ISO H — Hardened Steel · H20
H20 — Hardened steel (high)
Hardness range: 60–68 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 — H20
- ISO designation
- H20 (ISO H — Hardened Steel)
- Material
- Hardened steel (high)
- Hardness
- 60–68 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 (60–68 HRC) — starting point
- ISO application class
- H (hardened steel). At 60–68 HRC, CBN / PCBN is mandatory; carbide and most ceramics will not survive. 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
- High-content CBN / PCBN with a honed or chamfered edge. This is a finishing operation, not roughing.
- Geometry
- Negative geometry with a strong chamfer plus hone, a large nose radius, and an extremely rigid setup. Run dry.
- Starting parameters
- CBN Vc ≈ 100–180 m/min, fn ≈ 0.05–0.12 mm/rev, ap ≈ 0.05–0.15 mm. Finishing only — confirm in the advisor or on a sample part.
hardened steel (60–68 HRC): what goes wrong, and what to check first
- Edge chipping
- CBN is hard but brittle; any interruption or too keen an edge chips it. Use a strong chamfer plus hone, a robust grade, and zero-interruption passes where possible.
- Thermal cracking
- Avoid water-based coolant on CBN; thermal shock cracks the edge. Run dry.
- Dimensional drift
- Edge wear shifts size on tight-tolerance finishing. Monitor and index on a schedule.
- Chatter
- Rigidity is everything at this hardness. Use the shortest, most rigid tool and workholding.
Reference data
Insert grade index
ISO insert-code index
CNMG120408 — general turning
CCMT09T304 — positive finishing
Tool-wear diagnosis
Get cutting parameters for Hardened steel (high)
The AI advisor maps your specific material condition and operation to a verified insert grade, coating, and Vc/fn range — with live search across the latest tooling catalogs.
Related materials