Welding Commercially Pure (CP) Titanium: Grades 1-4, Filler Selection, and Parameters

Commercially pure (CP) titanium Grades 1 through 4 are the workhorses of the titanium family. They’re unalloyed, meaning they’re essentially pure titanium with controlled amounts of oxygen, nitrogen, carbon, and iron as the only intentional compositional differences between grades. Grade 2 is the most common for welded fabrication, handling chemical processing equipment, heat exchangers, marine components, and medical implants.

All CP grades weld with the same process: DCEN TIG, 100% argon shielding, ERTi-2 filler (or grade-matched filler), and full inert gas coverage on all surfaces above 500F. The difference between grades is how much oxygen the base metal contains, which directly controls the balance between strength and ductility.

CP Titanium Grade Comparison

The only significant compositional difference between Grades 1-4 is oxygen content. More oxygen means higher strength but lower ductility and toughness.

Grade Selection for Welded Fabrication

Grade 1: Maximum ductility and formability. Used for strip-lined vessels, explosive cladding, and applications where the titanium must be formed into complex shapes after welding. Lowest strength of the CP grades.

Grade 2: The default for welded construction. Best balance of strength, ductility, weldability, and cost. Covers chemical process equipment, heat exchangers, desalination plants, marine structures, and general fabrication. If someone says “titanium” without specifying a grade, it’s probably Grade 2.

Grade 3: Higher strength for applications where Grade 2 doesn’t quite meet structural requirements. Less commonly welded than Grade 2 because the higher oxygen content makes the HAZ slightly less ductile.

Grade 4: Highest strength CP grade. Used for high-stress applications (dental implants, springs, fasteners) where the strength of Grade 2 isn’t sufficient. Weldable, but the HAZ ductility is noticeably lower. Not typically used for pressure vessels or piping.

Filler Metal Selection

*ERTi-5 is the matching filler for Grade 5 (Ti-6Al-4V) and can be used on the Grade 5 side of a dissimilar joint, but the weld deposit will be much harder and less ductile than ERTi-2.

The general rule: use a filler grade equal to or one grade lower than the base metal. Lower-grade filler has less oxygen, producing a more ductile weld deposit that’s more tolerant of the residual stresses in the joint.

Filler Rod Handling

Titanium filler rod must be stored in sealed plastic tubes and handled with clean, lint-free gloves. Before welding:

1. Wipe each rod with acetone and a lint-free cloth.
2. Don’t set rods on the shop floor, workbench, or any contaminated surface.
3. Once a rod is out of its tube, use it within the same shift. Don’t return partially used rods to sealed storage without re-cleaning.
4. Never handle filler rod after touching steel, oil, or cutting fluid.

TIG Welding Parameters

All CP grades weld on DCEN TIG with 100% argon. Use 2% lanthanated tungsten (preferred) or 2% thoriated. Grind the tungsten to a sharp point with the grind lines running longitudinal (parallel to the rod axis), not circumferential.

Travel Speed

Travel speed on titanium matters more than on most metals. Too slow, and you dump excessive heat into the workpiece, widening the HAZ and increasing the volume of metal that needs inert gas protection. The weld and surrounding material stay above 500F longer, giving any shielding deficiency more time to cause contamination.

Too fast creates a narrow, undercut bead with inadequate fusion.

Target a consistent travel speed that produces a bead width of roughly 3-4 times the filler rod diameter. For 3/32 inch filler, that’s a bead about 3/8 inch wide. Keep the puddle moving.

Arc Length

Maintain a short arc length: 1/16 to 1/8 inch from tungsten tip to workpiece. A long arc spreads the heat column, reduces penetration, and allows air to mix into the shielding gas at the arc periphery. Short arc length also concentrates the gas coverage right where you need it.

Interpass Temperature

Keep interpass temperature below 350F (175C) for all CP grades. Higher interpass temperatures cause:

• Grain growth in the HAZ, reducing toughness
• Extended time above 500F, increasing oxygen pickup
• Wider HAZ, which means more material affected by the welding heat

Check with a contact pyrometer between passes. If the joint exceeds 350F, stop and let it cool naturally. Don’t accelerate cooling with compressed air or water. Compressed air introduces contaminants, and water quenching titanium can cause hydrogen pickup.

Joint Preparation

Titanium joint prep follows the same principles as other reactive metals: absolute cleanliness and no contact with carbon steel.

Cutting and Beveling

• Plasma cutting works on CP titanium. Run with clean, dry air or (better) argon plasma gas. Remove the recast layer by grinding at least 1/16 inch past the cut edge.
• Shearing and waterjet cutting produce clean edges with no heat-affected zone. Waterjet is the preferred cutting method for thin sheet.
• Mechanical machining with carbide or HSS tooling. Use soluble oil coolant only if you can thoroughly degrease the joint before welding.
• Abrasive cutting with aluminum oxide or silicon carbide discs. Don’t use discs previously used on steel.

Joint Cleaning

1. Degrease with acetone or MEK on lint-free wipes. No chlorinated solvents (they cause stress-corrosion cracking on titanium).
2. Stainless steel brush or Scotch-Brite pad (aluminum oxide type) to remove light oxide. Use tools dedicated to titanium only.
3. Re-wipe with acetone after mechanical cleaning to remove any abrasive residue.
4. Wear clean nitrile or lint-free cotton gloves when handling cleaned titanium. No leather gloves (oil contamination), no bare hands (fingerprint oils).
5. Weld within 2-4 hours of final cleaning. Cover the joint with clean paper or plastic if there’s a delay.

Joint Designs

Standard groove designs work for CP titanium. The same joint geometries used for stainless steel apply:

Post-Weld Considerations

CP titanium doesn’t need post-weld heat treatment (PWHT) in most applications. The as-welded microstructure is acceptable for service. Some exceptions:

• Stress relief at 900-1100F for 1-2 hours (in vacuum or inert atmosphere) may be specified for thick-wall pressure vessels or highly restrained joints to reduce residual stress.
• Annealing at 1200-1400F for 1-2 hours (in vacuum or inert atmosphere) may be needed if the weld must meet specific ductility requirements. Never anneal titanium in air; the surface contamination at these temperatures destroys the part.

After welding, inspect weld color on both sides of the joint per the titanium weld color chart. Silver or light straw is acceptable. Anything darker requires evaluation and possible removal.

Common Problems and Fixes

Contamination (color change): Purge failure. See the titanium purge procedures guide for troubleshooting each purge zone.

Porosity: Usually from contamination (same root cause as color change) or from moisture on the filler rod. Can also come from gas turbulence if the flow rate is too high, pulling air into the shielding column.

Tungsten contamination: Dipping the tungsten into the puddle deposits tungsten particles that show up as bright white spots in radiography. Regrind or replace the tungsten and remove the affected weld segment.

Cracking: Rare on CP grades but can occur on Grade 4 (highest oxygen) if the weld is excessively contaminated or the interpass temperature wasn’t controlled. Indicates significant embrittlement; the weld and possibly the base metal in the HAZ must be removed.

Excessive grain growth: From too-high heat input or too-high interpass temperature. Results in reduced toughness. Keep travel speed up and interpass temperature under 350F.

For full purge system design and oxygen monitoring, see the titanium purge procedures guide. For post-weld quality assessment by color, see the titanium weld color chart.

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