When the surface of 304 stainless steel strip is surfacing, due to the different metal properties of the surfacing layer, defects are prone to occur during surfacing, resulting in a decrease in the overall quality of the 304 stainless steel strip. What defects should we pay attention to during surfacing? How to solve the defect?
1. Slag inclusion
Slag inclusions are generally formed between tracks, and sometimes appear between layers. The main reason for the formation of slag inclusions in the weld bead is that the process performance of the flux is poor, resulting in too steep wetting angles on both sides of the weld bead of the deposited metal, and poor edge fusion. It is easy to appear slag inclusions between tracks. This defect can also occur if the welding is not standardized or the welding position is not correct.
Undercut mainly occurs in electroslag surfacing, especially when the 304 stainless steel strip is relatively wide. Due to the influence of the magnetic shrinkage effect, the surfacing layer has an undercut phenomenon. When the width of the 304 stainless steel strip increases , the surfacing current also increases, and the undercut phenomenon is more obvious.
If you want to solve the problem of undercut, you can add a magnetic field, and at the same time, arrange the position of the magnetic poles reasonably, choose a reasonable size of the excitation current, pay attention to control the magnetron current of the two magnetic poles, and the magnetic field cannot be too strong or too weak.
If the steel strip is non-preheated flat welding, and the range of the strip pole is 60mm × 0.5mm, the currents of the south and north poles controlled by the magnetron should be 1.5A and 3.5A respectively. If the range of the band pole is 90mm x 0.5mm, the currents at the south and north poles controlled by the magnetron should be 3A and 3.5A, respectively.
Cracks generally occur at the arc end, and sometimes in the weld bead. The surfacing layer cracks are mainly thermal cracks, which are caused by two reasons. First, the proportion of chromium and nickel in the deposited metal is not appropriate, resulting in too high or too low ferrite content in the surfacing metal. This is because the composition of the welding strip and the flux cannot be well matched. Second, the welding operation is not good. specification, the current is too large, which makes hot cracks appear during the surfacing process.
4. Not fused
The bonding surface or interlayer between the surfacing layer and the base metal is prone to lack of fusion. This is because the sintered flux is lighter in weight than the smelting flux surfacing, so its penetration depth is relatively small. During operation, once the operation is not standardized, or the parameters are not well grasped during welding, it is relatively easy to cause the defects of unfused or unfused between layers on the joint surface.
When 304 stainless steel strip is surfacing, if you want to prevent the occurrence of defects, you can take the following measures:
One is to strictly grind the base metal before surfacing to remove rust, oil stains, etc. on the material, because these stains will affect the quality of welding, and the material needs to be preheated.
The second is to control the thickness of the surfacing layer. When surfacing the transition layer, because the welding of dissimilar steels is used, it is easy to cause welding defects. Therefore, in order to ensure the quality of the surfacing welding, it is possible to ensure the preconditions for the formation of the weld bead. The thickness of the transition layer surfacing is reduced, and the general thickness is controlled at 3~3.5mm.
When surfacing the corrosion-resistant layer, because the same material is used for welding, it is not easy to cause welding defects. In the case of ensuring the formation of the weld bead, the thickness of the corrosion-resistant layer is appropriately increased, and the thickness can be controlled at 3.5. ~4mm, this can increase the effective thickness of the corrosion-resistant layer, but it should be noted that the thickness of the surfacing layer exceeds 5mm, which is more likely to cause welding slag, so the thickness should not be too thick.
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