Satisfactory metallographic structure can be obtained by eliminating work hardening of stainless steel pipes. The process equipment is a bright annealing furnace, mainly used for heat treatment of stainless steel products in a protective atmosphere. When the performance requirements for stainless steel pipes vary, the requirements for the metallographic structure after bright annealing vary, so the process of bright heat treatment will also be different.

The typical heat treatment process for 300 series austenitic stainless steel is solution treatment. During the heating process, the carbide is dissolved in the austenitic stainless steel, heated to 1050~1150 ℃, and then held for a short period of time. The carbide can be completely dissolved in the austenitic structure, and then rapidly cooled to below 350 ℃. Supersaturation Solid solution, that is, uniform unidirectional austenitic structure, can be obtained. The focus of this heat treatment process is to achieve rapid cooling, which requires a cooling rate of 55 ℃/s and then quickly pass through the re precipitation temperature range (550-850 ℃) after carbide solid solution. In addition, the insulation time of stainless steel pipes should be as short as possible, otherwise it will cause coarse grains and affect the surface smoothness.

The heating temperature of 400 series ferritic stainless steel is relatively low (around 900 ℃), and slow cooling is largely used to obtain annealed and softened microstructure. The annealing method used for Martensitic stainless steel can also be treated by sectional quenching and tempering.

From the above introduction, it can be seen that there are significant differences in heat treatment processing between the 300 series and the 400 series. To obtain qualified metallographic structure, it is necessary to have a large margin for adjustment of the cooling section equipment of the bright annealing furnace. Therefore, currently advanced bright annealing furnaces often use strong convection cooling in their cooling section, and have three cooling sections that can adjust the air volume separately. Along the width direction of the strip steel, it is divided into three sections, and the cooling speed in the width direction of the strip steel is adjusted through air flow diversion to control the plate shape.

Another important issue in the heat treatment of cold rolled strip steel for stainless steel pipes is the requirement for the entire strip steel to have a uniform structure in both width and length. The muffle type bright annealing furnace uses large-sized muffle tubes, which evenly organize heating airflow spiral around the outside of the muffle tubes to evenly heat the strip steel. To ensure the uniform organization of the strip steel along the length direction, it is necessary to maintain the constant linear velocity of the stainless steel strip steel in the heating furnace. Therefore, both the front and rear of the current advanced vertical bright heat treatment furnace are equipped with precision adjustable roller tension adjustment devices. It not only needs to ensure that the inlet and outlet speed of the strip steel meets the requirements of heat treatment speed, without being affected by the empty or full loop quantity, but also needs to establish and precisely adjust the small tension of the strip steel according to the plate shape of the strip steel to meet the requirements of stainless steel plate shape.