Stainless Steel 1.4903 +QT (Quenched and tempered)
Heat-treated state
EN 1.4903 · UNS K90901 · ASTM A335 Grade P91 · GB 10Cr9Mo1VNb
Chosen for very heavy sections (thick headers, valve bodies, closed-die forgings) where still-air normalizing cannot cool the core fast enough to fully martensitic structure.
Values for the +QT condition
Other 1.4903 tempers and conditions
1.4903 is listed in 3 conditions; see the grade overview at 1.4903.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Used only as an intermediate condition for heavy machining or cold work of bar/forging blanks; must be re-normalized and tempered before any creep service. | 380 | 590 | 26 | 10 HRC | 3 % IACS |
+NTDefault Normalized and tempered | Standard delivery condition for all P91 pipe, plate, forgings and fittings — full tempered-martensite creep structure for 550–600 °C service. | 490 | 660 | 23 | 19 HRC | — |
+QTThis page Quenched and tempered | Chosen for very heavy sections (thick headers, valve bodies, closed-die forgings) where still-air normalizing cannot cool the core fast enough to fully martensitic structure. | 520 | 700 | 21 | 21 HRC | — |
What is 1.4903 +QT?
1.4903 +QT is 1.4903 heat treated to +QT — chosen for very heavy sections (thick headers, valve bodies, closed-die forgings) where still-air normalizing cannot cool the core fast enough to fully martensitic structure. 1.4903 +QT has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 700 MPa (102 ksi) — stronger than 79% of stainless steel grades. Elongation at break is 21% and the elastic modulus is 218 GPa (31.6 Msi). 1.4903 +QT has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 58% of stainless steel grades. It melts at 1,450°C (2,642 °F). +NT is the default condition FabDigit quotes; +QT is available on request or by drawing note.
Advantages
- Low embodied carbon — 2.6 kg CO₂/kg, better than 100% of stainless steel grades
- Conducts heat well — 26.5 W/m·K (15.3 BTU/hr·ft·°F), better than 96% of stainless steel grades
- High electrical conductivity — 2.9 % IACS, better than 87% of stainless steel grades
- High strength — 520 MPa (75.4 ksi), better than 79% of stainless steel grades
Limitations
- Needs corrosion protection — 28/100, worse than 100% of stainless steel grades
- Difficult to weld — 42/100, worse than 81% of stainless steel grades
- Limited ductility — 21%, worse than 78% of stainless steel grades
1.4903 +QT properties
Typical room-temperature values for 1.4903 +QT; 15 are specific to this condition. Other listed values are 1.4903 reference data and may not represent this condition. Bars are the position among stainless steel grades.
Physical3
1.4903 +QT has a density of 7.77 g/cm³ (0.281 lb/in³), lighter than 58% of stainless steel grades. It melts at 1,450°C (2,642 °F).
Mechanical17
1.4903 +QT has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 700 MPa (102 ksi) — stronger than 79% of stainless steel grades. Elongation at break is 21% and the elastic modulus is 218 GPa (31.6 Msi).
Thermal6
1.4903 +QT is rated for continuous service to 600°C (1,112 °F). It conducts heat at 26.5 W/m·K (15.3 BTU/hr·ft·°F), better than 96% of stainless steel grades. Thermal expansion is 10.8 µm/m·K (6 µin/in·°F).
Electrical3
1.4903 +QT conducts electricity at 2.9 % IACS, better than 87% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is poor (28/100), worse than 100% of stainless steel grades.
Sustainability4
Producing a kilogram of 1.4903 +QT takes about 35 MJ of energy and emits 2.6 kg of CO₂ — less than 100% of stainless steel grades. Typical recycled content is 35%.
Manufacturability6
1.4903 +QT's machinability is fair (35/100, better than 51% of stainless steel grades); weldability fair (42/100); formability poor (27/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 1.4903 +QT
Is 1.4903 easy to machine?
Machine in +NT/+QT at ~215 HB with rigid setups, coated carbide, modest speeds and heavy positive feeds; it work-hardens and glazes if feed is too light, so avoid dwelling and use flood coolant.
Can 1.4903 be welded?
GTAW root / SMAW-FCAW fill with matching 9CrMoV consumables, 200–300 °C preheat and maintained interpass (<300 °C), no free cooling below ~80 °C before PWHT, then mandatory 750–770 °C temper; keep Ni+Mn low to protect Ac1 and avoid soft Type IV HAZ.
Can 1.4903 be formed, bent or molded?
Hot form at 1050–1150 °C followed by full normalize + temper; cold bending is limited and any strain above a few percent should trigger re-heat-treatment to restore creep properties.
What surface finishes work on 1.4903?
Not corrosion-resistant in wet ambient service — shot-blast and apply high-temperature aluminium/silicone paint or preservative for storage; it takes a fine metallographic polish but shows no stainless passivity.
1.4903 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 | 0.08 – 0.12 | 0.1 |
| Si | 0.2 – 0.5 | 0.35 |
| Mn | 0.3 – 0.6 | 0.45 |
| P | ≤ 0.02 | 0.01 |
| S | ≤ 0.01 | 0 |
| Cr | 8 – 9.5 | 8.8 |
| Mo | 0.85 – 1.05 | 0.95 |
| V | 0.18 – 0.25 | 0.21 |
| NbNb (Cb) | 0.06 – 0.1 | 0.08 |
| N | 0.03 – 0.07 | 0.05 |
| Ni | ≤ 0.4 | 0.2 |
| Almax (0.04 in some editions) | ≤ 0.02 | 0.01 |
| Ti | ≤ 0.01 | — |
| Zr | ≤ 0.01 | — |
| Fe | balance | — |
1.4903 +QT — frequently asked
What is 1.4903 +QT used for?
1.4903 +QT is typically used for boiler headers/piping, steam pipework and power plant components. In short: standard P91 creep steel; 600 °C piping grade; mandatory post-weld heat treatment.
What is the yield strength of 1.4903 +QT?
1.4903 +QT has a typical yield strength of 520 MPa (75.4 ksi) and a tensile strength of 700 MPa (102 ksi) — stronger than 79% of stainless steel grades. Strength varies by condition: see the 3 listed tempers.
Is 1.4903 +QT easy to machine?
Not especially — machinability is rated fair (35/100, better than 51% of stainless steel grades). Machine in +NT/+QT at ~215 HB with rigid setups, coated carbide, modest speeds and heavy positive feeds; it work-hardens and glazes if feed is too light, so avoid dwelling and use flood coolant.
Can 1.4903 +QT be welded?
With care — weldability is rated fair (42/100). GTAW root / SMAW-FCAW fill with matching 9CrMoV consumables, 200–300 °C preheat and maintained interpass (<300 °C), no free cooling below ~80 °C before PWHT, then mandatory 750–770 °C temper; keep Ni+Mn low to protect Ac1 and avoid soft Type IV HAZ.
What surface finishes work on 1.4903 +QT?
Not corrosion-resistant in wet ambient service — shot-blast and apply high-temperature aluminium/silicone paint or preservative for storage; it takes a fine metallographic polish but shows no stainless passivity.
Can 1.4903 +QT be formed, bent or molded?
Hot form at 1050–1150 °C followed by full normalize + temper; cold bending is limited and any strain above a few percent should trigger re-heat-treatment to restore creep properties.
What is the maximum service temperature of 1.4903 +QT?
1.4903 +QT is rated for continuous use to about 600°C (1,112 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- ASTM A335/A335M — Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service (Grade P91) — ASTM International (2022)
- EN 10216-2 — Seamless steel tubes for pressure purposes, X10CrMoVNb9-1 (1.4903) — CEN (2020)
- EN 10302 — Creep resisting steels, nickel and cobalt alloys (physical property data) — CEN (2008)
- GB/T 5310 — (10Cr9Mo1VNb) — SAC (2017)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- EPRI/ASME guidance on Grade 91 fabrication, welding and heat treatment — EPRI / ASME (2015)
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.