Common 4130 TIG welding questions and answers

Q. Can I weld 4130 using the TIG process?
A. Yes, 4130 Chrome-Moly has been TIG welded in the aerospace and aircraft industries for years. As with all welding, proper procedures and techniques must be followed.

Q. Do I need to preheat ?
A. Thin wall tubing (< 0.120" wall) applications do not typically require the normal 300ºF to 400ºF pre-heat to obtain acceptable results. However, tubing should be at room temperature (70ºF) or above before welding.

Q. What filler material do I use?

A. Although there are several good filler materials, ER80S-D2, is one you should consider. This filler material is capable of producing welds that approximate the strength of 4130. ER-70S-2 is an acceptable alternative to ER80S-D2, as is ER70S-6, although the weld strength will be slightly lower.

Q. When I use ER70S-2 filler material, do I give up strength for elongation?
A. Yes. The filler material, when diluted with the parent material, will typically undermatch the 4130. However, with the proper joint design (such as cluster or gusset, for example), the cross-sectional area and linear inches of weld can compensate for the reduced weld deposit strength.

Q. Why is 4130 filler metal not recommended?
A. 4130 filler typically is used for applications where the weld will be heat treated. Due to its higher hardness and reduced elongation, it is not recommended for sporting applications such as experimental airplanes, race car frames, roll cages, etc.

Q. Can I weld 4130 using any other filler metals?
A. Some fabricators prefer to use austenitic stainless steel fillers to weld 4130 tubing. This is acceptable provided 310 or 312 stainless steel fillers are used. Other stainless steel fillers can cause cracking. Stainless filler material is typically more expensive.

Q. Do I need to heat treat (stress relieve) 4130 after welding?
A. Thin wall tubing normally does not require stress relief. For parts thicker than .120", stress-relieving is recommended and 1,100ºF is the optimum temperature for tubing applications. An Oxy/Acetylene torch with neutral flame can be used. It should be oscillated to avoid hot spots.

Q. Do I have to pre-clean 4130 material?
A. Remove surface scale and oils with mild abrasives and acetone. Wipe to remove all oils and lubricants. All burrs should be removed with a hand scraper or de-burring tool. Better welding results with clean materials.

Q. Do I need to back-purge 4130 material?
A. Backpurging is not normally necessary, although some fabricators do. It will not hurt the weld and may improve the root pass of some welds.
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Q. Should I quench the metal after I finish welding?
A. ABSOLUTELY NOT! Rapid quenching of the metal will create problems such as cracking and lamellar tearing. Always allow the weld to slow cool.

AISI 4130 N CHROMIUM MOLYBDENUM (chromolly) STEEL TUBING - Part 2

Kinds of Strength

Previously we learned what 4130 N Chromolly is. Next we will answer the question, Why is it such a popular choice? Fabricators and engineers use 4130 tubing because of its outstanding strength, forgoing mild steel, where a thicker wall must be used to have equivalent strength as the 4130 chromolly steel tubing. Simply put it is stronger. "Stronger"? What does that mean?

Strength is the ability of a metal to withstand some kind of force without breaking down. For example a metal can resist failure from pulling, hitting, pressure, repeated bending, twisting or shearing. These strength properties are known as, respectively, tensile strength, impact strength, compressive strength, fatigue strength, torsional strength, and shear strength. In my experience tensile strength is the most commonly "advertised" although not necessarily the most useful.

The minimum Ultimate Tensile Strength for 4130 (Chromoly) Normalized Alloy Steel is 97,200 psi. A513 (alloy 1020-1026) Steel alloy is generally used for DOM tubing. A popular choice for our type of fabrication has a Ultimate Tensile Strength of psi 87,000. Fabricators and engineers use 4130 because they can use a thinner wall thickness tubing to get the required strength. Thinner equals lighter, lighter equals performance.

AISI 4130 N CHROMIUM MOLYBDENUM (chromolly) STEEL TUBING

4130 steel tubing (chromolly) is one of the most widely used materials in aviation and racing industries because of its weldability and ease of fabrication. 4130 steel is ideal when strong light weight steel tubing is needed. The weldability of 4130 chromolly steel tubing is excellent. 4130 tube is resistant to scaling and oxidation and has a clean, smooth finish both on the outside and inside of the tubing. Fabricators and engineers use 4130 tubing because of its outstanding strength, forgoing mild steel, where a thicker wall must be used to have equivalent strength as the 4130 chromolly steel tubing.

Who uses 4130 Chrome-Moly tubing. Chassis and components of NHRA and IHRA drag racing. NASCAR suspension components. IndyCars, Sprints and other open wheel cars. High end Bicycles, Experimental Aircraft as well as racing snowmobiles use 4130 tubing.


OK, so what is 4130. First let’s quickly understand steel. Merriam-Webster defines steel as commercial iron that contains carbon in any amount up to about 1.7 percent as an essential alloying constituent, is malleable when under suitable conditions, and is distinguished from cast iron by its malleability and lower carbon content. AISI4130 Chrome-Moly is a steel alloy or more simply a mixture of base metals.Chrome is short for Chromium. Moly is short for Molybdenum. “Chrome” and “Moly” are two of the added base metals that add to the alloys strength.


The number ‘4130’ is a code of the American Iron & Steel Institute (AISI 4-digit code system) The American Iron and Steel Institute (AISI) naming system is one of the most widely accepted systems that defines the approximate chemical composition of the steel.

Designations usually consist of a four digit number, but sometimes this extends to five. The first two digits indicate what the major alloying element is, while the last 2 or three indicate the carbon content in hundredths of a percent.

The ‘41’ indicates a low alloy steel containing chromium and molybdenum and the ‘30’ indicates a carbon content of 0.30 percent.Below is a table showing the chemical composition of 4130 Chrome-Moly shown in percentages.

Carbon	0.28 - 0.33
Chromium	0.8 - 1.1
Manganese	0.7 - 0.9
Molybdenum	0.15 - 0.25
Phosphorus	0.035 max
Silicon	0.15 - 0.35
Sulphur	0.04 max

Now you know what 4130 Chro-Mo is next time we'll talk about why it is used and how to weld it.