Stainless steel welding process
Stainless steel welding process
What are the welding processes for stainless steel? What precautions?
Welding is a process in which the material (same or different) of the workpiece to be welded is heated or pressurized or both, and filled with or without filler materials, so that the material of the workpiece can be bonded between atoms to form a permanent connection. So what are the key points and precautions for stainless steel welding?
Stainless steel electrodes can be divided into chromium stainless steel electrodes and chromium nickel stainless steel electrodes. Of these two types of electrodes, those that meet the national standard are assessed in accordance with the national standard GB/T983-2012.
Chromium stainless steel has certain corrosion resistance (oxidizing acid, organic acid, cavitation), heat resistance and corrosion resistance. It is usually selected as equipment materials for power stations, chemicals, petroleum and other equipment. However, the weldability of chromium stainless steel is generally poor, so attention should be paid to the welding process, heat treatment conditions and the selection of suitable welding rods.
Chromium-nickel stainless steel electrodes have good corrosion resistance and oxidation resistance, and are widely used in chemical, fertilizer, petroleum, and medical machinery manufacturing. In order to prevent intergranular corrosion due to heating, the welding current should not be too large, which is about 20% less than that of carbon steel electrodes, the arc should not be too long, and the interlayer cooling should be fast, and narrow welding bead is better.
One. Use a power supply with vertical external characteristics, and use positive polarity when DC (welding wire is connected to the negative electrode)
1. Generally suitable for the welding of thin plates below 6mm, with the characteristics of beautiful weld shape and small welding deformation. (Thanks for your attention to Dingding Automatic Welding)
2. The protective gas is argon with a purity of 99.99%. When the welding current is 50~150A, the argon flow is 8~10L/min, when the current is 150~250A, the argon flow is 12~15L/min.
3. The protruding length of the tungsten electrode from the gas nozzle is preferably 4~5mm, 2~3mm for fillet welding and other places with poor shielding, and 5~6mm for deep grooves, and the distance from the nozzle to the work is generally not more than 15mm.
4. In order to prevent the appearance of welding pores, the welding parts must be cleaned up if there is rust and oil stains.
5. For welding arc length, 2~4mm is better when welding ordinary steel, and 1~3mm is better when welding stainless steel. If it is too long, the protection effect will not be good.
6. In order to prevent the back side of the bottom weld bead from being oxidized, the back side also needs to implement gas protection.
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 welding workpiece 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. It is generally about 10°.
8. Windproof and ventilation. In windy places, be sure to take measures to block the net, and take appropriate ventilation measures indoors.
Two. Main points and precautions of stainless steel MIG welding
1. Use flat-characteristic welding power source, use reverse polarity when DC (welding wire is connected to the positive electrode)
2. Generally, pure argon gas (purity 99.99%) or Ar+2%O2 is used, and the flow rate is 20~25L/min.
3. Arc length, MIG welding of stainless steel is generally welded under the condition of spray transition, and the voltage should be adjusted to the degree of arc length 4~6mm.
4. Windproof. MIG welding is susceptible to the influence of wind, and sometimes breeze creates pores, so windproof measures should be taken where the wind speed is above 0.5m/sec.
Three, stainless steel flux cored wire welding main points and precautions
1. Use flat-characteristic welding power source and reverse polarity when DC welding. Welding can be performed using a general CO2 welder, but the pressure of the wire feeder should be loosened slightly.
2. The protective gas is generally carbon dioxide gas, and the gas flow rate is 20-25L/min.
3. The appropriate distance between the welding tip and the workpiece is 15~25mm.
4. Dry elongation, generally about 15mm when the welding current is below 250A, and about 20~25mm when above 250A, is more appropriate.
