Influence factors on anneal brightness of 304 stainless steel tube

The purpose of bright annealing furnace is mainly used for the heat treatment process of finished products under the condition of the protection of 304 stainless steel pipe material. When the performance requirements are different, the metallographic structure requirements after bright annealing are also different, so the process of bright heat treatment is also different.
The typical heat treatment process of 304 stainless steel tube is solid solution treatment, during the whole heating period, let carbides dissolve into austenite, when the heating temperature reaches 1050℃ ~ 1150℃, the appropriate heat preservation, and then let carbides dissolve in austenite, and then rapidly cool to 350℃ below, The supersaturated solid solution is uniform unidirectional austenite structure. The key of this process is rapid cooling, which requires a cooling rate of 55℃/s and a rapid precipitation temperature zone (550 ~ 850℃) after solid solution of carbide. The holding time is as short as possible, otherwise the coarse grain will affect the surface finish.
In order to obtain qualified metallographic structure, it is required that the cooling equipment of bright annealing furnace has a large adjustment space. Therefore, modern advanced bright annealing furnace, in the cooling section of 304 stainless steel pipe, usually adopts strong convection cooling, set up three cooling sections, can adjust the air volume separately.
Whether the annealing temperature reaches the specified temperature, the heat treatment process of 304 stainless steel tubes generally adopts solid solution heat treat-annealing, the temperature range is 1040 to 1120℃ (Japanese standard). It can also be observed through the observation hole in the annealing furnace. The 304 stainless steel tube in the annealing area should be incandescent, but there is no softening and sagging.
Annealing usually uses pure hydrogen as annealing, the purity should reach more than 99.99%, if the other part of the temperature is inert gas, the purity can be appropriately reduced.

Post time: May-13-2022