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1
Content available remote Modelowanie struktury i własności mechanicznych stali mikrostopowych
PL
Własności mechaniczne stali mikrostopowych zależą od zawartości i wielkości wydzieleń węglikoazotków, które tworzą mikrododatki takich pierwiastków jak: Ti, Nb, V, wprowadzane w ilościach nieprzekraczających 0,1%. W pracy zaprezentowano program komputerowy do obliczania zawartości i wielkości wydzieleń węglikoazotku M(C,N) oraz składu chemicznego austenitu przy danej temperaturze austenityzowania na podstawie składu chemicznego stali i warunków obróbki cieplnej. Przeprowadzono analizę wpływu składu chemicznego stali na parametry powstających w warunkach izotermicznych wydzieleń węglikoazotków M(C,N) oraz na efekt umocnienia wydzieleniowego z wykorzystaniem programu komputerowego. Zaprezentowano obrazy symulowanej mikrostruktury zawierającej wydzielenia.
EN
The mechanical properties of microalloyed steels depend on the content and size of carbonitride precipitates, which form micro-additions of such elements as Ti, Nb, and V, introduced in amounts not exceeding 0.1%. The paper presents a computer programme for calculating the content and size of M(C,N) carbonitride precipitates and the chemical composition of austenite at a given austenitizing temperature based on the chemical composition of steel and heat treatment conditions. An analysis of the influence of the chemical composition of steel on the parameters of M(C,N) carbonitride precipitates formed in isothermal conditions and on the effect of precipitation strengthening with the use of the computer programme was carried out. The images of simulated microstructure containing the precipitates are presented.
EN
This paper investigates the metallurgical behavior and mechanical properties of the P91 steel welds joint. The joint of heat-resistant P91 steel has been welded by the gas tungsten arc welding (GTAW) process using the dissimilar Inconel grade 617 filler. The P91 welds joints have been subjected to varying heat treatment regimes in the temperature range of 650–810 °C for 2 h. The normalizing-based tempering was also performed for the welded joint. The weld fusion zone (WFZ) with austenitic structure and heat-affected zones (HAZs) with martensitic structure was characterized using the optical microscope and scanning electron microscope (SEM). The detailed characterization of the weld metal and HAZ interface has also been performed for as-welded and post-weld heat treatment (PWHT) conditions. For mechanical properties of the welds joint, tensile testing and hardness testing were performed. The relationship between mechanical behavior and microstructure of the welded joint has been evaluated for as-welded and heat treatment conditions. The microstructure studies revealed the formation of an unmixed zone (UZ) close to the fusion line, and it was characterized as peninsula and island. The WFZ showed the complete austenitic mode of the solidification and revealed the austenitic structure with cellular and equiaxed grains in the center of the weld metal. The columnar and cellular dendrites were seen near the boat fusion line, i.e., interface of the weld metal and HAZ. The soft δ ferrite patches were observed near the fusion line in the area of HAZ and remain undissolved up to tempering temperature of 810 °C (PW 3). The dissolution of the ferrite patches was noticed for PW 4. The maximum and minimum tensile strength of the welds joint was measured 731 MPa and 502 MPa for PW 3 and PW 2, respectively. A uniform hardness variation in the transverse direction of the welded joint was observed for PW 3 and PW 4 conditions. The optimum combination of strength and ductility was obtained for the PW 3 condition.
EN
The work addresses physical simulation and dilatometric study of one-step and double-step heat treatments of medium-Mn steel designed for automotive sheets. The conventional one-step isothermal bainitic transformation was applied as the reference heat treatment. The newly implemented heat treatment consisted of isothermal holding in a bainitic region followed by additional holding of the material at reduced temperature also in the bainitic range. This step was added to refine the microstructure, which led to the stabilization of the retained austenite. Calculations of equilibrium state and non-equilibrium cooling and simulations of the developed thermal cycles were performed using the thermodynamic JMatPro software. The physical simulations of the heat treatment were performed in the dilatometer. The obtained samples were subjected to microscopic observations using light and SEM microscopy. One- and two-step heat treatments allowed to obtain bainitic structures with high contents of retained austenite. Lowering the temperature of one-step isothermal holding resulted in the bainite refinement and adjacent retained austenite. The increased Mn content in steel increased its susceptibility to form coalesced bainite resulting in the partial formation of thicker plates despite a decrease in a process temperature.
PL
W pracy przedstawiono wyniki badań wpływu odkształcenia plastycznego oraz szybkości chłodzenia na strukturę i postać krzywych przemian fazowych austenitu przechłodzonego stali mikrostopowej z Nb, Ti, V i B. Wyznaczono krzywe przemian austenitu przechłodzonego nieodkształconego plastycznie (CTPc) oraz odkształconego plastycznie (OCTPc).
EN
The aim of the paper is to investigate the influence of plastic deformation and cooling rate on the structure and shape of the supercooled austenite transformations diagrams of a Nb-Ti-V-B microalloyed steel. The CCT diagrams of underformed and plastically deformed supercooled austenite were developed. The plastic deformation of steel prior to the start of phase transformations results in a sharp acceleration of pearlitic transformation and a slight translation of bainitic transformation towards shorter times. The elaborated curves of supercooled austenite transformations of the steel create possibilities to develop an industrial technology for thermomechanically treated forgings of high mechanical properties.
EN
This research represents a unique approach in improving the fatigue life of 20MnCr5 (89–91 HR15N hardness) shafts which were surface treated through gas carburizing process in a sealed quench furnace followed by double tempering. Crack initiation on 20MNCr5 transmission shafts always occurs at the end of spline location (Location X), propagates longitudinally and finally ruptures at stem location. This was confirmed through optical microscope and SEM (make:Jeol) images. The fatigue experiments were carried out at room temperature in 11,500 Nm torque test machine (Model – MTS-663-144-01). The torque test was carried-out by applying a fully reversed cyclic load with the frequency of 5 Hz for the torsional load of ±3000 Nm. Effect of double tempering, surface roughness, carbon case depth, Microstructure such as retained austenite and non-martensitic transformation products (NMTP) have been investigated in this research. The outcome of the research shows that increase in case depth (CD) (out of increased gas carburising time) resulting in increased inter-granular oxidation (IGO) and NMTP in its microstructure. The presence of retained austenite on the surface of the shaft has not yielded any remarkable improvement in fatigue life of the shaft. Presence of tempered martensite with lesser percentage of retained austenite on the surface improved the fatigue life drastically from 12,000 cycles to greater than 35,000 cycles at high torque load of ±3000 Nm.
PL
W pracy badano skuteczność aktywacji stali nierdzewnej X5CrNi18-10 za pomocą cienkiej powłoki żelaza w zastosowaniu do niskotemperaturowego nawęglania oraz przydatność generatorowej atmosfery endotermicznej do tego procesu. W celu aktywacji powierzchni stali nakładano na nią elektrolitycznie bezprądowo powłokę żelaza o grubości 1–2 μm. Nawęglanie przeprowadzano w temperaturach 450–500oC w atmosferach na bazie generatorowej atmosfery endotermicznej z dodatkiem azotu lub wodoru. Modyfikacja powłoki przez dodanie kilku procent siarki do żelaza spowodowała zmniejszenie rozrzutu twardości na powierzchni, a pojawiająca się sadza wykazywała luźne powiązanie z powłoką. Alternatywna aktywacja za pomocą krótkotrwałego tlenoazotowania z następującym po nim wyżarzaniem dyfuzyjnym sprzyjała wzrostowi twardości na powierzchni i zmniejszeniu jej rozrzutu po nawęglaniu. Po nawęglaniu w endogazie stali X5CrNi18-10 w temperaturze 470oC w czasie 30 h uzyskano warstwę nawęgloną o grubości ok. 35 μm i twardość na powierzchni ok. 1150 HV0,05. Obniżenie temperatury nawęglania o 20oC spowodowało spadek grubości warstwy o 20% w przypadku 24 h nawęglania. Wyznaczono zmiany grubości warstwy nawęglanej w endogazie i twardości na powierzchni od czasu nawęglania.
EN
The study investigated the effectiveness of X5CrNi18-10 stainless steel activation by means of a thin iron coating for low temperature carburizing and the usefulness of the generator endothermic atmosphere for this process. In order to activate the steel surface an iron coating with a thickness of 1–2 µm was applied on it electrolytically electroless. Carburizing was carried out at the temperatures of 450–500oC in the atmospheres based on the generator endothermic atmosphere with the addition of nitrogen or hydrogen. Coating modification by adding a few per cent of sulphur to iron resulted in a reduction of the dispersion of hardness on the surface, and the appearing soot showed a loose connection with the coating. Alternative activation by means of the short-term oxy-nitriding and the following diffusion annealing promoted an increase of hardness on the surface and a reduction of its dispersion after carburizing. After carburizing in endogas of X5CrNi18-10 steel at 470oC during 30 h, a carburized layer with a thickness of approx. 35 μm and the surface hardness of approx. 1150 HV0,05 were obtained. Lowering the carburizing temperature by 20oC resulted in a decrease of the layer thickness by 20% after 24 hours of carburizing. The changes in the thickness of the layer carburized in endogas and the hardness on the surface since the carburization were determined.
EN
Determination of the ferrite content in austenitic steels, which solidified under defined conditions. Ferrite content in austenitic matrix was determined from samples with wall thickness of 60 mm. Measured ferrite contents served to propose the regression equations for the calculation of the ferrite content in steels with Cr content of 18 up to 22 % and Ni of 9 up to 11 %. An additional regression equation was proposed for steels with a higher Ni content. The proposed regression equations have been checked up on the operating melts. In conclusion, the ferrite content in the axis of the casting of wall thickness of 500 mm has been calculated and it was compared to the ferrite determined in the usual way from the cast-on test.
EN
Image analysis allows to acquire a number of valuable quantitative informations on the observed structure and make appropriate conclusions. So far, a large part of analyzed images came only from light microscopes, where it was a possibility of accurately distinguish the different phases on the plane. However, the problem happened in the case of the observation of images obtained by scanning electron microscopy. In this case, the presence of various shades of gray, and the spaciousness of the image attained. To perform the analysis the matrix images of the ausferritic ductile iron were used. Full analysis was carried out using the computer program MicroMeter 1.03. Results obtained in the analysis were related directly to the results from X-ray diffraction. Obtained as a result of the analysis were related directly to the results from X-ray diffractometer. The following technique has weaknesses, including the misinterpretation by the operator microscope or program. After all, it was possible to obtain similar results to the result that has been obtained from X-ray diffractometer.
EN
The paper presents continuous cooling transformation (CCT) diagram of selected low-alloy steel with high resistance to abrasion. Samples were prepared from examined material in as delivered conditions, then were austenitized at 900, 1000, 1100 and 1200 °C for 20 min, and then cooled with the rates of V800–500 = 50, 10, 5, 1, 0.5, 0.1 °C/s. During the dilatometric research, the critical temperatures were defined as well as the critical points specified for different cooling rates were designated. In addition, metallographic documentation of received microstructures after dilatometric investigations was prepared and hardness measurement was performed. The increase in the austenitizing temperature caused changes in the temperature of MS and in the size of the martensite laths. What is more, the increase in the austenitizing temperature in the case of the analyzed steel caused a displacement of the bainitic and diffusion transformations to longer times. During the analysis using the TEM and SEM it was found that the size of the austenite grains is largely controlled by precipitates of the nitrides of AlN, TiN and carbides, mainly Cr7C3 and M23C6.
EN
Austenitic stainless steels are materials, that are widely used in various fields of industry, architecture and biomedicine. Their specific composition of alloying elements has got influence on their deformation behavior. The main goal of this study was evaluation of magnetic properties of selected steels, caused by plastic deformation. The samples were heat treated in different intervals of temperature before measuring. Then the magnetic properties were measured on device designed for measuring of magnetism. From tested specimens, only AISI 304 confirmed effect of plastic deformation on the magnetic properties. Magnetic properties changed with increasing temperature.
PL
W artykule przedstawiono algorytm doboru wymiarów aktuatorów wykonanych ze stopów z pamięcią kształtu (SMA) aktywowanych cieplnie. Rozpatrzono dwa rodzaje aktuatorów: cięgnowe oraz sprężynowe. Opracowano również oprogramowanie wspomagające projektowanie aktuatorów liniowych wykonanych ze SMA. Bazując na opracowanym algorytmie oraz programie obliczeniowym zaprojektowano i zbudowano aktuatory cięgnowe wykonane z Flexinolu oraz sprężynowe wykonane z Nitinolu. Podano przykłady zastosowania zaprojektowanych aktuatorów.
EN
The paper presents the design strategy for shape memory alloy linear actuators thermally activated. The attention was focused on SMA wire actuator and SMA spring actuator. The in–house software for designing calculation of SMA actuators has been elaborated. On the basis on described algorithm and using in–house software the SMA wire actuator and SMA spring actuator have been designed and manufactured. The concept proposals of the linear actuator using as active element the Flexinol wire and actuator using Nitinol spring have been given.
EN
In this paper, the effect of changes the parameters of heat treatment on the structure and the degree of elements segregation was determined, in the context of corrosion resistance of ductile iron Ni-Mn-Cu, containing 7.2% Ni, 2.6% Mn and 2.4% Cu. In the condition after casting, castings of austenitic matrix and 160HBW hardness were obtained. The achieved castings were soaked at 450, 550 and 650°C for 4, 8 and 12 hours, then cooled down at the ambient air. In most cases, the heat treatment resulted in a change in the castings matrix, had the consequence of increasing their hardness in comparison to raw castings. Increasing the temperature and prolonging soaking time resulted in increasing the degree of transformation of austenite, while reducing the degree of elements segregation. This led to the formation of slightly bigger number of pitting due to corrosion, but not so deep and more evenly distributed in comparison to raw castings. Wherein the results of corrosion tests show that heat treatment of castings did not significantly change their corrosion resistance in comparison to raw castings, in contrast to the significant increase in mechanical properties.
EN
The formation of grain structures with boundaries similar to substructures is one of the factors contributing to grain refinement in hot-reduction carbon steel. At the forming of a rim, the slight cooling-down (100-150°С) of the surface volumes is sufficient to increase their strength characteristics. After that, an increase in the magnitude of the hot-hardening of metal in the central rim volumes will lead to the formation of a more uniform fine-grain austenite structure over the rim section.
14
Content available Rozwój technologii regulowanego walcowania stali
EN
The experience of many generations of researchers; metallurgists and designers have resulted in new types of steel, they called it: third generation.
PL
W artykule przybliżono postępy dokonane w pracach nad rozwojem technologii regulowanej przeróbki plastycznej na gorąco, które doprowadziły do wytwarzania stali o wielofazowej strukturze z wymaganym udziałem, rozmieszczeniem i morfologią poszczególnych składników strukturalnych. Wymaga to odpowiedniego sterowania procesami zachodzącymi już podczas obróbki plastycznej na gorąco, w zakresie stabilności austenitu i kontrolowanego przebiegu chłodzenia w warunkach przemiany fazowej austenitu przechłodzonego. Wytwarzane obecnie w tej technologii stale, tzw. trzeciej generacji, wymienione w końcowej części publikacji, są stosowane na elementy konstrukcyjne wymagające połączenia wysokiej wytrzymałości i plastyczności, zdolne do pochłaniania energii w warunkach odkształcenia plastycznego z dużymi prędkościami. Obecnie regulowane walcowanie, obok hartowania izotermicznego na bainit dolny, jest też jednym z finalnych zabiegów obróbki stali konstrukcyjnych wysokowęglowych oraz narzędziowych zarówno do pracy na zimno jak i szybkotnących.
EN
Investigations of the surface layer characteristics of selected kinds of low-alloy high-speed steel after grinding were carried out. They were carried out on the flat-surface grinder with a 95A24K grinding wheel without cooling. The influence of grinding parameters was defined especially for: the quantity of secondary austenite, surface roughness, microhardness and grinding efficiency with a large range of grinding parameters: grinding depth 0.005–0.035 mm, lengthwise feed 2–6 m/min, without a cross-feed on the whole width of the sample. It was found that improvement of grinding properties of low-alloy high-speed steels is possible by efficient selection of their chemical composition. The value of the grinding efficiency is conditioned by grinding forces, whose value has an impact on the grinding temperature. To ensure high quality of the tool surface layer (i.e. a smaller amount of secondary austenite, lack of wheel burn and micro-cracks) in the case of sharpening of tools made of low-alloy high-speed steel, the grinding temperature should be as low as possible.
EN
In this work, the constitutive model, derived with the use of thermodynamic of irreversible processes framework is presented. The model is derived under the assumption of small strains. Plastic strain induced martensitic phase transformation is considered in the austenitic matrix where the volume fraction of the martensite is reflected by a scalar parameter. The austenitic matrix is assumed as the elastic-plastic material and martensitic phase is assumed as randomly distributed and randomly oriented inclusions. Both phases are affected by damage evolution but there is no distinction in the model between damage in austenite and martensite.
PL
Austenit w żeliwie sferoidalnym ausferrytycznym jest fazą mającą specyficzne cechy zależne od wielu czynników. Te najczęściej badane i wymieniane są związane z wpływem składu chemicznego oraz parametrów obróbki cieplnej, co starano się uwypuklić w analizach przedstawionych w artykule. Można jednak przyjąć pewne uogólnienie, które jest związane z całą grupą żeliwa sferoidalnego ausferrytycznego — stwierdzono w badaniach, że w mikrostrukturze żeliwa sferoidalnego ausferrytycznego występuje austenit, którego temperatura MS znajduje się poniżej 0°C oraz że austenit ten nie jest jednorodny, na co wskazuje znaczny przedział temperatury przemiany pomiędzy MS i Mf. Niejednorodność właściwości magnetycznych austenitu oraz określenie wartości temperatury MS jako niewiele niższej od 0°C wskazują, że austenit w temperaturze pokojowej może wykazywać niestabilność mechaniczną. Celem przedstawionych w artykule badań było określenie stabilności mikrostruktury żeliwa sferoidalnego ausferrytycznego podczas zmian temperatury w zakresie 20÷300 K za pomocą określenia jego cech magnetycznych. Przeprowadzono pomiary w magnetometrze z wibrującą próbką (VSM) na próbkach ze stali austenitycznej Fe27Ni2TiMoAlNb oraz czterech rodzajów żeliwa sferoidalnego ausferrytycznego otrzymanego w różnych warunkach obróbki cieplnej. Na zarejestrowanych krzywych zmian magnetyzacji w funkcji temperatury zaobserwowano szereg charakterystycznych punktów związanych z przemianami zachodzącymi w mikrostrukturze. Dla każdego z materiałów zidentyfikowano temperaturę MS oraz przedział temperatury, w którym zachodzi przemiana martenzytyczna.
EN
Austenite in ausferritic ductile iron is a phase with some specific features dependent on many factors. As highlighted in the disclosed analysis, the factors most commonly studied and described are those related with the effect of chemical composition and heat treatment parameters. A few general statements can be made here, however, which will relate to the entire group of ausferritic ductile iron grades. These are the following statements: a) in the microstructure of ausferritic ductile iron, austenite is present and its MS temperature is below 0°C, b) this austenite is not homogeneous as indicated by a wide range of transformation temperatures between MS and Mf . The heterogeneity of the magnetic properties of austenite and the value of MS temperature at a level slightly lower than 0°C indicate that austenite at room temperature can be mechanically unstable. The aim of this article was to determine the stability of the austempered ductile iron (ADI) microstructure during temperature changes in a range of 20÷300 K through changes in magnetic properties. The measurements were taken in a vibrating sample magnetometer (VSM) using Fe27Ni2TiMoAlNb austenitic stainless steel and four types of austempered ductile iron. ADI samples were obtained under various heat treatment conditions. The plotted curves showing changes in the magnetization level as a function of temperature, illustrating changes taking place in the microstructure. For each of the materials examined, the MS and Mf temperature of the martensitic transformation takes place were identified.
EN
Grey cast iron belongs to materials for casting production, which have wide application for different industry branches. Wide spectrum of properties of these materials is given by the structure of base metal matrix, which can be influenced with heat treatment. Processes of annealing can be applied for grey cast iron without problems. During heat treatment processes, where higher cooling rates are used, the thermal and structural strains become important. Usage and conditions of such heat treatment for grey cast iron castings of common production are the subject of evaluation of this article.
EN
The results of the modification of austenitic matrix in cast high-manganese steel containing 11÷19% Mn with additions of Cr, Ni and Ti were discussed. The introduction of carbide-forming alloying elements to this cast steel leads to the formation in matrix of stable complex carbide phases, which effectively increase the abrasive wear resistance in a mixture of SiC and water. The starting material used in tests was a cast Hadfield steel containing 11% Mn and 1.34% C. The results presented in the article show significant improvement in abrasive wear resistance and hardness owing to the structure modification with additions of Cr and Ti.
PL
Prowadzone badania wykazują, że wprowadzenie sproszkowanego żelaza do wytapianego żeliwa o niskiej zawartości siarki przed zabiegiem modyfikacji prowadzonej konwencjonalnym modyfikatorem grafityzującym pozwala na uzyskanie właściwości mechanicznych zbliżonych do wartości uzyskiwanych w trakcie modyfikacji żeliwa o podwyższonej zawartości siarki. Prowadzony zabieg powoduje wzrost liczby zarodków krystalizacji dendrytów austenitu pierwotnego. W tym przypadku, cząsteczki sproszkowanego żelaza działają, jako substraty dla zarodkowania austenitu pierwotnego, podobnie do zachowania się sieci regularnej siatki krystalograficznej. Zwiększona liczba dendrytów austenitu pierwotnego powoduje zmniejszenie się przestrzeni międzydendrytycznych utrudniając tym samym tworzenie się ziaren eutektycznych, czego efektem jest wzrost właściwości mechanicznych.
EN
The study proves that by introducing the iron powder to low-sulphur cast iron still before the inoculation carried out with a conventional graphitising inoculant, the mechanical properties similar to those obtained during the inoculation treatment carried out on cast iron with the recommended high sulphur content are achieved. The said operation increases the number of crystallisation nuclei of the primary austenite dendrites. In this case, the iron particles act as substrates for the nucleation of primary austenite due to a similar crystallographic behaviour of the regular face cantered cubic lattice. The more numerous are the dendrites of primary austenite, the less free space is available in the interdendritic spaces for the formation of graphite eutectic grains, which makes the mechanical properties higher.
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