Double Group: Marine Forgings Provider

As one of the major suppliers of domestic marine forgings, Aozhong Group has formed a large-scale marine transmission system forging manufacturing system and a complete set of marine diesel forgings manufacturing system with 50-98 models. Therefore, the discussion on the manufacturing process of large forgings has practical significance.

The manufacturing process of large forgings is: 80t+60t electric furnace rough steel, 150t ladle furnace vacuum refining→vacuum casting process→forging→forging heat treatment. The quality of large forgings depends to a large extent on the quality of the ingots, and the quality of the ingots is the focus of control. Strict composition control must be used from smelting, and hydrogen, oxygen and other impurity elements are controlled under double vacuum. The whole process of monitoring the oxygen content in the molten steel, taking measures to timely and efficient rapid deoxidation, desulfurization, non-metallic inclusions denaturing treatment and fine adjustment of alloy composition. In addition, the cooling and heat transfer conditions of the molten steel in the ingot mold are very uneven, and the molten steel gradually condenses along the film wall toward the core and the bottom to the riser to select crystals, so as to form the crystal structure, chemical composition and inclusions of the steel ingot. The distribution is very uneven, and this degree of unevenness becomes more serious as the size of the ingot increases. Therefore, in the ingot casting, the cleanliness of the ingot mold, the vacuum degree of the vacuum chamber, the pouring temperature, and the casting speed are all strictly regulated to improve the crystallization conditions, and the operator must strictly perform it. Since the steel ingot used for large marine shaft forgings improves the purity of the molten steel during smelting, the adverse effects on subsequent processes are alleviated.

After hot-sending steel ingots to the hydraulic press workshop, it is ensured that the surface temperature is ≥550 °C to advance the furnace, which avoids the adverse effects caused by cold ingot heating and saves energy. The WHF method is used in the forging process, and the number of turns and the amount of reduction are specified. After the initial forging temperature, the strong forging by the WHF method creates a good hydrostatic stress state of the heart, completely improves the as-cast microstructure of the ingot, makes the dense inclusions diffusely distributed, and strictly controls the water and riser removal. Quantity, thus ensuring the effect of non-destructive testing.

After the large forging is finished with thermoplastic deformation, it is not directly cooled to room temperature by some cooling method, but is heat-sealed in a furnace of about 400-600 ° C. After the heat is kept, it is heated to the austenitizing temperature to complete the normalizing process. The microstructure of the steel before normalizing has a certain influence on the microstructure obtained by subsequent cooling. Therefore, before the normalizing after forging, the temperature is lowered by a large degree of subcooling to promote the transformation of the structure and reduce the precipitation of ferrite at the grain boundary. Probability. After a certain period of insulation, the austenite in the unstable state of the region can be used to fully complete the phase transformation process of the whole microstructure, reduce the existence of retained austenite structure, and transform the austenite transformation of normalizing. Control is also very important. In the case of normalizing cooling, the cooling by the blasting spray with strong cooling capacity will help to inhibit the growth of the flake ferrite and make the forging performance reach a more ideal index.