Factors affecting welding thermal cycle

Welding thermal cycle refers to the process that the temperature of a certain point on the edge of the tube changes over time under the action of the heat source generated by the high-frequency welding current. The welding thermal cycle reflects the thermal effect of the welding heat source on the weld and nearby metals, resulting in structure and performance At the same time, it also provides a way to find a good welding process, improve the weld structure and predict the weld stress through technological means.

Factors affecting welding thermal cycle

1. Welding process and heat input, under the premise that other conditions are stable and the input welding heat (power) is unchanged, the welding speed is fast, the heating time is short, the heating width is narrow, and the cooling is fast; the opposite is true when the welding speed is slow.

The heat input can comprehensively reflect the influence of welding current, welding voltage, welding speed, extrusion force, welded pipe variety, operation quality, etc. on the weld. When the heat input increases, the heat-affected zone becomes wider and the heating time becomes longer. The oxidized zone at the edge of the billet becomes wider and the cooling strength increases, which is detrimental to the quality of the weld. Similarly, when the welding heat input decreases, the heating range and heat-affected zone become narrower, and the heating time is shortened, which also affects the quality of the weld. 

2. Welded pipe specifications. An important feature of high-frequency welding current is the skin effect. It uses the tube blank as the loop. When the tube to be welded is large and thick, the longer loop and the longer heat transfer path are required. Consuming energy, causing other parts of the tube to heat up, which leads to an increase in linear energy and affects the thermal cycle.

3. The induction coil and the magnetic rod, the induction coil and the welded pipe are tightly coupled, that is, the gap between the induction coil and the welded pipe is small, the number of turns is matched, the skin effect and proximity effect of the edge induction of the tube blank are strong, and the edge of the tube blank receives more High-frequency current, thereby increasing the active power of the line energy. The function of the magnetic rod is to concentrate as much induced current as possible on the two edges of the blank to be welded, thereby increasing the efficiency of the welding energy. In this way, the completion of the welding only seems to be low but Effective line energy, on the contrary, if the induction coil is large, the magnetic rod is small, and the magnetic permeability is low, more welding current will be lost in the tube body, and less current will be collected to the edge to be welded. The energy of the characterizing line is large, but The actual energy used for welding is not much, which affects the thermal cycle of the tube body.

4. The forming quality of the formed tube blank. The high-quality formed tube blank can ensure the parallel butt joint of the edges to be welded, so as to achieve high-quality welding with lower heat input. If the edges to be welded are V-shaped butt joints, the inner and outer opening angles The shape will increase and decrease the welding heat, and the thermal cycle curve of the welded pipe will also change accordingly.

5. Opening angle, the opening angle is large, the proximity effect of high-frequency current is weak, the time for the tube blank to reach the welding temperature will be longer, the heating zone will become wider, and the line energy will increase; on the contrary, the opening angle is small, the current proximity effect is strong, and the welding edge The heating zone is narrow and the required heat input is small, which in turn changes the thermal cycle of the welded pipe. In addition, the welding extrusion force and the chemical composition of the tube blank will affect the actual effect of the heat input and the welding heat cycle.

Tips: the ASTM A500 specification covers cold-formed welded and seamless carbon steel tubing in round, square, rectangular, and “special” shapes for welded, riveted, or bolted construction applications, as well as for general structural purposes.


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