As the weight and size of forgings required for steel, energy, and petrochemicals increase, the weight of steel ingots continues to increase, and it becomes more difficult to prevent or reduce metallurgical defects inside the ingots. On the other hand, due to the increase in the weight of steel ingots, the tonnage of hydraulic presses is relatively reduced, and the quality standards for forgings are constantly increasing. Using the traditional upsetting and lengthening process to break the cast structure inside the steel ingot and repair the internal metallurgical defects can not meet the quality requirements of forgings. Stretching and upsetting are the two most widely used steps in forging for large forgings. Compared with upsetting, the length of the deformed part of the billet is small, the amount of deformation is large, and the stress in the defect area is high; Organization, the main steps to repair metallurgical defects. The following describes a new forging process for large forgings: a new process for concave anvils.
During the forging deformation process, due to the influence of friction and temperature gradient, there is always a large or small hard-to-deform area near the contact area of ​​the tool and the forging blank. The size and shape of the difficult-to-deformation zone have an important influence on the deformation distribution and stress state inside the forging, thus affecting the quality of the forging. When lengthening, there is a difficult deformation zone near the contact area between the anvil and the forging blank, and its pressing direction is perpendicular to the axis. Since the metallurgical defect of the ingot exists along the axis, in the lengthening step, it should be in the area near the axis. The formation of large deformation and good stress state is beneficial to the repair of metallurgical defects of steel ingots. There is a difficult deformation zone in the contact area between the forging blank and the anvil. It conforms to the deformation characteristic requirement of the lengthening step. From the perspective of deformation, when there is a difficult deformation zone in the contact area between the forging blank and the anvil, the core region is deformed. The amount is inevitably large; from the perspective of stress, in the lengthening step, due to the existence of the rigid-end constraint, when the flow velocity of the metal at the core is large, in order to maintain the continuity of the deformed body, the upper and lower two difficult-to-deform regions must pass through the metal near the axis of the rigid end. The flow causes a large axial compressive stress at the core. Therefore, the presence of a difficult deformation zone in the contact area between the forging blank and the anvil is advantageous for repairing the metallurgical defects of the steel ingot, and the larger the difficult deformation zone, the more obvious the effect. According to the above analysis, the bottom plane of the anvil is changed to a slightly concave surface in the middle, which can increase the hard deformation zone at the bottom of the anvil. The bottom surface of the anvil is a process of lengthening a concave curved surface, which is called a concave anvil. Studies have shown that the length of the concave anvil is better than that of the ordinary anvil in terms of loose compaction and void volume closure. Compared with other special forging methods, the concave anvil has the advantages of convenient application and wide application range.
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