How to avoid defects such as pores and cracks when welding stainless steel electric heating rings?

In order to avoid defects such as pores and cracks when welding stainless steel electric heating rings, corresponding measures need to be taken before, during and after welding, as follows:
Pre-welding preparation
Material cleaning: Before welding stainless steel electric heating rings, impurities such as oil, rust, and moisture on the surface of the weldment must be thoroughly removed. These impurities will decompose and produce gas during the welding process, which will lead to the formation of pores. You can use organic solvents such as acetone and gasoline to clean the surface of the weldment, and then polish it with sandpaper or wire brush to reveal the metallic luster.
Welding rod drying: The welding rod should be dried according to the instructions before use. For example, for common stainless steel welding rods, it is generally necessary to dry it at 250-300℃ for 1-2 hours. The dried welding rod should be placed in an insulation cylinder and taken out as needed to prevent the welding rod from absorbing moisture in the air and avoid pores due to moisture in the welding rod.
Welding process
Control welding parameters: Select appropriate welding current, voltage and welding speed. Too much current can easily cause the weld to overheat, so that the gas in the molten pool cannot escape in time and form pores, and it will also increase the tendency of cracks; too little current will lead to poor fusion and may also produce pores. If the welding speed is too fast, the molten pool will exist for too short a time and the gas cannot be fully discharged; if the speed is too slow, the weld will overheat and increase the possibility of cracks. Taking the common 3mm thick stainless steel electric heating ring as an example, when using tungsten inert gas arc welding, the welding current is generally 100-120A, the voltage is 12-15V, and the welding speed is controlled at 3-5mm/s.
Use short arc welding: short arc welding can concentrate the arc heat, reduce the chance of air intrusion into the molten pool, and thus reduce the probability of pores. At the same time, the short arc can also keep the molten pool under the protection of the arc, which is conducive to the escape of gas in the molten pool.
Ensure the gas protection effect: When using gas shielded welding, the purity and flow of the shielding gas must be guaranteed. The purity of argon should be no less than 99.99%. The flow rate is generally selected according to the welding current and the thickness of the weldment, usually 8-15L/min. In addition, check whether the gas nozzle of the welding gun is blocked or damaged to ensure that the gas is sprayed evenly to form a good protective gas hood to prevent air from entering the molten pool.
Control the welding environment: The temperature and humidity of the welding environment have an important impact on the welding quality. When the ambient temperature is too low, the weld cools too fast and cracks are likely to occur; when the humidity is too high, moisture will condense on the surface of the weldment, increasing the possibility of pore formation. Generally, the welding environment temperature is required to be no less than 5℃ and the relative humidity is not higher than 90%.
Post-weld treatment
Slow cooling treatment: After welding is completed, let the weldment cool naturally and avoid forced cooling to slow down the cooling rate of the weld, so that the gas in the molten pool has enough time to escape, reduce the formation of pores, and also reduce welding stress and prevent cracks. For stainless steel electric heating coils with large thickness or complex structure, asbestos cloth covering and other methods can be used for slow cooling.
Stress relief treatment: Large welding stress will be generated during welding, which is one of the important reasons for cracks. After welding, stress can be eliminated by heat treatment or mechanical vibration. For example, for some important stainless steel electric heating rings, stress relief annealing treatment can be performed after welding. The weldment is heated to 550-650℃, kept warm for a certain period of time, and then cooled with the furnace to eliminate welding stress and reduce the risk of cracks.