What defects are prone to occur during surfacing welding of 304 stainless steel strips

When surfacing welding is performed on the surface of 304 stainless steel strips, defects are prone to occur during surfacing welding due to the different metal properties of the surfacing layer, resulting in a decrease in the overall quality of 304 stainless steel strips. What defects during surfacing welding need our attention? How to solve the defects?

1. Slag inclusion
Slag inclusion is generally formed between passes, and sometimes between layers. The main reason for the formation of weld bead slag inclusion is the poor process performance of the flux, which leads to too steep wetting angles on both sides of the weld bead of the deposited metal, and poor edge fusion. In this way, when surfacing welding is performed after a weld bead, it is easy to have interpass slag inclusion. If the welding is not standardized or the welding position is incorrect, this defect will also occur.

2. Undercut
Undercut mainly occurs in electro-slag surfacing, especially when the 304 stainless steel strip is relatively wide, it is easy to occur. Due to the influence of the magnetic contraction effect, the surfacing layer produces an undercut phenomenon. When the width of the 304 stainless steel strip increases, the surfacing current also increases, and the undercut phenomenon becomes more obvious. To solve the problem of undercut, you can apply an external magnetic field, arrange the position of the magnetic poles reasonably, choose a reasonable excitation current, and pay attention to controlling the magnetron current of the two magnetic poles. The magnetic field should not be too strong or too weak. If the steel strip is a non-preheated flat weld, and the range of the strip pole is 60mm×0.5mm, the current of the south pole and the north pole controlled by the magnetron device should be 1.5A and 3.5A respectively. If the range of the strip pole is 90mm×0.5mm, the current of the south pole and the north pole controlled by the magnetron device should be 3A and 3.5A respectively.

3. Cracks
Cracks generally occur at the arc closing position, and sometimes also occur in the weld. The cracks in the cladding layer are mainly thermal cracks. There are two reasons for thermal cracks. One is that the ratio of chromium and nickel in the deposited metal is not appropriate, resulting in too high or too low ferrite content in the cladding metal. This is because the composition of the welding strip and the flux cannot be well matched. The second is that the welding operation is not standardized and the current is too large, which causes thermal cracks during the cladding process.

4. Unfused
The bonding surface or interlayer between the cladding layer and the base material is more likely to be unfused. This is because the weight of the sintered flux is lighter than that of the smelting flux, so its penetration is also relatively small. During operation, if the operation is not standardized or the parameters are not well controlled during welding, it is relatively easy to cause defects such as unfused bonding surface or unfused interlayer.

When cladding 304 stainless steel strip, if you want to prevent defects, you can take the following measures:
① Strictly grind the base material before cladding 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.
② Control the thickness of the cladding layer. When cladding the transition layer, because it is a dissimilar steel welding, it is easy to have welding defects. Therefore, to ensure the quality of cladding, the thickness of the transition layer cladding can be reduced under the premise of ensuring the formation of the weld bead. The general thickness is controlled at 3~3.5mm.

When surfacing the corrosion-resistant layer, welding defects are not likely to occur because the same material is used for welding. While ensuring the formation of the weld bead, the thickness of the corrosion-resistant layer is appropriately increased. The thickness can be controlled at 3.5~4mm. This can increase the effective thickness of the corrosion-resistant layer. However, it should be noted that if the thickness of the surfacing layer exceeds 5mm, it is easier to cause welding slag, so the thickness should not be too thick.