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Advanced high strength steels (AHSSs) are regarded as the most promising materials for vehicles in the 21st century. AHSSs are complex and sophisticated materials, with microstructures being controlled by precise thermomechanical processing (TMP) technologies. TMP is an established and strategic method for improving the mechanical properties of AHSSs through control of microstructures and is among the most important industrial technologies for producing high quality AHSSs with the necessary mechanical properties. This article aims to provide a comprehensive review of recent progress in TMP of AHSSs, with focus on the processing-microstructure-property relationships of the processed AHSSs. We first present an introduction to the background of the TMP of AHSSs. Then, the recent progress and the latest achievements in TMP of the first, second and third generations of AHSSs and Nano Hiten steels are reviewed in detail, and the mechanisms of the TMP-induced microstructural evolution and mechanical properties variation are addressed and discussed. The present review concludes with a summary on the TMP of AHSSs currently under development, and also offers an outlook of the future opportunities which will inspire more in-depth research and eventually advance practical applications of this innovative field. [ABSTRACT FROM AUTHOR]

In the current study, the effects of tungsten (W) addition on the microstructure, hardness, and room/low [223 K and 173 K (−50 °C and −100 °C)] temperature tensile properties of microalloyed forging steels were systematically investigated. Four kinds of steel specimens were produced by varying the W additions (0, 0.1, 0.5, and 1 wt pct). The microstructure showed that the addition of W does not have any noticeable effect on the amount of precipitates. The precipitates in W-containing steels were all rich in W, and the W concentration in the precipitates increased with the increasing W content. The mean sizes of both austenite grains and precipitates decreased with the increasing W content. When the W content was equal to or less than 0.5 pct, the addition of W favored the formation of allotriomorphic ferrite, which subsequently promoted the development of acicular ferrite in the microalloyed forging steels. The results of mechanical tests indicated that W plays an important role in increasing the hardness and tensile strength. When the testing temperature was decreased, the tensile strength showed an increasing trend. Both the yield strength and the ultimate tensile strength obeyed an Arrhenius type of relation with respect to temperature. When the temperature was decreased from 223 K to 173 K (from −50 °C to −100 °C), a ductile-to-brittle transition (DBT) of the specimen with 1 pct W occurred. The addition of W favored a higher DBT temperature. From the microstructural and mechanical test results, it is demonstrated that the addition of 0.5 pct W results in the best combination of excellent room/low-temperature tensile strength and ductility. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, the effects of tungsten (W) addition and heat treatment conditions on the microstructure, impact toughness and tensile properties of microalloyed forging steels were studied. Four kinds of microalloyed forging steels were produced by varying W additions (0, 0.5, 1 and 2wt%). Heat treatment was carried out at temperatures ranging from 840 to 950°C followed by air and furnace cooling. Mechanical tests were used to evaluate the room temperature Charpy impact and tensile properties. The resulting microstructures were analysed via optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the microstructure and mechanical properties of the microalloyed forging steels are closely related to the W content. Correct selection of heat treatment temperature and cooling method is very important to enhance the mechanical properties. The optimum heat treatment temperatures obtained in this study are 920, 900, 880 and 860°C for the steels with 0%, 0.5%, 1% and 2% W, respectively. Both the impact toughness and tensile properties of the microalloyed forging steels have been significantly enhanced after heat treatment at the optimum temperatures followed by air cooling. [Copyright &y& Elsevier]

Abstract: In the present work, detailed studies were made on the optimization of microstructure and mechanical properties of a low-carbon microalloyed cast steel through control of heat treatment conditions. Specimens were austenitized at temperatures ranging from 950 to 1200°C for 2h followed by different cooling methods (furnace, air and water). For analyzing the effect of holding time on mechanical properties, some cast specimens were austenitized at 1100°C for different times followed by furnace cooling. After heat treatment, mechanical tests were employed to evaluate the room temperature Charpy impact and tensile properties. The characterization of complex precipitates formed during heat treatment process was investigated by using analytical electron microscopy. The results show that dissolution of vanadium-containing precipitates plays an important role in the abnormal growth of austenite grains at 1150°C. Further growth in austenite grains at 1200°C is caused by the dissolution of Ti-containing particles and the reduction of the amount of precipitates. Correct selection of the austenitizing temperature, holding time and cooling method is very important to improve the mechanical properties of the steel. Heat treatment at 1100°C for 2h followed by furnace cooling leads to the best combination of excellent Charpy impact and tensile properties. [Copyright &y& Elsevier]

A wet ball milling route was used to synthesise SiC-graphene core-shell nanoparticles in situ from graphite and SiC nanoparticles. Graphite flakes were gradually exfoliated into fresh graphene nanosheets (GNSs) without significant defects, which is attributed to mechanical shearing and moderate impaction forces between graphite flakes, milling balls and SiC nanoparticles during the wet milling. The non-destructive exfoliation is characterised by Raman, Fourier transform infrared and X-Ray photoelectron spectroscopies. The freshly produced GNSs are energetically unstable and thin enough to be flexible and this drives the in situ attaching and scrolling of GNSs on the SiC nanoparticles. The SiC nanoparticles and GNSs are well dispersed in the wet medium and the SiC nanoparticles are individually wrapped. It has been estimated that > 50% of the produced GNSs are wrapped around the SiC nanoparticles and these GNSs are generally ≤ 6 layers. [ABSTRACT FROM AUTHOR]

2 mm thick Al-7B04 alloy sheets under T6, T4 and O tempers were subjected to friction stir processing (FSP). The microstructure, Vickers hardness and tensile properties of the stir zone were characterized. The results show that the initial base metal temper has a significant impact on the microstructure and the mechanical properties of the stir zone. FSP led to the formation of full recrystallized microstructure, the average grain size in the stir zone ranged from 2.1 to 2.2 μm when the base metal tempers were T6 and T4. On account of the relatively strong pin force of the precipitates, the grains in the stir zone became finer when O temper base metal was applied. Besides, the stir zones produced using the base metal under T6 and T4 tempers were softened, while a significant strengthening was observed when the base metal temper was O. The softening in the stir zone for T6 and T4 temper is attributed to the dissolution of fine strengthening precipitates during FSP, and the strengthening for O temper arises from the grain refinement caused by FSP. [ABSTRACT FROM AUTHOR]

Samples with one through three passes with 100% overlap were created using friction stir processing (FSP) in order to locally modify the microstructure and mechanical properties of a cold-rolled Al-5083 alloy. A constant traverse speed and two different rotational speeds were used for processing. The results indicated that single-pass FSP caused dynamic recrystallization in the stir zone, leading to equiaxed grains with high angle grain boundaries. The grain size increased with increasing the rotational speed. The product of ultimate tensile strength and total elongation of the stir zone was significantly enhanced compared with that of the base metal. During the annealing heat treatment, abnormal grain growth (AGG) occurred throughout the stir zone when a low rotational speed was adopted. The stir zone produced with a high rotational speed was found to be more resistant to AGG. The application of multiple process passes did not change the grain size and mechanical properties of the stir zone significantly. The expanding of AGG in the stir zone was inhibited as the number of passes was increased. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of vacuum annealing temperature on the microstructure, mechanical properties and electrical resistivity of Mg–3Al–1Zn rapid solidification (RS) magnesium ribbons. The results indicate that when the annealing temperature is increased, the grain size of the ribbons is dramatically reduced from 10 to 1 μm. The highest break stress and micro-hardness is obtained at 673 K. These effects are ascribed to the dispersion strengthening caused by the high amount of fine nanoparticles distributed in the material. Electrical resistivity-temperature ( ρ–T ) curves have been used to provide useful information about the effects of the annealing temperature on the grain size, grain orientation and crystal structure of the ribbons. In this way, a new lightweight electric wire or connection cable line could be produced which would have good electromagnetic interference (EMI). [ABSTRACT FROM AUTHOR]