Steel A387 Gr 91 Cl 2
ASTM A387 Gr 91 Cl 2 · UNS K90901 · EN X10CrMoVNb9-1, 1.4903
Modified 9Cr-1Mo-V-Nb creep-strength-enhanced ferritic steel plate (P91 family) offering markedly higher creep rupture strength than plain 9Cr-1Mo, widely used in advanced power plant and petrochemical construction.
Reference datasheet — A387 Gr 91 Cl 2 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the N+T condition
A387 Gr 91 Cl 2 tempers and conditions
A387 Gr 91 Cl 2 is supplied in 5 conditions, soft to hard. N+T is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
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?
Modified 9Cr-1Mo-V-Nb creep-strength-enhanced ferritic steel plate (P91 family) offering markedly higher creep rupture strength than plain 9Cr-1Mo, widely used in advanced power plant and petrochemical construction. A387 Gr 91 Cl 2 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). A387 Gr 91 Cl 2 has a yield strength of 490 MPa (71.1 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 61% of steel grades. Elongation at break is 23% and the elastic modulus is 218 GPa (31.6 Msi).
What is A387 Gr 91 Cl 2 used for?
- ultra-supercritical boiler components
- high-temperature reactor vessels
- power plant headers and vessels
Advantages
- High service temperature — 600°C (1,112 °F), better than 98% of steel grades
- Good corrosion resistance — 25/100, better than 92% of steel grades
- Tough — resists crack growth — 130 MPa·√m (118.3 ksi·√in), better than 89% of steel grades
Limitations
- Poor heat conductor — 26 W/m·K (15 BTU/hr·ft·°F), worse than 87% of steel grades
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
- Difficult to machine — 38/100, worse than 80% of steel grades
A387 Gr 91 Cl 2 properties
Typical room-temperature values for A387 Gr 91 Cl 2-N+T; bars are the position among steel grades.
Physical3
A387 Gr 91 Cl 2 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 has a yield strength of 490 MPa (71.1 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 61% of steel grades. Elongation at break is 23% and the elastic modulus is 218 GPa (31.6 Msi).
Thermal6
A387 Gr 91 Cl 2 is rated for continuous service to 600°C (1,112 °F). It conducts heat at 26 W/m·K (15 BTU/hr·ft·°F), worse than 87% of steel grades. Thermal expansion is 10.8 µm/m·K (6 µin/in·°F).
Electrical2
A387 Gr 91 Cl 2 has an electrical resistivity of 6×10⁻⁷ 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 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's machinability is fair (38/100, worse than 80% of steel grades); weldability fair (45/100); formability fair (35/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. A387 Gr 91 Cl 2 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with A387 Gr 91 Cl 2
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.
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 |
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.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel A387 Gr 91 Cl 2 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- K90901
- ASTM
- A387 Grade 91 Class 2
- EN / DIN / Werkstoff-Nr.
- X10CrMoVNb9-11.4903
- Trade names
- P91/T91
- Similar grades
- 10Cr9Mo1VNbN
How much does A387 Gr 91 Cl 2 cost?
A387 Gr 91 Cl 2 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
A387 Gr 91 Cl 2 — frequently asked
What is A387 Gr 91 Cl 2 used for?
A387 Gr 91 Cl 2 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?
A387 Gr 91 Cl 2 has a typical yield strength of 490 MPa (71.1 ksi) and a tensile strength of 660 MPa (95.7 ksi) — stronger than 61% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is A387 Gr 91 Cl 2 easy to machine?
Not especially — machinability is rated fair (38/100, worse than 80% 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 be welded?
With care — weldability is rated fair (45/100). 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?
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 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?
A387 Gr 91 Cl 2 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 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.
How much does A387 Gr 91 Cl 2 cost?
A387 Gr 91 Cl 2 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.