Welding wire for 4130 Steel with post-weld normalization

[Composites Guy]

I'm making a-arms, push rods, and tie rods, and thought it would be a good idea to have them normalized/stress relieved. I am going to send them to a local heat-treat shop to be normalized at ~1100F in an oven and slowly cooled. I don't think I need the extra strength of heat-treating, quenching, and tempering. I have a hefty jig that will go in the oven to minimize distortions.

I'm not sure what welding wire to use. The recommendations I've seen are vacuum melted 4130 wire, and also ER80S-D2. Do any of you have any thoughts?

[Composites Guy]

I'm making a-arms, push rods, and tie rods, and thought it would be a good idea to have them normalized/stress relieved. I am going to send them to a local heat-treat shop to be normalized at ~1100F in an oven and slowly cooled. I don't think I need the extra strength of heat-treating, quenching, and tempering. I have a hefty jig that will go in the oven to minimize distortions.

I'm not sure what welding wire to use. The recommendations I've seen are vacuum melted 4130 wire, and also ER80S-D2. Do any of you have any thoughts?

[Conor]

Why send them all the way to a heat treater? Just use some temperature sensitive paint and an oxy-acetaline torch. Once you've got them to the right temp, put them in a hood to slowly cool (the hood will keep the surrounding air from circulating too much). Just make sure you don't get the torch so close to the paint that it torches it off.

[Drew Price]

If you are sending them to a shop anyways, how come you aren't having them tempered?

You should only be using 4130 filler rod for weldments which will be heat treated for additional strength. Use ER70-S2 or ER80-S2 for weldments which will be annealed or normalized, especially if you do it with a torch. It keeps the joint a little more ductile, and gives some assurance that the weld will yield, rather than fracture if you overload it.

I use only ER70-S2 for frame and suspension components which do not get hardened, more ductile than the 80. All the joints are torch normalized using 1600*F temperature indicating liquid for a few inches around the weld.

One of the drivers curbed the left front wheel during testing, and buckled the lower rear leg of the a-arm. We have threaded rod ends on the inboard mounts, and you can see the very top threads on the forward pulled up and out of the threaded fitting, but the weld did not fracture and pull the mount free.

Best,
Drew

[exFSAE]

Used 70S-2 for years worth of frames and a-arms.. no problems. Welds like a charm.

[Kurt Bilinski]

An article from the Welding Journal of the American Welding Society

What about Welding 4130?
In the mid 1970s, while managing an R&D group for a welding filler metals manufacturer, I received a phone call from a dragster chassis builder. The company wanted to weld 4130 tubing and needed a filler metal recommendation. After careful review of the requirements and desired welding practices, the solution was defined. The company was welding 4130 normalized tubing. It would not be heat-treated after welding, and preheat was not desirable. Most of the weld joints were intersecting tubes that required fillet welds.

Filler Metal Choice
The main objective was to produce porosity- and crack-free weld deposits. The best filler material to use was a low-carbon alloy, AWS ER70S-2. This welding alloy has a very low carbon content, nominally 0.06, which can handle dilution into the relatively high (in terms of weld metal) 0.30 carbon in the 4130. The resulting diluted weld deposit has a tensile strength of approximately 590 to 620 MPa (85,000 to 90,000 lb/in.2) The actual strength will depend on the amount of dilution with the 4130, weld bead size, and material thickness. This is usually an under match for the 4130 tubing, which could have 760 to 800 MPa (100,000 to 115,000 lb/in.2) tensile strength, depending on how the material was processed. However, if extra joint strength is required, a slightly larger fillet size or gussets can be employed. In addition, this welding wire contains small amounts of Aluminium, titanium, and zirconium. Although these elements were initially added to handle welding over mill scale, they also contribute to a less fluid weld pool. The benefit to the welder is easier out-of-position welding. Note: It is recommended all welding on 4130 be performed on ground surfaces free of oil or grease.

Several years after making this recommendation, when looking at a catalog from the dragster chassis manufacturer, it was interesting to note it advertising its use of the ER70S-2 filler metal for their 4130 welding. In fact, offering it for sale for those customers purchasing frame parts and doing their own welding!

The Internet was searched to see what current recommendations were being made for joining 4130 tubing. Several hundred sites were found that recommend the ER70S-2 welding wire alloy. It was the predominant recommendation. Typical of the Internet, however, there were many improper descriptions of why this alloy should be used and several incorrect recommendations.

Go for Higher Strength
If a higher strength weld is required for perhaps a butt-joint weld that cannot be reinforced, strengthened with a gusset, or put in a less critically stressed area, there are several possible solutions. The use of AWS ER80S-D2, which contains 0.50 moly, will provide a weld deposit with higher strength. When diluted into the 4130 base material, a weld tensile level of 760 to 800 MPa (110,000 to 115,000 lb/in.2) can be achieved. If this higher strength welding wire is employed, a minimum preheat of 65¡C (150¡F) is recommended. It is also possible to use an AWS ER312 stainless steel welding wire. Weld strength can increase to a level slightly higher than with AWS ER80S-D2.

Generally, the use of this high chrome stainless alloy is only needed when welding stainless to steel. Do not use an austenitic stainless steel such as an ER308L, which is, unfortunately, sometimes recommended. Diluting this or similar austenitic stainless alloys with 4130 can lead to cracks. Also, consider that providing a higher strength weld deposit cannot compensate for the reduction in strength that will most likely occur in the base metal immediately next to the weld deposit. To achieve the higher strength, the base metal was heat-treated, reducing the weld heat-affected zone area hardness.

If the part is heat-treated after welding to achieve very high strength, a matching chemistry filler metal to the 4130 must be employed. Because of the relatively high carbon content, a minimum of 200¡C, (400¡F) preheat and very slow cooling after welding should be used to avoid cracking. After welding, the part can be heated to 870¡C (1600¡F), quenched in oil or water then tempered back to 370¡C (700¡F). This might be considered a complex cycle, but it will result in a tensile strength of approximately 1380 MPa (200,000 lb/in.2). Since the weld is the same chemistry as the base metal, it and the heat-affected zone will have properties similar to the base metal when heat-treated. All critical welds of this type should be inspected for internal soundness to assure they are free from cracks.

Closing Advice
When welding 4130 chrome moly in the normalized condition, AWS ER70S-2 filler metal, with its low carbon content; is the proper choice. If the part is to be heat-treated after welding, then a filler metal matching the 4130 chemistry should be employed. This requires preheat and special precautions to avoid cracking.