Welding my GM 10 bolt axle tubes - the basic test: Iron or steel? Mine is cast STEEL

First step in welding axles tubes it determining the housing material by doing a small test drill and observing the shavings, a sharp bit will produce a spiral shaving as shown first, and the metal is shiny if cast STEEL. Cast IRON will produce almost perfectly uniform looking pieces that are long and have a grey dull color.
Knowing what material you have is crucial in your approach.
Cast STEEL is alot easier and requires alot less skill. Preheat preferred to 200 to 300 degrees, but you can also just weld it straight mig stick or tig and get good results.
Cast IRON requires pre and post heating to higher temps, peening, blanket wrapping and alot more care and skill and 90 or 99 nickel rods.

[@Fix_It_Again_Tony]

Cast iron is a term that applies to a very wide range of materials. There is grey, white, ductile (nodular) and malleable. Even among a given class like ductile, there are a variety of alloys. The ductile variety is the one typically found in automotive applications. It can produce some spiral shavings when drilled, but they are distinct from steel in their grey color (as you noted) versus a more silver color with steel and the shorter, rougher spiral shavings versus steel's clean long spiral shavings.
Personally I think the drill test is the most conclusive (short of a lab analysis, which is out of reach of most hobbyists). I've tried this on a DANA 44 from the front of a '77 Ford F150. I compared the housing, tubes, inner C's and knuckles. The housing and knuckles are ductile iron and the tubes and C's are steel. The C's are cast, but they are steel.
One interesting choice when welding ductile iron is ER NiFeMn-CI filler. You can buy smaller spools for MIG welding in 0.035" diameter from Crown Alloys under the brand Royal 44-30. You can use this wire with C25 shielding gas and pre and post heat may not be required, but for large work pieces a moderate pre-heat may be a good idea to enhance penetration, like you would with a large steel work piece.
See: app.aws.org/wj/supplement/WJ_1985_03_s79.pdf
It's a bit technical, but the addition of Mn lowers the solidification temperature of the filler and allows it to more closely match the thermal expansion of ductile iron which reduces stress in the HAZ. This is what prevents cracking.

[@sterlingwitherspoon5709]

Was your axel tubes leaking? Is that why youre welding it

[@ayzoidz2651]

Probably to lower the risk of it spinning

[@naranjoceidy]

Leaking. My friend said to put caulking to seal it and avoid leaking

[@moejr14]

Finished product?

[@fstarockaburns425]

Yes it's finished but the point of the video is to demonstrate how I checked if mine was iron or steel-

[@moejr14]

@@fstarockaburns425 I guess I should have asked. Did you preheat and did it crack after welding to it

[@fstarockaburns425]

@@moejr14 steel doesnt require preheating, cast IRON does- these differentials are cast steel so you can use flux core wire or pref a 7018 rod, 1 inch every 90 degrees so it can cool down during beads. There is a groove i just cleaned it VERY well with a wire brush and brake cleaner.. hth

[@lanebigham6570]

It isn't known what kind of metal GM used to build these ??

[@bigtsmotorizedbikes4242]

They did both