ASTM A387 Grade 91 Cl.2 — Chemical Composition & Mechanical Properties
ASTM A387 Grade 91 Cl.2 is a chrome-moly alloy steel grade for pressure-vessel plate (UNS K90901, EN / W.Nr 1.4903 (X10CrMoVNb9-1)). It is also known as 9Cr-1Mo-V plate. This sheet summarises its chemical composition limits, minimum mechanical properties, heat treatment and typical service. Teshi Group supplies this grade as a stockist and supplier.
ASTM A387 Grade 91 Cl.2 at a glance
| Specification | ASTM A387 Grade 91 Cl.2 |
|---|---|
| Material family | Chrome-moly alloy steel |
| Product form | Pressure-vessel plate |
| UNS number | K90901 |
| EN / W.Nr equivalent | 1.4903 (X10CrMoVNb9-1) |
| Also known as | 9Cr-1Mo-V plate |
| Document | TG-MG-155 · Rev. 1 · October 2026 |
Typical service
Grade 91 plate for headers and high-temperature vessels
Heat treatment
Normalised 1040–1080 °C and tempered 730–800 °C
Chemical composition of ASTM A387 Grade 91 Cl.2 (weight %)
Other elements and limits: V 0.18–0.25; Nb 0.06–0.10; Al 0.02 max; Ti 0.01 max; Zr 0.01 max
Single values are maximums unless shown as a range or “min”.
Mechanical properties
| Tensile strength, min | 585 MPa |
|---|---|
| Yield strength (0.2 % offset), min | 415 MPa |
| Elongation, min | 18 % |
| Tensile strength, max | 760 MPa |
| Hardness | Not specified |
About chrome-moly alloy steel
Chrome-moly steels are low-alloy steels with 1–9 % chromium and 0.5–1 % molybdenum. Chromium gives oxidation and sulphidation resistance; molybdenum gives creep strength at high temperature. They are the standard choice for steam and hot hydrocarbon service above the carbon-steel range.
Reference information compiled from the published standard for convenience. It does not replace the current edition of the governing standard, which takes precedence. Verify critical dimensions and properties before design, purchase or fabrication. Teshi Engineers & Sales Promoters (P) Ltd accepts no liability for errors or omissions.
International equivalents of ASTM A387 Grade 91 Cl.2
All equivalents| Standard system | Nearest equivalent grade |
|---|---|
| USA — ASTM / ASME | ASTM A387 Grade 91 Cl.2 · ASME SA-387 Grade 91 Cl.2 |
| USA — UNS | K90901 |
| Europe — EN designation | X10CrMoVNb9-1 (EN 10028-2) |
| Europe — W.Nr | 1.4903 |
| Japan — JIS | SCMV28 (JIS G4109) |
Equivalents are the nearest commonly cited grades. Chemistry, mechanical properties and testing differ between standards — compare them before substituting one for another.
Same alloy in other product forms
| Product form | Specification / grade |
|---|---|
| Forged flanges & fittings | ASTM A182 F91 |
| Seamless pipe | ASTM A335 P91 |
| Wrought butt-weld fittings | ASTM A234 WP91 Type 1 |
Standards for ASTM A387 Grade 91 Cl.2
All material standardsFAQ
ASTM A387 Grade 91 Cl.2: common questions
What is the minimum yield strength of ASTM A387 Grade 91 Cl.2?
415 MPa, with a minimum tensile strength of 585 MPa.
What is the carbon content of ASTM A387 Grade 91 Cl.2?
0.08–0.12 %.
What is the UNS number and EN equivalent of ASTM A387 Grade 91 Cl.2?
UNS K90901; the nearest European designation is W.Nr 1.4903 (X10CrMoVNb9-1). Equivalents are close but not identical — check the specification if substituting.
How is ASTM A387 Grade 91 Cl.2 heat treated?
Normalised 1040–1080 °C and tempered 730–800 °C.
What is the JIS equivalent of ASTM A387 Grade 91 Cl.2?
The nearest Japanese (JIS) equivalent is SCMV28 (JIS G4109).
Does Teshi Group supply ASTM A387 Grade 91 Cl.2?
Teshi Group supplies this grade as a stockist and supplier. Send your size, rating and quantity to info@teshigroup.com for a quotation with EN 10204 3.1 certificates.
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