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Slag inclusion
Slag remaining in the weld during welding
There are massive or dispersed non-metallic slag inclusions in the weld, and there are particles different from the collective metal composition inside or on the surface of the casting. Above the molten metal before pouring
scum
There is no cleaning, the slag is not good when pouring, and the scum enters the casting mold with the metal liquid;
Gating system
The design is not reasonable, the slag blocking effect is poor, and the slag entering the pouring system directly enters
cavity
Without being expelled.
- Chinese name
- Slag inclusion
- Foreign name
- Slag
- exegesis
- Residual in the weld during welding slag
- Principal body
- Welds, castings
- Formation reason
- Current size, fracture design and processing
- Shadow resonance
- Reduce the plasticity and toughness of the weld
Slag inclusion
The welding current is too small to
Liquid metal
It's indistinguishable from the slag. The welding speed is too fast, so that the slag can not float. Multilayer welding. The floors are not clean.
Weld form factor
Too small and electrode arc welding electrode Angle is not correct.
In addition, the operation technology is not skilled, improper selection of welding rods,
groove
Improper design and processing, the diameter of the electrode is thick, the welding area is not polished clean, the electrode coating penetrates into the weld metal, the slag is not cleaned when welding in multiple layers, and the chemical composition of the welding material and the base material is not properly matched.
[1]
(1) The slag between the edge of the welding part, the welding layer and the welding pass is not cleared. Especially use
Basic electrode
If the slag is not removed, it is easier to produce slag inclusion.
(2) The welding current is too small, the heat obtained by melting metal and slag is insufficient, so that its fluidity is reduced, and the melting metal solidification speed is fast, and the slag is too late to emerge.
(3) When welding, the Angle of the electrode and the method of transporting the electrode are inappropriate, the slag and hot metal are not clear, and the slag and the molten metal are mixed together, which hinders the floating of the slag.
(4) Improper chemical composition of base metals and welding materials. For example, when the molten pool contains more oxygen, nitrogen, sulfur and other components, the products (oxides, nitrides, sulfides, etc.) in the case of faster solidification of the molten metal, it will remain in the weld to form slag inclusion.
Rust and oil should be cleaned within 120mm of the welding area before welding. Use the welding rod with good process performance, and prohibit the use of expired, deteriorated and cracked electrode. The Angle of the groove should not be too small, and the slag in and on both sides of the groove and between the layers must be cleaned. When selecting welding parameters, the current should not be too small, and the welding speed should not be too fast. Adjust the electrode Angle and swing Angle at any time during welding.
When casting, the pouring system should make the metal liquid flow smoothly, and set the slag collecting device; Reduce sulfur content in liquid metal as much as possible; Try to increase the temperature of molten metal; Ladle to keep clean, use teapot type
Pouring ladle
; Slag removal agents can be added before pouring, such as straw ash,
cryolite
Let's wait.
[2]
weldment
The electrode with good desagging property should be selected. Clean up the slag between layers carefully; Reasonable selection of welding process parameters; Adjust the Angle of the electrode and the method of transporting the electrode. Control the current size and energizing time, using the appropriate diameter of the electrode; Replace the flux or add a certain proportion of fluorite to increase the fluidity of the slag; At the same time, increase the top pressure appropriately.
(1) Carefully remove the rust and slag between the welding layer, and flatten the pits before welding.
(2) Select the electrode with good process performance, select the appropriate welding current, and slow down the welding speed. Increasing welding current can improve the condition of slag emergence and prevent slag inclusion.
(3) Pay attention to the direction of slag flow, adjust the electrode Angle and transport method at any time, so that the slag can float smoothly to the surface of the molten pool.
(4) Adjust the chemical composition of the electrode coating or flux to reduce the melting point and viscosity of the slag to help prevent the generation of slag inclusion.
[3]
In the use of protective casting, the root cause of slag inclusion is due to the instability of the liquid level of the mold. Therefore, the depth of the nozzle insertion is not appropriate, and the sudden change of pulling speed will cause
crystallizer
Liquid level fluctuation, in severe cases resulting in slag inclusion. In terms of its slag inclusion content, there are unmelted powdery protective slag, and there are floating Al that has not been absorbed by liquid slag
2
0
3
Inclusions, and high viscosity protective slag that absorbs and dissolves excess Al, etc.
(1) Ensure the stability of the liquid surface. Liquid level fluctuation should be as small as possible (≤±5mm). For this reason, cesium source type (Cs137) crystallizer liquid level is used in the steelmaking plant
Automatic control system
The fluctuation of the liquid level of the mold is controlled within ±2mm to ensure the stability of the liquid level of the mold. At the same time, the automatic protection slag system is adopted to add the protection slag regularly and quantitatively, and ensure the uniformity of the protection slag.
(2) Warranty
Immersion nozzle
Appropriate immersion depth. The immersion depth should be 100 ~ 150mm. Most tundish in steelmaking plant is deformed to some extent due to its long service time. At the same time, after the transformation of the intermediate car, the height increases, resulting in the original 580mm long immersion nozzle can not meet the requirements of the immersion depth of 100 ~ 150mm, the actual immersion depth is only 50 ~ 80mm, and the phenomenon of the liquid surface of the mold often occurs in use, increasing the incidence of slag inclusion on the surface of the casting billet. After measuring the distance between the bottom of the middle bag and the mold, the length of the immersion nozzle is increased to 640mm, which ensures that the immersion depth of the water nozzle is within a reasonable range, and the liquid surface of the mold is no longer billowing.
(3) The viscosity of the slag is one of the important properties that determine the consumption and uniform penetration. In order to improve uniform heat transfer and good lubrication at high drawing speed, maintain sufficient thickness of liquid slag layer and protection slag consumption, measures should be taken to reduce viscosity. However, too low viscosity of the slag will reduce the anti-mixing ability of the slag and increase the probability of slag rolling. Therefore, the viscosity of the protective slag should be appropriately increased to ensure that the thickness of the liquid slag layer is 8 ~ 12mm to avoid the involvement of unmelted slag in the billet shell under the condition of ensuring that the protective slag can flow smoothly into the mold and the continuous slag film is formed between the casting blank and the mold.
[4]
1) After arc initiation of vertical fillet welding, if the long arc enters the welding spot to preheat, and the welding forms external expansion difficulties, the current should be appropriately increased at this time. Cardinal point
Molten pool
After the formation, when the arc stays on one side, the slag should emerge from the other side under the purging of the arc to form the molten pool of the flash metal liquid. Then slightly laterally arc (see Figure 2-91) so that the liquid metal level extends from side A to side B. When the arc reaches the B side, the slag should quickly emerge from the A side. If the arc arc stays from one side, the slag can not mostly emerge from the other side, because the welding current is too small, the melting pool temperature is low, and the arc residence time is short. This will lead to the formation of a thin pool, weld formation is too wide.
Figure 2-91
3) If both sides of the surface forming weld are deep grooves when the first layer is welded, the arc purging when the weld pool is formed for the second layer of vertical fillet welding should make the weld pool rapidly form outward expansion, and make the weld pool and the inner surface slightly bite marks. In this way, the slag at the root melting point of the second layer welding pool can emerge quickly. If the outer expansion surface of the second layer welding pool is small and there is no fusion trace between the molten pool and the bottom weld, it will inevitably lead to strip or local point slag inclusion on both sides of the molten pool.
4) In order to avoid slag inclusion deficiency in vertical fillet welding, it is necessary to increase the current appropriately and extend the time for the arc to stay on both sides of the molten pool, so that the molten pool forms a clear surface of the flash metal liquid and then make a rapid transverse arc action.
[5]
