Steel 20MnMoNi4-5-QT (Quenched and tempered)
Heat-treated state · default condition
EN 20MnMoNi4-5
Standard delivery condition for heavy pressure-vessel forgings, shells and tube sheets — best strength/toughness balance in thick section.
Values for the QT condition
Other 20MnMoNi4-5 tempers and conditions
20MnMoNi4-5 is listed in 6 conditions; see the grade overview at 20MnMoNi4-5.
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 |
QTDefaultThis page 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-QT?
20MnMoNi4-5-QT is 20MnMoNi4-5 heat treated to QT — standard delivery condition for heavy pressure-vessel forgings, shells and tube sheets — best strength/toughness balance in thick section. 20MnMoNi4-5-QT 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). 20MnMoNi4-5-QT 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).
Advantages
- Tough — resists crack growth — 200 MPa·√m (182 ksi·√in), better than 100% of steel grades
20MnMoNi4-5-QT properties
Typical room-temperature values for 20MnMoNi4-5-QT; 14 are specific to this condition. Other listed values are 20MnMoNi4-5 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
20MnMoNi4-5-QT 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-QT 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-QT 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-QT 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-QT 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-QT'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. Confirm any required mill or lot documentation when quoting.
Working with 20MnMoNi4-5-QT
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.
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.
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 | — |
20MnMoNi4-5-QT — frequently asked
What is 20MnMoNi4-5-QT used for?
20MnMoNi4-5-QT 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-QT?
20MnMoNi4-5-QT 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-QT 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-QT 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-QT?
No anodizing; protect by shot blast + epoxy paint, phosphating, or stainless/Inconel weld overlay and cladding on wetted vessel surfaces.
Can 20MnMoNi4-5-QT 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-QT?
20MnMoNi4-5-QT 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.