Carbon and alloy steels
The group most general-engineering parts fall into. It is chosen for the balance of strength, price and predictability at the cutting edge - not for peak performance, but for known and repeatable behaviour.
Usual grades
How it behaves at the cutting edge
The backbone of general engineering. S235 is a plain structural steel - cheap and forgiving. S355J2 and C45 are the grades machined as a matter of course: S355J2 is the structural steel with the higher yield strength, and C45 can be quenched and tempered. 42CrMo4 usually arrives already in the quenched-and-tempered condition, with uniform hardness through the section: it turns predictably, but demands tougher tooling than C45 and punishes a dull edge. 16MnCr5 is a case-hardening steel - machined soft and hardened only at the surface after carburising, so final dimensions are cut before heat treatment with an allowance for grinding. 11SMn30 is a free-cutting steel with sulphur: it cuts easily with short chips and suits large runs of small parts, but it cannot be welded or hardened.
What to state on the drawing
The grade and the condition are stated on the drawing, not just “steel”. As-rolled 42CrMo4 and quenched-and-tempered 42CrMo4 are turned with different tooling and priced differently. If the part is case-hardened, the grinding allowance is marked explicitly, together with the dimensions cut before treatment. For 11SMn30, the drawing states whether welding or hardening follows: it takes neither, and swapping the grade is cheaper discovered at quotation than at goods-in.
What it means for the routing
Case-hardening steels - 16MnCr5 is the usual one - have the longest routing: machined soft, carburised, then ground to size. Functional dimensions are cut after treatment; before it they stay with an allowance. Quenched-and-tempered steels arrive already treated and turn straight to size, but they demand a fresh edge: a dull tip does not cut them, it rubs, and the surface shows it immediately.
Where it is used
- Shafts and bearing journals
- Flanges and bushings
- Drivetrain parts
- Hydraulic and pneumatic bodies
- High-volume free-cutting steel parts
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