Titanium IMI 550
IMI 550 is a silicon-bearing alpha-beta titanium alloy of British origin, specified for aero-engine parts that must hold strength at temperature.
Reference datasheet — IMI 550 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 STA condition
IMI 550 tempers and conditions
IMI 550 is supplied in 5 conditions, soft to hard. STA is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Softer intermediate condition for machining, straightening or further hot working before final ageing. | 900 | 1,000 | 16 | 32 HRC | — |
Hot rolled | Semi-finished mill stock bought for re-forging or customer heat treatment; properties not guaranteed. | 950 | 1,050 | 12 | 33 HRC | 1.1 % IACS |
forged above beta transus then solution treated and aged | Chosen when higher fracture toughness and crack-growth resistance matter more than smooth fatigue strength and ductility. | 1,010 | 1,110 | 8 | 35 HRC | 1.1 % IACS |
alpha-beta forged then solution treated and aged | Disc, ring and structural forgings; equiaxed alpha-beta structure with balanced strength and fatigue life. | 1,030 | 1,130 | 12 | 35 HRC | 1.1 % IACS |
STADefault Solution treated and aged | Standard supply condition for bar, billet and forgings where maximum strength to 400 °C is needed. | 1,050 | 1,150 | 13 | 36 HRC | — |
What is IMI 550?
IMI 550 is a silicon-bearing alpha-beta titanium alloy of British origin, specified for aero-engine parts that must hold strength at temperature. It retains useful properties to about 400 °C and delivers 1050 MPa yield, 1150 MPa tensile, 13% elongation and 36 HRC in STA; forms are forgings, bar and hot-rolled product in STA, ANN, FORGED-STA, BETA-STA and HR conditions. Limits are low machinability (score 16) at roughly 350 HV, hot-work-only forming, and fusion welding that is generally avoided because silicon and the aged microstructure embrittle the HAZ. Ti-6Al-4V is the more widely stocked alternative where 400 °C capability is not needed. IMI 550 has a density of 4.6 g/cm³ (0.166 lb/in³), heavier than 87% of titanium grades. It melts at 1,590°C (2,894 °F). IMI 550 has a yield strength of 1,050 MPa (152 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 96% of titanium grades. Elongation at break is 13% and the elastic modulus is 115 GPa (16.7 Msi).
What is IMI 550 used for?
- aeroengine compressor blades
- discs
- high-temperature fasteners
Advantages
- High strength — 1,050 MPa (152 ksi), better than 96% of titanium grades
- High service temperature — 400°C (752 °F), better than 78% of titanium grades
Limitations
- Difficult to weld — 25/100, worse than 100% of titanium grades
- Low fracture toughness — 45 MPa·√m (41 ksi·√in), worse than 98% of titanium grades
- Limited formability — 15/100, worse than 93% of titanium grades
- Low electrical conductivity — 1.1 % IACS, worse than 78% of titanium grades
IMI 550 properties
Typical room-temperature values for IMI 550-STA; bars are the position among titanium grades.
Physical3
IMI 550 has a density of 4.6 g/cm³ (0.166 lb/in³), heavier than 87% of titanium grades. It melts at 1,590°C (2,894 °F).
Mechanical16
IMI 550 has a yield strength of 1,050 MPa (152 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 96% of titanium grades. Elongation at break is 13% and the elastic modulus is 115 GPa (16.7 Msi).
Thermal6
IMI 550 is rated for continuous service to 400°C (752 °F). It conducts heat at 7.1 W/m·K (4.1 BTU/hr·ft·°F), worse than 68% of titanium grades. Thermal expansion is 9.4 µm/m·K (5.22 µin/in·°F).
Electrical3
IMI 550 conducts electricity at 1.1 % IACS, worse than 78% of titanium grades.
Chemical & Environmental3
Corrosion resistance is excellent (85/100), worse than 93% of titanium grades.
Sustainability4
Producing a kilogram of IMI 550 takes about 650 MJ of energy and emits 42 kg of CO₂ — less than 75% of titanium grades. Typical recycled content is 20%.
Manufacturability8
IMI 550's machinability is poor (16/100, worse than 93% of titanium grades); weldability poor (25/100); formability poor (15/100).
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 titanium family
Yield strength against density for every titanium grade FabDigit runs. IMI 550 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with IMI 550
Is IMI 550 easy to machine?
Machine like a high-strength alpha-beta Ti: rigid setups, low surface speed (~20–35 m/min carbide), heavy positive-rake sharp tools, high-pressure flood coolant, never dwell — work-hardening and galling are severe at 350 HV.
Can IMI 550 be welded?
Fusion welding is generally avoided (silicon and aged microstructure embrittle the HAZ); if required use inert-gas-shielded EB/TIG on annealed material followed by full re-solution and ageing.
Can IMI 550 be formed, bent or molded?
Hot work/forge in the 850–950 °C alpha-beta range with controlled cooling; cold forming is impractical, so bend and stretch operations are done hot or by machining from solid.
IMI 550 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 |
|---|---|---|
| Alalpha stabiliser | 3 – 5 | 4 |
| Mobeta stabiliser | 3.5 – 4.5 | 4 |
| Sn | 1.5 – 2.5 | 2 |
| Sicreep/strength enhancement via silicide precipitation | 0.3 – 0.7 | 0.5 |
| Feimpurity limit | ≤ 0.2 | |
| Oimpurity limit | ≤ 0.2 | |
| Cimpurity limit | ≤ 0.08 | |
| Nimpurity limit | ≤ 0.05 | |
| Himpurity limit | ≤ 0.01 | |
| Ti | balance |
What surface finishes work on IMI 550?
Grit blast + pickle or chemical mill to remove alpha case after hot work; anodic/conversion coatings for colour and galling control, ion nitriding or hard coatings for wear surfaces.
Surface treatments FabDigit runs on titanium 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).
Thermal Spray
How much does IMI 550 cost?
IMI 550 is a high-cost titanium ($$$$), 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.
IMI 550 — frequently asked
What is IMI 550 used for?
IMI 550 is typically used for aeroengine compressor blades, discs and high-temperature fasteners. In short: 400 °C service capability; silicon-strengthened alpha-beta Ti; generally not fusion welded.
What is the yield strength of IMI 550?
IMI 550 has a typical yield strength of 1,050 MPa (152 ksi) and a tensile strength of 1,150 MPa (167 ksi) — stronger than 96% of titanium grades. Strength varies by condition: see the 5 listed tempers.
Is IMI 550 easy to machine?
Not especially — machinability is rated poor (16/100, worse than 93% of titanium grades). Machine like a high-strength alpha-beta Ti: rigid setups, low surface speed (~20–35 m/min carbide), heavy positive-rake sharp tools, high-pressure flood coolant, never dwell — work-hardening and galling are severe at 350 HV.
Can IMI 550 be welded?
Not readily — weldability is rated poor (25/100). Fusion welding is generally avoided (silicon and aged microstructure embrittle the HAZ); if required use inert-gas-shielded EB/TIG on annealed material followed by full re-solution and ageing.
What surface finishes work on IMI 550?
Grit blast + pickle or chemical mill to remove alpha case after hot work; anodic/conversion coatings for colour and galling control, ion nitriding or hard coatings for wear surfaces.
Can IMI 550 be formed, bent or molded?
Hot work/forge in the 850–950 °C alpha-beta range with controlled cooling; cold forming is impractical, so bend and stretch operations are done hot or by machining from solid.
What is the maximum service temperature of IMI 550?
IMI 550 is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between IMI 550-STA and IMI 550-ANN?
STA is the default condition — standard supply condition for bar, billet and forgings where maximum strength to 400 °C is needed. ANN: softer intermediate condition for machining, straightening or further hot working before final ageing. Yield strength is 1,050 MPa in STA versus 900 MPa in ANN.
How much does IMI 550 cost?
IMI 550 is a high-cost titanium ($$$$), 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
- IMI 550 (Ti-4Al-4Mo-2Sn-0.5Si) alloy data sheet — IMI Titanium / TIMET UK (1995)
- BS TA 45–48 — Titanium alloy bar, billet and forgings (Ti-4Al-4Mo-2Sn-0.5Si) — BSI (1990)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys and Special-Purpose Materials — ASM International (1990)
- Materials Properties Handbook: Titanium Alloys — ASM International (1994)
- ASM Handbook Vol. 19 — Fatigue and Fracture — ASM International (1996)
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.