Papers by Keyword: Martensite

Abstract: In this investigation specimens of the austenitic steels AISI 304, AISI 321 and AISI 348 were investigated in fatigue tests in the temperature range -60°C ≤ T ≤ 550°C. A detailed microstructure-based characterization of the cyclic deformation behavior of austenitic steels was performed by means of stress-strain hysteresis, electrical resistance and magnetic measurements. Up to ambient temperature the occurring deformation induced martensite formation was measured in-situ with a ferritescope during cyclic loading. The temperature range for dynamic strain aging was reliably identified by means of a temperature increase fatigue test with one single specimen.

Abstract: Low cycle fatigue of high-chromium 13Х11Н2В2МФ stainless steel has been studied after cyclic tests at room temperature with the frequency of loading, 0.45Hz and amplitude, ± 1mm. The samples were v-notched with the dimensions x2x50, where =3mm. The peculiarities of fatigue crack propagation and influence of heat treatment, sizes of grains and laths, and disposition of microcrack and microstructure elements of the steel were studied. Next, the main effect on propagation direction is caused by the shape of grains and laths. It turned apparent that main microcrack is composed of individual micro-components with the lengths correlating with the dimensions of grains and martensitic laths. During growth crack propagation direction changes from lath to lath; however, general trend remains unchanged. The results of tests indicate that speed of fatigue failure rises when the frequency and amplitude of loading increases. The work includes x-ray characterization of the steel, statistical distribution curve for angles between the main direction of macrocrack propagation and micro-components, and explanation of micro- and macrocrack propagation alteration is given.

Abstract: Low thermal expansion ductile cast iron is expected to become a new structural material with high dimensional stability against temperature change. We tried to develop a new low thermal expansion ductile cast iron by means of adding C and Si to Superinver alloy. In this study we prepared four kinds of ductile cast irons whose Co contents vary from 0% to 12 %, and investigated about the effects of Co content and solution-treatments on several main characteristics such as coefficient of thermal expansion and mechanical properties. The results obtained are as follows: With increase of Co content the amount of martensite increases but this martensite can be inverse-transformed to austenite totally or greatly by solution-treatment followed with water-quenching. In the case of Co content less than some 9 % the ability of relatively larger plastic deformation can be expected in inverse-transformed austenite.

Abstract: This work addresses an urgent problem which is saving alloying elements (Ni, Mo, Nb, V, W and others) -which very scarce in Ukraine and other countries- while increasing the physical, mechanical and operational properties of the new designed and developed wear-resistant cast irons. Optical microscopy, x-ray structure analysis, transmission and scanning (fracture) electron microscopy methods, different-thermal, magnetometric and x-ray analyses, as well as hardness and micro-hardness tests, impact energy, and abrasive wear tests in environments of cast-iron shots were employed in the research. The work summarizes the controlling conditions for forming various metastable phases by including deformation (or strain) induced phase transformation (DIPT) and through realization in the process of testing. New wear-resistant economical alloyed cast irons with a metastable austenite-carbide and austenite-martensite-carbide structure are developed, which are being strain- hardened under impact-abrasive wearing operation conditions due to the realization of process DIPT in the superficial layer. These new cast irons are intended for manufacturing parts of different equipment (protective plates of sinter machines, furnaces, tracks for transferring raw materials at iron and steel works, etc.). These cast irons do not contain expensive and deficit alloying components, like nickel, molybdenum, vanadium, and more expensive similar materials. Simultaneously they possess enhanced impact-abrasive wear resistance.

Abstract: Many controversial data and contradictions about basic feature and behaviour of martensite were exhibited in available investigations. New opinions for following questions, such as the nature and kind of packet martensite, the stereo morphology of lath and plate martensite, the habit plane of martensite etc., have been proposed by the authors through the observation of thirteen steels under optical microscope, scanning electron microscope. It was found that packet M in iron-base alloys can should be divided three kinds: packet thin sheet M, (111) packet plate M and (225) packet plate M

Abstract: A high strength low alloy wear-resistant steel was quenched at 900°C and tempered at varying temperatures. The microstructures were observed utilizing optical and electron microscope. Results show that microstructures consist of predominantly martensite and lots of bainite in the as-quenched specimens. When the specimen was tempered at 250°C, no obvious change in the microstructure was observed. It has an optimized strength and elongation in this condition of heat treatment. With the increase of tempering temperature, the lath or plate of martensite were coalescenced. The strength of the steel is thus greatly reduced and the elongation was accordingly increased.

Abstract: A thermomechanically coupled constitutive model for finite strain elasto-plasticity is formulated and numerically implemented. The model gives a physically sound description of an initially austenitic material influenced by martensitic phase transformation. The heat dissipated by plastic slip deformation and by phase transformation is allowed to influence the material behavior and appears as a key influencing factor on the growth of the martensitic phase. The model is calibrated using a common stainless steel as prototype material, allowing numerical simulations of crack propagation to be performed. Alterations of the crack growth behavior are observed as different simulation scenarios are compared.

Abstract: Deep Cryogenic treatment (DCT) is a one time permanent process, carried out in such a way that the material is slowly cooled down to the cryogenic temperature, after which it is held at that temperature for a specified period of time and is heated back to room temperature at slow rate followed by low temperature tempering. In this study, the orthogonal experiment method was used to study the DCT process of YT30 cemented carbide inserts. The primary relation of the different factors of DCT was analyzed. TH300 sclerometer was used to measure the hardness of inserts. The microscopes were used to observe the wearing profiles of inserts and microstructures before and after DCT. The orthogonal experiment results show that the effect of soaking temperature on the properties of inserts is the first factor, the soaking time is second one, the cooling rate is third one, and the last one is the tempering temperature. DCT improves the multi-type martensite transformation of Co. Therefore DCT increases hardness and enhance wear resistance of the cemented carbide inserts.

Abstract: The emphasis, in respect of content regarding the here presented project, lies within the production of localized reinforcements, by means of transformation-induced α’ martensite formation in solid and sheet metal components. During the forming process of metastable austenitic steels, high-strength martensite areas, next to ductile austenitic regions, are to be adjusted to enable the production of load-adapted components. To this end, extensive basic analyses are also necessary in order to determine the description of the mechanical behavior of α’-martensite structures, as well as to determine the extension of the numerical simulation as regards the structural change. The results achieved within the area of steel forming include the development of a temperable deep-drawing die (T = -35 °C until T = 100 °C) that carefully facilitates structural conversion at a constant forming-degree. Moreover the crash performance, based on transformation-induced martensite structures is improved. So-called Forming Curves (FCs) were developed as a new approach towards the material characterization of structured steel. In bulge forming components, comprised of chrome and nickel steels as well as manganous hard steel, martensite was specifically generated under the use of differing forming parameters. The tool design was aided by Finite Element Analysis (FEA). Moreover, fundamental simulations were carried out in order to calculate the structural change. The modification and extension of a semi-analytical model of the material followed so that the martensite content could be calculated in the previously examined sheet components, as in the massive forming.

Abstract: Thermal cycles of conventional galvanizing and galvannealing processes were applied to low carbon martensitic steels to examine the mechanical property of martensitic steels after their processing in conventional Continuous Galvanizing Lines (CGL). During the thermal cycle simulation, tempering phenomena occurred resulting in changes of microstructure and mechanical properties. In this study, the tensile deformation behavior of martensitic steels was studied in detail in order to understand the tempering phenomena occurring during their processing. It was found that, after tempering, the strain hardening ability decreased drastically and that the plastic flow became localized. An experimental analysis of this phenomenon will be presented based on TEM microstructural observation and Internal Friction measurements.