--- title: "P21 — composition, equivalents and standards" description: "P21: 2 equivalent designations across 2 standards, with the recorded chemical composition shown next to the source text." canonical: https://steelequivalents.com/materials/astm/p21 language: en robots: index, follow og_type: website type: material-detail language_alternates: en: https://steelequivalents.com/materials/astm/p21.md cs: https://steelequivalents.com/cs/materiály/astm/p21.md de: https://steelequivalents.com/de/werkstoffe/astm/p21.md es: https://steelequivalents.com/es/materiales/astm/p21.md fr: https://steelequivalents.com/fr/matériaux/astm/p21.md hu: https://steelequivalents.com/hu/anyagok/astm/p21.md it: https://steelequivalents.com/it/materiali/astm/p21.md nl: https://steelequivalents.com/nl/materialen/astm/p21.md pl: https://steelequivalents.com/pl/materiały/astm/p21.md pt: https://steelequivalents.com/pt/materiais/astm/p21.md ru: https://steelequivalents.com/ru/материалы/astm/p21.md tr: https://steelequivalents.com/tr/malzemeler/astm/p21.md zh: https://steelequivalents.com/zh/材料/astm/p21.md ja: https://steelequivalents.com/ja/材料/astm/p21.md ar: https://steelequivalents.com/ar/المواد/astm/p21.md ko: https://steelequivalents.com/ko/재료/astm/p21.md pt-br: https://steelequivalents.com/pt-br/materiais/astm/p21.md hi: https://steelequivalents.com/hi/सामग्री/astm/p21.md content_hash: sha256:1f3beb1ee0aca31e3b4f577e3d1a2f9fa6f98259ff9f3de84cf9267f8ad9e8e5 generated: 2026-09-24 --- > **Machine-readable Markdown rendering.** This is a Markdown representation of a web page, > served for AI agents and crawlers as a token-efficient alternative to the full HTML. > Full interactive HTML version: https://steelequivalents.com/materials/astm/p21 > Canonical URL: https://steelequivalents.com/materials/astm/p21 > Available languages: en, cs, de, es, fr, hu, it, nl, pl, pt, ru, tr, zh, ja, ar, ko, pt-br, hi > Change detection: `content_hash` is the SHA-256 of this document's Markdown body — everything > below this block, whitespace-trimmed, excluding the front-matter. Compare it to detect a real > content change; `generated` moves on every render and is not a change signal. ASTM · United States · 2 designations # P21 1Ni3MnCuMoAl is a grade designated under GB. Its recorded composition includes C 0.1–0.2%, Al 0.7–1.2%, Mn 1.4–2%, Ni 2.9–3.4% and Cu 0.8–1.2%. We list one designation recorded for this grade, in the standard ASTM. - *Designations* **2** [Search](/search "Steel grade search")[Inquiry](/inquiry?material=d3c76240-9009-4b7c-80b5-340d5140ee41&designation=460e5d86-cc16-41b6-8bdd-634a63e2682f "Inquiry")[**Datasheet as PDF** Print-ready A4 document **Generating …** **Download started** **Try again**](/materials/astm/p21.pdf "Datasheet as PDF") ## If you came for one of these The most-used names for this grade. - [GB 1Ni3MnCuMoAl This grade’s own name](/materials/gb/1ni3mncumoal "GB 1Ni3MnCuMoAl") ## Also known as 2 designations · 2 standards · nothing hidden This grade’s own name recorded in our sources as this grade’s own designation under that standard. Indicative taken from a published cross-reference table; a close match, not a guarantee of interchangeability. Verify against the mill certificate before ordering. Withdrawn designation no longer current — a separate column from the two above, so a name can be same grade and withdrawn at once. ASTM United States · 1 - **P21 Indicative** GB China · 1 - [1Ni3MnCuMoAl This grade’s own name](/materials/gb/1ni3mncumoal "GB 1Ni3MnCuMoAl") Every designation on file is listed — no truncation, no “+ n more”. Each one is itself a route that leads back here. ## Chemical composition 9 elements on file · weight % What this alloy is Fe Ni Mn Cu Iron — the balance, never listed by a standard — 92.2 % Ni — 3.2 % Mn — 1.7 % Cu — 1 % Traces & impurities · 1.9 % Logarithmic scale, 0.01 % to 100 % — every value here compares directly, decade by decade. | Element | % by weight | |---|---| | C | 0.1–0.2 | | Si | ≤ 0.45 | | Mn | 1.4–2 | | P | ≤ 0.03 | | S | ≤ 0.015 | | Mo | 0.2–0.5 | | Ni | 2.9–3.4 | | Cu | 0.8–1.2 | | Al | 0.7–1.2 | Carbon Silicon Manganese Phosphorus Sulfur Molybdenum Nickel Copper Aluminium 0.01 % 0.1 % 1 % 10 % 100 % The scale is logarithmic, not the element’s raw share of the alloy — the only honest way to fit 0.01 % and 100 % in one picture, and it means every value here can be compared with every other. | Element | As published source text, verbatim | Min% by weight | Max% by weight | Bound | |---|---|---|---|---| | C | 0.1-0.2 | 0.100 | 0.200 | Range | | Al | 0.7-1.2 | 0.700 | 1.200 | Range | | Si | ≤0.45 | — | 0.450 | Max | | P | ≤0.03 | — | 0.030 | Max | | S | ≤0.015 | — | 0.015 | Max | | Mn | 1.4-2 | 1.400 | 2.000 | Range | | Ni | 2.9-3.4 | 2.900 | 3.400 | Range | | Cu | 0.8-1.2 | 0.800 | 1.200 | Range | | Mo | 0.2-0.5 | 0.200 | 0.500 | Range | The published column is the source string byte-for-byte, decimal comma and all; Min and Max are the parsed bounds. Elements not listed have no value on file — they are omitted, never inferred. ## Predicted transformation temperatures Not enough recorded composition to predict a transformation temperature for this grade — missing: Cr. ## Physical & mechanical properties An absent property means we hold no value for it — it is left out rather than estimated, interpolated from a neighbouring grade, or filled from a handbook. It does not mean the property is undefined for the material. ## Looking for this grade under another name? Search the catalogue by designation, material number or composition — every name on this page is itself a way in. [Search](/search "Steel grade search")[Inquiry](/inquiry?material=d3c76240-9009-4b7c-80b5-340d5140ee41&designation=460e5d86-cc16-41b6-8bdd-634a63e2682f "Inquiry")[**Datasheet as PDF** Print-ready A4 document **Generating …** **Download started** **Try again**](/materials/astm/p21.pdf "Datasheet as PDF")