As the heat treatment temperature increases, the diffusion speed of carbon elements from the carbon steel side to the
stainless steel plate side at the interface will increase. The longer the heat treatment time is, the more serious the migration of carbon elements will be, resulting in formation of Ferrite decarburization layer, thereby reducing the strength of the material, and the side of the stainless steel plate will become harder and brittle due to carburization, weakening the impact toughness, and becoming a hidden danger of welded joint failure.
Clad stainless steel plate should minimize post-weld heat treatment. When post-weld heat treatment is required, it is necessary to prevent the precipitation of chromium carbides and the formation of α-phase in the base metal of the clad stainless steel plate and the welded joint as much as possible. The holding time of heat treatment after welding should be determined according to the total thickness of the clad stainless steel plate. The welded components of the clad stainless steel plate to be heat treated need to be welded at the base, and the internal and external quality of the weld should be tested before heat treatment, and the temperature should not exceed 400 °C, and the holding time can be slightly extended at this temperature. Proper post-weld heat treatment at this temperature can reduce the residual stress by about 40%, and it will not affect the corrosion resistance of the cladding stainless steel plate, and the carbon element diffusion between the cladding and the base layer is not suitable. After the heat treatment, the isolation layer and the cladding stainless steel plate can be welded. After the cladding stainless steel plate is welded, no heat treatment is required.
The following are the matters needing attention when the clad stainless steel plate is heat treated.
First, if the cladding is made of 06Cr13 composite stainless steel plate pressure vessel, when austenitic stainless steel welding consumables are used to weld the cladding and the base material, post-weld heat treatment cannot be required, and post-weld heat treatment can be avoided. Otherwise, post-weld heat treatment should be done according to the cladding material requirements.
The post-weld heat treatment of composite stainless steel pressure vessels whose secondary cladding is not 06Cr13 needs to be carried out according to the requirements of the base material. If the composite stainless steel pressure vessel whose cladding layer is surfacing metal needs to undergo post-weld heat treatment, it must be done after surfacing cladding.
