Galvanised stainless steel 7x19 wire rope pole surfacing welding is performed on the surface of the workpiece, and the performance of the surfacing metal is different depending on the structure of the surfacing layer. The properties of surfacing metal include appearance forming, mechanical properties, bending properties, corrosion resistance, wear resistance, etc. However, in addition to these contents, we also care about the common quality problems, cause analysis and preventive measures during surfacing welding.
1. Macro Defects
(1) Slag inclusion Slag inclusion often occurs in the form of inter-channel, and sometimes inter-layer slag inclusion occurs. The main reason for the formation of slag inclusion in the weld bead is the poor process performance of the flux, which makes the wetting angle on both sides of the weld bead of the deposited metal too steep, resulting in poor edge fusion. scum. In addition, unqualified welding specifications and welding positions are also prone to form such defects.
(2) Undercut undercut mainly occurs in electroslag surfacing. For wide-band pole (with pole width greater than 60mm) electroslag surfacing, due to the magnetic shrinkage effect, the surfacing layer will have undercut, and with the strip pole As the width increases, the surfacing current increases, and the undercut phenomenon becomes heavier. Therefore, an external magnetic field must be used to prevent the occurrence of undercut (magnetron method). At the same time, the position of the magnetic poles must be arranged reasonably, and the size of the excitation current must be selected reasonably. If the external magnetic field is too strong or too weak, the formation of the surfacing weld bead will be affected. The magnetron currents of the two poles should be adjustable separately. For example, for the workpiece in the non-preheated flat welding position, when the belt pole is 60mm × 0.5mm, the south and north pole control currents of the magnetic control device are 1.5A and 3.5A respectively; for the belt pole of 90mm × 0.5mm, respectively 3A and 3.5A.
(3) Cracks Cracks mainly appear at the arc end, and sometimes also in the weld bead. The cracks in the surfacing layer are mainly hot cracks. There are two reasons: the chromium-nickel ratio of the deposited metal is not suitable, resulting in too low or too high ferrite content of the surfacing metal, which is mainly caused by improper matching of the composition of the welding strip and flux. ; Improper welding specifications and excessive current can easily cause thermal cracks.
(4) Unfused The bonding surface between the surfacing layer and the base metal or between the layers is prone to unfused phenomenon. Since the sintered flux is lighter than the smelted flux surfacing, the penetration depth is relatively small. Once the operation is improper or the welding specification parameters are not well grasped, the defects of unfused joints or unfused between layers are prone to occur.
The common macro defects and preventive measures are described above. In addition, the following points should be paid attention to when surfacing the actual product. First, the base metal is strictly ground before welding to remove rust, oil stains and other factors that affect welding and must be preheated. The second is to control the thickness of the surfacing layer. During the surfacing welding of the transition layer, welding defects are easy to occur due to the welding of dissimilar steels. The general method is to reduce the thickness of the surfacing layer of the transition layer as much as possible (3~3.5 mm); during the surfacing welding of the corrosion-resistant layer, due to the welding of the same material, it is not easy to produce welding defects. At the same time, the effective thickness of the corrosion-resistant layer is also increased. When the thickness of the surfacing layer exceeds 5mm, it will cause welding bumps, which is easy to cause welding slag.