Steel 20MnMoNi4-5
EN 20MnMoNi4-5
20MnMoNi4-5 (1.6311) is a low-carbon Mn-Mo-Ni pressure vessel steel from the EN quenched-and-tempered alloy steel family, relying on molybdenum and nickel for through-hardenability in heavy sections rather than on high carbon.
Reference datasheet — 20MnMoNi4-5 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the QT condition
20MnMoNi4-5 tempers and conditions
20MnMoNi4-5 is supplied in 6 conditions, soft to hard. QT is the default FabDigit quotes; the values on this page are for it.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Choose for rough machining of heavy forgings or as an intermediate condition before final quench and temper. | 330 | 540 | 27 | 160 HB | — |
Hot rolled | Mill-supplied semi-finished bar, billet or slab intended for subsequent forging and heat treatment; not a service condition. | 390 | 620 | 21 | 195 HB | 7.8 % IACS |
Normalized | Grain-refining condition for plate and smaller sections where full Q&T properties are not required. | 400 | 600 | 24 | 180 HB | 7.8 % IACS |
Normalized and tempered | Plate and moderate-section forgings needing stable properties and good toughness without a water quench. | 430 | 610 | 24 | 190 HB | 7.8 % IACS |
Quenched, tempered and simulated post-weld heat treated | Qualification condition for welded vessels: properties after the full simulated PWHT cycle (typ. 600–620 °C, long hold) — slightly lower strength, high toughness. | 445 | 610 | 24 | 190 HB | 7.8 % IACS |
QTDefault Quenched and tempered | Standard delivery condition for heavy pressure-vessel forgings, shells and tube sheets — best strength/toughness balance in thick section. | 470 | 640 | 23 | 200 HB | — |
What is 20MnMoNi4-5?
20MnMoNi4-5 (1.6311) is a low-carbon Mn-Mo-Ni pressure vessel steel from the EN quenched-and-tempered alloy steel family, relying on molybdenum and nickel for through-hardenability in heavy sections rather than on high carbon. In the default condition it provides 470 MPa yield, 640 MPa tensile, 23 % elongation and about 200 HB, with service to 371 °C, and is supplied as thick plate, heavy forgings and rolled rings. It has no inherent corrosion resistance and needs 150–200 °C preheat plus mandatory PWHT at 590–620 °C after welding. Where creep strength above 400 °C is required, 15NiCuMoNb5-6-4 (WB36) is the usual alternative. 20MnMoNi4-5 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,450°C (2,642 °F). 20MnMoNi4-5 has a yield strength of 470 MPa (68.2 ksi) and a tensile strength of 640 MPa (92.8 ksi) — stronger than 57% of steel grades. Elongation at break is 23% and the elastic modulus is 210 GPa (30.5 Msi).
What is 20MnMoNi4-5 used for?
- Reactor pressure vessels
- Heavy boiler drums
- Large forged pressure components
Advantages
- Tough — resists crack growth — 200 MPa·√m (182 ksi·√in), better than 100% of steel grades
20MnMoNi4-5 properties
Typical room-temperature values for 20MnMoNi4-5-QT; bars are the position among steel grades.
Physical3
20MnMoNi4-5 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,450°C (2,642 °F).
Mechanical16
20MnMoNi4-5 has a yield strength of 470 MPa (68.2 ksi) and a tensile strength of 640 MPa (92.8 ksi) — stronger than 57% of steel grades. Elongation at break is 23% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
20MnMoNi4-5 is rated for continuous service to 371°C (700 °F). It conducts heat at 41 W/m·K (23.7 BTU/hr·ft·°F), worse than 62% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical2
20MnMoNi4-5 has an electrical resistivity of 2.2×10⁻⁷ Ω·m.
Chemical & Environmental3
Corrosion resistance is not recommended (14/100), better than 70% of steel grades.
Sustainability4
Producing a kilogram of 20MnMoNi4-5 takes about 30 MJ of energy and emits 2.2 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 25%.
Manufacturability8
20MnMoNi4-5's machinability is good (55/100, better than 62% of steel grades); weldability good (65/100); formability fair (45/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. 20MnMoNi4-5 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 20MnMoNi4-5
Is 20MnMoNi4-5 easy to machine?
Machines like Q&T 4140 at ~200 HB — rigid setups, carbide inserts, 90–140 m/min; rough machine before final temper where possible to control distortion in heavy sections.
Can 20MnMoNi4-5 be welded?
Weldable by SAW/SMAW/GTAW with matching Mn-Mo-Ni consumables, preheat/interpass 150–200 °C, low-hydrogen practice, and mandatory PWHT at 590–620 °C.
Can 20MnMoNi4-5 be formed, bent or molded?
Hot forge/roll at 1150–850 °C with controlled finish temperature, then normalize or austenitize 870–900 °C, water quench and temper 620–660 °C; cold forming is limited.
20MnMoNi4-5 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CSEW 590 / KTA 3201.1 | 0.17 – 0.23 | 0.2 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 1.2 – 1.5 | 1.35 |
| Pnuclear heats often ≤0.008 | ≤ 0.01 | 0.01 |
| Slow-S for through-thickness toughness | ≤ 0.01 | 0 |
| Cr | ≤ 0.2 | 0.1 |
| Mo | 0.4 – 0.55 | 0.5 |
| Ni | 0.5 – 0.8 | 0.7 |
| V | ≤ 0.02 | 0.01 |
| Culimited for irradiation embrittlement | ≤ 0.12 | 0.05 |
| Algrain refining | 0.01 – 0.04 | 0.03 |
| N | ≤ 0.01 | 0.01 |
| Fe | balance |
What surface finishes work on 20MnMoNi4-5?
No anodizing; protect by shot blast + epoxy paint, phosphating, or stainless/Inconel weld overlay and cladding on wetted vessel surfaces.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel 20MnMoNi4-5 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- EN / DIN / Werkstoff-Nr.
- 1.6311
How much does 20MnMoNi4-5 cost?
20MnMoNi4-5 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
20MnMoNi4-5 — frequently asked
What is 20MnMoNi4-5 used for?
20MnMoNi4-5 is typically used for reactor pressure vessels, heavy boiler drums and large forged pressure components. In short: thick-section pressure vessel steel; weldable with mandatory PWHT; tough in heavy forgings.
What is the yield strength of 20MnMoNi4-5?
20MnMoNi4-5 has a typical yield strength of 470 MPa (68.2 ksi) and a tensile strength of 640 MPa (92.8 ksi) — stronger than 57% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is 20MnMoNi4-5 easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machines like Q&T 4140 at ~200 HB — rigid setups, carbide inserts, 90–140 m/min; rough machine before final temper where possible to control distortion in heavy sections.
Can 20MnMoNi4-5 be welded?
Yes — weldability is rated good (65/100). Weldable by SAW/SMAW/GTAW with matching Mn-Mo-Ni consumables, preheat/interpass 150–200 °C, low-hydrogen practice, and mandatory PWHT at 590–620 °C.
What surface finishes work on 20MnMoNi4-5?
No anodizing; protect by shot blast + epoxy paint, phosphating, or stainless/Inconel weld overlay and cladding on wetted vessel surfaces.
Can 20MnMoNi4-5 be formed, bent or molded?
Hot forge/roll at 1150–850 °C with controlled finish temperature, then normalize or austenitize 870–900 °C, water quench and temper 620–660 °C; cold forming is limited.
What is the maximum service temperature of 20MnMoNi4-5?
20MnMoNi4-5 is rated for continuous use to about 371°C (700 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 20MnMoNi4-5-QT and 20MnMoNi4-5-A?
QT is the default condition — standard delivery condition for heavy pressure-vessel forgings, shells and tube sheets — best strength/toughness balance in thick section. A: choose for rough machining of heavy forgings or as an intermediate condition before final quench and temper. Yield strength is 470 MPa in QT versus 330 MPa in A.
How much does 20MnMoNi4-5 cost?
20MnMoNi4-5 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- SEW 590 — Heat-treatable steels for pressure vessel components — Stahl-Eisen-Werkstoffblatt / VDEh (1996)
- DIN 17182 — Cast and forged steels for pressure purposes — DIN (1992)
- KTA 3201.1 — Components of the reactor coolant pressure boundary, Part 1: Materials — Kerntechnischer Ausschuss (2017)
- VdTÜV-Werkstoffblatt 401 — 20MnMoNi5-5 / 20MnMoNi4-5 — VdTÜV (2010)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASME BPVC Section II Part A — SA-508 Gr.3 Cl.1 (comparable grade) — ASME (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.