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The oxygen content of M2 high-speed steel has not been intentionally controlled in industrial production through secondary refinement in vacuum furnaces. However, a lower oxygen content has a significant effect on the cleanliness, toughness, and addition of rare-earth elements to M2 high-speed steel. The changes in total oxygen content controlled by vacuum carbon deoxidation (VCD) treatment and inclusion evolution were investigated in M2 high-speed steel to understand the effects of carbon on dissolved oxygen and oxides in the carbon–oxygen (C-O) reaction process. Furthermore, the microstructure and properties of M2 high-speed steel caused by vacuum insulation and the role of reducing oxygen content in rare-earth alloying were briefly demonstrated. The results showed that the [O%] decreased from 30 ppm to 3 ppm in a vacuum at holding times above 25 min through the C-O reaction, leading to an inclusion reduction of approximately 70%. In the case of [O%] = 3 ppm in M2 high-speed steel, the addition of rare-earth elements has a greater effect on the inclusion characteristics. Lowering the oxygen content of M2 high-speed steel improves cleanliness and plays a significant role in rare-earth alloying. [ABSTRACT FROM AUTHOR]

Fe–Mn–Al–C low-density steels are regarded as promising materials applied in the automotive industry to achieve the minimization of vehicular emissions and fuel consumption. This study investigates the high-temperature strength and hot ductility of Fe–22Mn–9Al–0.6C low-density steel through high-temperature tensile tests at 800–950 °C. The high-temperature strength decreases with an increasing deformation temperature. This indicates that the precipitation of B2 reduces the hot ductility during the hot deformation of steel, where the results are consistent with those during the solid-solution treatment at 800–950 °C with a holding time of 0.5 h. Furthermore, at 800 °C the γ transforms into a mixture of α + DO3 and κ-carbide precipitates. A transformation of κ + DO3→B2 occurs in the temperature range of 850–900 °C, and at this point the κ-carbide dissolves into the matrix and B2 is generated, resulting in a significant decrease in hot ductility. As the temperature increases up to 950 °C, B2 emerges and transforms into the δ phase, and the κ-carbide precipitates along the γ/γ grain boundaries. The precipitation of B2 during high-temperature treatments in Fe-Mn-Al-C low-density steels is the critical factor affecting hot ductility, leading to crack generation; therefore, it is extremely essential to prevent the temperature interval of B2 precipitation during hot deformation processes. [ABSTRACT FROM AUTHOR]

For the application of forged medium-Mn steels on flywheel rotors, the effect of annealing temperatures from 300 °C to 650 °C on the impact toughness of 0.16C-6.5Mn forged steel was investigated to demonstrate the microstructural characteristics and austenite reverse transformation determining the impact toughness. The results obtained through standard Charpy V-notch impact tests at ambient temperature show that the impact absorbed energy holds at lower than 10 J almost constantly at annealing temperatures of 300 °C to 500 °C, and a representative intergranular fracture is presented. At an annealing temperature of 600 °C, the impact absorbed energy increases to 147 J, with the ductile fracture characteristics showing plenty of fine dimples, and the high impact toughness is attributed to the high volume fraction above 30% and the moderate stability of reverted austenite. Subsequently, the annealing temperature rises higher than 600 °C, the impact absorbed energy decreases, and the fracture morphology shows brittleness characterized by more flat facets of intergranular fractures and small quasi-cleavage facets, presumably corresponding to the insufficient transformation and twinning-induced plasticity effect due to weakening the Mn partitioning from quenched martensite to reverted austenite, which results in lower austenitic stability. Furthermore, the ductile-to-brittle transition temperature (DBTT) of the 0.16C-6.5Mn forged steel annealed at 600 °C, which holds the highest impact absorbed energy, and is explored for the possibility of flywheel rotor application in a service environment. The DBTT reaches −21 °C, obtained through the Boltzmann function, and the impact absorbed energy is approximately 72 J. [ABSTRACT FROM AUTHOR]

Secondary phase precipitation in Fe-22Mn-9Al-0.6C low-density steel was investigated during a continuous cooling process with different cooling rates through a DIL805A thermal expansion dilatometer, and the changes in microstructures and hardness by different cooling rates were discussed. The results showed that the matrix of the Fe-22Mn-9Al-0.6C was composed of austenite and δ-ferrite; moreover, the secondary phases included κ-carbide, β-Mn and DO3 at room temperature. The precipitation temperatures of 858 °C, 709 °C and 495 °C corresponded to the secondary phases B2, κ-carbide and β-Mn, respectively, which were obtained from the thermal expansion curve by the tangent method. When the cooling rate was slow, it had enough time to accommodate C-poor and Al-rich regions in the austenite due to amplitude modulation decomposition. Furthermore, the Al enrichment promoted δ-ferrite formation. Meanwhile, the subsequent formation of κ-carbide and β-Mn occurred through the continuous diffusion of C and Mn into austenite. In addition, the hardness of austenite was high at 0.03 °C/s due to the κ-carbide and β-Mn production and C enrichment, and it was inversely proportional to the cooling rate. It can be concluded that the presence of κ-carbide, DO3 and β-Mn produced at the austenitic/ferrite interface when the cooling rate was below 0.1 °C/s resulted in κ-carbide and β-Mn precipitating hardly at cooling rates exceeding 0.1 °C/s, which provides a guideline for the industrial production of Fe-Mn-Al-C low-density steel in the design of the hot working process. [ABSTRACT FROM AUTHOR]

The impact behaviors of N‐bearing QN1803 and 304 stainless steels are studied using instrumented Charpy impact test in the range of −192–100 °C. The fracture and deformation substructures are systematically investigated by scanning electron microscopy and transmission electron microscopy. The results show that QN1803 presents ductile–brittle transition temperature (DBTT) and 304 shows ductile fracture. With increasing temperature, the stacking fault energy (SFE) of QN1803 and 304 increases, but the former is always lower than the latter. QN1803 presents low impact toughness with low‐density dislocation at −192 °C. At high temperature, QN1803 and 304 show good impact toughness and the deformation substructures are dominated by high‐density dislocations and deformation twinning. [ABSTRACT FROM AUTHOR]

The flow stress curves of Fe‐31.7Mn‐11.5Al‐0.9C low‐density steel are obtained by a hot‐compression test with a Gleeble‐3500 thermomechanical simulator. It is shown in the results that the dynamic recovery and dynamic recrystallization (DRX) of δ‐ferrite occur preferentially under the same deformation condition, inducing a "yield point‐like" phenomenon in the true stress–strain curves. The Zener–Hollomon parameter is introduced to fit the characteristic parameters used to establish the flow stress model according to Arrhenius hyperbolic sine relationship and Avrami equation, and the DRX activation energy of austenite is 414.12 KJ mol−1. The hot‐processing maps at different true strains are simulated based on the dynamic material model to determine the suitable hot‐rolling process and the optimal hot‐working process selection of high strain rate and high deformation temperature combination, 1100–950 °C/1–0.2 s−1, is recommended. [ABSTRACT FROM AUTHOR]

The microstructural evolution of the rail steels manufactured by Hanyang Iron Works was investigated through optical microscopy (OM), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). The OM and SEM images reveal that the microstructures are ferrite with a small amount of pearlite in the rail steel 1904, reticular ferrite and pearlite in the rail steels 1911 and 1921, and full pearlite in the rail steels 1917 and 1919, respectively. The EBSD results show that the rail steel 1904 holds the smallest average grain diameter owing to the pearlite with small size. Moreover, the average grain diameter of the pearlite cluster decreases in the rail steels manufactured after 1908, except for 1921, when it was on the verge of bankruptcy. The rail steels 1917 and 1919 exhibit a higher proportion of low angle grain boundaries and local misorientation with angles lower than 1°. Besides, the grain boundary misorientation holds a lower proportion in the range of 40~50° in the rail steels 1917 and 1919. [ABSTRACT FROM AUTHOR]

A concentration retrieval algorithm is presented, which is applied to in-situ measurement of the concentration of SO 2 based on Ultraviolet-visible Differential Optical Absorption Spectroscopy (UV-DOAS). The algorithm uses the standard deviation of the differential absorbance to represents the gas concentration. Empirical Mode Decomposition (EMD) and Principle Component Analysis (PCA) are used to process the differential absorbance spectrum to improve the SNR. In the algorithm, the basis data for the concentration retrieval of SO 2 is the combination of the EMD & PCA processing result and the standard deviation of the differential absorbance to improve the SNR. The algorithm is applied for a Continuous Emission Monitoring System (CEMS) whose optical path length is 0.3 m. The nonlinear calibration for the system was executed. The relative error of the retrieving concentration is less than 4.68%. The measuring result is −2.05 mg/m 3 during the concentration of SO 2 is zero. For testing the effect of in-situ application, the contrast experiment was implemented in one coil-fired power plant. And the result proof that the algorithm has high stability and durability. [ABSTRACT FROM AUTHOR]