempered steel were established. Quenched and tempered steel hardness is predicted based on as-quenched hardness of steel. In the relation between quenched and tempered steel hardness and as-quenched hardness of steel the hardenability of steel is taken in account. Yield strength and Charpy-V notch toughness of steel are predicted based on hardness of quenched and tempered steel. The relation of E. Just was use for prediction of tensile strength and yield strength of quenched and tempered steel. Charpy-V notch toughness is predicted by new relation between Charpy-V notch toughness and hardness HV. This expression is established by regression analysis.

Results of experimental investigations concerning a quantitative assessment of the influence of corrosion intensity in sheets applied to side surface of tanks for liquid fuels on values of mechanical properties of steel they have been made from, have been presented and analysed. Noticeable reduction of steel yield point as well as growth of its brittleness have been observed mainly in sheet zones with not uniform and pitting corrosion. The reason for such an occurrence is associated to impairment of cementite skeleton of steel, as well as to accumulation of micro‐damages and micro‐notches, both inside of material structure and on its surface, what resulted in local stress concentrations. Surūdijusių lakštų, naudotų skystojo kuro talpyklų išoriniams paviršiams, plieno savybių blogėjimas Santrauka.Pateikti ir aptarti eksperimentinių tyrimų, susijusių su lakštų, naudotų skystojo kuro talpyklų išoriniams paviršiams, rūdijimo intensyvumo poveikio į plieno, iš kurio jie buvo pagaminti, mechaninių savybių skaitiniu įvertinimu, rezultatai. Vertas dėmesio plieno takumo ribos sumažėjimas, taip pat jo trapumo padidėjimas, buvo pastebėti lakštų srityse, pakenktose tolygiojo ir taškinio rūdijimo. Tokio atvejo priežastis siejama su plieno cementito griaučių gadinimu, taip pat su mikropažaidų ir mikrogriovelių sankaupa, abiems esant medžiagos sandaroje ir ant jos paviršiaus. Tai sukėlė vietinių įtempių santalką. Reikšminiai žodžiai: rūdijimas, plieninės skysčių talpyklos, plieno savybės, tempiamasis stipris, smūginė laikomoji galia, trapumas, mikrogrioveliai. First Published Online: 14 Oct 2010

Effects of such thermochemical processes as carburising, nitriding and boriding on properties of maraging steel grades have been investigated. Despite certain improvements in the properties of the obtained surface, at present, carburising and boriding cannot be recommended owing to problems in the layer quality and difficulties in dimension control processes. Nitriding has proved to be the most suitable process and subsequent surfacing with a TiN layer on the previously nitrided substratum of maraging steel provided additional improvement in properties.

Over the past few years a detailed study of artificial neural network, genetic algorithm and programming, as well as the expert systems in predicting the steel properties and determination of heat treatment process parameters has been performed at the Department for Materials of FMENA. This paper presents the short overview of applied methods and results in predicting different properties of the heat treatable steels and process parameters. Based on known chemical composition and heat treatment condition the following properties has been predicted by means of neural network: tempering curve of tool steels, coefficient of heat conductivity. The duration and surface hardness of gas and plasma nitriding has been also successfully determined using neural network. The genetic algorithm and genetic programming has been used for definition of the relations between different variables, for optimisation of neural network parameters, as well as for determination of carburising parameters. The expert system for selection of steel and surface modification treatment has been developed, which integrate the above-mentioned methods. The results are encouraging and open the wide possibilities for further investigation in heat treatment and surface engineering technologies.

Effects of thermochemical processes of carburizing, nitriding and boriding upon properties of MARAGING steel grades have been considered. Despite certain improvements in properties of surface achieved, due to problems in layer quality and difficulties in dimensions control processes of carburizing, and boriding can not be recommended currently. Nitriding has proved to be most suitable process, and subsequent surfacing with TiN layer on the previously nitrided surface of MARAGING steel provided additional improvement of the properties.

The comparative testing of properties for the steel grade Ck45 (AISI-1045) after salt bath nitrocarburizing (TENIFER process) without and with post-oxydation (TENIFER QPQ process) was performed. To evaluate the effects of post-oxidation on differently nitrocarburized specimens metallographic testing, investigation of chemical composition through the sample cross-section, testing of hardness, roughness, corrosion and tribological properties were carried out. The results indicate that post-oxidation has no significant effect on the hardness decrease, it lowers, however the friction coefficient and improve the corrosion resistance in comparison to the non-oxidized steel. That enhancement in properties is effect of the formation of iron oxide layer on the compound zone during the cooling after nitrocarburizing and especially during the subsequent treatment in the oxidizing bath.

Results of investigation of influence of post-oxidation of nitrocarburised carbon steel of case hardening class upon the improvement of resistance to wear and corrosion have been reported in the contribution. Oxidation of test samples has been conducted in the oxidizing AB1 bath, subsequent to the nitrocarburising in the TENIFER salt bath. Test pieces have been subjected to corrosion and tribological investigation. Corrosion testing has been done applying electrochemical methods, while trobological testing included investigation of resistance to adhesion. The obtained results indicate favorable effects of post-oxidation of nitrocarburised layer upon both, resistance to adhesion wear and corrosion.

Over the past few years a detailed study of artificial neural network application in material engineering has been performed at the Department for Materials of FMENA. This paper presents the applied methods and results in predicting different steel properties. Hardenability Jominy curves, i.e. hardness at different Jominy distances are predicted for different groups of nonboron constructional steel grades for hardening and tempering, and for carburising. Input parameters were the results of chemical analysis of melt. A set of different heats was used to test the neural network efficiency in predicting J- hardness. Furthermore, a similar method was used to predict the tempering curve of tool steels, using the given chemical composition and austenising temperature. The mean error and standard deviation for the learning and for the testing dataset were small and acceptable. Another very important physical property that was determined was the heat conductivity. Heat conductivity versus temperature, which is needed in calculation and simulation of heating and cooling processes, is predicted using both the regression analysis and the neural network method.