--- title: "K12121 — Heat-resistant structural steels" description: "K12121 in UNS: material number 1.5421, also listed as 20MnMo3-5. Category: Heat-resistant structural steels. Designations recorded for this grade: 3." canonical: https://steelequivalents.com/materials/uns/k12121 language: en robots: index, follow og_type: website type: material-detail language_alternates: en: https://steelequivalents.com/materials/uns/k12121.md cs: https://steelequivalents.com/cs/materiály/uns/k12121.md de: https://steelequivalents.com/de/werkstoffe/uns/k12121.md es: https://steelequivalents.com/es/materiales/uns/k12121.md fr: https://steelequivalents.com/fr/matériaux/uns/k12121.md hu: https://steelequivalents.com/hu/anyagok/uns/k12121.md it: https://steelequivalents.com/it/materiali/uns/k12121.md nl: https://steelequivalents.com/nl/materialen/uns/k12121.md pl: https://steelequivalents.com/pl/materiały/uns/k12121.md pt: https://steelequivalents.com/pt/materiais/uns/k12121.md ru: https://steelequivalents.com/ru/материалы/uns/k12121.md tr: https://steelequivalents.com/tr/malzemeler/uns/k12121.md zh: https://steelequivalents.com/zh/材料/uns/k12121.md ja: https://steelequivalents.com/ja/材料/uns/k12121.md ar: https://steelequivalents.com/ar/المواد/uns/k12121.md ko: https://steelequivalents.com/ko/재료/uns/k12121.md pt-br: https://steelequivalents.com/pt-br/materiais/uns/k12121.md hi: https://steelequivalents.com/hi/सामग्री/uns/k12121.md content_hash: sha256:208117036625726fa0b6a56327094ff5aee1ad5d1e47d4a78ff063bfc1557c9d generated: 2026-09-22 --- > **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/uns/k12121 > Canonical URL: https://steelequivalents.com/materials/uns/k12121 > 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. UNS · United States · 3 designations # K12121 K12121 is a designation in UNS for the material held under material number 1.5421, also listed as 20MnMo3-5. It is a material in the category Heat-resistant structural steels. We list 3 designations recorded for this grade, in the standards DIN / EN and UNS. - [*Material no.* **1.5421**](/materials/material-no/1.5421 "Material no.: 1.5421") - [*Category* **Heat-resistant structural steels · 62 grades**](/categories/heat-resistant-structural-steels "Category: Heat-resistant structural steels · 62 grades") - *Designations* **3** [Search](/search "Steel grade search")[Inquiry](/inquiry?material=656950bc-8a0a-4468-b678-7130bc99c2c4&designation=ead8e8b8-15b5-4fd8-8e72-aad3f3f20697 "Inquiry")[**Datasheet as PDF** Print-ready A4 document **Generating …** **Download started** **Try again**](/materials/uns/k12121.pdf "Datasheet as PDF") ## If you came for one of these The most-used names for this grade. - [DIN / EN 20MnMo3-5 This grade’s own name](/materials/din-en/20mnmo3-5 "DIN / EN 20MnMo3-5") - [UNS K12822 This grade’s own name · 3 grades on that route](/materials/uns/k12822 "UNS K12822") ## About Heat-resistant structural steels Heat-resistant structural steels are structural steels designed to retain useful strength and dimensional stability at elevated temperatures. They are used for load-bearing components in hot-service equipment where mechanical performance must be maintained during heating. This describes the material class as a whole. Always confirm the individual grade against the standard before ordering. ## Also known as 3 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. DIN / EN Europe · 1 - [20MnMo3-5 This grade’s own name](/materials/din-en/20mnmo3-5 "DIN / EN 20MnMo3-5") UNS United States · 2 - **K12121 This grade’s own name** - [K12822 This grade’s own name](/materials/uns/k12822 "UNS K12822") Every designation on file is listed — no truncation, no “+ n more”. Each one is itself a route that leads back here. ## Chemical composition 6 elements on file · weight % What this alloy is Fe Mn Mo C Iron — the balance, never listed by a standard — 98.2 % Mn — 0.9 % Mo — 0.5 % C — 0.2 % Traces & impurities · 0.2 % Logarithmic scale, 0.01 % to 100 % — every value here compares directly, decade by decade. | Element | % by weight | |---|---| | C | 0.15–0.25 | | Si | 0.15–0.25 | | Mn | 0.7–1 | | P | 0.025 | | S | 0.025 | | Mo | 0.4–0.6 | Carbon Silicon Manganese Phosphorus Sulfur Molybdenum 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 | 0,15-0,25 | 0.150 | 0.250 | Range | | Si | 0,15-0,25 | 0.150 | 0.250 | Range | | P | 0,025 | 0.025 | 0.025 | Exact | | S | 0,025 | 0.025 | 0.025 | Exact | | Mn | 0,70-1,00 | 0.700 | 1.000 | Range | | Mo | 0,40-0,60 | 0.400 | 0.600 | 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: Ni, Cr. ## 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. ## Similar grades — and why Selection rule, stated so you can disagree with it: same number class 1.5, a shared category, and a published range for Mn / Mo that overlaps this grade’s. These are neighbours in composition space — they are not equivalents, and none is claimed to be interchangeable with this grade. [G20Mo5 1.5419 Mn 0,50-1,00 · Mo 0,40-0,60 - ΔMn 0.10 - ΔMo 0.00 - 6 designations](/materials/din-en/g20mo5 "G20Mo5")[21MoV5-3 1.5404 Mn 0,50-0,80 · Mo 0,45-0,55 - ΔMn 0.20 - ΔMo 0.00 - 1 designations](/materials/din-en/21mov5-3 "21MoV5-3")[8MoB5-4 1.5450 Mn 0,60-0,80 · Mo 0,40-0,50 - ΔMn 0.15 - ΔMo 0.05 - 1 designations](/materials/din-en/8mob5-4 "8MoB5-4")[17MnMoCrV3-6 1.5405 Mn 0,60-0,80 · Mo 0,50-0,60 - ΔMn 0.15 - ΔMo 0.05 - 1 designations](/materials/din-en/17mnmocrv3-6 "17MnMoCrV3-6")[G18Mo5 1.5422 Mn 0,80-1,20 · Mo 0,45-0,65 - ΔMn 0.15 - ΔMo 0.05 - 1 designations](/materials/din-en/g18mo5 "G18Mo5")[11MnMo4-5 1.5425 Mn 0,85-1,15 · Mo 0,48-0,62 - ΔMn 0.15 - ΔMo 0.05 - 5 designations](/materials/din-en/11mnmo4-5 "11MnMo4-5") ## 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=656950bc-8a0a-4468-b678-7130bc99c2c4&designation=ead8e8b8-15b5-4fd8-8e72-aad3f3f20697 "Inquiry")[**Datasheet as PDF** Print-ready A4 document **Generating …** **Download started** **Try again**](/materials/uns/k12121.pdf "Datasheet as PDF")