In actual production, most forgings are normalized and tempered in a hot charging furnace after forging. After forging, air-cooled forgings can only be normalized and tempered in a cold-loading furnace. The purpose of supercooling after normalizing is to reduce the core temperature of the forgings, make the temperature uniform after proper heat preservation, and also play a role in removing hydrogen. The subcooling temperature varies with different steel grades. Generally, the hot charging furnace is 350-400 °C or 400-450 °C, and the cold charging furnace is 300-450 °C.
In order to avoid high-temperature forgings from producing crude products, attention should also be paid to the coarse grains of high-temperature forgings during forging. The raw materials and all aspects of the forging process (including heating, deformation, mold, lubrication, operation, etc.) are related. Therefore, in order to ensure the forgings. The quality is stable, the process preparation should be detailed and correct, and the implementation process should be strict and accurate. Important forgings of high-temperature alloys should be die-forged even if they are produced in small quantities.
The recrystallization characteristics of different grades of high-temperature forgings are different. For example, the critical deformation degree of most superalloys is 3%-5%, while the GH135 alloy is 4%-6%, and the deformation degree of each part should exceed the above value during forging.
Due to the difference in the actual content of chemical components, the actual recrystallization temperature and the aggregation recrystallization temperature are often different for high-temperature forgings of the same spleen number with different smelting methods and different heat numbers. The influence of the forming elements carbon, molybdenum, titanium, etc. of strong carbides and intermetallic compounds is more obvious. For example, production and tests have proved that the optimum maximum heating temperature for GH33 alloys with different heat numbers and different smelting methods varies between 1070-U401C. Therefore, specific and effective measures should be taken according to the situation of each batch of materials.
The section size of large forgings is large and the production process is complicated. The following characteristics should be considered in the heat treatment: the microstructure and properties are very uneven; the grain size is uneven; there is large residual stress; some forgings are easy to wear and cause white spot defects.
Therefore, the task of heat treatment of large forgings, in addition to eliminating stress and reducing hardness, is mainly to prevent white spots from appearing in forgings; the second is to homogenize the chemical composition of forgings and adjust and refine the forging structure. Also, heat treatment of large forgings is usually carried out in combination with post-forging cooling.
Prevention of white spot treatment: When a large forging sensitive to white spot is subjected to post-forging cooling and heat treatment, white spots can be avoided if a large amount of hydrogen can be diffused out and the structural stress can be minimized at the same time.
Normalizing and tempering treatment: For large forgings with insensitive steel grades and ingots that have undergone vacuum treatment, since the forgings basically do not produce white spots, normalizing and tempering treatment is adopted after forging to refine the grains of the forgings. Evenly organized.
