Post 4130 Care

[Jet109]

After having finished the 4130 uprights, Lower boxed arms, tube top arms and frame, I'm after some answers regarding post care for the material.

I have access to a oven for the parts, so would like to know what I should do and what the process is.

Annealing Or normalising? Clearly I used 4130 for it's strength, but don't want it to be cracking up. hence why I was leaning towards Annealing? If correct, what temperature and for what time do I put each part in the oven, and how should I ramp down or cool afterwards?

Thanks for any input!
Phil

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[scottm]

What filler rod did you use? Search the forums for a lot of info, but also a lot of conflicting advice. I made a post here a couple days ago:

http://www.race-dezert.com/forum/sho...Chromoly-Frame

[Jet109]

Hey Scott, I used ER70S-6.
Yes Noticed that, seems to be a bit of a black trade!

[scottm]

Hey Scott, I used ER70S-6.
Yes Noticed that, seems to be a bit of a black trade!

Its not really a black art, its more a matter of 4130 being forgiving enough so that pretty much every approach works for us offroaders. If you were building an engine mount for an airplane, the requirements are much stricter. For 70s-x filler you dont need to do anything else. Most pro fabricators weld with 70s specifically so they dont have to take further steps. If you used 80s or 100s, you would have to at least stress relieve. Like I said in the other thread, there is a lot of misunderstanding about heat treating. Annealing, normalizing, stress releiving, quench and temper, etc are all forms of heat treating. The only thing that will produce higher strength than normalizing is q&t, but you can not quench a welded structure like an a-arm or spindle. Normalizing is the only option available to improve the properties over your as-welded parts. But its really only worth the expense when you weld with a high strength filler like er80 or 100s, as 70s filler will hold back the potential max strength of the weldment. Any heat treating shop should have a large enough oven for an a-arm or trailing arm. If you have trouble finding one, look around airports for a welding shop that does aircraft repairs.

For your frame, the relevant options are stress-relieving, normalizing, or annealing. A lot of people misunderstand the term heat treating with regard to large frames. The term can have many different meanings, from a full anneal to a quench-and-temper. Quench-and-temper is the 'main' form of heat treating, as it produces the highest hardness and strength possible, but only for relatively small parts like drill bits and hardware. Q&T obviously requires a quenching tank of oil or water, depending on the steel alloy. But aircraft structures and race car chassis are not quenched for several reasons, primarily the fact that there are no quenching tanks large enough! So 4130 was developed for aircraft in the 1930's to produce a decent improvement in strength from 'normalizing', which is heating to the austinatizing temp (about 1550 F for 4130) and air cooling. In other words, getting it up to temp then dragging it out of the furnace to cool in open air.

Your choice of heat treatment depends on many factors, from the actual level of strength required for your part, to the type of filler you weld it with. If you weld with high strength filler like er100S-x, you MUST at least stress relieve to remove brittleness in the weld. For offroad race chassis specifically, most fabricators use a mild filler rod like er70S2 with a little preheat, (300F) then you dont have to worry about additional heat treatment. If you really want to achieve optimum properties, I suggest welding with er80s, with 300F preheat, and have it normalized at Burn-A-Rod down there by Phx Sky harbor airport. From one asu engineering student to another, good luck and have fun!

[CRAIG_HALL]

Annealing would make it softer, Normalize would bring it back to it's pre-welded state. if you want more strength, heat-treat.

[Jet109]

Thanks Craig,
Oviously from the first to the ast choice the risk of crack would increase? So I'm trying to find a happy point? And with that happy point, what is the necessary steps in doing so?
For sure I would like more strength, but I Strongly do not want cracking to occur. Would Normalize be okay?

[atomicjoe23]

What is the wall thickness of the frame and the tubular UCA's? What thickness plate did you use for the boxed LCA's? Finally what is the thickest cross-section of the uprights?

Post up those answers and I will post up the info for you on what you are looking for temp's and times for each process. . .I will also include the ultimate tensile strengths and the yield strengths of each process. . .I doubt you have an oven that has the capability to heat the 4130 hot enough to heat treat or anneal it. . .that would require a temp of ~1600-1700*. . .you would then normalize the material by allowing to coiol to room temperature in air and you would heat treat it by placing back in a cooler oven (the temperature will determine how hard the material ends up being) for a specified period of time based on the cross-sectional thickness of the material.

. . .you do not want to anneal the 4130, annealing makes the material very soft and ductile (very soft and ductile being relative terms of course). . .annealing is the process that is performed when sheetmetal guys want material soft enough to hammer form (think making motorcycle gas tanks and fenders by hand), so I would suggest staying far away from that. . .normalizing takes the material above the transformation temperature (where austenite forms) and then it is allowed to room temperature at room temperature in air vs. hardening which normally has a quench of one type or another (precipitation hardening being an exception to this. . .like 17-4 pH stainless steel. . .the pH stands for precipitation hardening which basically means age hardening, it gets harder from age and it is cooled to room temperature in room temperature air. . .I've been heat treating a LOT of 17-4 lately!!!).

I've posted it many times, but I will say it again. . .if the 4130 is a 1/4" thick or less it doesn't need any post-weld heat treatment (assuming it wasn't overheated in the process of welding). . .this comes from 30+ years of aerospace welding experience with Boeing.

[Jet109]

Hi mate, Thanks for the reply!
I work in the furnace industry, in developing ovens etc. Not so much experienced in the actual process of heat treating as most of the ovens we produce are used to create beads for mineral sampling requirements.
we have an oven here which can go to 2200*F.
The frame wall thickness is 1.5" x 0.100" 4130, with 1" x 0.065" 4130 brace work.
The Lower Arms are made from 0.065" 4130 plate (yes, I know, that's very thin!)
The Top Arms are 1.25" x 0.083" 4130 Tube
The thickest section in the Upright is 0.1875" not including the welded on Stub. (which is drilled out for a max thickness of (1/2")
It is safe to assume I overheated it in a few spots during welding.
I highly value your experienced input on this mate, looking forward to your reply!

Cheers
Jet

[Jet109]

Hi Scott, Thanks for the reply.
I do agree with you on the fact that it is not necessary, but because I am in a situation where I can utilise an oven for free, I thought I might as well go for it. I put all my time and effort into building this new car, and if I can do anything extra to ensure I wont see cracking later on, and it's free, I thought I might as well go for it!

Cheers mate
Phil

[scottm]

Well in that case by all means normalize it. Set the oven to 1000 F and let the temp stablize with nothing in it. Put in the parts and reset the controller to 1550 F. Wait for it to reach 1550 inside, then start timing. Let it soak for 1 hour per inch of thickness at the thickest section - for you probably 20-30 min will be fine. Then pull it out and let it air cool. Be careful when you pull it out as it may bend if it drags. I like to put the parts on a pan or a sheet of thin steel, so you can remove them by dragging the sheet out. Its also a good idea to keep them off the floor with square tube or angle so air can circulate around your parts.