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EN
Purpose: The aim of the proposed research is to investigate the regularities of the microstructure change, fracture micromechanism and mechanical service characteristics of the high-strength wheel steel with a lowered carbon content under static, impact and cyclic loading depending on the total content of vanadium and nitrogen and also the steel heat treatment modes. Design/methodology/approach: Alloying with vanadium was carried out in the range of 0.09-0.23% and nitrogen in the range of 0.006-0.018%. All steels were heat treated by normalizing and subsequent tempering at different temperatures in the range of 450-650°C. Steels microstructure was investigated by the optical metallography methods on the microscope EPITIP-2 (Carl Zeiss Jena). Scanning electron microscope Zeiss-EVO40XVP was also used for microstructural and microfractography investigations. Static strength (UTS), relative elongation (TEL), impact toughness tests (KCV) and fatigue crack growth resistance characteristics (fatigue threshold ΔKth, cyclic fatigue fracture toughness ΔKfc) were determined on standard specimens. Rolling contact fatigue testing was carried out on the model specimens. Findings: The regularities of the change of microstructure, fracture micromechanism and mechanical characteristics of the high-strength wheel steel with a lowered carbon content under static, impact and cyclic loading depending on the total content of vanadium and nitrogen and also the steel heat treatment modes are studied. Research limitations/implications: The results obtained on laboratory samples should be tested during a real railway wheels investigation. Practical implications: The steel with the optimal parameter [V∙N]∙104 = 22.1% provides high tread surface damaging resistance established on the model wheels. Originality/value: It was established that after normalization at 950°C and tempering at 550°C the increase of ultimate strength UTS and cyclic fracture toughness ΔKfc by 4% and 19%, respectively; impact toughness at room (KCV+20) and low temperature (KCV-40) in 1.5 and 3.3 times, respectively, when parameter [V∙N]∙104 changes from 7.8 to 22.1% and carbon content from 0.63 to 0.57%.
EN
Purpose: The aim of the paper is to determine the impact of vanadium microaddition on mechanical properties and microstructure of two steel grades with a different content of V, applied for production of casing pipes used in the extractive industry. Design/methodology/approach: Pilger process technology with subsequent normalizing was used. The tests were carried out on an industrial batch produced in the Rurexpol Department, and the research was done with the use of industrial research laboratories of Alchemia S.A. Group. The microstructure and mechanical properties were determined in the initial state and after normalizing at two temperatures: 940°C and 880°C. Static tensile test and Charpy V impact test have been applied. Findings: Mechanical properties, macrostructure and microstructure of steel pipes, obtained during production under industrial conditions, have been analyzed in the article. The effects of V content and hot-working and normalizing treatment affect substantially the mechanical properties and microstructure of the investigated steels. Research limitations/implications: It was found that the application of vanadium microaddition to the normalizing process after the hot-rolling has a beneficial effect on a strength-toughness balance only at a narrow range of technological parameters of the normalizing. Practical implications: The knowledge of the vanadium microaddition effect on the industrial production route is indicated in the paper. Originality/value: : The effect of vanadium microaddition has been proved to be very sensitive to the temperature conditions of the heat treatment.
EN
The paper addresses the macro- and microsegregation of alloying elements in the new-developed Mn-Al TRIP steels, which belong to the third generation of advanced high-strength steels (AHSS) used in the automotive industry. The segregation behaviour both in the as-cast state and after hot forging was assessed in the macro scale by OES and by EDS measurements in different structural constituents. The structural investigations were carried out using light and scanning electron microscopy. A special attention was paid to the effect of Nb microaddition on the structure and the segregation of alloying elements. The tendency of Mn and Al to macrosegregation was found. It is difficult to remove in Nb-free steels. Microsegregation of Mn and Al between austenite and ferritic structural constituents can be removed.
EN
Purpose: The aim of the paper is to determine the effect of the isothermal holding temperature in a bainitic transformation range on a fraction of retained austenite for a new-developed medium-carbon TRIP steel containing Nb and Ti microadditions. Design/methodology/approach: The thermo-mechanical processing was carried out by a multi-stage compression test using the Gleeble thermomechanical simulator. The steel was subjected to 5 variants of processing with an isothermal bainitic transformation temperature in a range from 250 to 450°C. Identification of structural constituents was done using microscopic observations and X-ray diffraction. To determine the fraction of retained austenite the Rietveld method was applied. Findings: It is possible to obtain a high fraction of retained austenite characterized by the high thermodynamic stability in a C-Mn-Si-Al steel containing 0.43% C. The maximal fraction of austenitic phase equal above 20% was obtained for the wide temperature range of isothermal holding from 350 to 450°C. The maximal carbon content in the retained austenite equal 1.84 wt.% is present for the temperature range from 350 to 400°C. Below 350°C due to relatively low carbon diffusivity and high Msγ temperature, a part of austenite transforms to marteniste. Above 400°C there is still a high fraction of retained austenite but it contains a lower C content. Practical implications: The obtained austenite volume fraction and carbon content in a γ phase determined as a function of isothermal holding temperature can be useful in optimization of thermo-mechanical processing conditions for medium-C TRIP steels. Originality/value: The research was performed on a new-developed medium-carbon Si-Al steel microalloyed with Nb and Ti. There is a lack of data on microstructure and stability of retained austenite in such advanced group of high-strength TRIP steels.
EN
Purpose: The aim of the research presented in the paper is to design the cooling routes after plastic deformation ensuring the multiphase structure with a high fraction of retained austenite on the basis of DCCT diagram for a new-developed Si-Al microalloyed TRIP steel. Design/methodology/approach: The CCT and DCCT diagrams were developed. Eight variants of the thermomechanical processing were designed on the basis of the DCCT diagram. The thermomechanical processing consisted of a multi-stage compression and various cooling strategies in the γ→α transformation range and isothermal holding temperature at a bainitic transformation region. Findings: The usefulness of DCCT diagram for designing the thermomechanical processing conditions for TRIP steels was demonstrated. The fraction of ferrite and retained austenite are highly dependent on a cooling path applied in the γ→α transformation region and a fraction of retained austenite especially on the isothermal holding temperature. The highest fraction of retained austenite as irregular grains located in a ferritic matrix and fine islands or interlath regions in bainitic regions were obtained at temperature of 400 and 450°C. Research limitations/implications: To determine precisely a fraction of retained austenite, the X-ray investigations has to be applied additionally to the image analysis. Practical implications: The designed cooling conditions are of great importance for the thermomechanical strategy for manufacturing the advanced high strength TRIP steels. Originality/value: The thermomechanical processing was carried out for a new group of TRIP steels with Si partially replaced by Al and containing microadditions of Nb and Ti.
PL
Niniejszy artykuł dotyczy prac prowadzonych w Mennicy Metale Szlachetne S.A. i w Politechnice Warszawskiej nad uzyskaniem drutów z mikrodomieszkowanych stopów platyny. Druty te, przeznaczone na siatki katalityczne dla przemysłu azotowego, wykonywane były z materiału konsolidowanego wstępnie metodą metalurgii proszków. Dalsza konsolidacja zachodziła w procesie obróbki plastycznej na gorąco i ciągnienia. Uzyskane druty charakteryzowały się większą wytrzymałością na zrywanie i mniejszym wydłużeniem w stosunku do drutów niedomieszkowanych, otrzymywanych w sposób tradycyjny. Zbadano własności katalityczne próbek siatek wykonanych z nowych drutów. Nie stwierdzono pogorszenia własności katalitycznych.
EN
The aim of the article, based on earlier investigations made in The Mennica Metale Szlachetne plc and at the Warsaw Technical University, was the wire production from microalloyed platinum alloys. This wire, assigned for catalytic wire net for the nitric industry, was made of material initially consolidated with method of the powder metallurgy. The more further consolidation occurred through the hot processing and wire drawing. Wire was characterized by a higher tensile strength and lower elongation in the relation to wire without microadditions, received in the traditional way. Catalytic properties of the wire net samples made from new wire were examined. The worsening of catalytic properties wasn’t stated.
7
Content available remote Ductilization of Ni3Al by alloying with boron and zirconium
EN
Purpose: The investigation of Ni₃AlBZr alloys was carried out to determine the influence of small zirconium and boron additions on the microstructure and mechanical properties, particularly with respect to room-temperature, and different strain rate conditions. Design/methodology/approach: Additions of both boron 0.26 at.% and zirconium from 0.3 to 1.5 at.% results in higher strength than exhibited by unalloyed Ni3Al. The sequence of structural changes of Ni3Al-based alloy has been correlated with mechanical properties, determined in uniaxial compression tests. Two ranges of work hardening have been identified on the stress-strain curves of these alloys. It was found that the first range of deformation corresponds to the intergranular slip system operating within individual grains, while the second one is connected with transgranular slip. Findings: Structural observations of A and B alloys showed that zirconium addition causes a decrease of the average grain size. On the mechanical properties of investigated alloys the increasing yield stress and hardness were observed in enlarging zirconium additions. However, the enlarged addition of zirconium causes a decrease of extension. Addition to an intermetallics compound Ni₃Al of such elements as boron (0.26 at.%) and zirconium (0.3 - 1.5 at.%) can be accepted as optimum from susceptibility to plastic deformation point of view. Research limitations/implications: The main limits for application of the polycrystalline Ni3Al phases is a poor strength and creep properties at high temperatures. The improvement of mechanical proprieties of Ni₃Al phase required small addition of suitable alloying elements. Practical implications: The results of investigations as well as the conclusions may be used for improvement of alloys processing based on Ni₃Al intermetallics compound. In well-considered peculiarity selection of alloyed additions and also processing parameters it is possible to steer in a limited range of mechanical properties of these alloys. Originality/value: The results of investigations expand knowledge about processing of the alloys based on Ni₃Al phase, and in consequence, to apply it in many branches of industry.
8
Content available remote The influence of hot-working conditions on a structure of high-manganese steel
EN
The high-manganese steels with the austenitic structure belong to a group of modern steels predicted to use in the automotive industry. The chemical composition of the steel containing 25% Mn, solution hardened by Si and Al was developed. Microadditions of Nb and Ti introduced into the steel creating stable nitrides and carbides should act by precipitation hardening and inhibit a grain growth of recrystallized austenite. The aim of the work was to determine the influence of various hot-working conditions on a structure of the investigated steel. The processes controlling work-hardening and removing strengthening after finishing the hot-working were identified. The preliminary upset forging by the use of eccentric press with a degree of deformation in a range of 20 to 60% and at temperatures of 850 and 1000 C was carried out. On the basis of determined conditions the multi-stage axial compression tests ensuring the finegrained austenite structure were performed.
PL
Stale wysokomanganowe o strukturze austenitycznej należą do grupy nowoczesnych stali przewidzianych do zastosowania w przemyśle motoryzacyjnym. Opracowano skład chemiczny stali zawierającej 25% Mn, umacnianej roztworowo przez Si i Al. Mikrododatki Nb i Ti wprowadzone do stali, tworząc stabilne azotki i węgliki powinny powodować umocnienie wydzieleniowe i hamować rozrost ziaren austenitu zrekrystalizowanego. Celem pracy było określenie wpływu zmiennych warunków obróbki plastycznej na gorąco na strukturę badanej stali. Zidentyfikowano procesy kontrolujące umocnienie odkształceniowe i usuwające umocnienie po zakończeniu obróbki plastycznej na gorąco. Przeprowadzono wstępne spęczanie w temperaturach 850 i 1000 C przy użyciu prasy mimośrodowej, stosując stopień gniotu w zakresie od 20 do 60%. Na podstawie wyznaczonych warunków przeprowadzono kilkustopniowe próby ściskania osiowosymetrycznego zapewniające uzyskanie drobnoziarnistej struktury austenitu.
EN
As it is known for increasing of properties (YTS ≥ 380 MPa) of cast steels it is effective to increase content of substitutional alloying elements, (Si, Mn, Cr, Ni). However it leads to rising in price of Steel ton. Increasing of Si and Mn content only is limited by decreasing of ductility and weld ability. As a rule Silicon content at these steels is not higher than 0.4-0.6% and Si:Mn ratio is not higher than 1:2. Now for grain refinement uses inoculation of steel by nitrogen and elements with high chemical affinity to nitrogen. Mostly vanadium is used, however niobium sometime is used. Disadvantages of this are high cost of alloying elements and low thermodynamic stability of vanadium and niobium nitrides. Particles of V(C, N) and Nb(C, N) dissolve during heating for heat treatment or during welding. It leads to decreasing of grain refinement effect. Adaptation of this microalloying strategy for casts producing for freight railway cars let estimate possibility of application these casts in a new generation freight railway cars.
PL
Celem przedstawionych badań jest analiza możliwości zastosowania utwardzania węglikowo-azotkowego staliwa zawierającego 0,2% C w celu zapewnienia możliwości zastosowania tego materiału do celów wykonania odpowiedzialnych odlewów kolejowych. Metoda wykorzystania mikrododatków stopowych, znana w produkcji wyrobów walcowanych, została zaadaptowana do produkcji odlewów kolejowych części wagonów towarowych nowej generacji. Wykonano serię wytopów doświadczalnych, na podstawie których otrzymano zakresy stężeń pierwiastków bazowych i dodatków modyfikujących.
EN
The aim of the paper is to present the recent developments (in Sweden) regarding microstructure and mechanical property enhancement through thermo-mechanical controlled processing (TMCP) of structural steel plate and the use of predictive models. The key to success with TMCP-processing is to define rolling schedules combining a maximum degree of microstructural refinement with acceptably low rolling loads, good shape and surface control and high productivity. In this context, the simulation of the TMCP treatment in laboratory scale as well as the computer models for calculation of microstructure development and precipitate evolution during hot rolling are invaluable for design of rolling schedules. For good control of final microstructure, it is invaluable to have a computer model for prediction of microstructure evolution during TMCP, to enable optimal design of rolling and cooling schedules. By modelling of microstructure evolution, the steel composition and the properties of the final product can be optimised without expensive testing, so reducing the production cost of high strength steels and making them competitive in more applications. It is intended that the developed models will give steel producers essential advantages in thermo-mechanical processing, applicable to structural/microalloyed steels, so achieving optimisation of process parameters and steel chemistry. Several models based on empirical and/or semi-empirical equations describing recrystallization and recovery and have been developed around the world and applied successfully to specific steels. However, such models have limited improvement potential and typically suffer from difficulties in applicability to different steels even when these are quite similar in chemical composition. In order to gain flexibility, the models should be based on a physical description of microstructure evolution, including deformation, recovery, recrystallization, precipitation and phase transformation. Such so-called physical models should be intrinsically capable of handling multi-component systems. A brief survey is made of the models developed at the Corrosion & Metals Research Institute and used by the Swedish Steel Industry. The models can be used for predictions of recrystallization and grain growth of austenite after deformation, precipitation or dissolution of microalloying carbo-nitrides in austenite and phase transformation behaviour during accelerated cooling. The effect of TMCP- parameters, low reheating and high finish rolling temperature, as well as rolling schedules, cooling / quenching rate will be discussed with regard to the transformation characteristics as well as the strength, hardness and microstructure of structure steels.
PL
Celem artykułu jest przedstawienie ostatnich osiągnięć (w Szwecji) w zakresie poprawy mikrostruktury i własności stali poprzez termomechaniczne walcowanie (TMCP thermo-mechanical controlled processing). Przedstawienie zastosowań komputerowego modelowania w tym zakresie jest drugim celem artykułu. Symulacja TMCP w skali laboratoryjnej oraz komputerowe modelowanie w celu przewidywania rozwoju mikrostruktury i procesów wydzieleniowych podczas walcowania na gorąco są ważnym wspomaganiem projektowania technologii walcowania. W pracy przedstawiono krótki przegląd modeli opracowanych w Corrosion & Metals Research Institute i sto­sowanych przez przemysł metalurgiczny w Szwecji. Modele są stosowane do przewidywania rekrystalizacji i rozrostu ziarna austenitu po odkształceniu, procesów wydzieleniowych i rozpuszczalności węgliko-azotków w austenicie oraz przemian fazowych podczas przyspieszonego chłodzenia. Otrzymane parametry TMCP - niższe temperatury wygrzewania i wysokie temperatury końca walcowania, plany przepustów, i prędkości chłodzenia są omówione w artykule ze względu na ich wpływ na charakter przemiany fazowej oraz na mikrostrukturę i wytrzymałość wyrobów ze stali konstrukcyjnych.
EN
The solution of the problem of casting quality improvement depends first of all on the methods and techniques used to make effect on the melt bath during pre-crystallization period and solidification process of metal. The authors’ investigations have shown that the late microalloying and modification of steel are one of the most effective methods of influence on the melt during solidification.
PL
Rozwiązanie kwestii udoskonalenia jakości odlewania zależy przede wszystkim od stosowanych metod i zabiegów technologicznych na ciekłej kąpieli dla uzyskania odpowiednich efektów w okresie przed krystalizacją i podczas krzepnięcia metalu. Badania autorów pokazały, że późne wprowadzanie mikrostopów i modyfikowanie stali są jednymi z najbardziej efektywnych metod oddziaływania na ciekły metal podczas krzepnięcia.
EN
The problem of improving reliability and casting of fast wearing machine parts, which were manufactured from steel cast, has been required of creation and using practice of various materials. One of most rational ways to cast quality increasing is the using of middle-carbon microalloyed in return for expensive high alloyed steels. For this, the microalloyed steels must possess good casting properties and enough high density of metal and surface quality of cast. [...]
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