The effects of tempering temperature on the microstructure and mechanical properties of Cronidur 30 bearing steel were investigated by XRD, SEM, TEM, EBSD, and mechanical testing. The microstructure evolves systematically with increasing tempering temperature. At 400 °C, the matrix is dominated by lath martensite with fragmented boundaries. At 450 °C, the martensitic laths are refined, the geometrically necessary dislocation (GND) density reaches its maximum, and carbonitrides are most finely and uniformly distributed. When the tempering temperature increases to 500 °C, cementite enrichment along lath boundaries becomes evident. Further increasing the temperature to 550–600 °C promotes the formation of tempered sorbite and coarsening of carbonitrides. At 450 °C, the average surface carbonitride size decreases to approximately 0.39 μm, while the GND density reaches 20.80 × 1014 m−2. Under this condition, the hardness and tensile strength reach peak values of 60.3 HRC and 2226.5 MPa, respectively. The hardening response at 450 °C is attributed to the combined effects of fine carbonitride strengthening, high dislocation density, and grain-boundary strengthening.
This study investigates the relationships between chemical composition, microstructure, and mechanical properties in the Nb–Ta–B ternary alloys over a wide composition range after long-term heat treatment at 1323 K for approximately 2900 h. In particular, the phase composition and resulting microstructures were analyzed, and nanomechanical properties, namely indentation hardness and indentation modulus, of the individual phases and two-phase microstructural constituents were evaluated. Microstructural and phase analyses performed using scanning electron microscopy and X-ray diffraction revealed single-phase, two-phase, and three-phase microstructures depending on the composition. The presence of the BCC + MB eutectic microstructure confirms the extension of the binary eutectic reaction, L → BCC + MB, into the ternary compositional range. In the Ta-rich alloy, the Ta2B boride was observed, despite being stable only at substantially higher temperatures in the corresponding binary system. Within the investigated alloy compositions, no ternary phase was identified, and all observed borides correspond to binary borides exhibiting solubility of the third element. Nanomechanical measurements were performed on the MB, MB2, and M3B4 phases, as well as on the BCC + MB, BCC + Ta2B, and M3B4 + M5B6 regions. The eutectic BCC + MB structure exhibited the lowest hardness and indentation modulus, whereas the MB boride in the Ta-rich alloy showed the highest values. The M3B4 and M5B6 phases exhibited similar hardness values. Overall, the results provide new experimental insights into the phase constitution and nanomechanical behavior of the investigated Nb–Ta–B alloys and establish an experimental basis for future thermodynamic modeling of the B–Nb–Ta ternary system.
This study investigates a two-stage duplex process for producing low-carbon ferrochrome based on sequential mixing of molten ore–lime and metallic melts, with emphasis on its adaptation to the raw materials and operating conditions of the Aktobe Ferroalloy Plant. Unlike the conventional process, in which the chromite ore–lime charge directly interacts with ferrosilicochromium, the proposed approach distributes FeSiCr between two successive stages of melt interaction to improve chromium reduction and metal–slag separation. Kempirsai chromite ore, lime, and ferrosilicochromium (FeSiCr 48) were used as raw materials. Thermodynamic analysis using HSC Chemistry 6.0 confirmed the feasibility of the main reduction reactions at 1600–1800 °C. Pilot-industrial trials produced ferrochrome containing 71.42–73.15% Cr and 1.28–1.31% Si, while the final slag contained 1.54–1.58% Cr2O3 and 0.11–0.14% FeO. X-ray diffraction analysis identified merwinite, gehlenite, and spinel-type solid solutions containing chromium. Dicalcium silicate was not detected, consistent with the observed stone-like structure of the cooled slag. Chromium recovery reached approximately 70%, compared with approximately 65% for the conventional process. The results demonstrate the potential of sequential FeSiCr distribution to improve chromium utilization and reduce chromium losses to slag under the specific conditions of ferrochrome production at the Aktobe Ferroalloy Plant.
To address the task allocation problem of a gantry-type dual-arm welding robotic system subject to heavy and diverse welding workloads as well as limited operating span, a Dynamic Small-World Genetic Algorithm (DSWGA) for multi-objective optimization is proposed to obtain optimal welding task allocation. To meet the operational requirements of workload balancing and high-efficiency welding for ship multi-subassembly components, a multi-objective optimization model is established to minimize the system makespan and the load imbalance rate, and the small-world genetic algorithm is adopted to solve this model. To tackle the drawback of fixed parameters in the small-world network, a dynamic network parameter adjustment mechanism is developed. By dynamically tuning the connectivity among individuals in the population, the scope of information exchange is adjusted throughout the optimization process to enhance the global search capability of the algorithm. To overcome the limitation of fixed crossover and mutation probabilities in conventional genetic operations, adaptive crossover and mutation strategies are designed based on the structural differences between parents and the structural similarity between offspring and non-dominated solutions, which improves the search efficiency and solution-set quality. Test results for each improvement strategy demonstrate that the three strategies show potential complementary effects, and their combination yields better overall performance in terms of the mean values of HV, GD, and Spread, with a statistically significant advantage in HV. Task allocation experiments are conducted in three typical welding scenarios with different task scales and constraint characteristics. The results indicate that DSWGA achieves competitive overall performance in convergence, solution set quality, and distribution uniformity compared with NSGA-II, SPEA2, and MOPSO. In the more complex test scenario, the makespan of the selected compromise solution obtained by DSWGA is reduced by approximately 1.03%, 3.72%, and 2.68% compared with NSGA-II, SPEA2, and MOPSO, respectively, while the robot load balancing rate reaches 99.7%.
This study investigates the compressive response of a caisson-ceiling-inspired (CC) lattice developed from curved supporting paths and hierarchical nesting in traditional Chinese caisson ceilings. Four lattice configurations were compared numerically, and CC and CUBIC+BCC specimens were fabricated and subjected to quasi-static compression. Under the investigated nominal geometry, loading direction and material condition, the CC lattice showed higher nominal compressive stress and volumetric energy absorption than CUBIC+BCC in the available representative records. The numerical and experimental results gave the same performance ranking and broadly similar deformation characteristics, whereas the numerical stress levels remained lower than the experimental values.
