Biao Guo

To address incomplete die filling, high cracking tendency, and severe die wear in the conventional forging of AISI-410 martensitic stainless steel U-shaped forgings, an optimized billet volume pre-allocation strategy was proposed. Two improved forging schemes for the U-shaped forgings were designed: the Arc Concave Flattening Scheme (adding arc-shaped concave features to the flattening die for corner volume compensation) and Preformed Volume Allocation Scheme (incorporating a preforming step for strategic volume pre-allocation at ends and corners). Finite Element Analysis employing the Oyane damage model and Archard wear model was employed to simulate and optimize the forging process. The optimal scheme was applied to production trials. The results demonstrated that the Preformed Volume Allocation Scheme significantly improved the geometric compatibility between the billets and the final forging die cavity. As a result, the billet’s temperature, strain, and equivalent stress uniformity increased, reducing cracking tendency. Moreover, the rise in the mitigated temperature and stress concentration resulted in reduced final forging die wear. Production trials confirmed a qualified rate of ~96% (34% higher than the Original Scheme). The final forging die service life reached 300 pieces per refurbishment cycle, showing a 50% improvement. This work provides theoretical and practical guidance for optimizing the forging processes of complex martensitic stainless steel components.

The carbothermic reduction of calcined magnesite in vacuum was studied. By thermodynamic analysis, the starting temperature of reduction reaction dropped from 2173K to 1523K when system pressure dropped from 1 atmosphere to 100 Pa. The experiments were carried out at different conditions under 10~100 Pa and the experimental results shown that the reduction extent of MgO improved by increasing the reaction temperature and time, the pellet forming pressure as well as adding fluoride as catalyst. The rate-determining step of carbothermic reduction process was gas diffusion with the apparent activation energy of 241.19~278.56 kJ/mol.

Combining Gleeble hot compression and tensile tests with finite‐element (FE) simulations, this study delivers a robust assessment of the elevated temperature damage and cracking of AISI 410 martensitic stainless steel. The effects of hot deformation parameters on the macroscopic flow and deformation behaviors as well as microscopic damage and fracture characteristics are discussed, determining the critical damage values with the aid of FE calculations. Furthermore, a novel critical damage value model is proposed using the Zener–Hollomon parameter to establish the normalized Oyane fracture criterion coupling hot deformation parameters. The results reveal that the flow stress and tensile load both increase, as the strain rate increases and the temperature decreases and vice versa. The occurrence of localized necking and internal damage cracking causes the tensile load to decline drastically. The hot deformation parameters manipulate not only the plat and dimple fractures, each caused by intergranular and transgranular fractures, but also the internal damage cracking before the final fracture. The established criterion predicts outcomes in good agreement with experimental results. This work provides essential information and a model for the cracking prediction of AISI 410 steel at elevated temperatures, helping to derive a rational hot forming design to prevent cracking.