316Ti Stainless Steel (UNS S31635): Titanium-Stabilized Austenitic Grade for High-Temperature Service

316Ti fills the gap between standard 316, which sensitizes in the heat-affected zone of welds and in the 425-815°C service range, and costly nickel-base alloys. Titanium has a stronger affinity for carbon than chromium, so the carbon is locked into stable titanium carbides and chromium stays in solid solution, preserving the passive film at grain boundaries. The principal designations are UNS S31635, EN 1.4571 (X6CrNiMoTi17-12-2), JIS SUS316Ti and GB 06Cr17Ni12Mo2Ti; product forms are covered by ASTM A240 for plate and sheet, ASTM A312/A213 for pipe and tube, and ASTM A479 for bars.

Chemical Composition per ASTM A240

The composition limits for UNS S31635 plate, sheet and strip follow ASTM A240.

Mechanical Properties

Minimum room-temperature properties in the annealed condition per ASTM A240 are shown below.

At elevated temperature 316Ti retains a useful fraction of its room-temperature strength: in the 650-900°C range its creep and stress-rupture behavior is superior to that of standard 316, because the fine titanium carbides restrict grain-boundary sliding. EN 1.4571 is commonly supplied with slightly higher minimum proof strength than the ASTM grade, reflecting typical mill practice.

Corrosion Resistance and Stabilization Behavior

316Ti matches the chloride and pitting resistance of 316 thanks to its 2-3% molybdenum, so it resists pitting and crevice corrosion in seawater, brine and chemical chloride solutions. The stabilization advantage appears after thermal exposure: a 316Ti weld joint or a component heated into the sensitization range keeps its intergranular corrosion resistance, because titanium carbides, not chromium carbides, precipitate at the grain boundaries. This is verified in practice by intergranular corrosion tests such as the ASTM A262 Practice E copper-sulfate test on sensitized specimens. In strongly oxidizing acids, the corrosion rate of titanium-stabilized grades is marginally higher than that of 316L, but for the high-temperature service where 316Ti is used this difference is negligible.

Welding, Fabrication and Heat Treatment

316Ti welds readily by GTAW, GMAW and SMAW. Use a titanium-stabilized filler such as ER316Ti so the joint retains the same stabilization as the base metal; an unstabilized filler such as ER316L re-introduces sensitization risk in the weld metal. Post-weld annealing is generally not required, even for thick sections, because titanium prevents carbide formation during welding. Pre-weld cleaning of oil and oxide is important because titanium oxidizes easily. The solution annealing range for 316Ti is about 950-1100°C followed by rapid cooling; avoid slow cooling through 425-815°C. Cold forming work-hardens the grade faster than 316 in some product forms, so intermediate annealing may be needed for severe deep drawing.

Applications and Selection

Typical applications are chemical processing equipment such as cracking-furnace tubes and acid-handling vessels, power plant heat exchangers and steam generators, offshore platforms and marine heat exchangers, pulp and paper digesters, and food processing plant where hot chlorides are present. Selection guidance: choose 316Ti when the part is welded and the service combines heat with chlorides; choose standard 316 for mild heat and corrosion below the sensitization range; choose 316H where dry high-temperature strength dominates and corrosion is not the issue; and move to higher-alloy grades such as 6% molybdenum super-austenitic or duplex stainless steels where pitting resistance must exceed that of the 316 family.

Frequently Asked Questions

Q1: What does titanium do in 316Ti? A1: Titanium binds carbon into titanium carbides so that chromium is not depleted at grain boundaries during welding or service at 425-815°C. This preserves the passive film and prevents intergranular corrosion, which is the sensitization failure of standard 316.

Q2: What is the maximum service temperature of 316Ti? A2: Continuous service is generally cited up to about 900°C in oxidizing atmospheres for lightly loaded parts. For load-bearing service above about 550°C, design to creep and stress-rupture data; above 900°C select a higher-alloy heat-resistant grade.

Q3: How does 316Ti behave in chloride environments? A3: It matches 316: the 2-3% molybdenum provides good resistance to pitting and crevice corrosion in seawater and brine, and unlike 316 this resistance survives welding and high-temperature exposure.

Q4: Does 316Ti need post-weld heat treatment? A4: No. Stabilization prevents chromium-carbide precipitation during welding, so solution annealing after welding is not required for corrosion resistance in most thicknesses. Pickling and passivation of the weld zone are still recommended.

Q5: What filler metal should be used for welding 316Ti? A5: A titanium-stabilized filler such as ER316Ti per AWS A5.9. Using ER316L is acceptable in some codes but the weld deposit then lacks titanium stabilization and may sensitize in severe service.

Q6: How does 316Ti compare with 316H? A6: 316H carries 0.04-0.10% carbon for higher high-temperature strength but is not stabilized, so it can sensitize in welded or corrosive service. 316Ti is the choice where heat and corrosion act together; 316H suits dry high-temperature applications such as furnace parts.