Journal of Iron and Steel Research(International)最新文献

The microstructures and mechanical properties of ferrite-based lightweight steel with different compositions were investigated by tensile test, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermodynamic calculation (TC). It was shown that the ferrite-based lightweight steels with 5 wt. % or 8 wt. % A1 were basically composed of ferrite, austenite and κ-carbide. As the annealing temperature increased, the content of the austenite in the steel gradually increased, while the κ-carbide gradually decomposed and finally disappeared. The mechanical properties of the steel with 5 wt.% A1 and 2 wt. % Cr, composed of ferrite and Cr₇C₃ carbide at different annealing temperatures, were significantly inferior to those of others. The steel containing 5 wt. % Al, annealed at 820 °C for 50 s then rapidly cooled to 400 °C and held for 180 s, can obtain the best product of strength and elongation (PSE) of 31242 MPa · %. The austenite stability of the steel is better, and its PSE is higher. In addition, the steel with higher PSE has a more stable instantaneous strain hardening exponent (n value), which is mainly caused by the effect of transformation induced plasticity (TRIP). When the κ-carbide or Cr₇C₃ carbide existed in the microstructure of the steel, there was an obvious yield plateau in the tensile curve, while its PSE decreased significantly.

The interface associativity and energy absorption capability of composite structure with anti-vibration porous Al-MM (cerium-rich mischmetal) alloy core and iron alloy skin were investigated. Porous aluminum core/iron alloy skin structures were fabricated considering an iron alloy tube as its shell and closed-cell porous Al-MM alloy as its core. A peeling experiment was carried out to calculate the capacity of interfacial bonding and a compression test was carried out to determine the energy absorption capability. The results showed that the addition of MM significantly enhanced both the interfacial bonding and the energy absorption capacity.

The phase diagram of superaustenitic stainless steel 654SMO was calculated by thermodynamic software and the precipitated phases in the specimens aged at 800 – 1100 °C for 1 h were studied by methods of physicochemical phase analysis, scanning electron microscopy and transmission electron microscopy. The results showed that the size of precipitated particles increased with increasing the temperature. The amount of second phases reached the maximum value at 900 °C, but decreased above 900 °C. There were about eight kinds of precipitated phases in 654SMO including σ phase, Cr₂N, μ phase, χ phase, Laves phase, M₂₃C₆, M₆C and M₃C, in which the σ phase and Cr₂ N were the dominant precipitated phases.

The segregation of Cu and Ni in a 17-4PH stainless steel piston rod has been confirmed to be responsible for the cracking after heat treatment. Further investigation showed that the segregation zone was composed of three layers, namely the fine grain martensitic layer, the coarse grain martensitic layer and the coarse grain austenitic layer from the matrix to the crack surface. Three button ingots with the same chemical compositions as those three layers have been prepared to evaluate the grain size distribution, microstructure and mechanical properties. The effects of Cu and Ni segregation on the microstructures of those three layers have been explored by thermodynamic calculation. Based on the microstructure and mechanical properties results, an intensive understanding of the cracking in the segregation zone was therefore reached.

The RAFM (reduced activation ferritic/martensitic) steels containing different tantalum contents (0 wt. %, 0. 027 wt. %, 0. 073 wt. %) were designed and cast. Differential scanning calorimetry and optical microscopy were employed to explore the influence of tantalum content on the austenitic transformation of RAFM steels. The austenitic transformation kinetics was described by a phase-transformation model. The model, involving site saturation nucleation, diffusion-controlled growth and impingement correction, was established based on the classical Johnson-Mehl-Avrami-Kolmogorov model. The phase-transformation kinetics parameters, including D₀ (pre-exponential factor for diffusion) and Q_d (activation energy for diffusion), were calculated by fitting the experimental data and the kinetic model. The results indicated that the average grain size is decreased with the increase of tantalum. The values of A_c1 and A_c3 (onset and finish temperature of austenitic transformation, respectively) are increased by increasing the tantalum content. The increase of tantalum caused the decrease of D₀. However, Q_d is increased with the increase of tantalum. In addition, as a carbides forming element, tantalum would reduce the carbon diffusion coefficient and slow down the austenitic transformation rate.

Dynamic continuous cooling transformation (CCT) behavior of medium-carbon forging steels microalloyed with different V contents up to 0.29% was investigated by means of dilatometric measurement, microstructural observation and hardness measurement. The results showed that the dynamic CCT diagrams were similar and the main difference was that the fields of the transformation products were shifted to the right side of the diagrams with the increase of V content, and this effect was more noticeable with an addition of 0.29% V. The A_c1 and A_c3 temperatures showed increasing trends with increasing V content, while the critical cooling rates decreased with increasing V content. The increase of V content resulted in significant increase of hardness and this tendency was enhanced with increasing cooling rate until the formation of acicular ferrite (AF). A promising approach of remarkably improving the toughness of ferritic-pearlitic medium-carbon forging steels with suitable V addition and the introduction of AF without notable penalty on its strength level was suggested.

Blast furnace (BF) slag is a by-product of the ironmaking process and could be utilized to manufacture slag fiber by adding iron ore tailing. The crystallization behavior of the modified BF slag is significant to the fibrosis process. To investigate the influence of basicity on the crystallization behavior, BF slag was modified by adding iron ore tailing at room temperature and melted at 1500 °C. FactSage simulation, X-ray diffraction, scanning electron microscopy backscattered electron imaging coupled to an energy dispersive spectrometer, and hot thermocouple technique analysis were performed to explore the crystallization behavior of the modified BF slag during the cooling process. It was found that the initial crystallization temperature increased with the increase in basicity. Melilite, anorthite, clinopyroxene, and wollastonite could be generated during the cooling process as basicity ranged from 0.7 to 0.9. Spinel could be found as one of the phases; however, wollastonite disappeared under a basicity of 1.0. The initial crystallization temperature was controlled by the crystallization of melilite during the cooling process when the basicity of the modified BF slag ranged from 0.7 to 1.0. Moreover, the cooling rate could also influence the crystallization of the modified BF slag.

Aiming at the current characteristics of blast furnace (BF) process, carbon saving potential of blast furnace was investigated from the perspective of the relationship between degree of direct reduction and carbon consumption. A new relationship chart between carbon consumption and degree of direct reduction, which can reflect more real situation of blast furnace operation, was established. Furthermore, the carbon saving potential of hydrogen-rich oxygen blast furnace (OBF) process was analyzed. Then, the policy implications based on this relationship chart established were suggested. On this basis, the method of improving the carbon saving potential of blast furnace was recycling the top gas with removal of CO₂ and H₂O or increasing hydrogen in BF gas and full oxygen blast. The results show that the carbon saving potential in traditional blast furnace (TBF) is only 38–56 kg · t⁻¹ while that in OBF is 138 kg · t⁻¹. Theoretically, the lowest carbon consumption of OBF is 261 kg · t⁻¹ and the corresponding degree of direct reduction is 0.04. In addition, the theoretical lowest carbon consumption of hydrogen-rich OBF is 257 kg · t⁻¹. The modeling analysis can be used to estimate the carbon savings potential in new ironmaking process and its related CO₂ emissions.

The hot deformation behavior of GH4945 superalloy was investigated by isothermal compression test in the temperature range of 1000–1200 °C with strain rates of 0.001–10.000 s⁻¹ to a total strain of 0.7. Dynamic recrystallization is the primary softening mechanism for GH4945 superalloy during hot deformation. The constitutive equation is established, and the calculated apparent activation energy is 458.446 kJ/mol. The processing maps at true strains of 0.2, 0.4 and 0.6 are generally similar, demonstrating that strain has little influence on processing map. The power dissipation efficiency and instability factors are remarkably influenced by deformation temperature and strain rate. The optimal hot working conditions are determined in temperature range of 1082–1131 °C with strain rates of 0.004–0.018 s⁻¹. Another domain of 1134–1150 °C and 0.018–0.213 s⁻¹ can also be selected as the optimal hot working conditions. The initial grains are replaced by dynamically recrystallized ones in optimal domains. The unsafe domains locate in the zone with strain rates above 0.274 s⁻¹, mainly characterized by uneven microstructure. Hot working is not recommended in the unsafe domains.