--- title: "X80 — Fine-grain structural steels" description: "X80 in AISI / SAE: material number 1.8978, also listed as L555MB. Category: Fine-grain structural steels. Designations recorded for this grade: 5." canonical: https://steelequivalents.com/materials/aisi-sae/x80 language: en robots: index, follow og_type: website type: material-detail language_alternates: en: https://steelequivalents.com/materials/aisi-sae/x80.md cs: https://steelequivalents.com/cs/materiály/aisi-sae/x80.md de: https://steelequivalents.com/de/werkstoffe/aisi-sae/x80.md es: https://steelequivalents.com/es/materiales/aisi-sae/x80.md fr: https://steelequivalents.com/fr/matériaux/aisi-sae/x80.md hu: https://steelequivalents.com/hu/anyagok/aisi-sae/x80.md it: https://steelequivalents.com/it/materiali/aisi-sae/x80.md nl: https://steelequivalents.com/nl/materialen/aisi-sae/x80.md pl: https://steelequivalents.com/pl/materiały/aisi-sae/x80.md pt: https://steelequivalents.com/pt/materiais/aisi-sae/x80.md ru: https://steelequivalents.com/ru/материалы/aisi-sae/x80.md tr: https://steelequivalents.com/tr/malzemeler/aisi-sae/x80.md zh: https://steelequivalents.com/zh/材料/aisi-sae/x80.md ja: https://steelequivalents.com/ja/材料/aisi-sae/x80.md ar: https://steelequivalents.com/ar/المواد/aisi-sae/x80.md ko: https://steelequivalents.com/ko/재료/aisi-sae/x80.md pt-br: https://steelequivalents.com/pt-br/materiais/aisi-sae/x80.md hi: https://steelequivalents.com/hi/सामग्री/aisi-sae/x80.md content_hash: sha256:0c8129a287e1b139cd583bb6c06b3d02d192839d1c93f664fef7dc4ac61c30ec 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/aisi-sae/x80 > Canonical URL: https://steelequivalents.com/materials/aisi-sae/x80 > 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. AISI / SAE · United States · 5 designations # X80 X80 is a designation in AISI / SAE for the material held under material number 1.8978, also listed as L555MB. It is a material in the category Fine-grain structural steels. We list 5 designations recorded for this grade, in the standards DIN / EN, UNS and AISI / SAE. - [*Material no.* **1.8978**](/materials/material-no/1.8978 "Material no.: 1.8978") - [*Category* **Fine-grain structural steels · 50 grades**](/categories/fine-grain-structural-steels "Category: Fine-grain structural steels · 50 grades") - *Designations* **5** [Search](/search "Steel grade search")[Inquiry](/inquiry?material=e4b5a625-5848-4958-ade6-473fd2b27030&designation=66964818-749c-4b07-b98a-4f16e64983d0 "Inquiry")[**Datasheet as PDF** Print-ready A4 document **Generating …** **Download started** **Try again**](/materials/aisi-sae/x80.pdf "Datasheet as PDF") ## If you came for one of these The most-used names for this grade. - [DIN / EN L555MB This grade’s own name](/materials/din-en/l555mb "DIN / EN L555MB") - [UNS K12700 This grade’s own name](/materials/uns/k12700 "UNS K12700") ## About Fine-grain structural steels Fine-grain structural steel is a name for structural steels whose properties are particularly suitable for welding. They have a higher yield strength than comparable steels. Due to the negative influence of carbon on the weldability of a material, the maximum carbon content in fine-grained structural steels is less than 0.2%. These properties are achieved in steelmaking by the addition of oxygen and nitrogen-binding elements. The fine grain in the metallurgical structure is achieved by alloying elements whose nitrides and carbides only dissolve at higher temperatures. With the same composition, they are stronger and tougher than coarse-grained steels. Fine-grained structural steels are used above all in reinforced concrete structures such as bridges, in the construction of cranes, hydraulic cylinders or other welded structures due to their special welding suitability and in the offshore area. This describes the material class as a whole. Always confirm the individual grade against the standard before ordering. ## Also known as 5 designations · 3 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. DIN / EN Europe · 2 - [L555MB This grade’s own name](/materials/din-en/l555mb "DIN / EN L555MB") - [StE 550.7 TM This grade’s own name Withdrawn](/materials/din-en/ste-550-7-tm "DIN / EN StE 550.7 TM") UNS United States · 2 - [K12700 This grade’s own name](/materials/uns/k12700 "UNS K12700") - [K12709 This grade’s own name](/materials/uns/k12709 "UNS K12709") AISI / SAE United States · 1 - **X80 Indicative** Every designation on file is listed — no truncation, no “+ n more”. Each one is itself a route that leads back here. ## Chemical composition 14 elements on file · weight % What this alloy is Fe Mn Si Cr Iron — the balance, never listed by a standard — 96.3 % Mn — 1.8 % Si — 0.5 % Cr — 0.3 % Traces & impurities · 1.1 % Logarithmic scale, 0.01 % to 100 % — every value here compares directly, decade by decade. | Element | % by weight | |---|---| | C | ≤ 0.16 | | Si | ≤ 0.45 | | Mn | ≤ 1.8 — Unusual | | P | 0.025 | | S | 0.02 | | Cr | ≤ 0.3 | | Mo | ≤ 0.1 | | Ni | 0.3 | | V | ≤ 0.1 | | Cu | ≤ 0.25 | | Al | 0.015–0.06 | | Ti | ≤ 0.06 | | Nb | ≤ 0.06 — Unusual | | N | 0.012 | Carbon Silicon Manganese Phosphorus Sulfur Chromium Molybdenum Nickel Vanadium Copper Aluminium Titanium Niobium Nitrogen 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 | ≤0,16 | — | 0.160 | Max | | N | 0,012 | 0.012 | 0.012 | Exact | | Al | 0,015-0,060 | 0.015 | 0.060 | Range | | Si | ≤0,45 | — | 0.450 | Max | | P | 0,025 | 0.025 | 0.025 | Exact | | S | 0,02 | 0.020 | 0.020 | Exact | | Ti | ≤0,06 | — | 0.060 | Max | | V | ≤0,10 | — | 0.100 | Max | | Cr | ≤0,30 | — | 0.300 | Max | | Mn | ≤1,80 | — | 1.800 | Max | | Ni | 0,3 | 0.300 | 0.300 | Exact | | Cu | ≤0,25 | — | 0.250 | Max | | Nb | ≤0,06 | — | 0.060 | Max | | Mo | ≤0,10 | — | 0.100 | Max | 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 computed from composition · °C Predicted Ae3 815 °C Predicted Ae1 710 °C Predicted Acm 406 °C Predicted Bs 546 °C These four temperatures are a CALCULATION from this grade's own composition, using the published Li, Niebuhr, Meekisho & Atteridge (1998) model — never a measurement, and computed from the UPPER BOUND of each element's specified range, not a mid-range figure. Where this grade also has a measured transformation point (Ac1, Ac3, Ar1, Ar3) on file, it is shown separately, in Physical & mechanical properties, and is never replaced by the predicted figures here — Ae (predicted, equilibrium) and Ac/Ar (measured, on heating or cooling) are different physical quantities and can differ by tens of degrees; a mismatch between the two is not an error in either. ## Physical & mechanical properties Density 7,85 g/cm³ Exact 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=e4b5a625-5848-4958-ade6-473fd2b27030&designation=66964818-749c-4b07-b98a-4f16e64983d0 "Inquiry")[**Datasheet as PDF** Print-ready A4 document **Generating …** **Download started** **Try again**](/materials/aisi-sae/x80.pdf "Datasheet as PDF")