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The welding defects - slag inclusion

By Thomas Huang April 19th, 2024 93 views

I, What is slag inclusion


The defective of having slag in the weld is called slag inclusion.

slag inclusion diagrammatic sketch Sample of slag inclusion weld

II  Hazardous 


Slag inclusion will reduce the plasticity and toughness of the weld; its sharp corners often cause stress concentration, especially in the weld with a large tendency to air quenching, sharp corners often form cracks.

III Causes and preventions


Welding method Causes Prevention measures
Manual arc welding (1)The previous welding slag was not completely removed.
(2)The welding current is too low.
(3)The welding speed is too slow.
(4)Electrode swing too wide.
(5)Poor weld combination and design.
(1)Thoroughly remove the welding slag from the front layer.
(2)Use higher current.
(3)Increase welding speed.
(4)Reduce electrode swing width.
(5)Correct groove angle and clearance.
CO2 gas arc welding (1)The base metal tilts (downhill) to advance the slag.
(2)After the previous welding, the welding slag is not clean.
(3)Too little current, too slow speed, too much welding.
(4)When welding with advance method, the welding slag in groove is ahead too much.
(1)Position weldments as horizontal as possible.
(2)Pay attention to the cleanliness of each weld bead.
(3)Increase current and welding speed to make slag float easily.
(4)Increase welding speed
Submerged arc welding (1)The welding direction is inclined toward the base metal, so the slag flow is advanced.
(2)In multi layer welding, the groove surface is dissolved by welding wire, and the welding wire is too close to the groove side.
(3)Slag inclusion is easy to occur at the welding starting point where there is a guide plate.
(4)Current is too small, the second layer between welding slag retention, easy to produce cracks in the welding sheet.
(5)Too low welding speed leads to slag advance.
(6)The high arc voltage in the final finish layer causes free slag to curl up at the weld bead end.
(1)Change welding direction to opposite direction, or change base metal to horizontal direction as much as possible.
(2)The distance between groove side and welding wire shall be at least larger than welding wire diameter.
(3)Guide plate thickness and slot shape shall be the same as base metal.
(4)Increase welding current to melt residual slag easily.
(5)Increase welding current and welding speed.
(6)Reduce voltage or increase welding speed, change overlay from single pass welding to multi-pass welding if necessary.
self-shielded flux-cored wire (1)Arc voltage too low.
(2)Welding wire arc swing improper.
(3)The welding wire extends too far.
(4)Low current, slow welding speed.
(5)First weld slag, not fully removed.
(6)The first link is poorly integrated.
(7)The groove is too narrow.
(8)The weld slopes downward.
(1)Adjust appropriate voltage.
(2)Practice more.
(3)Operate as per welding wire usage instructions.
(4)Adjust welding parameters.
(5)Complete clearance 
(6) Use appropriate voltage, watch for arcing.
(7)Correct groove angle and clearance.
(8)Leveling out, or moving faster.
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