Titanium Ti Grade 21-ST (Solution annealed)
Heat-treated state · default condition
UNS R58210 · also Beta 21S
Softest, most formable condition — pick for cold forming, deep drawing, foil/honeycomb and welding before final aging.
Values for the ST condition
Other Ti Grade 21 tempers and conditions
Ti Grade 21 is listed in 4 conditions; see the grade overview at Ti Grade 21.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
STDefaultThis page Solution annealed | Softest, most formable condition — pick for cold forming, deep drawing, foil/honeycomb and welding before final aging. | 805 | 830 | 18 | 28 HRC | — |
Solution treated then cold rolled strip/foil | Cold-worked thin strip/foil supplied for honeycomb and springs where extra strength is wanted without aging. | 960 | 1,000 | 8 | 33 HRC | 1.3 % IACS |
STA | Overaged balance condition — lower strength but better ductility, toughness and thermal stability for 500–565 °C airframe/engine parts. | 1,150 | 1,220 | 9 | 39 HRC | — |
STA | Maximum strength condition (≈1400 MPa) for fasteners, springs and highly loaded fittings where ductility and toughness can be traded away. | 1,310 | 1,400 | 6 | 44 HRC | — |
What is Ti Grade 21-ST?
Ti Grade 21-ST is Ti Grade 21 heat treated to ST — softest, most formable condition — pick for cold forming, deep drawing, foil/honeycomb and welding before final aging. Ti Grade 21-ST has a yield strength of 805 MPa (117 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 58% of titanium grades. Elongation at break is 18% and the elastic modulus is 79 GPa (11.5 Msi). Ti Grade 21-ST has a density of 4.94 g/cm³ (0.178 lb/in³), heavier than 97% of titanium grades. It melts at 1,600°C (2,912 °F).
Advantages
- Tough — resists crack growth — 85 MPa·√m (77.4 ksi·√in), better than 91% of titanium grades
- Forms and bends easily — 80/100, better than 90% of titanium grades
- High service temperature — 425°C (797 °F), better than 85% of titanium grades
Limitations
- Low stiffness — 79 GPa (11.5 Msi), worse than 98% of titanium grades
- High embodied carbon — 48 kg CO₂/kg, worse than 95% of titanium grades
Ti Grade 21-ST properties
Typical room-temperature values for Ti Grade 21-ST; 16 are specific to this condition. Other listed values are Ti Grade 21 reference data and may not represent this condition. Bars are the position among titanium grades.
Physical3
Ti Grade 21-ST has a density of 4.94 g/cm³ (0.178 lb/in³), heavier than 97% of titanium grades. It melts at 1,600°C (2,912 °F).
Mechanical15
Ti Grade 21-ST has a yield strength of 805 MPa (117 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 58% of titanium grades. Elongation at break is 18% and the elastic modulus is 79 GPa (11.5 Msi).
Thermal6
Ti Grade 21-ST is rated for continuous service to 425°C (797 °F). It conducts heat at 7.6 W/m·K (4.39 BTU/hr·ft·°F), worse than 59% of titanium grades. Thermal expansion is 8.6 µm/m·K (4.78 µin/in·°F).
Electrical3
Ti Grade 21-ST conducts electricity at 1.3 % IACS, worse than 51% of titanium grades.
Chemical & Environmental3
Corrosion resistance is excellent (92/100), better than 53% of titanium grades.
Sustainability4
Producing a kilogram of Ti Grade 21-ST takes about 700 MJ of energy and emits 48 kg of CO₂ — more than 74% of titanium grades. Typical recycled content is 25%.
Manufacturability8
Ti Grade 21-ST's machinability is poor (20/100, worse than 68% of titanium grades); weldability very good (75/100); formability very good (80/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Ti Grade 21-ST
Is Ti Grade 21 easy to machine?
Machine in the solution-treated state where possible: rigid setups, sharp uncoated-carbide or PVD-coated tools, low surface speed (15–30 m/min), heavy feed, flood high-pressure coolant; never dwell — low conductivity concentrates heat in the edge and work-hardened aged material cuts even slower.
Can Ti Grade 21 be welded?
GTAW/plasma/EBW readily in ST condition with full argon trailing and back purge; weld before aging and re-solution/age afterwards, since as-welded aged joints lose ductility and heat tint must be removed by pickling.
Can Ti Grade 21 be formed, bent or molded?
Outstanding cold formability as solution-treated strip and foil (tight bends, deep draws, honeycomb node forming); hot work above the ~800 °C beta transus, then solution treat 870–925 °C and age 8 h at 480–620 °C to set the strength level.
What surface finishes work on Ti Grade 21?
Pickle in HNO3/HF to remove alpha case and heat tint, then bead blast, passivate, or Type II colour anodize; hard anodize is not applicable — use ion nitriding or coatings for wear/galling surfaces.
Ti Grade 21 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 |
|---|---|---|
| Moprincipal beta stabilizer | 14 – 16 | 15 |
| Nb | 2.4 – 3.2 | 2.8 |
| Aloxidation resistance / alpha strengthening | 2.5 – 3.5 | 3 |
| Sicreep and oxidation resistance | 0.15 – 0.25 | 0.2 |
| Fe | ≤ 0.4 | — |
| O | ≤ 0.17 | — |
| C | ≤ 0.05 | — |
| N | ≤ 0.05 | — |
| H0.020 max for bar/billet per B348 | ≤ 0.02 | — |
| Ti | balance | — |
Ti Grade 21-ST — frequently asked
What is Ti Grade 21-ST used for?
Ti Grade 21-ST is typically used for aircraft exhaust and hot structure components, fuel cell bipolar plates and high-temperature fasteners. In short: oxidation-resistant beta alloy; formable then age-hardened; service to 425 °C.
What is the yield strength of Ti Grade 21-ST?
Ti Grade 21-ST has a typical yield strength of 805 MPa (117 ksi) and a tensile strength of 830 MPa (120 ksi) — stronger than 58% of titanium grades. Strength varies by condition: see the 4 listed tempers.
Is Ti Grade 21-ST easy to machine?
Not especially — machinability is rated poor (20/100, worse than 68% of titanium grades). Machine in the solution-treated state where possible: rigid setups, sharp uncoated-carbide or PVD-coated tools, low surface speed (15–30 m/min), heavy feed, flood high-pressure coolant; never dwell — low conductivity concentrates heat in the edge and work-hardened aged material cuts even slower.
Can Ti Grade 21-ST be welded?
Yes — weldability is rated very good (75/100). GTAW/plasma/EBW readily in ST condition with full argon trailing and back purge; weld before aging and re-solution/age afterwards, since as-welded aged joints lose ductility and heat tint must be removed by pickling.
What surface finishes work on Ti Grade 21-ST?
Pickle in HNO3/HF to remove alpha case and heat tint, then bead blast, passivate, or Type II colour anodize; hard anodize is not applicable — use ion nitriding or coatings for wear/galling surfaces.
Can Ti Grade 21-ST be formed, bent or molded?
Outstanding cold formability as solution-treated strip and foil (tight bends, deep draws, honeycomb node forming); hot work above the ~800 °C beta transus, then solution treat 870–925 °C and age 8 h at 480–620 °C to set the strength level.
What is the maximum service temperature of Ti Grade 21-ST?
Ti Grade 21-ST is rated for continuous use to about 425°C (797 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Ti Grade 21-ST and Ti Grade 21 STA-H?
ST is the default condition — softest, most formable condition — pick for cold forming, deep drawing, foil/honeycomb and welding before final aging. STA-H: maximum strength condition (≈1400 MPa) for fasteners, springs and highly loaded fittings where ductility and toughness can be traded away. Yield strength is 805 MPa in ST versus 1,310 MPa in STA-H.
Sources
- ASTM B265 — Titanium and Titanium Alloy Strip, Sheet, and Plate (Grade 21) — ASTM International (2020)
- ASTM B348 — Titanium and Titanium Alloy Bars and Billets (Grade 21) — ASTM International (2021)
- TIMETAL 21S (Beta 21S) alloy data sheet — TIMET / Titanium Metals Corp. (2018)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys, Titanium section — ASM International (1990)
- Materials Properties Handbook: Titanium Alloys (beta alloys chapter) — ASM International (1994)
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.