Metals

The seamless flatness roll is a critical inspection device in cold-rolled strip flatness control systems. Prolonged service causes cracks and scratches on the roll surface, while repeated grinding gradually removes the hardened layer, potentially rendering the roll unusable. To address the risk of thermal damage to internal sensors during the laser cladding repair of seamless flatness rolls, this study proposes a process optimization strategy using the Finite Element Method (FEM) and Response Surface Methodology (RSM). Focusing on an 820 mm roll, a regression prediction model for laser spot and internal component temperatures was constructed using a Box–Behnken design (BBD) based on an experimentally calibrated FEM model. Multi-objective optimization determined the optimal process parameters: laser power of 1.43 kW, laser radius of 3.73 mm, scanning speed of 23.45 mm/s, and overlap rate of 50.40%. Under these conditions, the average error between the predicted and experimental results was only 4.14%. The results confirm that the optimized process ensures the formation of a molten pool while maintaining internal components within safety thresholds, validating the feasibility of this non-destructive repair method.

To synergistically enhance the strength and toughness of low-alloy cast steels, a quenching–partitioning–tempering (Q-P-T) heat treatment process was specifically performed based on the “Constrained Carbon Equilibrium” thermodynamic model. The effects of partitioning temperature on microstructure and mechanical properties were examined. The Q-P(210)-T approach successfully produced an ultra-high strength cast steel (48SiNiMnCrMoAl6-4-4-3-8-14) with a tensile strength exceeding 2000 MPa and an elongation greater than 19.0%. The microstructure of this cast steel consists of tempered martensite (TM), bainite, ferrite, and retained austenite (RA). During tensile deformation, dislocations from adjacent martensite are absorbed by the film-like RA, thereby alleviating stress concentration induced by dislocations. Meanwhile, the transformation-induced plasticity (TRIP) effect of the RA significantly enhances the toughness of the cast steel. Furthermore, the ultra-high strength of the cast steel is jointly ensured by the fine crystalline strengthening of the martensite and the precipitation strengthening of the transitional carbides in the microstructure of the cast steel. This work provides a good reference for the development of high-performance cast steels.

The revelation of the distribution of twin boundaries on three-dimensional (3D) grains is of critical importance for the comprehension of their influence on material properties. However, this remains a significant challenge in the field of 3D material characterization. In this study, the distribution of twin boundaries on the surfaces of 3D grains in solution-annealed 316L stainless steel was systematically and quantitatively characterized using 3D electron backscatter diffraction. The results show that the average size of twin boundaries is significantly larger than that of random boundaries (approximately 52% larger). Although the size distributions of grains, random boundaries, and twin boundaries, as well as the distributions of the total number of grain boundaries and the number of twin boundaries per grain, all conform to a lognormal distribution, the area fraction of twin boundaries on grain surfaces exhibits a typical Lorentz distribution, while their number fraction shows no clear pattern. On average, each grain possesses 9.6 boundaries, of which 1.7 are twin boundaries, and the average area coverage of twin boundaries on grain surfaces reaches 38.4%. The findings offer a 3D statistical foundation for optimizing grain boundary engineering strategies in austenitic alloys.