Steel X11CrMo9-1 +I (Isothermally annealed)
Heat-treated state
EN X11CrMo9-1 · ASTM A335 P9
Pick for bar/forging stock that must be machined or cold worked before final normalizing and tempering; softest, most uniform structure.
Values for the +I condition
Other X11CrMo9-1 tempers and conditions
X11CrMo9-1 is listed in 4 conditions; see the grade overview at X11CrMo9-1.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Use when maximum softness for deep machining or cold bending is required; strength/creep properties must be restored by later +NT. | 245 | 455 | 30 | 150 HB | 3 % IACS |
+IThis page Isothermally annealed | Pick for bar/forging stock that must be machined or cold worked before final normalizing and tempering; softest, most uniform structure. | 260 | 470 | 28 | 160 HB | — |
+NTDefault Normalized and tempered | Standard supply condition for boiler tubes, headers and P9 process piping; best creep strength and toughness combination. | 300 | 520 | 26 | 185 HB | — |
Quenched and tempered | Used for heavy-wall forgings, valve bodies and thick flanges (EN 10222-2) where through-thickness strength and toughness are needed. | 360 | 570 | 22 | 18 HRC | — |
What is X11CrMo9-1 +I?
X11CrMo9-1 +I is X11CrMo9-1 heat treated to +I — pick for bar/forging stock that must be machined or cold worked before final normalizing and tempering; softest, most uniform structure. X11CrMo9-1 +I has a yield strength of 260 MPa (37.7 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 92% of steel grades. Elongation at break is 28% and the elastic modulus is 213 GPa (30.9 Msi). X11CrMo9-1 +I has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 93% of steel grades. It melts at 1,420°C (2,588 °F). +NT is the default condition FabDigit quotes; +I is available on request or by drawing note.
Advantages
- High service temperature — 550°C (1,022 °F), better than 95% of steel grades
- Good corrosion resistance — 30/100, better than 95% of steel grades
- Ductile — tolerates forming and impact — 28%, better than 89% of steel grades
Limitations
- Low electrical conductivity — 2.9 % IACS, worse than 93% of steel grades
- Low strength — 260 MPa (37.7 ksi), worse than 92% of steel grades
- Poor heat conductor — 29 W/m·K (16.8 BTU/hr·ft·°F), worse than 84% of steel grades
X11CrMo9-1 +I properties
Typical room-temperature values for X11CrMo9-1 +I; 15 are specific to this condition. Other listed values are X11CrMo9-1 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
X11CrMo9-1 +I has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 93% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
X11CrMo9-1 +I has a yield strength of 260 MPa (37.7 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 92% of steel grades. Elongation at break is 28% and the elastic modulus is 213 GPa (30.9 Msi).
Thermal6
X11CrMo9-1 +I is rated for continuous service to 550°C (1,022 °F). It conducts heat at 29 W/m·K (16.8 BTU/hr·ft·°F), worse than 84% of steel grades. Thermal expansion is 11.3 µm/m·K (6.28 µin/in·°F).
Electrical3
X11CrMo9-1 +I conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (30/100), better than 95% of steel grades.
Sustainability4
Producing a kilogram of X11CrMo9-1 +I takes about 31 MJ of energy and emits 2.4 kg of CO₂ — more than 64% of steel grades. Typical recycled content is 25%.
Manufacturability7
X11CrMo9-1 +I's machinability is good (55/100, better than 62% of steel grades); weldability fair (40/100); formability fair (50/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with X11CrMo9-1 +I
Is X11CrMo9-1 easy to machine?
Machines like a medium-hard low-alloy steel — best in +I/+A condition with rigid setups, sharp carbide, moderate speeds and generous coolant; work-hardening tendency is low but tool wear from Cr carbides is noticeable.
Can X11CrMo9-1 be welded?
Weldable with matching 9Cr-1Mo (E505/ER90S-B8) consumables; preheat 200–300 °C, maintain interpass, avoid interruption, and apply 730–780 °C PWHT to avoid hard untempered martensite and hydrogen cracking.
Can X11CrMo9-1 be formed, bent or molded?
Hot form/bend at 900–1050 °C then re-normalize and temper; cold bending is limited and any cold work above ~5–10 % should be followed by stress relief or full +NT.
What surface finishes work on X11CrMo9-1?
No anodizing; protect with high-temperature aluminium/silicone paint, aluminizing or phosphate primer for wet service — the 9 % Cr gives oxidation resistance hot but not rust resistance cold.
X11CrMo9-1 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 – 0.15 | 0.12 |
| Si | 0.25 – 1 | 0.5 |
| Mn | 0.3 – 0.6 | 0.45 |
| PEN limit; ASTM A335 P9 allows 0.025 | ≤ 0.02 | — |
| SEN limit; ASTM A335 P9 allows 0.025 | ≤ 0.01 | — |
| Cr | 8 – 10 | 9 |
| Mo | 0.9 – 1.1 | 1 |
| Niresidual | ≤ 0.3 | — |
| Fe | balance | — |
X11CrMo9-1 +I — frequently asked
What is X11CrMo9-1 +I used for?
X11CrMo9-1 +I is typically used for superheater and reheater tubes, high-temperature, high-pressure process piping, refinery heater tubes, hydrogen-service piping, catalytic reformer piping and forged fittings and valve bodies. In short: highest-temperature Cr-Mo here; 9 % Cr oxidation resistance; hardest of family to weld.
What is the yield strength of X11CrMo9-1 +I?
X11CrMo9-1 +I has a typical yield strength of 260 MPa (37.7 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 92% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is X11CrMo9-1 +I easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machines like a medium-hard low-alloy steel — best in +I/+A condition with rigid setups, sharp carbide, moderate speeds and generous coolant; work-hardening tendency is low but tool wear from Cr carbides is noticeable.
Can X11CrMo9-1 +I be welded?
With care — weldability is rated fair (40/100). Weldable with matching 9Cr-1Mo (E505/ER90S-B8) consumables; preheat 200–300 °C, maintain interpass, avoid interruption, and apply 730–780 °C PWHT to avoid hard untempered martensite and hydrogen cracking.
What surface finishes work on X11CrMo9-1 +I?
No anodizing; protect with high-temperature aluminium/silicone paint, aluminizing or phosphate primer for wet service — the 9 % Cr gives oxidation resistance hot but not rust resistance cold.
Can X11CrMo9-1 +I be formed, bent or molded?
Hot form/bend at 900–1050 °C then re-normalize and temper; cold bending is limited and any cold work above ~5–10 % should be followed by stress relief or full +NT.
What is the maximum service temperature of X11CrMo9-1 +I?
X11CrMo9-1 +I is rated for continuous use to about 550°C (1,022 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- EN 10216-2 — Seamless steel tubes for pressure purposes, alloy steel with specified elevated temperature properties — CEN (2020)
- ASTM A335/A335M — Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service (Grade P9) — ASTM (2023)
- ASTM A213/A213M — Seamless Ferritic Alloy-Steel Boiler Tubes (Grade T9) — ASTM (2022)
- ASME BPVC Section II Part D — Materials, Properties (9Cr-1Mo) — ASME (2023)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- GB/T 5310 — Seamless steel tubes for high pressure boilers (12Cr9Mo1 ) — SAC (2017)
- Mysteel / SMM (2026)
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.