Heat treating welds?

[mexracer10]

I have been reading all of the recent tig wleding threads, but i have not found what i am looking for. I am biulding some class 12 front lower trailing arms, the materials are 1.75 od 4130 x .250 wall and 1.75 x 3/8 wall dom for the shank that sits in the beam. What filler rod should i use to weld these arms? They are going to get heat treated and to what hardness should they be treated to? r31-33?? Thats what i have read on line from various sources but i have never had anything heat treated so any input from the resident experts would be very much appreciated.

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[BajaFand]

I believe if you are heat treating you can get away with using 4130 filler rod, because after heat treating the entire part will be of the same properties and quality. 4130 is too brittle for parts that won't be heat treated, it will crack and break apart. ER70s2 will also work for heat treating.

[ACID_RAIN28]

Using 70s2 will not make the heat treat process worth it, the rod you want is a 502/ER-80s Finding 502 is a little difficult but 80s will deliver the similar end results and is readily available. How ever why heat treat the part if you are using DOM in the first place? is The DOM 1018/1020/1040? and the range is 32-36Rockwell C scale. Don't use the 4130 rod

[scottm]

1020 dom can not be hardened by heat treating. There is not enough carbon and/or alloying elements such as chromium and molybdenum to make it hardenable. Well thats not true, it can be carburized, but that does not apply to suspension parts. To make a hardenable arm, you neeed to build it from 4130 chro-moly materials. Then weld it with 4130 filler or ER80Sx filler.

Low carbon steels and 300 series stailess steels can only be hardened by cold working. Cold working is cold rolling for sheet, and cold drawing (DOM) for tubing. DOM and cr sheet is about 50% stronger than hot rolled sheet and tube. BUT all the mechanical hardness will be lost in the heat affected zone of the weld. 4130 will actually self quench when welding, which makes it gain hardness, but can also become brittle. Thats why the proper way to weld 4130 is to pre heat it to 300° F, as that reduces the cooling rate and excess hardness formed. A lot of fabricators use 70Sx filler on 4130 with no further treatment and no concern about brittleness. If you mig weld 4130 with 70S filler, you still need to preheat, as mig goes on so fast.

[mexracer10]

So i should not even heat treat these arms and weld them with er70s2 for now. Later i can buy all 4130 material and weld it with 80sx rod and then have that heat treated. The only reason i used dom was because then thinkness i needed they only had in dom. But for next time i can just use 1.75 x .250 wall 4130.

[ACID_RAIN28]

Yes unless they are 100% 41xx alloy, there is no need to heat treat the part.

[A Vance]

it is always good to atleast stress relieve any parts after being welded in an impact type of part. when welded the area around the weld will become hard but the surounding area of the weld will be britle and not as strong. 4130 was created for aerospace and the proper way to weld it is to preheat and post heat and slow cool.