Precautions for Heat Treatment of Square Tubes
Date:2022-03-25View:512Tags:Square Tube,Heat Treatment
Square tube is a kind of hollow square section steel pipe with square cross-section shape and size, which is made of hot-rolled or cold-rolled galvanized strip steel or galvanized coil as blank, cold-bending, and then high-frequency welding. What precautions should be taken when the square tube is heat treated?
The square tube and fixture should be cleaned of foreign objects such as oil, residual salt, paint, etc. before heat treatment. The fixture used in the vacuum furnace should be degassed and purified in advance under the vacuum degree not lower than that required by the workpiece.
Workpieces that are easily deformed during heat treatment should be heated on a special fixture. The method of preheating has a preheating of 800 °C, a second preheating of 500-550 °C and 850 °C, and the speed of temperature increase in the first preheating should be limited.
For workpieces with complex shapes or sharp changes in cross-section and large effective thickness, preheating should be performed. Workpieces with grooves and non-through holes, castings and welded parts, and processed stainless steel workpieces are generally not suitable for heating in a salt bath furnace.
The square tube heating should have sufficient holding time, which can be based on the effective thickness of the workpiece and the thickness of the conditions. The square tube can be cleaned, cryogenically treated or tempered after it has been quenched and cooled to room temperature. The time interval between welding and subsequent heat treatment should not exceed 4 hours.
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 a setting fixture combined with tempering for correction; when the mechanical properties of the square tube are unqualified, the heat treatment can be repeated, but the number of repeated quenching or solid solution generally does not exceed two times; the supplementary tempering of the square tube is not regarded as repeated treatment; the martensitic stainless steel and heat-resistant steel workpieces in the quenched state or after low temperature tempering should be pre-treated before repeated quenching. Hot, annealed or high temperature tempered.
Linkedin
