The Three Families of Titanium Mill Product
Titanium grades are grouped by crystal structure, and that grouping predicts how a material behaves in the workshop. Commercially pure grades are single phase alpha, which makes them highly weldable and formable but limits their strength. Alpha-beta alloys such as Grade 5 contain a controlled amount of beta phase and can be strengthened by heat treatment. Modified grades keep a similar structure but add a small amount of palladium, molybdenum, nickel or ruthenium to widen corrosion resistance in reducing acids. Understanding the family first prevents most specification mistakes.
Grade to Specification Map
The table below lists the grades seen most often in industrial purchasing, together with the American Society for Testing and Materials specifications that govern them and the corresponding wrought mill forms. Sheet, plate and strip follow ASTM B265; seamless tube follows ASTM B338 for heat exchanger service; bar and billet follow ASTM B348; wire follows ASTM B863; castings follow ASTM B367; forgings follow ASTM B381; welded pipe follows ASTM B862 and seamless pipe follows ASTM B861. Surgical applications add ASTM F67 for unalloyed grades and ASTM F136 for the extra low interstitial version of Ti-6Al-4V. Fasteners are covered by ASTM F467 for nuts and ASTM F468 for bolts.
| Grade | UNS | Type | Tensile min | Yield 0.2% min | Elongation min |
|---|---|---|---|---|---|
| Grade 1 | R50250 | Commercially pure alpha | 240 MPa | 170 MPa | 24% |
| Grade 2 | R50400 | Commercially pure alpha | 345 MPa | 275 MPa | 20% |
| Grade 3 | R50550 | Commercially pure alpha | 450 MPa | 380 MPa | 18% |
| Grade 4 | R50700 | Commercially pure alpha | 550 MPa | 483 MPa | 15% |
| Grade 5 | R56400 | Alpha-beta, Ti-6Al-4V | 895 MPa | 828 MPa | 10% |
| Grade 7 | R52400 | Alpha, palladium modified | 345 MPa | 275 MPa | 20% |
| Grade 9 | R56320 | Alpha-beta, Ti-3Al-2.5V | 620 MPa | 483 MPa | 15% |
| Grade 12 | R53400 | Alpha, molybdenum nickel modified | 483 MPa | 345 MPa | 18% |
Choosing Between the Families
Strength first: Grade 5 delivers the highest strength of the common grades and is heat treatable, at the cost of lower ductility and harder cold forming.
Formability first: Grade 1 and Grade 2 are chosen for deep drawn, expanded or coiled parts where ductility matters more than strength.
Pressure duty: Grade 3 and Grade 4 give higher allowable stress than Grade 2 so that wall thickness can be trimmed.
Reducing acids and chlorides: Grade 7 uses a small palladium addition for markedly better resistance to hydrochloric and sulfuric acid service, while Grade 12 uses molybdenum and nickel for moderate reducing conditions at lower cost.
Weight critical tubing: Grade 9 fills the gap between pure titanium and Grade 5, with about 30 percent more strength than Grade 2 and far better cold workability than Grade 5.
How the Choice Changes Fabrication
Pure and near alpha grades are welded with simple purge procedures and produce ductile joints. Grade 5 and other alpha-beta alloys weld readily too, but the weld zone loses some ductility and the joint usually needs post weld stress relief for demanding service. Cold forming tells a similar story: Grade 2 accepts tight bend radii, Grade 9 needs moderately larger radii, and Grade 5 tube generally requires hot forming or generous radii. Machining all grades requires sharp tooling, generous coolant and low cutting speed because the low thermal conductivity of titanium concentrates heat at the cutting edge and promotes work hardening.
Quality Control Expectations for Each Family
Commercially pure and modified grades are verified by chemical analysis for the interstitial elements that govern strength, namely oxygen, nitrogen, carbon, hydrogen and iron. Alpha-beta alloys add aluminium and vanadium to the analysis and, when heat treated, a microstructure check plus hardness testing to confirm the aging response. Mill test certificates to EN 10204 3.1 are standard, and every lot should be traceable to heat number. For corrosion critical service, an actual corrosion test in the process medium is worth more than any generic table, because the resistance of titanium depends on whether the environment is oxidising or reducing.
Frequently Asked Questions
Q: Which titanium grade is the most commonly used overall?
A: Grade 2 for general corrosion and process work, and Grade 5 for structural and aerospace parts. Together they cover the majority of titanium tonnage in industrial use.
Q: Is Grade 7 stronger than Grade 2?
A: No. ASTM B338 and B265 set the same minimum tensile and yield strength for both. Grade 7 adds palladium for corrosion resistance, not strength.
Q: What does commercially pure actually mean?
A: It means the material is unalloyed titanium, with no deliberate aluminium, vanadium or other alloying addition. Strength is controlled instead through the interstitial content, chiefly oxygen.
Q: Can Grade 5 be used in place of Grade 4 for a thin wall tube?
A: Only if the tube can be formed to shape. Grade 5 cannot be cold drawn into tight radius coils as easily as Grade 4, so the wall saving may be lost to higher forming cost and scrap.
Q: When should a modified grade be chosen?
A: Whenever the process stream is reducing rather than oxidising, for example hydrochloric acid or hot sulfuric acid, because unalloyed grades rely on an oxidising environment to maintain their passive film.
