C7
Grade · default condition
GB YT15 · ISO P20
C7 = steel finishing grade, WC-TiC-TaC-Co, uncoated
Default uncoated finishing grade for continuous turning/boring of steel where surface finish and crater resistance matter.
Values for the C7 condition
Other C7 tempers and conditions
C7 is listed in 3 conditions; see the grade overview at C7.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
GB/T 18376.1 WC-15TiC-6Co steel cutting grade | Chinese-market equivalent for semi-finish/finish turning of carbon and alloy steel; widest domestic availability as brazed tips and blanks. | — | 700 | 0.05 | 1,480 HV | 21 W/m·K |
C7DefaultThis page Steel finishing grade, WC-TiC-TaC-Co, uncoated | Default uncoated finishing grade for continuous turning/boring of steel where surface finish and crater resistance matter. | — | 800 | 0.05 | 1,600 HV | 30 W/m·K |
ISO 513 general-purpose steel turning/milling grade | Pick when the cut is interrupted or feeds are heavier: higher Co and TaC give more toughness at the cost of some hot hardness. | — | 900 | 0.05 | 1,500 HV | 35 W/m·K |
What is C7?
C7 is C7 in the C7 grade — default uncoated finishing grade for continuous turning/boring of steel where surface finish and crater resistance matter. C7 has a tensile strength of 800 MPa (116 ksi), stronger than 79% of ceramic grades. Elongation at break is 0.05% and the elastic modulus is 540 GPa (78.3 Msi). C7 has a density of 11.1 g/cm³ (0.401 lb/in³), heavier than 79% of ceramic grades. It melts at 1,320°C (2,408 °F).
Advantages
- Stiff — 540 GPa (78.3 Msi), better than 86% of ceramic grades
- Tough — resists crack growth — 8.5 MPa·√m (7.74 ksi·√in), better than 79% of ceramic grades
- Polishes to a fine finish — 90/100, better than 78% of ceramic grades
Limitations
- High embodied carbon — 28 kg CO₂/kg, worse than 84% of ceramic grades
- Needs corrosion protection — 52/100, worse than 81% of ceramic grades
- Heavy — 11.1 g/cm³ (0.401 lb/in³), worse than 79% of ceramic grades
C7 properties
Typical room-temperature values for C7; 14 are specific to this condition. Other listed values are C7 reference data and may not represent this condition. Bars are the position among ceramic grades.
Physical3
C7 has a density of 11.1 g/cm³ (0.401 lb/in³), heavier than 79% of ceramic grades. It melts at 1,320°C (2,408 °F).
Mechanical13
C7 has a tensile strength of 800 MPa (116 ksi), stronger than 79% of ceramic grades. Elongation at break is 0.05% and the elastic modulus is 540 GPa (78.3 Msi).
Thermal5
C7 is rated for continuous service to 900°C (1,652 °F). It conducts heat at 30 W/m·K (17.3 BTU/hr·ft·°F), better than 60% of ceramic grades. Thermal expansion is 6.7 µm/m·K (3.72 µin/in·°F).
Electrical1
C7 has an electrical resistivity of 5.5×10⁻⁷ Ω·m.
Chemical & Environmental2
Corrosion resistance is fair (52/100), worse than 81% of ceramic grades.
Sustainability4
Producing a kilogram of C7 takes about 400 MJ of energy and emits 28 kg of CO₂ — more than 88% of ceramic grades. Typical recycled content is 25%.
Manufacturability3
C7's machinability is not recommended (4/100, worse than 85% of ceramic grades).
Common Calculations4
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with C7
Is C7 easy to machine?
Only diamond grinding, lapping, wire/sinker EDM and laser — no conventional cutting; grind wet to avoid thermal cracks.
Can C7 be welded?
Not fusion weldable; joined by silver-brazing (Ag-Cu-Zn/Cu-Mn) with a copper or nickel interlayer to absorb CTE mismatch, or by shrink fit.
Can C7 be formed, bent or molded?
Net-shape route only: powder pressing or extrusion of a WC-TiC-TaC-Co blend, dewaxing, then liquid-phase vacuum sintering or sinter-HIP at ~1400–1500 °C with ~18–20 % linear shrinkage.
What surface finishes work on C7?
Diamond lapping/polishing to Ra <0.1 µm for cutting edges; edge honing before CVD/PVD coating; do not electroplate over the Co binder without careful pretreatment.
C7 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Cobinder phase; higher Co = tougher, softer | 5 – 8 | 6 |
| TiCcubic gamma phase, crater/oxidation resistance | 8 – 16 | 12 |
| TaCTaC+NbC, grain refinement and thermal shock | 2 – 8 | 5 |
| WCbalance, hard skeleton phase | balance | — |
C7 — frequently asked
What is C7 used for?
C7 is typically used for steel finishing inserts, high-speed light turning of steel, boring bars and tips for steel, finish facing tools, CVD-coated indexable inserts and semi-finish turning of alloy steels. In short: finishing-grade steel carbide; high TiC/TaC crater resistance; 900 °C service limit.
What is the tensile strength of C7?
C7 has a typical tensile strength of 800 MPa (116 ksi) — stronger than 79% of ceramic grades. Strength varies by condition: see the 3 listed tempers.
Is C7 easy to machine?
Not especially — machinability is rated not recommended (4/100, worse than 85% of ceramic grades). Only diamond grinding, lapping, wire/sinker EDM and laser — no conventional cutting; grind wet to avoid thermal cracks.
Can C7 be welded?
Not fusion weldable; joined by silver-brazing (Ag-Cu-Zn/Cu-Mn) with a copper or nickel interlayer to absorb CTE mismatch, or by shrink fit.
What surface finishes work on C7?
Diamond lapping/polishing to Ra <0.1 µm for cutting edges; edge honing before CVD/PVD coating; do not electroplate over the Co binder without careful pretreatment.
Can C7 be formed, bent or molded?
Net-shape route only: powder pressing or extrusion of a WC-TiC-TaC-Co blend, dewaxing, then liquid-phase vacuum sintering or sinter-HIP at ~1400–1500 °C with ~18–20 % linear shrinkage.
What is the maximum service temperature of C7?
C7 is rated for continuous use to about 900°C (1,652 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- ISO 513 — Classification and application of hard cutting materials — ISO (2012)
- ISO 3327 / ISO 4505 — TRS test and porosity classification of hardmetals — ISO (2009)
- ASM Handbook Vol.2 — Properties of Cemented Carbides — ASM International (1990)
- ASM Handbook Vol.16 — Machining, Cutting Tool Materials — ASM International (1989)
- Cemented carbide grade property tables (steel-cutting P grades) — Sandvik Hard Materials / Kennametal (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.