Steel X8Ni9 +QT (Quenched and tempered)
Heat-treated state · default condition
EN X8Ni9
Highest strength cryogenic condition — standard for LNG inner-tank plate where design stress and thickness savings matter.
Values for the +QT condition
Other X8Ni9 tempers and conditions
X8Ni9 is listed in 3 conditions; see the grade overview at X8Ni9.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Normalized and tempered | Pick when thicker sections, better weld-zone uniformity or lower distortion are preferred over maximum yield strength. | 570 | 700 | 26 | 200 HB | — |
Double normalized and tempered | ASTM A353 route: two normalizing cycles plus temper give very fine grain and the most reliable -196 °C CVN for heavy plate. | 600 | 730 | 26 | 205 HB | — |
+QTDefaultThis page Quenched and tempered | Highest strength cryogenic condition — standard for LNG inner-tank plate where design stress and thickness savings matter. | 690 | 745 | 24 | 215 HB | — |
What is X8Ni9 +QT?
X8Ni9 +QT is X8Ni9 heat treated to +QT — highest strength cryogenic condition — standard for LNG inner-tank plate where design stress and thickness savings matter. X8Ni9 +QT has a yield strength of 690 MPa (100 ksi) and a tensile strength of 745 MPa (108 ksi) — stronger than 80% of steel grades. Elongation at break is 24% and the elastic modulus is 195 GPa (28.3 Msi). X8Ni9 +QT 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).
Advantages
- Tough — resists crack growth — 200 MPa·√m (182 ksi·√in), better than 100% of steel grades
- High strength — 690 MPa (100 ksi), better than 80% of steel grades
Limitations
- High embodied carbon — 3.3 kg CO₂/kg, 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
- Low electrical conductivity — 3.8 % IACS, worse than 84% of steel grades
- Difficult to machine — 40/100, worse than 77% of steel grades
X8Ni9 +QT properties
Typical room-temperature values for X8Ni9 +QT; 16 are specific to this condition. Other listed values are X8Ni9 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
X8Ni9 +QT 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).
Mechanical16
X8Ni9 +QT has a yield strength of 690 MPa (100 ksi) and a tensile strength of 745 MPa (108 ksi) — stronger than 80% of steel grades. Elongation at break is 24% and the elastic modulus is 195 GPa (28.3 Msi).
Thermal6
X8Ni9 +QT is rated for continuous service to 350°C (662 °F). It conducts heat at 29 W/m·K (16.8 BTU/hr·ft·°F), worse than 84% of steel grades. Thermal expansion is 10.2 µm/m·K (5.67 µin/in·°F).
Electrical3
X8Ni9 +QT conducts electricity at 3.8 % IACS, worse than 84% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (18/100), better than 83% of steel grades.
Sustainability4
Producing a kilogram of X8Ni9 +QT takes about 40 MJ of energy and emits 3.3 kg of CO₂ — more than 91% of steel grades. Typical recycled content is 25%.
Manufacturability6
X8Ni9 +QT's machinability is fair (40/100, worse than 77% of steel grades); weldability good (60/100); formability fair (52/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with X8Ni9 +QT
Is X8Ni9 easy to machine?
Machines like a tough 200 HB low-alloy steel — rigid setups, sharp positive-rake carbide, moderate speed and heavy feed to cut under the work-hardened skin; keep tool pressure steady to avoid smearing.
Can X8Ni9 be welded?
Weld with nickel-base consumables (ENiCrMo-6 / ERNiCrMo-3 / ENiCrFe-2), low heat input and interpass ≤150 °C, no preheat needed above ~5 °C; demagnetize plate to prevent arc blow and normally weld in the as-heat-treated condition without PWHT.
Can X8Ni9 be formed, bent or molded?
Cold rolls and presses well but with high springback due to the high yield strength; hot form 850–1000 °C and then re-apply the full +NT/+QT or +NNT cycle to restore cryogenic toughness.
What surface finishes work on X8Ni9?
Not a stainless — shot-blast and coat (epoxy/zinc-rich) or keep in a dry-purged insulation space; electroplating and painting behave like ordinary low-alloy steel, anodizing is not applicable.
X8Ni9 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; ASTM A353/A553 allow ≤0.13 | ≤ 0.1 | 0.06 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.3 – 0.8 | 0.55 |
| Plow P for cryogenic toughness | ≤ 0.02 | 0.01 |
| S | ≤ 0.01 | 0 |
| NiASTM A353/A553: 8.50–9.50 | 8.5 – 10 | 9 |
| Crresidual | ≤ 0.3 | 0.05 |
| Moresidual | ≤ 0.1 | 0.02 |
| Curesidual | ≤ 0.3 | 0.05 |
| Vresidual | ≤ 0.05 | 0.01 |
| Algrain refinement (total Al) | 0.02 – 0.06 | 0.03 |
| N | ≤ 0.01 | 0.01 |
| Fe | balance | — |
X8Ni9 +QT — frequently asked
What is X8Ni9 +QT used for?
X8Ni9 +QT is typically used for LNG storage tanks, cryogenic vessels and piping for low temperature service. In short: cryogenic-tough 9% nickel steel; highest yield of the 9Ni grades; needs nickel-base filler.
What is the yield strength of X8Ni9 +QT?
X8Ni9 +QT has a typical yield strength of 690 MPa (100 ksi) and a tensile strength of 745 MPa (108 ksi) — stronger than 80% of steel grades. Strength varies by condition: see the 3 listed tempers.
Is X8Ni9 +QT easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% of steel grades). Machines like a tough 200 HB low-alloy steel — rigid setups, sharp positive-rake carbide, moderate speed and heavy feed to cut under the work-hardened skin; keep tool pressure steady to avoid smearing.
Can X8Ni9 +QT be welded?
Yes — weldability is rated good (60/100). Weld with nickel-base consumables (ENiCrMo-6 / ERNiCrMo-3 / ENiCrFe-2), low heat input and interpass ≤150 °C, no preheat needed above ~5 °C; demagnetize plate to prevent arc blow and normally weld in the as-heat-treated condition without PWHT.
What surface finishes work on X8Ni9 +QT?
Not a stainless — shot-blast and coat (epoxy/zinc-rich) or keep in a dry-purged insulation space; electroplating and painting behave like ordinary low-alloy steel, anodizing is not applicable.
Can X8Ni9 +QT be formed, bent or molded?
Cold rolls and presses well but with high springback due to the high yield strength; hot form 850–1000 °C and then re-apply the full +NT/+QT or +NNT cycle to restore cryogenic toughness.
What is the maximum service temperature of X8Ni9 +QT?
X8Ni9 +QT 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 A353/A353M Double-Normalized and Tempered 9% Nickel Alloy Steel Plate — ASTM International (2023)
- ASTM A553/A553M Quenched and Tempered 7, 8, and 9% Nickel Alloy Steel Plate — ASTM International (2022)
- ASME BPVC Section II, Part D — Material Properties (SA-553 Type I) — ASME (2023)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- 9% nickel cryogenic steel plate datasheets (LNG tank plate) — Dillinger / JFE / Nippon Steel (2022)
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.