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Originally Posted by mgarblik
Wonder if they got the idea from ArmaSteel which also wasn't steel, just a specific ductile cast iron. At least it was good quality.
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Actually, there were multiple grades of "Armasteel", but you're right, it was high-carbon, nodular cast-iron not "steel". However, it was not "ductile" iron. It was "malleable" iron.
Malleable iron is nodular iron where the carbon nodules are formed primarily with heat-treatment.
Ductile iron is nodular iron where the carbon nodules are formed primarily with chemical elements in the alloy.
Ductile iron is more popular now because it's cheaper to put stuff in the alloy than to go through an extensive (expensive) heat-treatment process. I'm not saying that ductile iron is not heat treated, but it's not heat treated in the specific way required to turn flakes of graphite into nodules of graphite.
Chrysler was more honest. Their crankshafts were "Pearlitic Malleable Iron" which is to say the functional equivalent to Armasteel, but without the trade-name and royalty payments to GM.