ISO H — Hardened Steel · H01
H01 — Hardened steel (low)
Hardness range: 45–55 HRC. Part of the ISO H — Hardened Steel group. Hard turning replaces grinding for many finishing operations on hardened steel above 45 HRC. CBN (cubic boron nitride) and PCBN inserts are required above 55 HRC. Dry machining is preferred — coolant causes thermal shock cracking. Tight radius inserts (rε 0.4–0.8 mm) and low feed rates preserve surface finish.
Material profile — H01
- ISO designation
- H01 (ISO H — Hardened Steel)
- Material
- Hardened steel (low)
- Hardness
- 45–55 HRC
- ISO group colour
- Hardened Steel
Tooling guidance — H-group
- Group summary
- CBN/PCBN required above 55 HRC. Dry machining preferred — coolant causes thermal shock.
Insert selection for hardened steel (45–55 HRC) — starting point
- ISO application class
- H (hardened steel). At 45–55 HRC hard turning replaces grinding for many finishing cuts; a hard coated carbide works near 45 HRC, with ceramic or CBN as hardness climbs toward 55. Match the ISO H class across brands rather than the brand name (Sandvik, Kennametal, Iscar, Walter, Seco and Mitsubishi each publish one), then confirm the exact grade for your condition.
- Grade & coating
- Hard coated carbide near 45 HRC; ceramic or low-content CBN toward 55 HRC. A honed or chamfered edge is essential.
- Geometry
- Negative geometry with a T-land or chamfer plus a hone, a large nose radius for finish, and a very rigid setup. Usually run dry.
- Starting parameters
- Carbide near 45 HRC Vc ≈ 80–140 m/min; CBN higher, ≈ 120–200 m/min; fn ≈ 0.05–0.20 mm/rev, light ap. Finishing regime — confirm in the advisor or on a sample part.
Selection table: hardened steel (45–55 HRC)
| Operation | Geometry | ISO class | Coating family | Coolant | First check |
|---|---|---|---|---|---|
| Roughing | Not a roughing material at this hardness: hard turning is a light-ap finishing regime | H | Hard coated carbide near 45 HRC; ceramic or low-content CBN toward 55 HRC | Usually dry | Is the hardness really in band for the grade chosen |
| Finishing | Negative with T-land or chamfer plus hone, large nose radius | H | Hard coated carbide near 45 HRC; ceramic or CBN as hardness climbs | Usually dry | Edge wear: a worn edge overheats the surface and leaves a white layer |
| Interrupted cut | Honed or chamfered edge, robust grade | H | Tougher hard coated carbide or ceramic grade | Usually dry | Grade too brittle for the interruption, or edge too keen |
| Low rigidity / thin wall | Negative with chamfer plus hone; shortest overhang, rigid clamping | H | As finishing | Usually dry | Chatter is rigidity, not the grade: shorten overhang |
hardened steel (45–55 HRC): what goes wrong, and what to check first
- Edge chipping
- A grade too brittle for the interruption, or too keen an edge. Use a honed or chamfered edge, a robust grade, and a rigid setup.
- White layer / thermal damage
- A worn edge or too-high speed overheats the surface. Replace edges on schedule and keep speed in band.
- Rapid wear with too-soft a grade
- Below ~50 HRC a hard carbide can work; as hardness rises move to ceramic then CBN.
- Chatter
- In hard turning this is rigidity, not the grade. Shorten overhang and clamp rigidly.
Reference data
Frequently asked questions
What insert should I use for steel at 45–55 HRC?
A hard coated carbide works near 45 HRC; move to ceramic or CBN as hardness climbs toward 55, always with a honed or chamfered edge. Match the ISO H class across brands and confirm the grade in the advisor.
Is 45–55 HRC carbide or CBN?
Carbide can still cut near 45 HRC, but ceramic and then CBN take over as hardness rises toward 55 HRC and above. CBN is required past ~55 HRC.
Can hard turning replace grinding at this hardness?
For many finishing operations above ~45 HRC, yes, given a rigid machine and a honed edge.
Why does my edge chip on hardened steel?
Too brittle a grade for any interruption, or too keen an edge. Use a honed or chamfered edge and a rigid setup.
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