What is welding slag inclusion?
Welding slag inclusions are generally divided into two categories. The first category is metal slag inclusion, which refers to the residual metal particles such as tungsten and copper in the weld, which is customarily called tungsten inclusion and copper inclusion; the second category is non-metallic slag inclusion, which specifically refers to the residual metal particles in the weld after welding. The slag, including electrode coating or flux, sulfides, oxides and nitrides, etc. According to its formation, it can be divided into point slag inclusions, linear slag inclusions, chain slag inclusions and dense slag inclusions.
Slag inclusion will reduce the plasticity and toughness of the weld, and the slag inclusion with sharp corners will cause stress concentration at the tip, and the tip will also develop into a crack source, especially in welds with a high tendency to air quenching. Under the stress of the casting, cracks will first appear at the slag inclusions in the weld and spread along, resulting in a decrease in strength and cracking of the weld.
There are many factors for the formation of welding slag inclusions. If there are many inclusions in the welding materials (including base metal, gas and welding materials, etc.), it will inevitably cause inclusions in the weld; in addition, technological factors also have a great impact on welding slag inclusions .
01.The slag between the edges of the weldment, the weld layer and the weld bead is not cleaned.
Especially with alkaline electrodes, if the slag is not removed, it is more likely to produce slag inclusions;
02.Welding current is too low
The heat obtained by melting the metal and the slag is insufficient, which reduces its fluidity, and the molten metal solidifies quickly, and the slag does not have time to surface.
03.Improper chemical composition of base metal and welding consumables
For example, when the molten pool contains a lot of oxygen, nitrogen, sulfur and other components, its products (oxides, nitrides, sulfides, etc.) will remain in the weld when the molten metal solidifies quickly, and will remain in the weld. Slag.
An important aspect of preventing inclusions in welds is the correct selection of welding materials, better deoxidation, desulfurization, etc., followed by attention to process measures.
1. Use welding consumables with good process performance, and prohibit the use of expired, deteriorated and defective welding consumables;
2. Before welding, clean up rust, oil stains and other harmful impurities in the welding area. The angle of the groove should not be too small, and the slag in the groove and on both sides and between layers must be cleaned up.
3. Select reasonable welding process parameters through the welding process evaluation, and select the appropriate diameter electrode according to the thickness of the plate; according to the direction of slag flow, adjust the angle of the electrode and the method of transportation at any time, so that the slag can smoothly float to the surface of the molten pool.
