Dayang Welding Materials Lecture Hall | Take you to understand welding defects-welding slag
Before, we have learned the knowledge of welding cracks and porosity. Today, we lead you to understand the welding slag in welding defects.
What is welding slag?
Welding slag is divided into two categories. The first category is metal slag inclusions, specifically referring to metal particles such as tungsten and copper remaining in the weld, which is traditionally referred to as tungsten and copper inclusions. The slag in the slag includes electrode coating or flux, sulfide, oxide and nitride. According to its formation, it can be divided into point slag inclusion, linear slag inclusion, chain slag inclusion and dense slag inclusion.
Slag inclusion will reduce the plasticity and toughness of the weld. Slag inclusions with sharp corners will produce stress concentration at the tip, and the tip will also develop as a source of cracks, especially in welds with a large tendency to air quenching. Under the stress of the casting, cracks will first appear in the weld slag and spread along, resulting in a decrease in strength and cracking of the weld.
There are many factors for the formation of welding slag. If there are many inclusions in the welding material (including base metal, gas and welding material, etc.), it will inevitably cause inclusions in the weld; in addition, the process factors also have a great influence on the welding slag .
01.The slag on the edge of the weldment, between the welding layer and the weld bead has not been removed.
Especially with alkaline electrodes, if the slag is not removed, it is more likely to produce slag inclusions;
02.Welding current is too small
Insufficient heat is obtained from molten metal and slag, which reduces its fluidity, and the molten metal solidifies quickly, and the slag does not have time to float out.
03.Improper chemical composition of base metal and welding material
For example, when there are many components such as oxygen, nitrogen, and sulfur in the molten pool, its products (oxides, nitrides, sulfides, etc.) will remain in the weld seam if the molten metal solidifies faster and does not have time to float out Slag.
An important aspect of preventing inclusions in the weld is the correct selection of welding consumables to better deoxidize and desulfurize, followed by attention to process measures.
01. Welding consumables with good process performance are used, and it is forbidden to use consumables that have expired, deteriorated and have defective appearance;
02.Before welding, clean the rust, oil and other harmful impurities in the welding area. The angle of the groove should not be too small. The slag in the groove and on both sides and between layers must be cleaned.
03.Choose reasonable welding process parameters through welding process evaluation, and select electrodes of appropriate diameter according to the thickness of the plate; according to the direction of slag flow, adjust the electrode angle and the method of transport at any time, so that the slag can smoothly float to the surface of the molten pool.
All right,
That's all for today's lecture.
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