NEWS

Austenitic stainless steel forgings are more difficult to forge than ordinary steel, but there are few surface defects. Most austenitic stainless steel forgings can be forged over a wide temperature range above 927°C. Since austenitic stainless steel forgings have no phase transformation in the high temperature range, the forging temperature is higher than that of martensitic stainless steel, but high chromium or low carbon stainless steel does not have the above properties, because when the temperature is higher than 1093 ℃, high chromium or low carbon stainless steel will produce different contents of ferrite according to the composition, which is harmful to forgeability.

Austenitic stainless steel forgings are more difficult to forge than ordinary steel, but there are few surface defects. Most austenitic stainless steel forgings can be forged over a wide temperature range above 927°C. Since austenitic stainless steel forgings have no phase transformation in the high temperature range, the forging temperature is higher than that of martensitic stainless steel, but high chromium or low carbon stainless steel does not have the above properties, because when the temperature is higher than 1093 ℃, high chromium or low carbon stainless steel will produce different contents of ferrite according to the composition, which is harmful to forgeability.

For austenitic stainless steel forgings, controlled forging is also important. Except for stable and ultra-low carbon stainless steels, the forging temperature of almost all austenitic stainless steels should be controlled above the sensitive temperature zone and quickly cooled to below 871°C. This is because austenitic stainless steel is prone to form hot cracks and phases at low temperatures.

Sulfur or selenium can improve the mechanical properties of austenitic stainless steels. The deleterious lath of selenium is unlikely to be present. The 06 Crl8NillTi(321) steel with titanium addition also has a segregated lath structure, which is easy to cause surface cracks during the forging process. 347 steel stabilized with cobalt is less prone to lath segregation and is therefore a stable steel suitable for forging.

When heating austenitic steel, the atmosphere in the furnace should be slightly oxidizing; decarburization atmosphere and peroxide atmosphere will produce harmful inclusions or poor chromium, thereby reducing the corrosion resistance of steel. 16 Cr23Nil3(309) and 20 Cr25Ni20(310) steel chromium deficiency is particularly serious.

(1) Forging process characteristics

18-8 austenitic stainless steel is commonly used in the manufacture of boiler and steam turbine parts that work for a long time below 610 ℃, as well as various parts in chemical production. Its forging process features:

① 18-8 austenitic stainless steel surface is easy to carburizing when heated in a coal furnace, so contact with carbon-containing substances should be avoided during the heating process, and heating with oxidizing medium should be used to reduce the carburizing of steel and prevent intergranular corrosion.

When the thermal conductivity of austenitic steel is poor at low temperature, it should be heated slowly, and the initial forging temperature should not be too high. If it is too high, the S phase tends to be formed. At the same time, grains also grow rapidly, generally 1150~1180 ℃.

③ The surface defects of the blank must be removed before forging heating to prevent further expansion during the forging process, resulting in the scrap of the forging.

④ The forging temperature shall not be too low. At the same time, it will precipitate after slow cooling at 700-900°C, and cracks will appear if forging continues.

⑤ After forging, air cooling should be adopted, and solid solution treatment must be carried out.

(2) Forging temperature range

The initial forging temperature of austenitic stainless steel: generally not more than 1200 ℃; forging temperature: generally 825~850 ℃. The forging temperature is mainly limited by the carbide precipitation sensitive temperature (480~820 ℃). Once the forging temperature is within this temperature range, due to carbide precipitation, the deformation resistance will increase and the plasticity will decrease, resulting in forging cracking.