Start with the Duty
Torque, shock, speed, size, environment and life decide the steel. The cheapest steel that meets the duty is the right one.
Carbon Steel
EN8 and EN9 are medium-carbon steels, normally hardened and tempered, sometimes with the teeth induction hardened. They suit moderate-torque drives and cost least.
Through-Hardening Alloy Steel
EN19 and EN24 are hardened and tempered right through. They are strong and tough and suit medium to heavy duty, and large gears where a case-hardened layer would be impractical.
Case-Hardening Alloy Steel
16MnCr5, 20MnCr5, EN353 and SAE 8620 are carburised so the surface is very hard, around 58 to 62 HRC, while the core stays tough. This is the usual choice for heavy and shock-loaded drives.
Stainless Steel
SS316 and SS304 resist corrosion but cannot be hardened, so their strength is limited. SS410 and SS420 can be hardened. Use stainless where corrosion matters more than load.
Size and Case Depth
A larger module needs a deeper case. State the module and duty so that the case depth can be chosen.
Certificates
If you need a mill test certificate, say so with the enquiry. See alloy steel, carbon steel and stainless steel gears.
