1075 Spring Steel Machining
1075 is a high-carbon steel — about 0.75% carbon — chosen for what it becomes after heat treatment rather than for what it is on the bench. In the annealed state it machines reasonably; hardened and tempered it holds an edge, resists wear and carries a spring load. The specification therefore has two halves, and the second half is the one that decides the part.
Specification at a glance
- Standard
- AISI/SAE 1075 · equivalent grades: C75, 1.1750
- Composition
- ≈ 0.70–0.80% C, 0.60–0.90% Mn, balance Fe
- Density
- 7.85 g/cm³
- Annealed hardness
- ≈ 190–230 HB
- Hardened hardness
- 60–64 HRC as quenched · 40–48 HRC tempered for springs
- Tensile (annealed)
- ≈ 700–800 MPa
- Machinability
- Good in the annealed condition · hard to machine after hardening (grinding instead)
- Typical finish
- Black oxide, phosphate, or bare with a protective oil · grind after hardening if tight
- MOQ
- From 50 pieces (samples from 1)
High-carbon steel is specified in two stages, and buyers who specify only the first stage usually discover the second one at first article. The drawing says “1075, 45 HRC” — that is two instructions: a material and a heat treatment, and the second one changes the dimensions.
What 1075 is
A plain carbon steel with roughly 0.75% carbon and no significant alloying. Cheap compared with alloy and tool steels, hardenable by quenching, and tough enough for springs and struck tools at the carbon level above 1.0% would make brittle.
The annealed condition — around 190–230 HB — is what arrives at the machine. It cuts like a medium-carbon steel: carbide tooling, moderate speeds, no drama. The properties that make the grade worth choosing appear only after hardening and tempering.
The two halves of the specification
Before hardening. Machine oversize, leaving grinding stock on any dimension that has to be precise. Holes, slots and threads are cut now, because after hardening the part is ground, not drilled.
After hardening. Quench and temper to the required hardness, then grind the critical dimensions. Distortion from the quench is not a defect — it is a property of the process, and the specification has to allow for it.
That is why a hardened 1075 part with a ±0.01 mm tolerance is a grinding job with a heat-treat step in the middle, not a turning job. The price reflects the sequence, not the material.
Hardness by application
Springs and spring washers: temper to roughly 40–48 HRC. Enough to carry load and return, not so hard that it cracks.
Blades and cutting edges: 58–64 HRC at the edge, with the spine softer if the part is thick enough to differentially treat.
Wear plates: 50–58 HRC, often with a phosphate or black oxide finish.
The number on the drawing should be the hardness the function needs, not the highest number the grade can reach. Every point of hardness added costs toughness, and a part that chips in service is worse than one that wears.
1075 against 1095
The difference is 0.2% carbon, and it shows up in three places:
- Edge holding: 1095 wins, which is why it dominates knife blades.
- Toughness: 1075 wins, which is why it is more forgiving in thin spring sections.
- Cracking risk in the quench: 1075 is lower, again because of the carbon level.
For a spring or a wear part where the load is cyclic, 1075 is usually the safer specification. For a cutting edge that must last, 1095.
Corrosion and finish
Unprotected high-carbon steel rusts within days in a humid workshop. The practical options:
Black oxide — thin, cheap, slightly improves corrosion resistance and looks right on tools.
Phosphate (manganese or zinc) — a porous conversion coating that holds oil, which is why it appears on fasteners, springs and stamped parts.
Plating — zinc or nickel, where the part is exposed. Hydrogen embrittlement is a real risk on hardened high-carbon parts, so a post-plate bake is specified.
What to send with a 1075 inquiry
The hardness and the tempering temperature if they are known, whether the part is a spring or a cutting edge, the tolerance on the critical dimensions, the finish, and the quantity. If the heat treatment is unclear, say what the part has to do — we will propose a hardness rather than guessing at a number on the drawing.
Frequently asked
- What is 1075 steel used for?
- Springs, flat spring washers, blades, wear plates, striking tools and any part that needs high hardness with reasonable toughness. It is also common for hand tools and agricultural wear parts.
- 1075 vs 1095 — what is the difference?
- Carbon content: 1075 is about 0.75%, 1095 about 0.95%. 1095 takes a higher hardness and holds an edge longer; 1075 is slightly tougher and less prone to cracking in thin sections. For springs, 1075 is usually the more forgiving choice.
- Can 1075 be machined after hardening?
- No, not practically. At 40+ HRC the material is ground rather than cut, so the sequence is: machine oversize, harden and temper, then grind to final tolerance.
- Why does a hardened 1075 part move?
- The quench introduces distortion, and thin sections move more. Leaving grinding stock, and specifying the heat treatment before the final dimensions are fixed, is how the tolerance survives.
- Does 1075 need a coating?
- Unprotected high-carbon steel rusts quickly. Black oxide, phosphate or a protective oil is normal; for outdoor parts, plating or a coating is usually specified.
Have a part in Steel 1075?
Send the drawing, the grade and the quantity. You get DFM feedback and a price within 24 hours, and orders start at 50 pieces per style and material.