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The crystallographic orientation and texture evolution mechanism of equiaxed Ti60 alloy plates were investigated in this study through plane strain compression tests. The EBSD analysis revealed that the received plate contained two characteristic textures that were perpendicular to each other, i.e., c-axis//TD (Component 1) and c-axis//RD (Component 2), with the latter being caused by the change in direction of the TD texture that was generated during the previous unidirectional rolling process into an RD direction in the cross-rolling process. The results demonstrated that, with increasing the deformation temperature from 930 °C to 960 °C and 990 °C, the intensity of the c-axis//TD texture (Component 1) initially rose to a peak value of 5.07, which then—subsequently—decreased significantly to 2.96 at 960 °C and 3.11 at 990 °C. Conversely, the intensity of the c-axis//RD texture (Component 2) remained relatively unchanged. These texture changes were correlated with slip system activity and the spheroidization of the primary alpha phase. For the c-axis//TD texture, the initial intensity of the texture components during compression at lower temperatures could be attributed to the incomplete dynamic spheroidization process of the α phase, which leads to the reinforcement of the c-axis//TD due to prismatic slip. As the deformation temperature increased, the dynamic spheroidization process became more prominent, thereby leading to a significant reduction in the intensity of the c-axis//TD texture. In contrast, the c-axis//RD texture exhibited difficulty in activating the prismatic slip and basal slip; in addition, it also encountered resistance to dynamic spheroidization, thus resulting in negligible changes in the texture intensity.

A self-designed Ti-35421 (Ti-3Al-5Mo-4Cr-2Zr-1Fe wt%) titanium alloy is a new type of low-cost high strength titanium alloy. In order to understand the hot deformation behavior of Ti-35421 alloy, isothermal compression tests were carried out under a deformation temperature range of 750–930 °C with a strain rate range of 0.01–10 s−1 in this study. Electron backscatter diffraction (EBSD) was used to characterize the microstructure prior to and post hot deformation. The results show that the stress–strain curves have obvious yielding behavior at a high strain rate (>0.1 s−1). As the deformation temperature increases and the strain rate decreases, the α phase content gradually decreases in the α + β phase region. Meanwhile, spheroidization and precipitation of α phase are prone to occur in the α + β phase region. From the EBSD analysis, the volume fraction of recrystallized grains was very low, so dynamic recovery (DRV) is the dominant deformation mechanism of Ti-35421 alloy. In addition to DRV, Ti-35421 alloy is more likely to occur in continuous dynamic recrystallization (CDRX) than discontinuous dynamic recrystallization (DDRX).

Skew rolling is a manufacturing process in which two or three rolls are used to reduce the diameter or modify the shape of a cylindrical workpiece, which is used to manufacture mechanical components such as shafts, rods or balls. Hot conditions are used to overcome limitations related to material ductility, residual stress and machine capacity. In this paper, the warm skew rolling (WSR) process of 42CrMo4 rods is modeled by the finite element method. The effects of forming parameters, namely initial temperature and roll rotational velocity, on the material strain rate, thermal properties, microstructure and hardness were analyzed. Simulation results were validated by experimental process data, while hardness tests and SEM-EBSD microscopy were used to assess mechanical properties and microstructure, respectively. The WSR resulting microstructure is different from the normalized ferritic–pearlitic initial one. The degree of spheroidization (DoS) of cementite increases with temperature. The maximum DoS of 86.5% occurs at the initial temperature of 750 °C, leading to the highest material softening. Rolling from lower temperatures favors grain fragmentation and the achievement of incomplete spheroidization, which, in combination with the highest proportion of high-angle boundaries, contributes to a higher hardness of the rods with respect to those rolled at higher temperatures. The highest reduction in hardness takes place at 750 °C and 30 rpm, leading to 209.4 HV1 (30.7% reduction) and 194.1 HV1 (35.7% reduction) in the near-surface and internal regions, respectively. The driving factor is the transformation of cementite precipitates into a spheroidal form characterized by the greatest degree of dispersion.

This paper presents the results of experimental studies on the treatment of Fe–23Cr–11Mn–1N high-nitrogen stainless steel powder alloys, synthesized by the mechanical alloying (MA) of elemental powders in the flow of a thermal plasma. Fe–23Cr–11Mn–1N high-nitrogen stainless steel powder alloys were prepared by MA in the attritor under an argon atmosphere. For spheroidization of Fe–23Cr–11Mn–1N high-nitrogen stainless steel powder alloys, the TekSphero 15 plant manufactured by Tekna Plasma Systems Inc was used. The studies have shown the possibility of obtaining Fe–23Cr–11Mn–1N high-nitrogen spherical powders steel alloys from the powder obtained by MA. According to the results of a series of experiments, it was found that the results of plasma spheroidization of powders essentially depend on the size of the fraction due to some difference in the particle shape and flowability, and on the gas regime of the plasma torch. It is established that during the plasma spheroidization process, some of the nitrogen leaves the alloy. The loss rate of nitrogen depends on the size of the initial particles.

Spheroidization heat treatments were carried out at 700 °C in two industrially produced hypo-eutectoid pearlitic steels. The heat treatments lead to change in microstructure in terms of volume fraction and morphology of the cementites. Magnetic hysteresis loop measurement was carried out along with bulk hardness and mechanical properties of the steels at various lengths of time up to 100 h. A linear decrease in tensile strength, breaking strength, bulk hardness and coercivity was found with increase in annealing time for the spheroidization of cementites leading to decrease in pinning density for dislocations movement and magnetic domain wall motion for the increase in inter lamellae spacing and carbide spacing. The uniform elongation and total elongation were increased with spheroidization annealing. A strong correlation of coercivity with the mechanical properties indicates their precise evaluation by measuring coercivity in the spheroidization heat treated steels through a portable magnetic NDE device.

The hot deformation behavior of Ti-5322 alloy are researched at compression temperatures range of 750-1050 °C and strain rate range of 0.01-10 s−1, to optimize its hot workability. Processing map analysis and microstructure observations reveal that the optimal processing parameters of Ti-5322 alloy are temperatures of 750-825 °C and strain rates of 0.01-0.05 s−1, and temperatures of 925-975 °C and strain rates of 0.01-1 s−1. The peak efficiency of power dissipation can reach 40% owing to the transformation from phase to β phase, spheroidization behavior and dynamic recrystallization of the β phase. The dynamic recrystallization was the primary form of microstructure evolution above 900 °C, while the spheroidization of phase below 900 °C. The spheroidization of lamellae can be attributed to the instability of subgrain boundaries appeared in the phase during hot deformation. The β phase wadges into the / subgrain boundary and /β interface migration induced the phase spheroidization. In addition, three instability domains are detected in the processing maps, which confirmed by the presence of microstructures with wedge cracking and adiabatic shear bands.

Effect of initial pearlite morphology on the microstructure evolution during spheroidization annealing and subsequent hardening treatment was studied in hot-rolled 1.0C–1.5Cr bearing steel. The ferrite-to-austenite transformation in spheroidization annealing can be accelerated by refining the pearlite interlamellar spacing and pearlite colony size. Decreasing interlamellar spacing is also beneficial to increasing the number density of undissolved cementite, leading to the refining of final spheroidized cementite. During the re-austenitizing process of hardening treatment, the smaller initial spheroidized cementite leads to faster cementite dissolution and finer undissolved cementite particles. The prior austenite grain size after hardening treatment can also be decreased by refining the initial pearlite microstructure.

In order to allow more practical prediction of RF (radio-frequency)–ICP (inductively coupled plasma) spheroidization results of titanium metal powder, numerical analyses under single particle and dense loading conditions were carried out and the results were compared. First, both of the numerical results for Ar inductively coupled plasma with the power level of 30 kW revealed that the injected particles can experience not only spheroidization by melting, but also size reduction by evaporation. In addition, this size reduction was found to strongly depend on the initial sizes of the injected particles, due to the relatively short heating time. For example, the 100 µm Ti particles were computed to hardly experience size reduction by evaporation regardless of feeding rates. However, relatively small Ti particles < 100 µm can be rapidly heated up to boiling points during the short flight of plasma, resulting in the size reduction by the surface evaporation. In particular, numerical results under dense loading condition showed that the final sizes of these small Ti particles can be changed depending on the feeding rate. For example, a single 60 µm Ti particle was calculated to be a 51 µm spherical Ti particle due to the excessive heating. However, with the increase of feeding rate up to 1.0 kg/h, the final sizes of the as-treated Ti powder could be improved to 55 µm due to the plasma temperatures decreasing through complicated plasma–particle interactions. By predicting the relationships between the feeding rates and the initial diameters of Ti powders at a given plasma power level, numerical modellings under single particle and dense loading conditions can help in optimizing the RF–ICP spheroidization process of titanium metal powder.Graphic Abstract

Results of a study of the production of spherical-shape powder from shavings of high-alloy high-temperature steel 13Kh11N2V2MF (ÉI961) are presented. It is shown that the rate of feeding of the powder into the flow of thermal plasma affects the process of spheroidization of the particles. The chemical composition of the powder is compared to that required by the GOST standard.

The effect of silicon on the spheroidization of cementite in hypereutectoid high carbon chromium bearing steels has been investigated on the basis of microstructural analysis and thermodynamic calculations. The results showed that an increase of silicon content in high carbon chromium bearing steels retards the spheoridization of cementite. The thermodynamic calculations revealed that the shrinkage of the austenite phase field in bearing steels with increasing silicon content gave rise to an increase of volume fraction of cementite at an annealing temperature, possibly resulting in incomplete spheroidization. Furthermore, due to the low solubility of silicon in cementite, an increase of silicon content can raise the activity or chemical potential of carbon atoms in austenite at the austenite/cementite interfaces. Consequently, the difference in chemical potential of carbon atoms at the interfaces would be reduced with increasing silicon content, causing a decrease of the driving force for their diffusion from cementite to austenite.