My home inspection of Speedmaster heads

Krooser said
You thinking of Isky "Tool Room Steel"? Just a fancy name for the same materials everyone else uses...

Oh the good ole tool room springs, that cost 300+ dollars anymore. Isky is great... but a racers brand for sure.
Nah, many use or have used tool steel.
Howard's for instance..
Pro - Series H - 11 Tool Steel Triple Valve Springs; 1.625 Howards Cams 98751-1 | Howards Cams

Chrome silicon, vanduim, all kinds of alloys used in some proprietary mix.