SUS321 vs SUS316Ti Stainless Steel: How Does Titanium Improve High-Temperature Resistance?

Chemical Composition Comparison

Element wt%	SUS321	SUS316Ti
Carbon	≤ 0.08	≤ 0.08
Chromium	17.0 – 19.0	16.0 – 18.0
Nickel	9.0 – 12.0	10.0 – 14.0
Molybdenum	Not required	2.0 – 3.0
Titanium	≥ 5 × C	≥ 5 × C

SUS321 is built around intergranular corrosion resistance and oxidation resistance at elevated temperature. SUS316Ti adds molybdenum on top of titanium stabilization, which significantly improves resistance to chloride-induced pitting and crevice corrosion while keeping the same high-temperature behavior.

How Titanium Stabilization Works at High Temperature

In unstabilized austenitic grades, carbon can react with chromium at grain boundaries during hot service or welding, forming chromium carbides and creating chromium-depleted zones that corrode preferentially. Titanium solves this by forming titanium carbides first, because titanium has a stronger affinity for carbon than chromium. The stable titanium carbides keep carbon out of the grain boundaries, maintaining the chromium content in solid solution and preserving corrosion resistance. Titanium also helps the steel form a stable protective oxide layer in hot oxidizing atmospheres, which is why both grades can serve continuously in the 600–900°C range.

High-Temperature and Corrosion Performance

Property	SUS321	SUS316Ti
Continuous service temperature	≤ 850°C	≤ 900°C
Oxidation resistance	Good in hot gas	Excellent, including sulfurous or humid atmospheres
Intergranular corrosion resistance	Low sensitivity	Very low
Chloride pitting and crevice corrosion	Moderate	Excellent due to molybdenum

Application Fields

Application	SUS321 advantage	SUS316Ti advantage
Heat exchangers	Long-term heat resistance for petrochemical piping	Better for hot systems with chloride media
Exhaust systems	Automotive and industrial exhaust handling	Higher anti-corrosion demand components
Pressure vessels	High temperature with neutral corrosion	Heat combined with mild chlorides
Food and pharma equipment	Withstands steam and sterilization	Heat plus aggressive cleaning agents

Selection Guidance

Choose SUS321 when the primary challenge is heat exposure up to 850°C with moderate corrosion: boiler tubes, hot gas ducts, heat-treatment components and general exhaust parts, where its cost efficiency is a real advantage. Choose SUS316Ti when the service combines heat with chlorides or more aggressive media: chemical reactors, marine heat exchangers, sterilization systems and equipment cleaned with aggressive agents, where molybdenum pays for itself in longer service life.

Frequently Asked Questions

Q1: What is the main difference between SUS321 and SUS316Ti?
A1: SUS316Ti contains 2.0–3.0% molybdenum, which adds chloride pitting and crevice corrosion resistance, while SUS321 has no molybdenum and is more economical for pure high-temperature duty.

Q2: Why does titanium improve high-temperature resistance?
A2: Titanium forms stable titanium carbides, preventing chromium carbide precipitation at grain boundaries, so the steel avoids chromium depletion and intergranular corrosion during hot service and welding.

Q3: Which grade can run hotter?
A3: SUS316Ti allows continuous service up to about 900°C, while SUS321 is rated to about 850°C.

Q4: Can SUS321 be used in chloride-rich high-temperature environments?
A4: Not ideally. Without molybdenum, SUS321 has only moderate resistance to chloride pitting; SUS316Ti is the better choice when chlorides are present.

Q5: Are the two grades weldable?
A5: Yes, both are titanium-stabilized and weldable without post-weld heat treatment in most services; use matching stabilized filler and keep interpass temperature controlled.

Q6: Which grade is more expensive?
A6: SUS316Ti is more expensive because of the molybdenum addition, so SUS321 is often preferred where chlorides are not a concern.