TIG Welding 4130 Chromoly Tubing
4130 chromoly steel has an excellent strength to weight ratio, is easily welded and is considerably stronger and harder than standard 1018 steel.
The 4130 grade of chromoly or chrome-moly is a high-strength low-alloy (HSLA) steel that contains molybdenum (0.15 – 0.25 percent by weight) and chromium (0.8 – 1.1 percent by weight) as strengthening agents. However, it has relatively low carbon content (nominally 0.30 percent), so it welds, machines and bends almost as easily as 1018 DOM mild steel tubing (which has an 0.18 percent carbon content). While the 4130 grades of steel do contain chromium, it is not in great enough quantities to provide the corrosion resistance found in stainless steel. Chromoly is not lighter than steel, a common misconception. Both weigh about 491 lbs. per cubic foot. However, chromoly offers a better strength-to-weight ratio and better elongation (a measure of ductility), which enables designers to use thinner wall and/or smaller diameter tubing to reduce overall weight.
Todd Bevis, chassis engineer, Cagnazzi Racing, discusses TIG welding 4130 chromoly tubing on an NHRA Pro Stock dragster.
Tig Welding 4130 Chromoly tubing
You can easily TIG weld 4130 chromoly tubing tubing with the proper techniques.
TIG welding 4130 Chromoly tubing techniques
Pre-heat Chromoly tubing before TIG welding
TIG Welding chromoly tubing does not require the normal 300ºF to 400ºF pre-heat to obtain acceptable strength. However, it is recommended that pre-heat of 100ºF to 125ºF be used to remove parent material moisture.
TIG Welding Chromoly tubing filler material
TIG Welding chromoly tubing filler material. 4130 filler typically is used for high strength and rigid applications, however it is not recommended for high stress applications, such as roll cages, race car, motorcycle or bicycle frames due to it’s hardness or lack of elongation, for these we recommend ER70S-2 for filler for roll cages, chassis and other applications requiring more flexibility or ER80S-D2 for areas requiring higher strength.
TIG Welding Chromoly tubing stress relief
When TIG Welding chromoly tubing stress-relieving is recommended. 1,100ºF is the optimum temperature for chromoly tubing applications. Use a 900ºF temperature crayon and mark approximately 1″away from weld areas. Use Oxy/Acetylene torch with neutral flame and oscillate to avoid hot spots.
NOTE: Excessive stress is induced by too much heat input, poor fit-up, or both, therefore stress relieving can be avoided if all fit-ups are precision and by applying minimum heat input, i.e. smaller welds. TIG welding should not require a weaving pattern in the welding technique.
Pre-clean Chromoly tubing before welding
Pre-clean chromoly tubing 4130 material before welding.
Remove surface scale and oils with mild abrasives and acetone. Wipe to remove all oils and lubricants. All burrs need to be removed with a hand scraper or de-burring tool.
Cooling Chromoly tubing after welding
Slow cool 4130 chromoly tubing after welding. Rapid quenching of 4130 chromoly tubing will create weld defects and problems such as cracking and lamellar tearing. Always allow the weld to cool slowly.
Preventing cracks when TIG Welding Chromoly tubing
When TIG welding chromoly tubing, taper off amperage slowly and maintain adequate postflow of your Argon to avoid crater holes that will turn into cracks later on.