Bar and Rod
Plate and Sheet
Strip
Pipe and Tube
Wire
Welding
Powder Material
Cast Products
Forged Products
Fittings
Fastening
Round Bar:
φ2–500 mm, 1–6 m length
Flat/Square Bar:
4–100 mm thickness/width
Hex Bar:
A/F 3–100 mm
Hollow Bar:
OD 20–300 mm
Sheet:
0.3–6 mm thickness
Medium Plate:
6–25 mm thickness
Heavy Plate:
25–100 mm thickness
Standard Strip:
0.05–3 mm thick,
10–600 mm wide
Precision strip:
0.01–0.5 mm thick,
tight tolerance ±0.005 mm
Foil:
0.005–0.1 mm thick
Seamless Tube:
OD 6–450 mm,
WT 1–50 mm,
1–12 m length
Welded Tube:
OD 10–600 mm,
WT 1–20 mm
Capillary Tube:
OD 1–10 mm,
WT 0.1–2 mm
Wire Form:
Cold Drawn Wire,
Bright Wire,
Spring Wire,
Fine Wire,
Ultra-fine Wire
General Diameter:
φ0.1–10 mm
Coil Weight:
50–500 kg,
customizable tolerance
Solid Wire:
φ0.8–4.0 mm
Flux-cored Wire:
φ1.2–4.0 mm
Welding Rod:
φ2.0–5.0 mm
Powder Form:
AM 3D Printing Powder,
Spherical Powder,
Gas-atomized Powder,
Water-atomized Powder
Particle Size:
10–150 μm
Sphericity:
≥90% for AM grade
Cast Ingot:
φ200–800 mm
Precision Casting:
min wall 0.5 mm
Cast Pipe:
OD 100–600 mm,
WT 10–50 mm
Forged Bar:
Φ35–500 mm
Forged Ring:
OD 200–2000 mm
Forging Weight:
1–5000 kg
Fittings Form:
Elbow, Tee, Reducer, Flange, Cap, Outlet, Lap Joint
Size range:
1/2''–24'' (DN15–DN600)
Wall thickness:
Sch10–Sch160, STD, XS, XXS
Pressure Class:
150–2500 LB
Fastening Form:
Bolt, Nut, Screw, Stud, Washer, Pin, Rivet
Metric: M3–M64
Imperial: #4–2.5''
Length: 6–500 mm
Grade 91 is a 9% chromium–1% molybdenum ferritic-martensitic creep-strength-enhanced alloy steel, microalloyed with vanadium, niobium and controlled nitrogen. This datasheet presents the material within the American (ASTM / ASME / UNS) standard system.
With nominally 9% chromium, 1% molybdenum and deliberate additions of vanadium, niobium and nitrogen, Grade 91 develops outstanding creep and rupture strength at elevated temperature through a tempered-martensite structure stabilised by fine V/Nb carbonitride precipitates. It offers high-temperature strength markedly greater than the lower-chromium Cr-Mo steels (such as Grade 22), good oxidation and steam-corrosion resistance, and good thermal conductivity and low thermal expansion relative to austenitic steels. It is supplied normalized and tempered, and is used in permanent service to about 600–650 °C. Correct normalising, tempering, welding and post-weld heat treatment are essential to its performance.
Typical applications include superheater and reheater tubing, headers and main steam piping in sub-critical and supercritical boilers, pressure vessels, and petrochemical heater and cracking-furnace tubes.
| Property | Value | Unit |
|---|---|---|
| Density | 7.77 | g/cm³ |
| Melting range | 1420–1480 | °C |
| Elastic modulus | 218 | GPa |
| Coefficient of thermal expansion (20–100 °C) | 11.0 | µm/m·°C |
| Thermal conductivity (100 °C) | 26.0 | W/m·K |
| Specific heat (20 °C) | 460 | J/kg·K |
| Structure | Tempered martensite | — |
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Iron | Fe | Balance | — | Base element |
| Chromium | Cr | 8.00 | 9.50 | Oxidation / steam-corrosion resistance |
| Molybdenum | Mo | 0.85 | 1.05 | Solid-solution / creep strength |
| Vanadium | V | 0.18 | 0.25 | Carbonitride precipitation (creep strength) |
| Niobium | Nb | 0.06 | 0.10 | Carbonitride precipitation (creep strength) |
| Nitrogen | N | 0.030 | 0.070 | Carbonitride formation |
| Manganese | Mn | 0.30 | 0.60 | Deoxidiser |
| Silicon | Si | 0.20 | 0.50 | Deoxidiser; oxidation resistance |
| Carbon | C | 0.08 | 0.12 | Strength |
| Nickel | Ni | — | 0.40 | Residual; toughness |
| Phosphorus | P | — | 0.020 | Residual impurity |
| Sulphur | S | — | 0.010 | Residual impurity |
Normalized-and-tempered condition, per ASTM A335 for grade P91.
| Condition | Property | Value |
|---|---|---|
| Normalized & tempered | Tensile strength (UTS) | ≥585 MPa |
| Normalized & tempered | 0.2% yield strength | ≥415 MPa |
| Normalized & tempered | Elongation at break | ≥20 % |
| Normalized & tempered | Hardness | ≤250 HB |
| — | Elastic modulus | 218 GPa |
Confirm against the mill test report. Creep-rupture strength at 600 °C far exceeds that of the lower-alloy Cr-Mo steels.
| Environment | Performance | Notes |
|---|---|---|
| High-temperature oxidation | Very Good | 9% Cr resists steam oxidation |
| Steam corrosion | Very Good | Suited to superheated steam to ~600–650 °C |
| Flue gas / combustion | Good | Better than low-Cr Cr-Mo steels |
| Aqueous / general | Limited | Not a stainless steel; will rust at ambient |
| Creep / thermal fatigue | Excellent | Primary design advantage |
Grade 91 is a heat-resistant alloy steel, not a stainless steel; its strength is in high-temperature oxidation and creep resistance rather than aqueous corrosion resistance.
A creep-strength-enhanced ferritic-martensitic steel; properties depend on correct normalising and tempering.
Normalize Normalise at approximately 1040–1080 °C and air cool to form martensite. Full austenitisation is required to dissolve V/Nb for subsequent precipitation.
Temper Temper at approximately 730–780 °C to produce tempered martensite with fine carbonitrides. Post-weld heat treatment in a similar range is mandatory; under-tempering leaves hard, brittle martensite and over-tempering reduces creep strength.
Weldable with strict control; matching (9Cr-1Mo-V) consumables are used. Preheat (~200–300 °C), interpass control and mandatory post-weld heat treatment (~750 °C) are required to avoid hard martensite and to restore toughness and creep strength.
| Welding Process | Applicability | Filler / Consumable |
|---|---|---|
| GTAW / TIG | Good (with PWHT) | Matching 9Cr-1Mo-V (e.g. AWS B9) |
| GMAW / MIG | Good (with PWHT) | Matching B9 consumable |
| SMAW / stick | Good (with PWHT) | Matching B9 electrode |
Preheat, interpass control and post-weld heat treatment are mandatory; follow the applicable code procedure.
Machining Guidelines
| Parameter | Recommendation |
|---|---|
| Preferred condition | Normalized and tempered |
| Machinability | Moderate; similar to other Cr-Mo alloy steels |
| Coolant | Ample flood coolant |
Forming Processes
| Process | Notes |
|---|---|
| Cold forming | Limited; stress-relieve as required |
| Hot forming | ~1100–900 °C; normalise and temper afterward |
| Industry | Typical Components | Key Requirements |
|---|---|---|
| Power generation | Superheater / reheater tubes, headers, steam piping | Creep strength to ~600–650 °C |
| Boilers | Sub-critical and supercritical boiler components | High-temperature strength + steam oxidation resistance |
| Pressure vessels | Elevated-temperature vessels | Creep + oxidation resistance |
| Petrochemical | Heater and cracking-furnace tubes | High-temperature strength |
| Product Form | ASTM Standard | ASME Code |
|---|---|---|
| Seamless pipe (P91) | ASTM A335 | ASME SA-335 |
| Seamless tube (T91) | ASTM A213 | ASME SA-213 |
| Plate (Grade 91) | ASTM A387 | ASME SA-387 |
| Forgings / fittings (F91) | ASTM A182 | ASME SA-182 |
Creep-strength-enhanced 9Cr-1Mo-V ferritic-martensitic alloy steel. UNS K90901 / K91560.
| Grade | Cr % | Mo % | Micro-alloy | Best Used For |
|---|---|---|---|---|
| Grade 91 | 8–9.5 | 0.85–1.05 | V, Nb, N | 9Cr-1Mo-V creep steel; superheaters, steam piping to ~650 °C |
| Grade 92 | 8.5–9.5 | 0.30–0.60 | W, V, Nb, N | Higher-creep 9Cr (W-bearing) |
| Grade 22 | 2.0–2.5 | 0.87–1.13 | — | 2.25Cr-1Mo Cr-Mo steel; lower temperature |
| Grade 911 | 8.5–9.5 | 0.90–1.10 | W, V, Nb, N | 9Cr-1Mo-W creep steel |
| Grade 9 | 8–10 | 0.90–1.10 | — | Plain 9Cr-1Mo (T9/P9) |
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