1. Galvanized pipes and fixtures should be cleaned of foreign objects such as oil, residual salt, paint, etc. before heat treatment;
2. The fixture used in the vacuum furnace for the first time should be degassed and purified in advance at a vacuum not lower than the required vacuum of the workpiece;
3. Workpieces that are easily deformed during heat treatment should be heated on special fixtures. The preheating methods are: the primary preheating is 800℃, the secondary preheating is 500-550℃ and 850℃, and the temperature rise rate of the primary preheating should be limited;
4. For workpieces with complex shapes or sharp changes in cross-section and large effective thickness, preheating should be carried out;
5. Workpieces with grooves but not through holes, castings and welded parts, and processed stainless steel workpieces are generally not suitable for heating in a salt bath furnace;
6. According to the effective thickness of the workpiece and the conditional thickness (the actual thickness is multiplied by the shape factor of the workpiece), the galvanized pipe should have enough heat preservation time for heating;
7. Martensitic stainless steel and heat-resistant galvanized steel pipes can be cleaned, cryogenically treated or tempered after being quenched to room temperature. The time interval between welding and subsequent heat treatment should not exceed 4 hours;
8. According to the requirements and surface conditions of the galvanized pipes, use alkaline washing, water-soluble cleaning agents, chlorine solvent sandblasting, shot blasting and other methods for cleaning;
9. After correction, stress relief annealing should be carried out at a temperature lower than the original tempering temperature. For workpieces with complex shapes or strict size requirements, after correction, use shaping fixtures combined with tempering for correction during tempering;
10. When the mechanical properties of the galvanized pipe are unqualified, repeated heat treatment can be carried out, but the number of repeated quenching or solid solution is generally not more than twice. Supplementary tempering of galvanized pipe is not counted as repeated treatment. Martensitic stainless steel and heat-resistant steel workpieces in the quenched state or after low-temperature tempering should be preheated, annealed or high-temperature tempered before repeated quenching.
