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T91 — ASTM Equivalent

Holding a datasheet that specifies T91 (DIN)? The valve-grade equivalent, its properties, and certified supply of the matching ASTM grade.

What is the ASTM equivalent of T91?

T91 is a DIN designation corresponding to ASTM A217 C12A (Grade 91 Cast Steel (C12A)) for industrial valve service. The full grade data is below - equivalence is by nominal chemistry and mechanical class, so confirm composition and heat-treat condition against the governing standard before substituting in critical service.

A217 C12A

Chrome-Moly / Alloy Steel

Grade 91 Cast Steel (C12A) - cast form.

Service temperature-29°C to +650°C
Nominal compositionCr 8.0-9.5%, Mo 0.85-1.05%, V 0.18-0.25%, Nb 0.06-0.10%, N 0.030-0.070%, C 0.08-0.12%. Normalised and tempered.

Typical service: Main steam isolation valves (MSIV) on ultra-supercritical power plants at 600°C / 250 bar; Hot reheat steam isolation valves on supercritical coal-fired boilers; High-pressure turbine bypass valves at 600°C main steam conditions

Also designated:1.4903 X10CrMoVNb9-1 [EN]J84090 [UNS]P91 [DIN]T91 [DIN]
Reviewed by Materials Engineering, Vajra Industrial SolutionsDiscipline: Valve Metallurgy & Materials SelectionLast reviewed: 20 June 2026

Connected Engineering

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A217 WC9 Chrome-Moly

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Engineering references

A217 C12A full grade pageGrade 91 Cast Steel (C12A)Equivalence MatrixAll 43 grades across 7 systemsDesignation lookup directoryEvery foreign designation indexed