What Should be Paid Attention to When Quenching Q345B Square Tube

In order to improve the surface hardness and wear resistance of the q345b square tube, it is necessary to perform surface treatment on the square tube, such as surface flame, high frequency surface quenching, chemical heat treatment, etc. Generally speaking, the heating temperature of most quenching on the surface of the square tube is 850-950 degrees; due to poor thermal conductivity, the heating speed should not be too fast, otherwise it will show melting cracks and quenching cracks. High-frequency quenching requires that the matrix is mainly pearlite after normalizing, and it is cooled by water spray or polyvinyl alcohol solution; the tempering temperature is 200-400 ℃, and the hardness is 40-50HRC, which can ensure the hardness and wear resistance of the surface of the square tube.

The following points should be paid attention to when quenching q345b square tube:

1) The slender tube should not be heated vertically in a salt bath furnace or a pit furnace, so as to reduce the deformation caused by its own net weight;

2) When heating pipes with different hollow sections in the same furnace, the small pipe should be placed on the outer end of the furnace, and the large pipe and the small pipe should be timed separately;

3) The amount of each charging should be adapted to the power level of the furnace. When the feeding amount is large, it is easy to pressurize and heat up, and the heating time needs to be prolonged;

4) The quenching temperature of the square tube quenched by water or salt water should be used as the lower limit, and the quenching temperature of oil or molten salt quenching should be used as the upper limit;

5) During dual medium quenching, the residence time in the first quenching medium should be controlled according to the above three methods, and the moving time from the first quenching medium to the second quenching medium should be as short as possible, preferably 0.5-2s .

6) Q345B 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 q345b square tube can be cleaned, cryogenically treated or tempered after being quenched and cooled to room temperature. The time interval between welding and subsequent heat treatment should not exceed 4 hours.

7) After correction, stress relief annealing should be performed at a temperature lower than the original tempering temperature. Workpieces with complex shapes or strict size requirements should be corrected with a setting fixture combined with tempering during tempering after correction. When the mechanical properties of the q345b square tube are unqualified, the heat treatment can be repeated, but the number of repeated quenching or solid solution generally does not exceed twice. Supplementary tempering of square tubes does not count as reprocessing. The martensitic stainless steel and heat-resistant steel workpieces in the quenched state or after low temperature tempering should be preheated, annealed or tempered at high temperature before repeated quenching.