There are 14 Steel/Cast-Iron and Heat-Treatment categories, each with 3 Quality levels - identical to the ISO 6336-5 Standard for Gears.
Steels Categories and Heat-Treatment
1.Normalized, Low-Carbon Wrought-Steelsa - St
2.Normalized, Low-Carbon, Cast-Steelsa - St(cast)
3.Black Malleable Cast-Iron - GTS (perl)
4.Nodular Spheroidal Cast-Iron - GGG ( - see image above )
5.Grey Cast-Iron - GG
6.Through-Hardened Wrought Carbon-Steelb - V
7.Through-Hardened Wrought Alloy-Steelsb - V
8.Through-Hardened Cast Carbon-Steel - V(cast)
9.Through-Hardened Cast Alloy-Steel - V(cast)
10.Case-Hardened Wrought-Steelsc - Eh
11.Flame or Induction-Hardened Wrought or Cast-Steels (IF)
12.Nitrided Nitriding Wrought-Steelsd - NT(nitr)
13.Through-Hardened Nitrided-Steelb - NV(nitr)
14.Through-Hardened Nitro-Carburized Wrought-Steele - (NV (nitr-car)
a - ISO 4948-2 (ISO10020) Part 2 - Classification of unalloyed and alloy steels according to main quality classes and main property or application
b - ISO 683-1 - Heat-treated Steels, alloy steels and free-cutting steel Part 1 - Quenched & Tempered unalloyed steels
c - ISO 683-11 - Heat-treated Steels, alloy steels and free-cutting steel Part 11 - Wrought Case Hardening steels
d - ISO 683-10 - Heat-treated Steels, alloy steels and free-cutting steel Part 1 - Quenched & tempered unalloyed steels
e - ISO 683-1, ISO683-10, or ISO 683-11
The Steel Quality Standards are:
ML - Modest demands on the material quality and the heat treatment process
MQ - Material Quality and Heat-Treatment standards met by experienced manufacturer.
ME - High degree of reliability of Material Quality and Heat-Treatment process.
The requirements to be met for different steel qualities include: Chemical Analysis, Melting Practice, Surface Crack Detection after machining, Hardness must be measured. Sometimes with a test piece of steel that is manufactured, and heat-treated together with cam - See ISO 3663-5.