Stainless steel plate casting heat treatment process

After the stainless steel plate castings are cast and formed, they are generally heat treated. Since the casting grains before heat treatment are relatively coarse, the structure directionality is obvious, and the mechanical properties are also low, the heat treatment process is formulated according to the different requirements of the castings.

Generally, steel castings require annealing treatment, which softens and makes processing easier; those that require strength require normalizing treatment, and those that require hardness require quenching treatment; solution treatment enhances the corrosion resistance of stainless steel plates.

Cast stainless steel plates are usually austenitic and do not undergo phase transformation when heated, so they cannot be strengthened by heat treatment. Heat treatment can only be done to enhance the corrosion resistance of stainless steel plates. The purpose of solid solution treatment is to completely dissolve the carbides and retain them in austenite at room temperature, so as to obtain a single-phase austenite structure at room temperature and make the stainless steel plate The corrosion resistance reaches the highest level.

The heating temperature for solid solution treatment is usually relatively high, between 1050-1100°C, and is appropriately adjusted according to the carbon content. Because the thermal conductivity of 18-8 stainless steel plate is very weak, it not only needs to be preheated before quenching and heating, but also the heat preservation time during solution treatment (quenching and heating) needs to be long. During solid solution treatment, special attention should be paid to avoid carbonization. Carburization will increase the intergranular corrosion tendency of 18-8 stainless steel. Cooling medium, usually water. The structure after solution treatment is usually single-phase austenite, but stainless steel containing titanium, niobium, and molybdenum, especially when it is a casting, also contains a small amount of ferrite. The hardness after solution treatment is usually around 135HBS.

Tempering is also called matching fire. A type of metal heat treatment process. Metal heat treatment in which the quenched workpiece is reheated to an appropriate temperature below the lower critical temperature, kept warm for a period of time and then cooled in air, water, oil and other media. Or heat the quenched alloy workpiece to an appropriate temperature, keep it warm for a certain period of time, and then cool it slowly or quickly. It is usually used to reduce or eliminate internal stress in quenched steel parts, or reduce its hardness and strength to enhance its ductility or toughness. Low temperature tempering, medium temperature tempering or high temperature tempering can be used according to different requirements. Generally, as the tempering temperature increases, the hardness and strength decrease, and the ductility or toughness gradually increases.

The stainless steel plate workpiece has the following characteristics after quenching. First, it obtains unbalanced structures such as martensite, bainite, and retained austenite. Secondly, there is large internal stress. The third mechanical properties cannot meet the requirements. Therefore, stainless steel plate workpieces generally undergo tempering treatment after quenching.