Ferritic Stainless Steel Seamless Pipe Welding And Post-weld Heat Treatment Process
1. For ordinary ferritic stainless seamless steel pipe, manual electrode arc welding can be used. Welding methods such as gas shielded welding and plasma arc welding. For specific welding, a small heat input should be used, and a small level of welding should be used to reduce the excessive growth of welds and HAZ grains and the precipitation of C and N compounds, causing joint embrittlement and intergranular corrosion.
2. Preheating before welding
Welding with the same kind of welding consumables, stainless steel seamless pipe wall thickness ≤ 6mm can not preheat, when it is more than 6mm, in order to prevent cold cracking caused by embrittlement, it is necessary to preheat 100-250 °C to make the welded structure in good condition and reduce welded joints. Contraction stress. As the Cr content of the ferritic stainless steel tube increases, the preheating temperature should be increased in an appropriate amount.
3. Post-weld heat treatment
Ferritic stainless steel seamless pipe with the same material welded joint, usually after 700-800 °C post-weld heat treatment, the holding time depends on the thickness of the stainless steel pipe wall, from a few minutes (thin wall pipe) to several hours (thick wall pipe) . The purpose of post-weld heat treatment is to improve the joint corrosion resistance and joint plasticity, but after heat treatment, avoid slow cooling below 600 °C (especially stainless steel thick-walled pipe), prevent 470 °C embrittlement, and spray water cooling if necessary. Generally, ferritic stainless steel pipe welding is not commonly used.
The welding of austenitic stainless steel seamless pipe welding materials usually does not require preheating and post-weld heat treatment, but the embrittlement and intergranular corrosion caused by the precipitation of HAZ coarse grains and CN compounds cannot be eliminated. Welding of high-purity ferritic stainless steel pipes. Manufacturers use GTAW, GMAW, PAW and other gas-shielded welding methods for welding. The following measures should be taken in the welding process;
Increase the protection of the molten pool. If double-layer gas protection is used to increase the nozzle diameter, increase the flow rate of argon gas properly. When filling the welding wire, prevent the high temperature end of the welding wire from leaving the protection zone.
Additional drag masks add extra-gas protection, which is especially important for multi-layer soldering. The back of the weld is protected by argon. It is best to use a water-cooled copper pad with argon to increase the cooling rate to reduce overheating. Minimize the welding heat input. When multi-layer multi-pass welding, the temperature between the control layers is lower than 100 °C.