Gennie/Shoreliner Carbody Material

Hey I have a question: What are the bodies of the P32s and other locos and the Shoreliners I-IV made of? Is it carbon steel, or something else? I ask because these units are painted while the M-series cars and the Comet Vs are not (presumably because these units are stainless steel).

The Genesis is High strenght steel
Bombardier cars are Alluminium
M2/4/6 are Stainless steel
VRE cars are Stainless Steel.

All Comet/Horizon/Shoreliner cars (except Comet V) are welded aluminum. This has been the case since the Comet I in 1970.

Thanks everyone!