Steel X7Ni9 +NNT
Heat-treated state
EN X7Ni9
+NNT = double normalized and tempered
ASTM A353-style delivery condition: two normalizing cycles plus temper for uniform toughness in heavy plate without quenching facilities.
Values for the +NNT condition
Other X7Ni9 tempers and conditions
X7Ni9 is listed in 4 conditions; see the grade overview at X7Ni9.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Soft interim condition for heavy machining or forming of forgings/bar; parts are re-hardened to +QT or +NT before cryogenic service. | 450 | 640 | 28 | 10 HRC | 3.8 % IACS |
Normalized and tempered | Lower-yield (490 MPa class) condition used for thick plate and forgings where quench distortion or hardenability limits apply. | 550 | 700 | 25 | 200 HB | — |
+NNTThis page Double normalized and tempered | ASTM A353-style delivery condition: two normalizing cycles plus temper for uniform toughness in heavy plate without quenching facilities. | 570 | 720 | 25 | 205 HB | — |
+QTDefault Quenched and tempered | Highest-strength standard condition for LNG inner-tank plate and pressure parts; pick when the design uses the 585 MPa yield class. | 640 | 730 | 24 | 19 HRC | — |
What is X7Ni9 +NNT?
X7Ni9 +NNT is X7Ni9 heat treated to +NNT — aSTM A353-style delivery condition: two normalizing cycles plus temper for uniform toughness in heavy plate without quenching facilities. X7Ni9 +NNT has a yield strength of 570 MPa (82.7 ksi) and a tensile strength of 720 MPa (104 ksi) — stronger than 74% of steel grades. Elongation at break is 25% and the elastic modulus is 195 GPa (28.3 Msi). X7Ni9 +NNT has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,430°C (2,606 °F). +QT is the default condition FabDigit quotes; +NNT 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
- Ductile — tolerates forming and impact — 25%, better than 77% of steel grades
Limitations
- High embodied carbon — 3 kg CO₂/kg, worse than 91% of steel grades
- Low electrical conductivity — 3.8 % IACS, worse than 84% of steel grades
- Poor heat conductor — 30 W/m·K (17.3 BTU/hr·ft·°F), worse than 83% of steel grades
X7Ni9 +NNT properties
Typical room-temperature values for X7Ni9 +NNT; 10 are specific to this condition. Other listed values are X7Ni9 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
X7Ni9 +NNT has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,430°C (2,606 °F).
Mechanical17
X7Ni9 +NNT has a yield strength of 570 MPa (82.7 ksi) and a tensile strength of 720 MPa (104 ksi) — stronger than 74% of steel grades. Elongation at break is 25% and the elastic modulus is 195 GPa (28.3 Msi).
Thermal6
X7Ni9 +NNT is rated for continuous service to 350°C (662 °F). It conducts heat at 30 W/m·K (17.3 BTU/hr·ft·°F), worse than 83% of steel grades. Thermal expansion is 10.2 µm/m·K (5.67 µin/in·°F).
Electrical3
X7Ni9 +NNT conducts electricity at 3.8 % IACS, worse than 84% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (16/100), better than 79% of steel grades.
Sustainability4
Producing a kilogram of X7Ni9 +NNT takes about 40 MJ of energy and emits 3 kg of CO₂ — more than 91% of steel grades. Typical recycled content is 25%.
Manufacturability7
X7Ni9 +NNT's machinability is fair (42/100, worse than 73% of steel grades); weldability good (55/100); formability fair (48/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with X7Ni9 +NNT
Is X7Ni9 easy to machine?
Machine like a tough 200–230 HB alloy steel: rigid setup, positive-rake carbide, moderate speed with heavy feed and copious coolant to avoid work-hardened glazing.
Can X7Ni9 be welded?
Weld with Ni-base consumables (ENiCrMo-6, ERNiCrMo-3/ERNiCrMo-4); control heat input, demagnetize plate before welding (arc blow), preheat usually ≤100 °C and PWHT normally not required.
Can X7Ni9 be formed, bent or molded?
Hot form at 850–950 °C followed by the specified NT/QT cycle; cold forming is possible but springback is high and severe cold work should be followed by re-heat treatment.
What surface finishes work on X7Ni9?
Not anodizable — shot-blast then epoxy/zinc-rich paint or metallize; keep surfaces dry, and verify residual magnetism and cleanliness before cryogenic commissioning.
X7Ni9 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 |
|---|---|---|
| CEN 10028-4 max; ASTM A553 Type I allows 0.13 max | ≤ 0.1 | 0.06 |
| Si | 0.1 – 0.35 | 0.25 |
| Mn | 0.3 – 0.8 | 0.55 |
| Plow P/S for cryogenic toughness | ≤ 0.02 | 0.01 |
| S | ≤ 0.01 | 0 |
| NiASTM A553 Type I: 8.5–9.5 | 8.5 – 10 | 9 |
| Crresidual | ≤ 0.3 | 0.05 |
| Moresidual | ≤ 0.1 | 0.03 |
| Curesidual | ≤ 0.3 | 0.05 |
| Vresidual | ≤ 0.05 | 0.01 |
| N | ≤ 0.01 | 0.01 |
| AlAl-killed / grain refinement | 0.02 – 0.06 | 0.03 |
| Fe | balance | — |
X7Ni9 +NNT — frequently asked
What is X7Ni9 +NNT used for?
X7Ni9 +NNT is typically used for LNG tanks, cryogenic pressure vessels and gas piping. In short: most weldable 9Ni grade; service near -196 °C; low-carbon cryogenic plate steel.
What is the yield strength of X7Ni9 +NNT?
X7Ni9 +NNT has a typical yield strength of 570 MPa (82.7 ksi) and a tensile strength of 720 MPa (104 ksi) — stronger than 74% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is X7Ni9 +NNT easy to machine?
Not especially — machinability is rated fair (42/100, worse than 73% of steel grades). Machine like a tough 200–230 HB alloy steel: rigid setup, positive-rake carbide, moderate speed with heavy feed and copious coolant to avoid work-hardened glazing.
Can X7Ni9 +NNT be welded?
Yes — weldability is rated good (55/100). Weld with Ni-base consumables (ENiCrMo-6, ERNiCrMo-3/ERNiCrMo-4); control heat input, demagnetize plate before welding (arc blow), preheat usually ≤100 °C and PWHT normally not required.
What surface finishes work on X7Ni9 +NNT?
Not anodizable — shot-blast then epoxy/zinc-rich paint or metallize; keep surfaces dry, and verify residual magnetism and cleanliness before cryogenic commissioning.
Can X7Ni9 +NNT be formed, bent or molded?
Hot form at 850–950 °C followed by the specified NT/QT cycle; cold forming is possible but springback is high and severe cold work should be followed by re-heat treatment.
What is the maximum service temperature of X7Ni9 +NNT?
X7Ni9 +NNT is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- EN 10028-4: Flat products of steels for pressure purposes — Nickel alloy steels with specified low temperature properties — CEN (2017)
- ASTM A553/A553M Quenched and Tempered 7, 8 and 9% Nickel Alloy Steel Pressure Vessel Plates — ASTM International (2022)
- ASTM A353/A353M Double-Normalized and Tempered 9% Nickel Alloy Steel Plates — ASTM International (2022)
- EN 10222-3 Steel forgings for pressure purposes — Nickel steels with specified low temperature properties — CEN (1998)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys (cryogenic Ni steels) — ASM International (1990)
- ASME BPVC Section II Part D — Material properties (thermal/elastic data, 9Ni) — ASME (2023)
- 9% Nickel cryogenic pressure vessel plate datasheets (Dillinger / JFE / Nippon Steel / ) — various mills (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.