Cobalt-Chrome Alloy F1537 Alloy 2-HW (Hot Worked)
Heat-treated state · default condition
ASTM F1537 Alloy 2 · UNS R31538 · ISO 5832-12 Alloy 2
Standard supply condition for implant bar and forgings: good balance of strength, ductility and fine grain size for femoral heads and stems.
Values for the HW condition
Other F1537 Alloy 2 tempers and conditions
F1537 Alloy 2 is listed in 3 conditions; see the grade overview at F1537 Alloy 2.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Pick for maximum ductility and for parts that will be further forged, formed or heavily machined before final heat treatment. | 620 | 1,000 | 32 | 28 HRC | — |
HWDefaultThis page Hot Worked | Standard supply condition for implant bar and forgings: good balance of strength, ductility and fine grain size for femoral heads and stems. | 950 | 1,280 | 22 | 35 HRC | — |
Warm Worked | Highest strength and fatigue capability — chosen for slender, highly loaded implant components such as small-diameter stems and modular necks. | 1,250 | 1,600 | 18 | 44 HRC | — |
What is F1537 Alloy 2-HW?
F1537 Alloy 2-HW is F1537 Alloy 2 heat treated to HW — standard supply condition for implant bar and forgings: good balance of strength, ductility and fine grain size for femoral heads and stems. F1537 Alloy 2-HW has a yield strength of 950 MPa (138 ksi) and a tensile strength of 1,280 MPa (186 ksi) — stronger than 85% of cobalt-chrome alloy grades. Elongation at break is 22% and the elastic modulus is 230 GPa (33.4 Msi). F1537 Alloy 2-HW has a density of 8.3 g/cm³ (0.3 lb/in³), lighter than 80% of cobalt-chrome alloy grades. It melts at 1,330°C (2,426 °F).
Advantages
- Polishes to a fine finish — 95/100, better than 100% of cobalt-chrome alloy grades
- Good corrosion resistance — 90/100, better than 95% of cobalt-chrome alloy grades
- Tough — resists crack growth — 80 MPa·√m (72.8 ksi·√in), better than 89% of cobalt-chrome alloy grades
- High strength — 950 MPa (138 ksi), better than 85% of cobalt-chrome alloy grades
- Ductile — tolerates forming and impact — 22%, better than 81% of cobalt-chrome alloy grades
Limitations
- Difficult to weld — 20/100, worse than 87% of cobalt-chrome alloy grades
- High embodied carbon — 16 kg CO₂/kg, worse than 84% of cobalt-chrome alloy grades
F1537 Alloy 2-HW properties
Typical room-temperature values for F1537 Alloy 2-HW; 18 are specific to this condition. Other listed values are F1537 Alloy 2 reference data and may not represent this condition. Bars are the position among cobalt-chrome alloy grades.
Physical3
F1537 Alloy 2-HW has a density of 8.3 g/cm³ (0.3 lb/in³), lighter than 80% of cobalt-chrome alloy grades. It melts at 1,330°C (2,426 °F).
Mechanical15
F1537 Alloy 2-HW has a yield strength of 950 MPa (138 ksi) and a tensile strength of 1,280 MPa (186 ksi) — stronger than 85% of cobalt-chrome alloy grades. Elongation at break is 22% and the elastic modulus is 230 GPa (33.4 Msi).
Thermal6
F1537 Alloy 2-HW is rated for continuous service to 600°C (1,112 °F). It conducts heat at 14 W/m·K (8.09 BTU/hr·ft·°F), worse than 55% of cobalt-chrome alloy grades. Thermal expansion is 12.8 µm/m·K (7.11 µin/in·°F).
Electrical3
F1537 Alloy 2-HW conducts electricity at 2 % IACS, better than 79% of cobalt-chrome alloy grades.
Chemical & Environmental3
Corrosion resistance is excellent (90/100), better than 95% of cobalt-chrome alloy grades.
Sustainability4
Producing a kilogram of F1537 Alloy 2-HW takes about 240 MJ of energy and emits 16 kg of CO₂ — more than 89% of cobalt-chrome alloy grades. Typical recycled content is 20%.
Manufacturability8
F1537 Alloy 2-HW's machinability is not recommended (8/100, worse than 64% of cobalt-chrome alloy grades); weldability poor (20/100); formability poor (18/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with F1537 Alloy 2-HW
Is F1537 Alloy 2 easy to machine?
Very difficult: rigid setups, sharp-edged carbide or ceramic tooling, low speed/high feed with flood coolant; avoid dwelling to prevent severe work hardening.
Can F1537 Alloy 2 be welded?
Fusion welding is discouraged on the high-carbon grade (carbide precipitation, hot cracking); if unavoidable use GTAW/laser with matching filler under argon plus post-weld solution anneal.
Can F1537 Alloy 2 be formed, bent or molded?
Hot or warm forging above ~1000 °C is the normal shaping route; cold forming is limited to small deformations because of the very high work-hardening rate.
What surface finishes work on F1537 Alloy 2?
Ground, lapped and mirror-polished to sub-0.05 µm Ra for bearing surfaces, then passivated per ASTM F86; optional DLC/TiN or plasma-sprayed HA coatings for tribology or fixation.
F1537 Alloy 2 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 |
|---|---|---|
| Cr | 26 – 30 | 28 |
| Mo | 5 – 7 | 6 |
| Chigh-carbon Alloy 2; carbides give wear resistance | 0.15 – 0.35 | 0.25 |
| Ni | ≤ 1 | — |
| Fe | ≤ 0.75 | — |
| Si | ≤ 1 | — |
| Mn | ≤ 1 | — |
| N | ≤ 0.25 | — |
| W | ≤ 0.2 | — |
| P | ≤ 0.02 | — |
| S | ≤ 0.01 | — |
| Co | balance | — |
F1537 Alloy 2-HW — frequently asked
What is F1537 Alloy 2-HW used for?
F1537 Alloy 2-HW is typically used for hip stems, knee femoral components and bone screws. In short: strongest F1537 alloy; high-carbon wear surfaces; poor weldability rating.
What is the yield strength of F1537 Alloy 2-HW?
F1537 Alloy 2-HW has a typical yield strength of 950 MPa (138 ksi) and a tensile strength of 1,280 MPa (186 ksi) — stronger than 85% of cobalt-chrome alloy grades. Strength varies by condition: see the 3 listed tempers.
Is F1537 Alloy 2-HW easy to machine?
Not especially — machinability is rated not recommended (8/100, worse than 64% of cobalt-chrome alloy grades). Very difficult: rigid setups, sharp-edged carbide or ceramic tooling, low speed/high feed with flood coolant; avoid dwelling to prevent severe work hardening.
Can F1537 Alloy 2-HW be welded?
Not readily — weldability is rated poor (20/100). Fusion welding is discouraged on the high-carbon grade (carbide precipitation, hot cracking); if unavoidable use GTAW/laser with matching filler under argon plus post-weld solution anneal.
What surface finishes work on F1537 Alloy 2-HW?
Ground, lapped and mirror-polished to sub-0.05 µm Ra for bearing surfaces, then passivated per ASTM F86; optional DLC/TiN or plasma-sprayed HA coatings for tribology or fixation.
Can F1537 Alloy 2-HW be formed, bent or molded?
Hot or warm forging above ~1000 °C is the normal shaping route; cold forming is limited to small deformations because of the very high work-hardening rate.
What is the maximum service temperature of F1537 Alloy 2-HW?
F1537 Alloy 2-HW is rated for continuous use to about 600°C (1,112 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between F1537 Alloy 2-HW and F1537 Alloy 2-ANN?
HW is the default condition — standard supply condition for implant bar and forgings: good balance of strength, ductility and fine grain size for femoral heads and stems. ANN: pick for maximum ductility and for parts that will be further forged, formed or heavily machined before final heat treatment. Yield strength is 950 MPa in HW versus 620 MPa in ANN.
Sources
- ASTM F1537 — Standard Specification for Wrought Cobalt-28Chromium-6Molybdenum Alloys for Surgical Implants (UNS R31537, R31538, R31539) — ASTM International (2020)
- ISO 5832-12 — Implants for surgery, Metallic materials, Part 12: Wrought cobalt-chromium-molybdenum alloy — ISO (2019)
- ASTM F86 — Standard Practice for Surface Preparation and Marking of Metallic Surgical Implants — ASTM International (2021)
- ASM Handbook: Materials for Medical Devices / Metals Handbook Vol. 2, Cobalt-base alloys — ASM International (2012)
- Implant-quality Co-28Cr-6Mo (high carbon) bar datasheets — Carpenter Technology / Sandvik / VDM (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.