Steel A387 Gr 91 Cl 2-ANN (Annealed)
Heat-treated state
ASTM A387 Gr 91 Cl 2 · UNS K90901 · EN X10CrMoVNb9-1, 1.4903
Soft, low-hardness intermediate condition for heavy machining or cold forming; must be re-normalized and tempered before service.
Values for the ANN condition
Other A387 Gr 91 Cl 2 tempers and conditions
A387 Gr 91 Cl 2 is listed in 5 conditions; see the grade overview at A387 Gr 91 Cl 2.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNThis page Annealed | Soft, low-hardness intermediate condition for heavy machining or cold forming; must be re-normalized and tempered before service. | 340 | 560 | 27 | 10 HRC | 3 % IACS |
N+T + simulated post-weld heat treatment | Ordered when the fabricator must qualify plate properties after the vessel's full PWHT cycle history; strength drops slightly, toughness improves. | 450 | 620 | 24 | 14 HRC | 2.9 % IACS |
N+TDefault Normalized and tempered | Standard commercial delivery condition for P91 plate — tempered martensite meeting Class 2 tensile/yield and code creep allowables. | 490 | 660 | 23 | 18 HRC | — |
Quenched and tempered | Used for very heavy plate where still-air normalizing cannot guarantee full martensite through thickness; slightly higher strength and better through-thickness uniformity. | 520 | 690 | 21 | 20 HRC | 2.9 % IACS |
As-normalized | Never a service condition — hard, brittle untempered martensite; shown only to bound properties if tempering is missed or interrupted. | 950 | 1,300 | 12 | 42 HRC | — |
What is A387 Gr 91 Cl 2-ANN?
A387 Gr 91 Cl 2-ANN is A387 Gr 91 Cl 2 heat treated to ANN — soft, low-hardness intermediate condition for heavy machining or cold forming; must be re-normalized and tempered before service. A387 Gr 91 Cl 2-ANN has a yield strength of 340 MPa (49.3 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 76% of steel grades. Elongation at break is 27% and the elastic modulus is 218 GPa (31.6 Msi). A387 Gr 91 Cl 2-ANN has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 92% of steel grades. It melts at 1,420°C (2,588 °F). N+T is the default condition FabDigit quotes; ANN is available on request or by drawing note.
Advantages
- Tough — resists crack growth — 150 MPa·√m (136.5 ksi·√in), better than 96% of steel grades
- High service temperature — 550°C (1,022 °F), better than 95% of steel grades
- Good corrosion resistance — 25/100, better than 92% of steel grades
- Ductile — tolerates forming and impact — 27%, better than 86% of steel grades
Limitations
- Poor heat conductor — 27 W/m·K (15.6 BTU/hr·ft·°F), worse than 86% of steel grades
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
- Low strength — 340 MPa (49.3 ksi), worse than 76% of steel grades
A387 Gr 91 Cl 2-ANN properties
Typical room-temperature values for A387 Gr 91 Cl 2-ANN; 23 are specific to this condition. Other listed values are A387 Gr 91 Cl 2 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A387 Gr 91 Cl 2-ANN has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 92% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
A387 Gr 91 Cl 2-ANN has a yield strength of 340 MPa (49.3 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 76% of steel grades. Elongation at break is 27% and the elastic modulus is 218 GPa (31.6 Msi).
Thermal6
A387 Gr 91 Cl 2-ANN is rated for continuous service to 550°C (1,022 °F). It conducts heat at 27 W/m·K (15.6 BTU/hr·ft·°F), worse than 86% of steel grades. Thermal expansion is 10.8 µm/m·K (6 µin/in·°F).
Electrical2
A387 Gr 91 Cl 2-ANN has an electrical resistivity of 5.8×10⁻⁷ Ω·m.
Chemical & Environmental3
Corrosion resistance is poor (25/100), better than 92% of steel grades.
Sustainability4
Producing a kilogram of A387 Gr 91 Cl 2-ANN takes about 34 MJ of energy and emits 2.5 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 25%.
Manufacturability7
A387 Gr 91 Cl 2-ANN's machinability is fair (48/100, worse than 57% of steel grades); weldability fair (48/100); formability fair (50/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with A387 Gr 91 Cl 2-ANN
Is A387 Gr 91 Cl 2 easy to machine?
Machine in the N&T (~210 HB) condition with rigid setups, carbide/coated inserts and moderate speeds; work-hardening is mild but the material is abrasive and gummy — heavy roughing is easier after a subcritical anneal.
Can A387 Gr 91 Cl 2 be welded?
Weld with matching 9CrMoV consumables (E9015-B9/ER90S-B9), preheat/interpass 200–300 °C, control interpass ≤ 300 °C, cool to below Ms (~80–100 °C) before a mandatory 750–780 °C PWHT; keep Ni+Mn low to avoid depressing Ac1 and watch Type IV HAZ creep damage.
Can A387 Gr 91 Cl 2 be formed, bent or molded?
Hot form at 950–1100 °C followed by full re-normalize and temper; cold forming beyond ~5 % strain requires re-heat treatment to restore creep properties.
What surface finishes work on A387 Gr 91 Cl 2?
Not stainless — shot blast and paint, aluminise or use thermal-spray/insulation for external protection; internal steam-side surfaces rely on the chromia scale formed in service.
A387 Gr 91 Cl 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 |
|---|---|---|
| C | 0.08 – 0.12 | 0.1 |
| Mn | 0.3 – 0.6 | 0.45 |
| P | ≤ 0.02 | 0.01 |
| S | ≤ 0.01 | 0 |
| Si | 0.2 – 0.5 | 0.35 |
| Cr | 8 – 9.5 | 8.8 |
| Mo | 0.85 – 1.05 | 0.95 |
| VMX carbonitride former | 0.18 – 0.25 | 0.21 |
| Nbcolumbium | 0.06 – 0.1 | 0.08 |
| N | 0.03 – 0.07 | 0.05 |
| Nimax; Ni+Mn often restricted to ≤1.0 % to keep Ac1 high | ≤ 0.4 | 0.15 |
| Almax, total | ≤ 0.02 | 0.01 |
| Ti | ≤ 0.01 | 0.01 |
| Zr | ≤ 0.01 | 0.01 |
| Fe | balance | — |
A387 Gr 91 Cl 2-ANN — frequently asked
What is A387 Gr 91 Cl 2-ANN used for?
A387 Gr 91 Cl 2-ANN is typically used for ultra-supercritical boiler components, high-temperature reactor vessels and power plant headers and vessels. In short: standard CSEF vessel plate; high creep strength to 600 °C; strict PWHT and chemistry control.
What is the yield strength of A387 Gr 91 Cl 2-ANN?
A387 Gr 91 Cl 2-ANN has a typical yield strength of 340 MPa (49.3 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 76% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is A387 Gr 91 Cl 2-ANN easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 57% of steel grades). Machine in the N&T (~210 HB) condition with rigid setups, carbide/coated inserts and moderate speeds; work-hardening is mild but the material is abrasive and gummy — heavy roughing is easier after a subcritical anneal.
Can A387 Gr 91 Cl 2-ANN be welded?
With care — weldability is rated fair (48/100). Weld with matching 9CrMoV consumables (E9015-B9/ER90S-B9), preheat/interpass 200–300 °C, control interpass ≤ 300 °C, cool to below Ms (~80–100 °C) before a mandatory 750–780 °C PWHT; keep Ni+Mn low to avoid depressing Ac1 and watch Type IV HAZ creep damage.
What surface finishes work on A387 Gr 91 Cl 2-ANN?
Not stainless — shot blast and paint, aluminise or use thermal-spray/insulation for external protection; internal steam-side surfaces rely on the chromia scale formed in service.
Can A387 Gr 91 Cl 2-ANN be formed, bent or molded?
Hot form at 950–1100 °C followed by full re-normalize and temper; cold forming beyond ~5 % strain requires re-heat treatment to restore creep properties.
What is the maximum service temperature of A387 Gr 91 Cl 2-ANN?
A387 Gr 91 Cl 2-ANN is rated for continuous use to about 550°C (1,022 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between A387 Gr 91 Cl 2 N+T and A387 Gr 91 Cl 2 AS-N?
N+T is the default condition — standard commercial delivery condition for P91 plate — tempered martensite meeting Class 2 tensile/yield and code creep allowables. AS-N: never a service condition — hard, brittle untempered martensite; shown only to bound properties if tempering is missed or interrupted. Yield strength is 490 MPa in N+T versus 950 MPa in AS-N.
Sources
- ASTM A387/A387M — Pressure Vessel Plates, Alloy Steel, Chromium-Molybdenum — ASTM International (2021)
- ASME BPVC Section II Part A (SA-387) and Part D (allowable stresses, physical properties) — ASME (2023)
- EN 10028-2 / EN 10216-2 X10CrMoVNb9-1 (1.4903) — CEN (2017)
- GB/T 3077 / NB/T 47008 10Cr9Mo1VNbN — SAC / NEA China (2017)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- P91/T91 grade property brochures — Vallourec / Industeel (ArcelorMittal) (2020)
- NIMS Creep Data Sheet — 9Cr-1Mo-V-Nb steel plate/tube — NIMS (2014)
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.