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.
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
Insert grade index
ISO insert-code index
CNMG120408 — general turning
CCMT09T304 — positive finishing
Tool-wear diagnosis
Get cutting parameters for Hardened steel (low)
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