ISO H — Hardened Steel · H10
H10 — Hardened steel (medium)
Hardness range: 55–60 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 — H10
- ISO designation
- H10 (ISO H — Hardened Steel)
- Material
- Hardened steel (medium)
- Hardness
- 55–60 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 (55–60 HRC) — starting point
- ISO application class
- H (hardened steel). Above ~45 HRC hard turning replaces grinding; above ~55 HRC CBN / PCBN is required. Match the ISO class across brands (Sandvik, Kennametal, Iscar, Walter, Seco and Mitsubishi) and confirm the CBN grade.
- Grade & coating
- CBN / PCBN for 55–60 HRC. A honed or chamfered edge prep is essential; carbide will not survive above ~55 HRC.
- Geometry
- Negative geometry with a T-land or chamfer plus a hone for edge security, and a large nose radius for finish. Very rigid setup. Run dry — coolant causes thermal-shock cracking on CBN.
- Starting parameters
- CBN Vc ≈ 100–200 m/min, fn ≈ 0.05–0.15 mm/rev, small ap ≈ 0.05–0.25 mm — a finishing regime, dry. Typical starting band — confirm in the advisor or on a sample part.
hardened steel (55–60 HRC): what goes wrong, and what to check first
- Edge chipping (CBN is brittle)
- Interruptions or too keen an edge chip CBN. Use a honed / chamfered edge, a robust CBN grade, a rigid setup, and minimise interruptions. See the tool-wear guide.
- White layer / thermal damage
- A worn edge or too-high speed overheats the surface and forms a white layer. Replace edges on schedule and keep speed in band, running dry.
- Chatter (rigidity is everything)
- In hard turning, chatter is setup, not grade. Shorten overhang and use a rigid tool and workholding.
- Rapid wear with the wrong grade
- Carbide will not survive above ~55 HRC — use CBN.
Reference data
Insert grade index
ISO insert-code index
CNMG120408 — general turning
CCMT09T304 — positive finishing
Tool-wear diagnosis
Get cutting parameters for Hardened steel (medium)
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