Precautions for heat treatment of a500 rectangular tube

Posted by chase Liu on April 10th, 2023

A500 rectangular tube is a hollow square cross-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 a blank, which is formed by cold bending and then high-frequency welding. What precautions should be taken when a500 rectangular tube is heat treated?

A500 rectangular tube and fixtures should be cleaned of oil, residual salt, paint and other foreign matter before heat treatment. The fixtures used in the vacuum furnace should be degassed and purified in advance at a 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 is 800°C for the first preheating, 500-550°C and 850°C for the second preheating, and the temperature rising speed of the first preheating should be limited.

For workpieces with complex shapes or sharp changes in cross-section and large effective thickness, preheating should be carried out. Workpieces with grooves and non-through holes, castings and weldments, and processed stainless steel workpieces are generally not suitable for heating in a salt bath furnace.

A500 rectangular tube heating should have sufficient holding time, which can be based on the effective thickness and conditional thickness of the workpiece. After the a500 rectangular tube is quenched and cooled to room temperature, it can be cleaned, cryogenically treated or tempered. The time interval between welding and subsequent heat treatment should not exceed 4 hours.

After straightening, 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, use setting fixtures combined with tempering for correction after straightening. 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. Supplementary tempering of square tubes 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.