Stainless Steel 418
AISI/SAE 418 · UNS S41800
418 (Greek Ascoloy, UNS S41800) is a Cr-Ni-W martensitic stainless developed for elevated-temperature strength in turbine blading.
Reference datasheet — 418 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the Q&T-650 condition
418 tempers and conditions
418 is supplied in 6 conditions, soft to hard. Q&T-650 is the default FabDigit quotes; the values on this page are for it.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest supply condition for rough machining and hot-worked stock before final hardening. | 620 | 830 | 22 | 22 HRC | — |
Cold drawn, annealed | Cold-finished annealed bar for close tolerance blanks that will be hardened afterwards. | 720 | 900 | 16 | 27 HRC | 2.5 % IACS |
Q&T-650Default Hardened and tempered ~650 °C | Default aerospace/turbine condition: best balance of ~1070 MPa strength, ductility and thermal stability to 590 °C. | 860 | 1,070 | 18 | 34 HRC | — |
Hardened and tempered ~620 °C | Intermediate temper for higher blade-root and fastener strength with still-adequate toughness. | 1,000 | 1,210 | 16 | 38 HRC | — |
Hardened and tempered ~540 °C | Choose for maximum strength/wear in short-life or lightly loaded-in-impact parts; toughness and corrosion resistance drop. | 1,140 | 1,380 | 13 | 42 HRC | — |
Hardened | Interim condition only — must be tempered promptly; brittle and prone to quench cracking. | 1,200 | 1,550 | 8 | 46 HRC | 2.3 % IACS |
What is 418?
418 (Greek Ascoloy, UNS S41800) is a Cr-Ni-W martensitic stainless developed for elevated-temperature strength in turbine blading. It is supplied as bar and forgings in annealed and quenched-and-tempered conditions, with default properties near 860 MPa yield, 1070 MPa tensile, 18 % elongation and 320 HB (34 HRC) and service to 590 °C — the highest strength in this martensitic group. The trade-offs are low machinability (score 35), poor formability (20) and restricted weldability (30) requiring preheat and full post-weld temper; where hot strength is not the driver, 415 or 410Cb are easier to fabricate. 418 has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 65% of stainless steel grades. It melts at 1,425°C (2,597 °F). 418 has a yield strength of 860 MPa (125 ksi) and a tensile strength of 1,070 MPa (155 ksi) — stronger than 98% of stainless steel grades. Elongation at break is 18% and the elastic modulus is 215 GPa (31.2 Msi).
What is 418 used for?
- Steam turbine blades
- Gas turbine blading and vanes
- High-temperature fasteners
- Turbine rotor blade roots
- Compressor blades
- Highly stressed shafts and pins
- Erosion-exposed steam path parts
Advantages
- High strength — 860 MPa (125 ksi), better than 98% of stainless steel grades
- Conducts heat well — 23 W/m·K (13.3 BTU/hr·ft·°F), better than 78% of stainless steel grades
Limitations
- Difficult to weld — 30/100, worse than 88% of stainless steel grades
- Limited formability — 20/100, worse than 86% of stainless steel grades
- Needs corrosion protection — 45/100, worse than 85% of stainless steel grades
- Limited ductility — 18%, worse than 83% of stainless steel grades
- Low fracture toughness — 70 MPa·√m (63.7 ksi·√in), worse than 83% of stainless steel grades
418 properties
Typical room-temperature values for 418-Q&T-650; bars are the position among stainless steel grades.
Physical3
418 has a density of 7.75 g/cm³ (0.28 lb/in³), lighter than 65% of stainless steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
418 has a yield strength of 860 MPa (125 ksi) and a tensile strength of 1,070 MPa (155 ksi) — stronger than 98% of stainless steel grades. Elongation at break is 18% and the elastic modulus is 215 GPa (31.2 Msi).
Thermal6
418 is rated for continuous service to 590°C (1,094 °F). It conducts heat at 23 W/m·K (13.3 BTU/hr·ft·°F), better than 78% of stainless steel grades. Thermal expansion is 10.6 µm/m·K (5.89 µin/in·°F).
Electrical3
418 conducts electricity at 2.5 % IACS, better than 75% of stainless steel grades.
Chemical & Environmental3
Corrosion resistance is fair (45/100), worse than 85% of stainless steel grades.
Sustainability4
Producing a kilogram of 418 takes about 57 MJ of energy and emits 5.2 kg of CO₂ — more than 62% of stainless steel grades. Typical recycled content is 35%.
Manufacturability8
418's machinability is fair (35/100, better than 51% of stainless steel grades); weldability poor (30/100); formability poor (20/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the stainless steel family
Yield strength against density for every stainless steel grade FabDigit runs. 418 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 418
Is 418 easy to machine?
Machine in the annealed or high-temper (32–38 HRC) condition with rigid setups, sharp carbide tooling, slow speeds and heavy positive feeds; work hardens and is abrasive due to the tungsten content.
Can 418 be welded?
Weldable by GTAW/GMAW with matching or 410/309 filler, but requires 200–300 °C preheat, controlled interpass and a full post-weld temper to avoid hard, cracking-prone martensitic HAZ.
Can 418 be formed, bent or molded?
Hot work at 1050–1150 °C and slow cool/anneal; cold forming is limited to mild bending of annealed stock only.
418 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 | 0.15 – 0.2 | 0.17 |
| Mn | ≤ 0.5 | 0.35 |
| Si | ≤ 0.5 | 0.3 |
| Pimpurity limit | ≤ 0.04 | |
| Simpurity limit | ≤ 0.03 | |
| Cr | 12 – 14 | 13 |
| Ni | 1.8 – 2.2 | 2 |
| Wtungsten gives elevated-temperature strength | 2.5 – 3.5 | 3 |
| Fe | balance |
What surface finishes work on 418?
Passivate (ASTM A967 nitric or citric) after machining; takes a good polish and accepts hard chrome, nitriding or high-temperature aluminide coatings for erosion protection.
Surface treatments FabDigit runs on stainless steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Passivation
Organic Coating
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Stainless Steel 418 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- S41800
- Also called
- Alloy 615
How much does 418 cost?
418 is a high-cost stainless steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
418 — frequently asked
What is 418 used for?
418 is typically used for steam turbine blades, gas turbine blading and vanes, high-temperature fasteners, turbine rotor blade roots, compressor blades and highly stressed shafts and pins. In short: strongest grade in family; tungsten-strengthened, hot-strong; turbine blading standard.
What is the yield strength of 418?
418 has a typical yield strength of 860 MPa (125 ksi) and a tensile strength of 1,070 MPa (155 ksi) — stronger than 98% of stainless steel grades. Strength varies by condition: see the 6 listed tempers.
Is 418 easy to machine?
Not especially — machinability is rated fair (35/100, better than 51% of stainless steel grades). Machine in the annealed or high-temper (32–38 HRC) condition with rigid setups, sharp carbide tooling, slow speeds and heavy positive feeds; work hardens and is abrasive due to the tungsten content.
Can 418 be welded?
Not readily — weldability is rated poor (30/100). Weldable by GTAW/GMAW with matching or 410/309 filler, but requires 200–300 °C preheat, controlled interpass and a full post-weld temper to avoid hard, cracking-prone martensitic HAZ.
What surface finishes work on 418?
Passivate (ASTM A967 nitric or citric) after machining; takes a good polish and accepts hard chrome, nitriding or high-temperature aluminide coatings for erosion protection.
Can 418 be formed, bent or molded?
Hot work at 1050–1150 °C and slow cool/anneal; cold forming is limited to mild bending of annealed stock only.
What is the maximum service temperature of 418?
418 is rated for continuous use to about 590°C (1,094 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 418 Q&T-650 and 418-H?
Q&T-650 is the default condition — default aerospace/turbine condition: best balance of ~1070 MPa strength, ductility and thermal stability to 590 °C. H: interim condition only — must be tempered promptly; brittle and prone to quench cracking. Yield strength is 860 MPa in Q&T-650 versus 1,200 MPa in H.
How much does 418 cost?
418 is a high-cost stainless steel ($$$$), pricier than about 78% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- AMS 5616 — Steel, Corrosion and Heat Resistant, Bars, Wire and Forgings 13Cr-2.0Ni-3.0W — SAE International (2018)
- ASTM A565/A565M — Martensitic Stainless Steel Bars for High-Temperature Service (Grade 615) — ASTM (2019)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Specialty Handbook — Stainless Steels — ASM International (1994)
- Greek Ascoloy (Type 418 / UNS S41800) alloy data sheet — specialty steel producer (2020)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.