CS · 10 grades
Carbon & Alloy Steels
Cheap, strong, and completely dependent on what you do to the surface.
Carbon and low-alloy steels are the value option: high stiffness for the money, and heat treatable to whatever strength the part needs. The range runs from 12L14, which machines faster than anything else on the shop floor and rusts if you look at it, to 4340, which will hold a hard-chrome plated surface under load for years. The choice is a trade between machinability, hardenability and corrosion.
What this family does well, and where it bites
- Cost per kilogram well below stainless or aluminium alloys
- Through-hardening, case hardening, nitriding and induction hardening all available
- Free-cutting grades (12L14, 1215) give the fastest cycles of any metal we cut
- Unprotected surfaces rust - plating, black oxide or painting is part of the design
Industries served
- Industrial Equipment
- Automotive & EV
- Energy & Oil & Gas
- Agricultural Machinery
- Rail
Carbon & Alloy Steels grades we machine
Each grade page carries the properties as supplied, what heat treatment does or does not do to it, the achievable surface finish, starting cutting parameters and the DFM notes that matter for that specific grade.
1018
8/10126 HB · 440 MPa
The baseline mild steel: soft, predictable, cheap.
1020
8/10119–159 HB · 420 MPa
Effectively 1018 with a slightly tighter carbon range.
1045
6/10179 HB (as-rolled) · 45–55 HRC hardened · 565 MPa (normalised) · 700 MPa+ heat treated
Medium carbon: the first grade on this list that actually hardens.
12L14
10/10163 HB · 480 MPa
The fastest-cutting metal on the shop floor and the 10 on our scale.
1215
10/10170 HB · 540 MPa
The other free-machining steel.
1137
8/10170–200 HB · 620 MPa
Medium carbon with sulphur added: it machines nearly as well as a free-cutting grade and still hardens.
4140
6/10197–235 HB annealed · 28–32 HRC quenched and tempered · 1,020 MPa (Q&T) · 655 MPa (annealed)
The workhorse alloy steel.
4340
5/10217–255 HB annealed · 36–40 HRC quenched and tempered · 1,100–1,200 MPa (Q&T)
Tougher and harder than 4140 at the same strength, and it machines accordingly - expect lower speeds, shorter tool life and a real grinding allowance after heat treatment.
8620
7/10149–200 HB (as-supplied) · 58–62 HRC case after carburising · 650 MPa core (hardened and tempered)
Low carbon and soft in the delivered state, so it machines like a mild steel - then it is carburised and hardened to give a hard case over a tough core.
A36
7/10119–159 HB · 400–550 MPa
Structural plate and section steel.
Questions buyers ask
- When is 4140 the answer rather than a stainless grade?
- When you need stiffness and fatigue strength per unit cost and the environment is not corrosive. 4140 quenched and tempered to 28–32 HRC is the standard answer for shafts, and it will outlast a 304 shaft in a plain bearing application because the 304 galls.
- How much does leaded steel actually save?
- Enough to notice on volume parts: 12L14 turns at roughly double the speed of 1018 with better chip control. It is not for anything welded, and it is not for anything that has to be certified for a safety-critical joint - leaded steels are restricted in some aerospace and nuclear specifications.