Weld/heat treat questions

[GTmule]

I'm thinking of doing a part (similar to a bellcrank) out of fabricated steel, for several reasons (cost, mostly). WhatI wanted to know was, how can I treat the welds form an analysis perspective? Say I'm doing FEA, what's a good safe way to create the model to know the weld strength? Just fillets/champhers? will this be too "strong"?

Secondly, I wondered about heat treating the part, I assume this should be done after all the welding, but for a part like a bellcrank (it will be similarly loaded, but is not for a FSAE car), would yall generally just recomment RC 35 or 40, after it's all welded? (I'm thinking the part will be 4140 or 4130) Can I assume the welds won't be weaker after treat, etc?

[GTmule]

I'm thinking of doing a part (similar to a bellcrank) out of fabricated steel, for several reasons (cost, mostly). WhatI wanted to know was, how can I treat the welds form an analysis perspective? Say I'm doing FEA, what's a good safe way to create the model to know the weld strength? Just fillets/champhers? will this be too "strong"?

Secondly, I wondered about heat treating the part, I assume this should be done after all the welding, but for a part like a bellcrank (it will be similarly loaded, but is not for a FSAE car), would yall generally just recomment RC 35 or 40, after it's all welded? (I'm thinking the part will be 4140 or 4130) Can I assume the welds won't be weaker after treat, etc?

[Frank]

4130 is generally the go for heat treated fabrications

you should use 4130 VM filler
see your local aircraft supply house for these.
DONT ask a weld consumable supplier, they wont know what you need (in my case they tried repetitively to sell me the wrong product)

yep 35-40 Rc is what I've used

hollow sections are quite stable under heat treatment

i heat treated a 1/2" OD 058" sway bar that was about a foot long, and it didn't move much

and yes all welding before heat treatment

be wary of the heat treatment company leaving indentations on your part (they test hardness after the process)... either specify an appropriate location, or supply a test coupon wired to the part

[GTmule]

I'll have two rather thin pieces of plate/sheet hanging out in the breeze parallel to each other (1/8" thick and about 5" long) should I send these to the treater with a spacer bolted into the holes, just to keep 'em form moving around too much (again, think about a bellcrank, it'd be similar to this).

[Dan B]

I've always had the best luck with just drilling the holes way under sized and doing "post heat-treat machining"

[RKemmet]

The coupon is very useful if you don't want a nice dimple. 35-40 hrc depending on the indenter will leave a noticable hit, you can request to have it done with a lighter test (15N) and will leave a much smaller hole.. most of all though, HAVE NO SHARP CORNERS! if at all possible try to have no pointy corners, thats just asking for a cracked part. Talk to the heat treater you are going to use and see if you can get them to throw yours into a batch with something else to keep the cost down. All welding and most machinging should be done prior to heat treating or else you will be cold working the part and change the properties. (I interned at Phoenix Heat Treating over the summer doing inspection of the heat treat.)