TIG Welding 4130 Steel Tubing Welding 4130 with TIG is not much different than welding  other steels as far as technique is concerned. The following  information generally addresses material under 0.120-  inch thick. Clean the steel of any oil or grease and use a stainless steel  wire brush to clean the work piece prior to welding. This is  to prevent porosity and hydrogen embrittlement during the  welding process. The TIG process is highly susceptible to  these problems, much more so than oxy-acetylene welding,  so care must be taken to ensure all oils and paint are removed  from all surfaces of the parts to be welded. Use a TIG welder with high-frequency starting to eliminate  arc strikes. Do not weld where there is any breeze or draft;  the welds should be allowed to cool slowly. Preheating  is not necessary for tubing of less than 0.120-inch wall  thickness; however, post-weld tempering (stress relieving) is  still recommended to prevent the possible brittleness of the  area surrounding the weld due to the untempered martensite  formations caused by the rapid cooling of the weld inherent  to the TIG process. If you use 4130 filler rod, preheat the work before welding  and heat treat afterward to avoid cracking. In a critical  situation such as this, engineering should be done to  determine preheat and post-weld heat treatment needed for  the particular application. Weld at a slower speed, make sufficiently large fillets, and  make them flat or slightly convex, not concave. After the  welding is complete, allow the weldment to cool to room  temperature. Using an oxy-acetylene torch set to a neutral  flame, heat the entire weldment evenly to 1,100 °F–1,200 °F;  hold this temperature for about 45 minutes per inch of metal  thickness. The temperature is generally accepted to be a dull  red in ambient lighting. Note that for most tubing sections, the  temperature needs to be held for only a minute or two. This  process is found in most materials engineering handbooks  written by The Materials Information Society (ASM) and  other engineering sources. When working on a critical  component, seek engineering help if there is any doubt.  Stainless steels, or more precisely, corrosion-resisting steels,  are a family of iron-based metals that contain chromium  in amounts ranging from 10 percent to about 30 percent.  Nickel is added to some of the stainless steels, which  reduces the thermal conductivity and decreases the electrical  conductivity. The chromium-nickel steels belong in the AISI  300 series of stainless steels. They are nonmagnetic and have  austenitic microstructure. These steels are used extensively  The base metal needs protection during the welding process  by either an inert gas shield, or a backing flux, on both sides  of the weld. Back purging uses a separate supply of shielding  gas to purge the backside of the weld of any ambient air.  Normally, this requires sealing off the tubular structures or  using other various forms of shields and tapes to contain  the shielding gas. A special flux may also be used on the  inside of tubular structures in place of a back purge. This is  especially advantageous with exhaust system repairs in which  sealing off the entire system is time consuming. The flux is  the same as is used for the oxy-acetylene welding process  on stainless materials. To form a weld bead, move the torch along the joint at  a steady speed using the forehand method. Dip the filler  metal into the center of the weld puddle to ensure adequate  shielding from the gas. Clean the base metal just prior to welding to prevent the  formation of oxides. Clean the surface and joint edges with  a nonchlorinated solvent, and brush with a stainless steel  wire brush to remove the oxides. Clean the filler material in  the same manner.  The selection of the filler metal alloy for welding the stainless  steel is based on the composition of the base metal. Filler  metal alloys for welding austenitic type stainless include  AISI No. 309, 310, 316, 317, and 347. It is possible to weld  several different stainless base metals with the same filler  metal alloy. Follow the manufacturer’s recommendations.  The austenitic stainless steels are slightly more difficult  to weld than mild-carbon steel. They have lower melting  temperatures, and a lower coefficient of thermal conductivity,  so welding current can be lower. This helps on thinner  materials because these stainless steels have a higher  coefficient of thermal expansion, requiring special  precautions and procedures to be used to reduce warping and  distortion. Any of the distortion-reducing techniques, such as  skip welding or back-step welding, should be used. Fixtures  and/or jigs should be used where possible. Tack welds should  be applied twice as often as normal.  All of the austenitic stainless steels are weldable with most  welding processes, with the exception of AISI 303, which  contains high sulfur, and AISI 303Se, which contains  selenium to improve its machinability.  in aircraft in which strength or resistance to corrosion at high  temperature is required.  TIG Welding Stainless Steel 5-23