Heating specification and forging of austenitic stainless steel forgings

2019-03-29 10:29:48 6

The austenitic stainless steel forgings have no isomorphous transformation during heating, and the heating temperature is too high, and the crystal grains grow vigorously. In addition, the α phase in the duplex stainless steel also increases. Tests on lCrl8Ni9Ti stainless steel show that the number of α phase increases rapidly after the heating temperature exceeds 1200 °C. Therefore, the initial forging temperature of austenitic stainless steel should not exceed 1200 °C.


Except for austenitic stainless steel stabilized with elements such as titanium and niobium and austenitic stainless steel with particularly low carbon content, the final forging temperature of other austenitic stainless steels should be higher than the sensitization temperature (this temperature is 815 °C). ~480 ° C, at this temperature, there will be chromium carbide precipitation along the grain boundary), the final forging temperature of the first two steels can not be too low, too low deformation resistance, and slow cooling in the 700 ° C ~ 900 ° C interval The α phase is precipitated and is easily cracked during forging, so the final forging temperature is generally 900 °C.

 

If austenitic stainless steel is carburized, it will cause the formation of niobium carbide, which will make the austenite grain boundary lean in chromium and reduce its intergranular corrosion resistance. Therefore, this kind of steel should avoid contact with carbon when heating, and it can not be reduced. Atmosphere; after forging, it should be chilled by sensitizing the Nirvana to avoid precipitation of excess phase and reduce corrosion resistance. In order to improve the corrosion resistance, the carbide precipitated during the deformation and cooling process of the forging is dissolved into the austenite, and the solution treatment should also be carried out.


Forging operation requirements: 1. Regardless of the surface defects of the ingot or forged billet (when the specified value is exceeded), it must be removed by stripping or other erasing methods before heating, otherwise it will be enlarged in the forging, resulting in the scrapping of the stainless steel forgings; When forging ingots, the cast structure has segregation and coarse columnar crystals and carbides. At the beginning, it is lightly hit with a small amount of deformation, and then hit hard after plastic lifting. When pulling out, it should be inverted and fed into the blank in the axial direction to avoid repeated hammering at the same position; 3. Select the appropriate forging ratio, 6~8 for forging ingots; The material can be selected from 4 to 6; in general, the forging ratio is ≥ 2; 4. The selection of equipment tonnage is one level larger than that of ordinary steel to overcome the high deformation resistance and achieve the purpose of forging and refining the grain; The amount of deformation at the final forging temperature is not allowed to be within the critical deformation range to avoid coarse grain.