1. Galvanized square pipes and fixtures should remove foreign matter such as oil, residual salt and paint before heat treatment.
2. The fixture used in the vacuum furnace for the first time should be degassed and purified in advance under the vacuum required by the workpiece.
3. Workpieces that are easily deformed during heat treatment should be heated on a special fixture. The preheating method is as follows: the primary preheating is 800℃, the secondary preheating is 500-550℃ and 850℃, and the primary preheating speed should be limited.
4. For workpieces with complex shapes or large cross-section changes and large effective thicknesses, preheating should be performed.
5. Workpieces with grooves and no through holes, castings, and welds, as well as processed and formed stainless steel workpieces, are generally not suitable for heating in a salt bath furnace.
6. The galvanized square pipes should be heated for a sufficient holding time, which can be multiplied by the effective thickness of the workpiece and the conditional thickness of the workpiece (the actual thickness multiplied by the shape factor of the workpiece).
7. After quenching and cooling to room temperature, the martensitic stainless steel and heat-resistant steel galvanized square pipes can be cleaned, low temperature treated or tempered. The interval between welding and subsequent heat treatment should not exceed 4 hours.
8. According to the requirements and surface conditions of galvanized square pipes, use alkali cleaning, water-soluble cleaning agents, chlorine solvent blasting, and shot peening to clean.
9. After rectification, stress relief annealing should be performed at a temperature below the original tempering temperature. Workpieces with complex shapes or strict dimensions are required. After rectification, the workpiece should be corrected by fixtures and tempering.
10. When the mechanical properties of the galvanized square tube can not reach the standard, the heat treatment can be repeated, but the number of repeated quenching or solid solution usually does not exceed two times. Supplementary tempering of galvanized square tubes is not considered a repeated treatment. Martensitic stainless steel and heat-resistant steel workpieces after quenching or low-temperature tempering should be preheated, annealed or tempered at high temperature before repeated quenching.
