When stainless steel plates are welded, defects often occur. The causes of these defects are different. This article describes some of the defect classification and avoidance methods.
The pores formed by the stainless steel plate weld can be divided into internal pores, surface pores, and joint pores.
There are two types of internal pores, one is that the spherical pores are mostly generated in the middle of the weld. The reasons for the formation are excessive welding current, long arc, too fast moving rod, unclean welding area, and moisture in the welding rod. . The above causes the pore causes to be solved if appropriate adjustments and pay attention to the welding process and operation method.
There are several reasons for the formation of surface pores. For example, if the base metal contains carbon, sulfur, and silicon, high content of the pores is likely to occur. The solution is either replacement of the base metal or the use of a low-hydrogen slag-based electrode. The welding site is also unclean and prone to blow holes. Therefore, the welding site requires welding. Before the removal of oil, rust and other dirt, the use of low-hydrogen welding rod welding requirements are more stringent; In addition, excessive welding current can also lead to surface pores, so that the second half of the electrode coating red, but also prone to air holes, so require the appropriate The welding specification, welding current to the maximum end of the electrode is not red is appropriate; low hydrogen electrode easy to absorb moisture, so before use are required to be baked at a temperature of 350 °C 1h or so, otherwise prone to air holes.
There are species of solder wave joint pores, the use of low hydrogen electrode is often easy to appear at the weld joint surface and internal porosity, the solution is in the solder wave joint, should be in the direction of the weld from the arc 9-10mm Start the arc, after the arc burns, first reverse the rod back to the crater position, fully melt forward and then advance, or arc at the weld to avoid this type of pore generation.
There are several types of cracks. The first is a rigid crack, which is usually the longitudinal crack in the weld where the weld joint is found, mainly due to the stress generated during welding. In the following cases, the welding stress is large, the rigidity of the welded structure is large, the welding current is large, the welding speed is fast, and the cooling rate of the weld metal is too fast. So it is very easy to form longitudinal cracks in the above situation. The solution is to use a reasonable welding sequence or preheat the workpiece where possible to reduce the rigidity of the structure. Special thick plates and rigid structures should use low hydrogen electrodes with appropriate current and welding speed.
The second is the crack caused by carbon and sulfur elements. When the carbon and sulfur of the base metal being welded are high or segregated, cracks are likely to occur. The solution is to preheat the weldment or use a low hydrogen electrode.
The third is a gap crack, which occurs inside the weld metal and does not develop external hairy micro cracks. Considering that the weld metal is subject to rapid cooling and embrittlement, local stress and hydrogen gas influence. The prevention method for this is to make the cooling rate of the weldment slower, to preheat the weldment under possible conditions, or to use a low hydrogen electrode to achieve a satisfactory solution.
When the welding is performed on a DC welding machine using a low-hydrogen electrode, blow-off occurs frequently. The solution is that the ground wire is placed in the direction of the arc blow; the ground wire is divided into two or more; welding is performed in the direction of the partial blow of the arc; and the welding is performed using the short arc operation.
Source: China Plate Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)