Iranian Journal of Materials Science and Engineering

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In principal, a proper combination of strength and ductility is achieved through micro component refinement in steels. This is particularly empowered with ferrite refinement down to micron sizes in ferrite pearlite engineering steels. The latter is achieved through various well-defined methods in which strain induced transformation (SIT) has shown spectacular capabilities. In the present study, to address the effect of thermo mechanical processing parameters on the (SIT) behavior, two plain carbon steels were studied through single pass rolling. This was carried out at the corresponding Ar_3 + 20°C temperature of the steels. The results indicated that the transformation behavior and ferrite morphology would be .strongly influenced by both the chemical composition (i.e., carbon content) and the amount of applied strain. Furthermore, a high volume fraction of very fine ferrite with mean grain size of less than 2 µm was obtained. This was attributed to the ferrite nucleation at deformation bands and serrated austenite grain boundaries.

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In this study the hot deformation behaviour of a precipitation hardened (PH) stainless steel at high strain rates has been predicted through hot compression testing. Stress-strain curves were obtained for a range of strain rates from 10-3 to 10+1 S-1 and temperatures from 850 to 1150°C. Results obtained by microstructure and stress-strain curves show that at low temperatures and high strain rates, where the Zener-Holman parameter (Z) is high, work hardening and dynamic recovery occure. By increasing temperature and decreasing strain rate, the Z parameter is decreased, so that dynamic recrystallization is the dominant softening mechanism. The results were fitted using a Log Z versus Log (sinh (a sp) diagram allowing an assessment of the behavior of the stresses measured at strain rates closer to those related to the industrial hot rolling schedules. It is clearly shown that the data collected from low strain rate testing can be fairly reasonably extrapolated to higher orders of magnitude of strain rate.

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Abstract: Austenitic stainless steels exhibit a low hardness and weak tribological properties. The wear behaviour of austenitic stainless steel AISI 316 was evaluated through the pin on disc tribological method. For investigating the effect of wear on the changes in microstructure and resistance to wear, optical microscopy and scanning electron microscope were used. The hardness of the worn surfaces was measured with a micro-hardness tester. Worn surfaces were analyzed through X-ray diffraction. Results showed that with increasing the sliding distance and applied load, the austenite phase partially transformed to ά martensite, and there was no trace of ε phase detected. Due to the formation of probably hard and strong martensite phase, as the sliding distance and applied load increased, the hardness and the wear resistance of the material was increased. Wear mechanism was on the base of delamination and abrasion.

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Abstract: In the current work, the strain hardening behavior of dual-phase steels with different silicon content (0.34- 2.26 Wt. %) was examined using the modified Crussard-Jaoul analysis. It was shown that these dual-phase steels deform in two stages over a uniform strain range. Each stage exhibited a different strain hardening exponent varying with silicon content. At the first stage, work hardening exponent remind significantly constant, while during the second stage, it decreased with increasing silicon content from 0.34% to 1.51% and then increased for the higher silicon contents (1.51% to 2.26%). It was found that the strain hardening behavior of these steels was predominantly affected by the volume fraction of martensite at low silicon contet and the ferrite strengthening induced by silicon at the higher silicon content. The effect of silicon content on the volume fraction of martensite and tensile properties were also considered.

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The aim of the present study is the prediction of critical conditions (including critical strain and flow stress) for the initiation of dynamic recrystallization during thermo-mechanical processing of plain carbon steels. For this propose, torsion tests were conducted at different temperature (1050, 1100 and 1150˚C) and strain rates (0.002, 0.02 and 0.2/s). All flow curves showed a peak stress indicating that dynamic recrystallization occurs during hot deformation. The critical stress and strain were then determined based on change in strain hardening rate as a function of flow stress. Finally, the effect of deformation conditions on these parameters was analyzed.

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High speed and absence of a precise control over pressure distribution confine sheet Electromagnetic Forming into a die to simple shapes having shallow depth. It is possible to reach a higher depth by using a convex punch instead of a concave die. In this study, sheet Electromagnetic Forming on a punch and sheet Electromagnetic Forming into a die are investigated. The electromagnetic part of the study is investigated analytically and its mechanical part is studied numerically. In order to couple electromagnetic with mechanical parts, no-coupling method is used. The obtained results are verified by comparing the obtained results with previous experimental ones in literature. Rate-dependent and rate-independent hardenings are taken into consideration for the mechanical behavior for material of AAl1050. Using appropriate hardening model for material yields acceptable results. Moreover, a convex punch instead of a concave die is used to reach to a higher depth in sheet Electromagnetic Forming.

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Nowadays, Ni-free austenitic stainless steels are being developed rapidly and high price of nickel is one of the most important motivations for this development. At present research a new FeCrMn steel was designed and produced based on Fe-Cr-Mn-C system. Comparative studies on microstructure and high temperature mechanical properties of  new steel and AISI 316 steel were done. The results showed that new FeCrMn developed steel has single austenite phase microstructure, and its tensile strength and toughness were higher than those of 316 steel at 25, 200,350 and 500°C. In contrast with 316 steel, the new FeCrMn steel did not show strain induced transformation and dynamic strain aging phenomena during tensile tests that represented higher austenite stability of new developed steel. Lower density and higher strength of the new steel caused higher specific strength in comparison with the 316 one that can be considered as an important advantage in structural applications but in less corrosive environment

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The present work deals with the hot deformation behavior of commercial Nb alloy C-103 and its microstructure evolution during uniaxial compression tests in the temperature range of 700-1100 °C and the strain rate range of 0.001-0.4 s^-1. Strain rate sensitivity, calculated from the compression tests data, was almost constant and showed a negative value in the temperature range of 700-900 °C but increased significantly beyond 900 °C. Dynamic strain aging was found to have a predominant effect up to 900 °C, beyond which dynamic recovery and oxidation influenced the compressive properties. The microstructure of the deformed samples showed indications of dynamic recrystallization within the high strain rate sensitivity domain and features of flow instability in the regime of low strain rate sensitivity. The 950–1000 °C temperature range and strain rate range of 0.001-0.1 s-1 were suggested as suitable hot deformation conditions. The constitutive equation was established to describe the alloy's flow behavior, and the average activation energy for plastic flow was calculated to be 267 kJ/mol.