Titanium IMI 550-STA (Solution treated and aged)
Heat-treated state · default condition
Standard supply condition for bar, billet and forgings where maximum strength to 400 °C is needed.
Values for the STA condition
Other IMI 550 tempers and conditions
IMI 550 is listed in 5 conditions; see the grade overview at IMI 550.
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 |
STADefaultThis page 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-STA?
IMI 550-STA is IMI 550 heat treated to STA — standard supply condition for bar, billet and forgings where maximum strength to 400 °C is needed. IMI 550-STA 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). IMI 550-STA 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).
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-STA properties
Typical room-temperature values for IMI 550-STA; 11 are specific to this condition. Other listed values are IMI 550 reference data and may not represent this condition. Bars are the position among titanium grades.
Physical3
IMI 550-STA 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-STA 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-STA 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-STA 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-STA 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-STA'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. Confirm any required mill or lot documentation when quoting.
Working with IMI 550-STA
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.
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.
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 | — |
IMI 550-STA — frequently asked
What is IMI 550-STA used for?
IMI 550-STA 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-STA?
IMI 550-STA 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-STA 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-STA 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-STA?
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-STA 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-STA?
IMI 550-STA 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.