Steel P91 · supply condition · default condition
Steel P91-HR
Properties of the HR condition, compared with the other P91 tempers.
Mill intermediate stock only: air-cooled hot-worked material with mixed hard martensite; P91 must be normalized and tempered before it can be used or certified.
What is P91-HR?
P91-HR is P91 supplied in the HR condition — mill intermediate stock only: air-cooled hot-worked material with mixed hard martensite; P91 must be normalized and tempered before it can be used or certified. P91-HR has a yield strength of 750 MPa (109 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 84% of steel grades. Elongation at break is 14% and the elastic modulus is 218 GPa (31.6 Msi). P91-HR has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 92% of steel grades. It melts at 1,450°C (2,642 °F).
Advantages
- Good corrosion resistance — 30/100, better than 95% of steel grades
- High strength — 750 MPa (109 ksi), better than 84% of steel grades
- Tough — resists crack growth — 120 MPa·√m (109.2 ksi·√in), better than 80% of steel grades
Limitations
- Difficult to machine — 22/100, worse than 96% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Poor heat conductor — 26 W/m·K (15 BTU/hr·ft·°F), worse than 86% of steel grades
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
- Limited formability — 20/100, worse than 80% of steel grades
P91-HR properties
Typical room-temperature values for P91-HR — 9 properties are specific to this condition; the rest are grade-level values shared by every P91 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
P91-HR has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 92% of steel grades. It melts at 1,450°C (2,642 °F).
Mechanical17
P91-HR has a yield strength of 750 MPa (109 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 84% of steel grades. Elongation at break is 14% and the elastic modulus is 218 GPa (31.6 Msi).
Thermal6
P91-HR is rated for continuous service to 200°C (392 °F). It conducts heat at 26 W/m·K (15 BTU/hr·ft·°F), worse than 86% of steel grades. Thermal expansion is 10.9 µm/m·K (6.06 µin/in·°F).
Electrical2
P91-HR has an electrical resistivity of 6×10⁻⁷ Ω·m.
Chemical & Environmental2
Corrosion resistance is poor (30/100), better than 95% of steel grades.
Sustainability4
Producing a kilogram of P91-HR takes about 34 MJ of energy and emits 2.5 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
P91-HR's machinability is poor (22/100, worse than 96% of steel grades); weldability fair (35/100); formability poor (20/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other P91 tempers and conditions
P91 is also supplied in 4 other conditions. The full side-by-side table is on the P91 overview.
- HRDefaultMill intermediate stock only: air-cooled hot-worked material with mixed hard martensite; P91 must be normalized and tempered before it can be used or certified.750 MPa yield · 35 HRC
- NormalizedIntermediate mill/repair condition only — very hard untempered martensite; must be tempered before service or further fabrication.950 MPa yield · 45 HRC
- Q&TUsed for heavy-wall forgings, valve bodies and thick headers where liquid quenching is needed to get full martensite through-thickness; properties and hardness limits match N&T.520 MPa yield · 20 HRC
- N&TThe only ASME/ASTM-acceptable service condition for P91 pipe, tube, forgings and plate — tempered martensite with balanced creep strength, toughness and 190–250 HB hardness.500 MPa yield · 19 HRC
- AnnealedSoftening treatment for heavy machining, cold forming or before re-normalizing; creep strength is not certified in this state.350 MPa yield · 180 HB
Working with P91-HR
Is P91 easy to machine?
Machines like ~215 HB low-alloy steel: rigid setups, carbide tooling, moderate speeds and heavy coolant; work-hardens locally and any cold-worked surface should be considered in later heat treatment.
Can P91 be welded?
Requires 200–250 °C preheat, matched 9CrMoV filler, tight interpass control (≤300 °C), cool to below Ms (~80–100 °C) before PWHT, then mandatory 750–780 °C PWHT; type-IV HAZ softening limits long-term creep life.
Can P91 be formed, bent or molded?
Hot form at 950–1150 °C; any hot bending or significant cold work must be followed by full re-normalizing and tempering to restore creep properties.
What surface finishes work on P91?
Not corrosion resistant at ambient — shot blast plus high-temperature aluminium paint, aluminizing or chromizing; no anodizing.
P91 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 |
|---|---|---|
| Ccarbide/carbonitride former, creep strength | 0.08 – 0.12 | 0.1 |
| Si | 0.2 – 0.5 | 0.35 |
| Mn | 0.3 – 0.6 | 0.45 |
| P | ≤ 0.02 | — |
| S | ≤ 0.01 | — |
| Crsteam oxidation resistance | 8 – 9.5 | 8.75 |
| Mosolid-solution creep strength | 0.85 – 1.05 | 0.95 |
| VMX precipitation | 0.18 – 0.25 | 0.21 |
| NbMX precipitation, grain refinement | 0.06 – 0.1 | 0.08 |
| Nnitride strengthening | 0.03 – 0.07 | 0.05 |
| Nimax; limited to keep Ac1 high | ≤ 0.4 | — |
| Almax; excess Al ties up N | ≤ 0.02 | — |
| Ti | ≤ 0.01 | — |
| Zr | ≤ 0.01 | — |
| Fe | balance | — |
P91-HR — frequently asked
What is P91-HR used for?
P91-HR is typically used for main steam piping, boiler headers, superheater and reheater tubing, forged pipe fittings and elbows, thick-wall pressure vessel plate and high-temperature valve and pump bodies. In short: high-temp power-plant pipe.
What is the yield strength of P91-HR?
P91-HR has a typical yield strength of 750 MPa (109 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 84% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is P91-HR easy to machine?
Not especially — machinability is rated poor (22/100, worse than 96% of steel grades). Machines like ~215 HB low-alloy steel: rigid setups, carbide tooling, moderate speeds and heavy coolant; work-hardens locally and any cold-worked surface should be considered in later heat treatment.
Can P91-HR be welded?
With care — weldability is rated fair (35/100). Requires 200–250 °C preheat, matched 9CrMoV filler, tight interpass control (≤300 °C), cool to below Ms (~80–100 °C) before PWHT, then mandatory 750–780 °C PWHT; type-IV HAZ softening limits long-term creep life.
What surface finishes work on P91-HR?
Not corrosion resistant at ambient — shot blast plus high-temperature aluminium paint, aluminizing or chromizing; no anodizing.
Can P91-HR be formed, bent or molded?
Hot form at 950–1150 °C; any hot bending or significant cold work must be followed by full re-normalizing and tempering to restore creep properties.
What is the maximum service temperature of P91-HR?
P91-HR is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in P91-HR?
Yes — P91-HR is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A335/A335M — Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service (Grade P91) — ASTM (2023)
- ASTM A213/A213M (T91) and A182/A182M (F91) — ASTM (2022)
- EN 10216-2 — Seamless steel tubes for pressure purposes, X10CrMoVNb9-1 (1.4903) — CEN (2020)
- GB/T 5310 — (10Cr9Mo1VNbN) — SAC (2017)
- ASME BPVC Section II Part D — allowable stresses and physical properties — ASME (2023)
- The Grades 91 Steel Handbook / CSEF steel guidelines — EPRI (2015)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels — ASM International (1990)
- Seamless P91/T91 tube datasheets — Vallourec / Tenaris / Sandvik (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.