Welding is a process in which the material (same or dissimilar) of the workpiece to be welded is heated or pressurized or both, and whether or not to use a filler material, so that the material of the workpiece can be bonded between atoms to form a permanent connection. So what are the points and precautions for stainless steel welding?
What electrode is used for welding stainless steel?
Stainless steel electrodes can be divided into chrome stainless steel electrodes and chrome-nickel stainless steel electrodes. Those two types of electrodes that meet the national standard shall be assessed in accordance with the national standard GB/T983-2012.
Chromium stainless steel has certain corrosion resistance (oxidizing acid, organic acid, cavitation) and heat resistance, and is usually selected as equipment materials for power stations, chemicals, and petroleum. However, the weldability of chromium stainless steel is generally poor, and attention should be paid to the welding process, heat treatment conditions and the selection of suitable electrodes. Chromium-nickel stainless steel electrodes have good corrosion resistance and oxidation resistance, and are widely used in chemical, fertilizer, and petroleum fields. In order to prevent intergranular corrosion due to heating, the welding current should not be too large, about 20% smaller than that of carbon steel electrodes, the arc should not be too long, and the layers are cooled quickly, and a narrow weld bead is appropriate.
Stainless steel welding points and precautions
1. Use a power supply with vertical external characteristics, and use positive polarity when DC (welding wire is connected to the negative electrode)
1. It is generally suitable for the welding of thin plates below 6mm. It has the characteristics of beautiful weld formation and small welding deformation.
2. The protective gas is argon with a purity of 99.99%. When the welding current is 50~150A, the argon gas flow is 8~10L/min, and when the current is 150~250A, the argon gas flow is 12~15L/min.
3. The length of the tungsten electrode protruding from the gas nozzle is preferably 4~5mm. It is 2~3mm in places with poor shielding such as fillet welding, 5~6mm in places where the groove is deep, and the distance from the nozzle to the working is generally not more than 15mm.
4. In order to prevent the occurrence of welding pores, the welding parts must be cleaned if there is rust, oil pollution, etc.
5. When welding ordinary steel, the length of the welding arc is preferably 2~4mm; when welding stainless steel, it is better to use 1~3mm, and the protection effect is not good if it is too long.
6. In order to prevent the backside of the bottom weld bead from being oxidized, the backside also needs to be protected by gas.
7. In order to make the argon gas well protect the welding pool and facilitate the welding operation, the center line of the tungsten electrode and the workpiece at the welding place should generally maintain an angle of 80°~85°, and the angle between the filler wire and the surface of the workpiece should be as small as possible. Usually about 10°.
8. Windproof and ventilation. In windy places, be sure to take measures to block the net, and take appropriate ventilation measures indoors.
Second, stainless steel MIG welding points and precautions
1. The flat characteristic welding power source is used, and the reverse polarity is used for DC (the welding wire is connected to the positive electrode)
2. Generally, pure argon gas (purity of 99.99%) or Ar+2%O2 is used, and the flow rate is preferably 20~25L/min.
3. Arc length, MIG welding of stainless steel is generally performed under the condition of spray transition, and the voltage should be adjusted to the extent that the arc length is 4~6mm.
4. Windproof. MIG welding is easily affected by wind, and blowholes are easily formed in windy places, so windproof measures should be taken in places where the wind speed is above 0.5m/s.
Three, stainless steel flux cored wire welding points and precautions
1. The flat characteristic welding power source is used, and the reverse polarity is used for DC welding. Welding can be performed by using a general CO2 welding machine, but please loosen the pressure of the wire feeder a little.
2. The protective gas is generally carbon dioxide gas, and the gas flow rate is 20~25L/min.
3. The distance between the welding tip and the workpiece should be 15~25mm.
4. Generally, the dry elongation length is about 15mm when the welding current is below 250A, and about 20~25mm when the welding current is above 250A.