Summary of welding process and common problems of 304 stainless steel seamless pipe

The 304 stainless steel seamless pipe is made of imported first-class regular stainless steel plate. Its characteristics are: no blisters, no sand holes, no black spots, no cracks, and smooth weld bead. Bending, cutting, welding performance advantages, stable nickel content. The welding process of 304 stainless steel seamless pipe adopts flat characteristic welding power supply, which is used in direct current (welding wire connection). Generally, pure argon gas (purity is 999% or Ax+2‰02, 20°25/min is suitable for the flow. The arc is generated between the refractory tungsten welding wire and the workpiece, and the generally used protective gas is pure argon. Gas, the feeding wire is not charged, it can be sent by hand or mechanically, and some special purposes do not need to feed the welding wire. The material to be welded determines whether to use DC or AC: when using DC, tungsten electric welding wire Set as negative, because of its deep penetration capability, it is suitable for different kinds of steel, but does not have any "cleaning effect" on the weld pool. The main advantage of TIG welding method is that it can weld a large range of materials Wide range, including workpieces with a thickness of 0.6mm and above. The materials include alloy steel, aluminum, magnesium, copper and its alloys, gray cast iron, ordinary dry, various bronzes, nickel, silver, titanium and lead. Main application fields It is used for welding thin and medium-thick workpieces, and is used as a root weld pass on thicker sections. Summary of welding processes and common problems for 304 stainless steel seamless pipes (Figure 1)
Key points and precautions for TIG welding of 304 stainless steel seamless pipes:
(1) The power supply with vertical external characteristics is used, and the positive polarity is used for DC (the welding wire is connected to the negative pole).
(2) It is generally suitable for welding thin plates below 6mm, and has the characteristics of beautiful weld shape and small welding deformation.
(3) The protective gas is argon with a purity of 99.99%. When the welding current is 50~150A, the flow rate of argon gas is 8~10L/min, when the current is 150~250A, the flow rate of argon gas is 12~15L/min.
(4) The protruding length of the tungsten electrode from the gas nozzle is preferably 4~5mm, 2~3mm in places with poor shielding such as fillet welding, and 5~6mm in places with deep slots. The distance from the nozzle to the work is generally not more than 15mm.
(5) In order to prevent the appearance of welding pores, if there is rust and oil stains on the welding parts, it must be cleaned up.
(6) The welding arc length is preferably 2~4mm when welding ordinary steel, and 1~3mm when welding stainless steel. If it is too long, the protection effect will not be good.
(7) In order to prevent the back of the bottom weld bead from being oxidized during butt priming, gas protection is also required on the back.
(8) In order to make the argon gas well protect the welding pool and facilitate the welding operation, the centerline 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 , generally around 10°.
(9) Windproof and ventilation. Where there is wind, please take measures to block the net, and take appropriate ventilation measures indoors.
Summary of welding process and common problems of 304 stainless steel seamless pipe (Figure 2)
The possible defects of 304 stainless steel seamless pipes in the process of smelting, forging and rolling:
(1) Shrinkage cavity: The shrinkage cavity formed when molten steel shrinks in the steel mold is called shrinkage cavity.
(2) Transverse cracks: Refers to the transverse cracks that occur on the surface of steel ingots, generally on steel ingots, generally shallow in depth, and can be removed by fine grinding.
(3) Longitudinal cracks: refers to the longitudinal cracks generated on the surface of steel ingots, generally in the upper part and corners of steel ingots, and the cracks in the upper part are very deep and difficult to eliminate by grinding.
(4) Scarring: on the surface of the steel ingot, the shell-like or tumor-like metal is called scarring, and the scarring mostly appears in the lower part of the steel ingot.
(5) Heavy skin: When the edge of the low-magnification test piece shows an irregular dark loose, a large number of oxide inclusions (mainly ferrous oxide) gather around it, which is called overturning.
(6) Surface inclusions: Refers to the non-subtractive inclusions embedded on the surface of the steel ingot that are visible to the naked eye.
(7) Surface porosity: Refers to the tiny pores visible to the naked eye exposed to the surface of the steel ingot, mostly found in the middle and lower parts of the steel ingot, generally not deep, and can be removed by finishing.
(8) Explosion: The cracking that occurs when the surface of the steel ingot is extremely cold is called explosion because the cracking is often accompanied by noise.
(9) Rising: The head of the steel ingot is irregularly raised. This defect is called rising, also called rising.
(10) Reticulation: The reticular protrusions appearing on the surface of the steel ingot are called reticulation.
(11) Pit: The pits on the surface of the steel ingot are called pits.
(12) Double pouring: rejoining traces are clearly visible around the surface of the steel ingot
(13) Flash: The metal flakes that exist at the head or tail of the ingot and are perpendicular to the surface of the ingot are called flash.
(14) Fins: The thin slices formed on the surface of the ingot perpendicular to the surface of the ingot are called fins.
(15) Bubbles: Bubbles are defects in steel ingots or steel ingots caused by poor degassing and deoxidation of molten steel or wet raw materials in the steel injection system, and are generally divided into subcutaneous bubbles and internal bubbles.
(16) White spots: White spots are actually a kind of fine cracks, which are radioactive and irregular jagged cracks on the horizontal low-magnification sample just now, and are round or elliptical silver bright spots on the longitudinal low-magnification sample. It's called Baidian.