Steel 15NiCuMoNb5-6-4-QT (Quenched and tempered)
Heat-treated state
EN 15NiCuMoNb5-6-4 · also WB36
Chosen for heavy-wall headers, forgings and thick plate where through-thickness strength and low-temperature toughness must be maintained.
Values for the QT condition
Other 15NiCuMoNb5-6-4 tempers and conditions
15NiCuMoNb5-6-4 is listed in 2 conditions; see the grade overview at 15NiCuMoNb5-6-4.
- NT
- QT
Compare all 2 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
NTDefault normalized and tempered | Standard delivery condition for WB36 seamless tube, pipe and plate for boiler feedwater and steam service. | 480 | 660 | 23 | 18 HRC | — |
QTThis page Quenched and tempered | Chosen for heavy-wall headers, forgings and thick plate where through-thickness strength and low-temperature toughness must be maintained. | 530 | 700 | 21 | 20 HRC | — |
What is 15NiCuMoNb5-6-4-QT?
15NiCuMoNb5-6-4-QT is 15NiCuMoNb5-6-4 heat treated to QT — chosen for heavy-wall headers, forgings and thick plate where through-thickness strength and low-temperature toughness must be maintained. 15NiCuMoNb5-6-4-QT has a yield strength of 530 MPa (76.9 ksi) and a tensile strength of 700 MPa (102 ksi) — stronger than 69% of steel grades. Elongation at break is 21% and the elastic modulus is 211 GPa (30.6 Msi). 15NiCuMoNb5-6-4-QT has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,460°C (2,660 °F). NT is the default condition FabDigit quotes; QT is available on request or by drawing note.
Advantages
- Tough — resists crack growth — 170 MPa·√m (154.7 ksi·√in), better than 98% of steel grades
15NiCuMoNb5-6-4-QT properties
Typical room-temperature values for 15NiCuMoNb5-6-4-QT; 20 are specific to this condition. Other listed values are 15NiCuMoNb5-6-4 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
15NiCuMoNb5-6-4-QT has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,460°C (2,660 °F).
Mechanical17
15NiCuMoNb5-6-4-QT has a yield strength of 530 MPa (76.9 ksi) and a tensile strength of 700 MPa (102 ksi) — stronger than 69% of steel grades. Elongation at break is 21% and the elastic modulus is 211 GPa (30.6 Msi).
Thermal6
15NiCuMoNb5-6-4-QT is rated for continuous service to 400°C (752 °F). It conducts heat at 40 W/m·K (23.1 BTU/hr·ft·°F), worse than 64% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical2
15NiCuMoNb5-6-4-QT has an electrical resistivity of 2.2×10⁻⁷ Ω·m.
Chemical & Environmental3
Corrosion resistance is poor (18/100), better than 83% of steel grades.
Sustainability4
Producing a kilogram of 15NiCuMoNb5-6-4-QT takes about 27 MJ of energy and emits 2.1 kg of CO₂ — less than 59% of steel grades. Typical recycled content is 25%.
Manufacturability5
15NiCuMoNb5-6-4-QT's machinability is fair (50/100, worse than 53% of steel grades); weldability good (60/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 15NiCuMoNb5-6-4-QT
Is 15NiCuMoNb5-6-4 easy to machine?
Machines like 4130/4140-class low-alloy steel at ~50–55 % of AISI 1212; use rigid setups, carbide inserts and moderate speeds with good coolant.
Can 15NiCuMoNb5-6-4 be welded?
Weldable by TIG/SMAW/SAW with matched Ni-Cu-Mo consumables; preheat about 150–250 °C and a post-weld heat treatment near 580–620 °C are normally specified to restore HAZ toughness.
Can 15NiCuMoNb5-6-4 be formed, bent or molded?
Hot forming above ~950 °C followed by re-normalizing and tempering is preferred; cold bending of tube is possible but requires generous radii and subsequent stress relief.
What surface finishes work on 15NiCuMoNb5-6-4?
No inherent corrosion protection — shot-blast and paint or metallize external surfaces; internal protection relies on boiler water chemistry rather than coatings.
15NiCuMoNb5-6-4 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 |
|---|---|---|
| C | 0.1 – 0.17 | 0.14 |
| Si | 0.25 – 0.5 | 0.35 |
| Mn | 0.8 – 1.2 | 1 |
| P | ≤ 0.03 | 0.01 |
| S | ≤ 0.01 | 0 |
| Cr | ≤ 0.3 | 0.15 |
| Mo | 0.25 – 0.5 | 0.35 |
| Ni | 1 – 1.3 | 1.15 |
| Cuprecipitation strengthening | 0.5 – 0.8 | 0.65 |
| Nbgrain refinement | 0.02 – 0.05 | 0.03 |
| Altotal Al | ≤ 0.05 | 0.03 |
| N | ≤ 0.02 | 0.01 |
| Fe | balance | — |
15NiCuMoNb5-6-4-QT — frequently asked
What is 15NiCuMoNb5-6-4-QT used for?
15NiCuMoNb5-6-4-QT is typically used for main steam piping, boiler headers and high-temperature pressure components. In short: creep-resistant boiler steel; service to 400 °C; stronger than Mn-Mo vessel steels.
What is the yield strength of 15NiCuMoNb5-6-4-QT?
15NiCuMoNb5-6-4-QT has a typical yield strength of 530 MPa (76.9 ksi) and a tensile strength of 700 MPa (102 ksi) — stronger than 69% of steel grades. Strength varies by condition: see the 2 listed tempers.
Is 15NiCuMoNb5-6-4-QT easy to machine?
Reasonably — machinability is rated fair (50/100, worse than 53% of steel grades). Machines like 4130/4140-class low-alloy steel at ~50–55 % of AISI 1212; use rigid setups, carbide inserts and moderate speeds with good coolant.
Can 15NiCuMoNb5-6-4-QT be welded?
Yes — weldability is rated good (60/100). Weldable by TIG/SMAW/SAW with matched Ni-Cu-Mo consumables; preheat about 150–250 °C and a post-weld heat treatment near 580–620 °C are normally specified to restore HAZ toughness.
What surface finishes work on 15NiCuMoNb5-6-4-QT?
No inherent corrosion protection — shot-blast and paint or metallize external surfaces; internal protection relies on boiler water chemistry rather than coatings.
Can 15NiCuMoNb5-6-4-QT be formed, bent or molded?
Hot forming above ~950 °C followed by re-normalizing and tempering is preferred; cold bending of tube is possible but requires generous radii and subsequent stress relief.
What is the maximum service temperature of 15NiCuMoNb5-6-4-QT?
15NiCuMoNb5-6-4-QT is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 15NiCuMoNb5-6-4-NT and 15NiCuMoNb5-6-4-QT?
NT is the default condition — standard delivery condition for WB36 seamless tube, pipe and plate for boiler feedwater and steam service. QT: chosen for heavy-wall headers, forgings and thick plate where through-thickness strength and low-temperature toughness must be maintained. Yield strength is 480 MPa in NT versus 530 MPa in QT.
Sources
- EN 10216-2 — Seamless steel tubes for pressure purposes, non-alloy and alloy steels with specified elevated temperature properties — CEN (2020)
- VdTÜV Werkstoffblatt 377 / WB 36 (15NiCuMoNb5-6-4) — VdTÜV (2011)
- DIN 17175 — Seamless tubes of heat-resistant steels (historic) — DIN (1979)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- Seamless boiler tube datasheets for WB36/1.6368 — European seamless tube producers (2021)
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.