316Ti Stainless Steel / US S31635 / ใน 1.4571

1. บทสรุปผู้บริหาร

316Ti is an austenitic stainless steel based on the 300-series (316) chemistry with a deliberate addition of ไทเทเนียม to stabilize carbon.

The titanium ties up carbon as stable titanium carbides, preventing chromium-carbide precipitation at grain boundaries when the alloy is exposed to temperatures in the sensitization range.

The result is an alloy with the corrosion resistance of 316 plus improved resistance to intergranular corrosion after high-temperature exposure.

316Ti is commonly specified for components that must operate or are fabricated in the ~425–900 °C temperature window (welded assemblies, heat-exposed plant components) where low-carbon grades alone may be insufficient.

2. คืออะไร 316Ti Stainless Steel?

316Ti is a titanium-stabilized, molybdenum-bearing austenitic สแตนเลส developed to enhance resistance to intergranular corrosion after welding or prolonged exposure to elevated temperatures.

By adding titanium in controlled proportions, carbon is preferentially tied up as stable titanium carbides rather than chromium carbides.

This stabilization mechanism preserves chromium at grain boundaries and significantly reduces sensitization risks in the temperature range of approximately 425–850 °C (800–1560 °F).

ส่งผลให้, 316Ti is particularly suitable for components that will be welded and placed into service without post-weld solution annealing, or for applications involving cyclic or sustained thermal exposure.

It combines the chloride corrosion resistance of conventional 316 stainless steel with improved structural stability at elevated temperatures. Common international identifiers include US S31635 และ ใน 1.4571.

Standard Designations & เทียบเท่าโลก

Key Variants and Related Grades

• 316ของ (US S31635 / ใน 1.4571)
  The titanium-stabilized form of 316 สแตนเลส, intended for welded structures or components exposed to intermediate and elevated temperatures where sensitization resistance is critical.
• 316 (US S31600 / ใน 1.4401)
  The base molybdenum-alloyed grade without stabilization. Suitable when post-weld heat treatment is feasible or when thermal exposure is limited.
• 316ล (US S31603 / ใน 1.4404)
  A low-carbon alternative to reduce sensitization risk through carbon control rather than stabilization. Commonly used in pressure vessels, ท่อ, and pharmaceutical equipment.
• 321 (ใน 1.4541)
  A titanium-stabilized alloy based on the 304 stainless steel chemistry. Used when molybdenum is not required but stabilization is still necessary.
• 347 (Nb-stabilized stainless steel)
  Uses niobium instead of titanium for carbide stabilization. Offers similar intergranular corrosion resistance, often preferred in certain high-temperature pressure equipment codes.
• 316ชม / 316แอลเอ็น
  Variants optimized for higher-temperature strength (316ชม) or increased nitrogen content (316แอลเอ็น). These grades improve mechanical performance but do not replace titanium stabilization.

3. Typical Chemical Composition of 316Ti Stainless Steel

Values are representative engineering ranges for wrought, solution-annealed material (US S31635 / ใน 1.4571 ตระกูล).

4. Microstructure and metallurgical behaviour

• Austenitic matrix (γ-Fe): stable at room temperature due to Ni. Microstructure is ductile, ไม่ใช่แม่เหล็ก (in annealed state) and work-hardening.
• Stabilization mechanism: Ti reacts to form titanium carbides (tic) or carbonitrides which remove C from matrix and prevent Cr₂₃C₆ precipitation at grain boundaries during exposure in ~425–900 °C.
• Sensitization window and limits: even with Ti, extremely long exposure in the sensitization range or improper Ti:C ratio can still permit chromium carbide formation or other intermetallics. Proper melt practice and heat treatment control are essential.
• Intermetallic phases: prolonged exposure in certain intermediate ranges (especially 600–900 °C) can encourage sigma (อัน) or chi (χ) phase formation in austenitic grades enriched in Mo/Cr;
  316Ti is not immune—designers must avoid prolonged dwell in these ranges or specify stabilised steels with controlled composition and thermomechanical history.
• Precipitation after service: Ti-stabilized alloys may show fine Ti-rich precipitates; these are benign or beneficial compared with Cr carbides as they do not deplete Cr at grain boundaries.

5. Mechanical properties — 316Ti stainless steel

The figures below are ตัวแทน values for wrought 316Ti supplied in the solution-annealed / อบอ่อน เงื่อนไข.

Actual values depend on product form (แผ่น, จาน, ท่อ, บาร์), ความหนา, supplier processing and heat lot.

6. ทางกายภาพ & thermal properties and high-temperature behaviour

• การนำความร้อน: relatively low (≈ 14–16 W·m⁻¹·K⁻¹ at 20 องศาเซลเซียส).
• ค่าสัมประสิทธิ์การขยายตัวเนื่องจากความร้อน: ~16–17 ×10⁻⁶ K⁻¹ (20–100 ° C) — higher than ferritic steels.
• ช่วงการหลอมละลาย: คล้ายกับ 316 (solidus ~1375 °C).
• Service temperature window: 316Ti is selected specifically for intermediate temperature exposure (ประมาณ. 400–900 ° C) where stabilization prevents intergranular attack.
  อย่างไรก็ตาม, prolonged exposure in the 600–900 °C window can risk sigma-phase formation and reduction in toughness — avoid continuous exposure to those temperatures unless metallurgical data confirm safety.
• Creep: for sustained loads at high temperature, 316Ti is not a creep-resistant alloy; use high-temperature grades (เช่น, 316ชม, 309/310, หรือโลหะผสมนิกเกิล).

7. Corrosion behaviour — strengths and limitations

จุดแข็ง

• Resistance to intergranular corrosion after thermal exposure in the sensitization range, provided Ti:C and Ti:available C ratios and heat treatment are correct.
• ความต้านทานการกัดกร่อนทั่วไปที่ดี in oxidizing and many reducing media; Mo contributes pitting/crevice resistance similar to 316.
• Preferred for welded structures that will see intermittent high-temperature service or where post-weld solution anneal is impractical.

ข้อจำกัด

• บ่อ & crevice corrosion in high-chloride environments: 316Ti has similar pitting resistance to 316; for severe seawater or warm chloride service consider duplex or higher-PREN alloys.
• คลอไรด์ SCC: not immune—SCC can occur in chloride + แรงดึง + temperature environments; duplex alloys or super-austenitics may be required where SCC risk is high.
• Sigma phase and intermetallics: long dwell at certain high temperatures can cause embrittling phases independent of Ti stabilization—design to avoid those thermal histories or test.
• Industrial contaminants: like all stainless steels, สารเคมีก้าวร้าว (กรดแข็งแรง, chlorinated solvents at high T) may attack; perform compatibility checks.

8. กำลังประมวลผล & Manufacturing Characteristics

316Ti’s austenitic microstructure + TiC precipitates enable excellent processability, with minor adjustments needed for titanium’s effects:

Welding Performance (ข้อได้เปรียบที่สำคัญ)

316Ti retains superior weldability, compatible with GMAW (ฉัน), GTAW (ทีไอจี), สมาว (stick), and FCAW – with the critical advantage of no post-weld heat treatment (PWHT) required for IGC resistance:

• อุ่นเครื่อง: Not required for sections ≤25 mm thick; ส่วนต่างๆ >25 mm may preheat to 80–150°C to reduce HAZ cracking risk.
• Welding consumables: Use ER316Ti (GTAW/GMAW) or E316Ti-16 (สมาว) to match titanium content and ensure stabilization in the weld metal.
• PWHT: Optional stress relief annealing (600–650°C for 1–2 hours) for thick-walled components, but not mandatory for corrosion resistance (unlike 316, which requires PWHT for IGC protection after welding).
• Welded joint performance: Tensile strength ≥460 MPa, elongation ≥35%, and passes ASTM A262 IGC test – weld metal corrosion resistance equivalent to base metal.

การขึ้นรูป & การผลิต

• Cold forming: Excellent ductility allows deep drawing, ดัด, และกลิ้ง. Minimum bend radius: 1× thickness for cold bending (≤12 mm thick), same as 316L – TiC precipitates do not impair formability.
• Hot forming: Performed at 1100–1250°C, followed by water quenching to retain austenitic microstructure and TiC distribution. Avoids the 450–900°C range during cooling to prevent accidental sensitization.
• เครื่องจักรกล: Moderate machinability (rated 55–60% vs. เอไอเอส 1018 เหล็ก) – TiC precipitates are harder than austenite, causing slightly more tool wear than 316L.
  Recommended cutting speed: 90–140 m/min (เครื่องมือคาร์ไบด์) with cutting fluid to reduce heat buildup.

การรักษาความร้อน

• การหลอมโซลูชัน: Primary heat treatment (1050–1150 ° C, hold 30–60 minutes, การดับน้ำ) – dissolves residual carbides (if any), refines grains, and ensures uniform TiC distribution. Critical for maximizing corrosion resistance and toughness.
• การหลอมบรรเทาความเครียด: 600–650°C for 1–2 hours, air cooling – reduces residual stress by 60–70% without affecting TiC stability or corrosion resistance.
• Avoid over-annealing: อุณหภูมิ >1200°C may cause TiC coarsening and grain growth, reducing high-temperature strength – limit solution annealing temperature to ≤1150°C.

การรักษาพื้นผิว

• การดอง & ทู่: Post-fabrication treatment (ASTM A380) to remove oxide scale and restore the Cr₂O₃ passive film – TiC precipitates do not interfere with passivation.
• ขัด: Achieves surface finishes ranging from Ra 0.02–6.3 μm. Mechanical or electropolishing improves hygiene and corrosion resistance, suitable for medical and food applications.
• การเคลือบผิว: Rarely required due to inherent corrosion resistance; galvanizing or epoxy coating may be used for extreme high-chloride environments (เช่น, marine offshore platforms).

9. Typical Applications of 316Ti Stainless Steel

316Ti’s unique combination of high-temperature stability, IGC resistance, and corrosion resistance makes it ideal for demanding environments where 316L or 316 may fail:

เคมี & อุตสาหกรรมปิโตรเคมี (35% of Demand)

• Core applications: High-temperature chemical reactors, เครื่องแลกเปลี่ยนความร้อน, คอลัมน์กลั่น, and piping for handling chlorides, กรด, and organic solvents.
• ข้อได้เปรียบที่สำคัญ: Resists IGC during repeated welding (เช่น, maintenance repairs) and high-temperature operation (up to 850°C) – used in ethylene crackers and sulfuric acid plants.

การบินและอวกาศ

• Core applications: Aircraft exhaust systems, ส่วนประกอบกังหัน, and rocket engine parts.
• ข้อได้เปรียบที่สำคัญ: High-temperature oxidation resistance (≤900°C) and non-magnetic properties – compatible with avionics and radar systems.

Nuclear Energy

• Core applications: Nuclear reactor cooling system components, steam generators, and fuel cladding (non-radioactive structural parts).
• ข้อได้เปรียบที่สำคัญ: IGC resistance in high-temperature, high-pressure water (280องศาเซลเซียส, 15 MPa) and compliance with nuclear safety standards (เช่น, ASME Section III).

High-Temperature Furnace Manufacturing

• Core applications: Furnace liners, หลอดรังสี, and heating elements for industrial furnaces (การรักษาความร้อน, sintering).
• ข้อได้เปรียบที่สำคัญ: Retains strength and corrosion resistance at 800–900°C, with a service life 2–3 times longer than 316L in continuous high-temperature operation.

ทางการแพทย์ & อุตสาหกรรมยา

• Core applications: Sterilizable medical devices, อุปกรณ์แปรรูปเภสัชกรรม, and cleanroom components.
• ข้อได้เปรียบที่สำคัญ: IGC resistance after repeated autoclaving (121องศาเซลเซียส, 15 ปอนด์ต่อตารางนิ้ว) and compliance with FDA 21 ส่วน CFR 177 – no risk of corrosion-induced contamination.

มารีน & Offshore Industry

• Core applications: Offshore platform piping, seawater desalination plants, and subsea components.
• ข้อได้เปรียบที่สำคัญ: Resists seawater corrosion and SCC, with NACE MR0175 compliance for sour service (H₂S-containing well fluids).

10. ข้อดี & ข้อจำกัด

Core Advantages of 316Ti Stainless Steel

• Superior IGC resistance: Titanium stabilization eliminates Cr₂₃C₆ precipitation, making it ideal for high-temperature or repeated welding scenarios – outperforming 316L/316H.
• Enhanced high-temperature performance: Retains strength, ความเหนียว, and oxidation resistance up to 900°C, 50–100°C higher than 316L.
• เชื่อมได้ดีเยี่ยม: No mandatory PWHT for corrosion resistance, reducing manufacturing costs and lead time.
• ความต้านทานการกัดกร่อนในวงกว้าง: Inherits 316’s resistance to chlorides, กรด, and sour service, with extended temperature limits for NACE compliance.
• การปรับแต่งข้าว: TiC precipitates inhibit grain growth, improving mechanical properties and dimensional stability.

Key Limitations of 316Ti Stainless Steel

• ต้นทุนที่สูงขึ้น: 15–20% more expensive than 316L (due to titanium addition), increasing material costs for large-scale non-critical applications.
• Reduced machinability: TiC precipitates cause more tool wear than 316L, requiring specialized tools or slower cutting speeds – increasing machining costs by ~10–15%.
• TiC coarsening risk: Prolonged exposure to >900°C causes TiC coarsening, reducing high-temperature strength and toughness.
• Limited super-high-temperature resistance: Not suitable for continuous service above 900°C – use super austenitic stainless steels (เช่น, 254 เรา) or nickel-based alloys (เช่น, อินโคเนล 600) แทน.
• Lower strength than duplex stainless steels: ความต้านทานแรงดึง (485–590 MPa) is lower than duplex grades (เช่น, 2205: 600–800 MPa), requiring thicker sections for structural loads.

11. Comparative analysis — 316Ti vs 316L vs 321 vs Duplex 2205

12. บทสรุป

316Ti is a pragmatic stabilized variant of the 316 ตระกูล, engineered to preserve austenitic stainless steel corrosion resistance in welded and heat-exposed components.

When titanium content and heat-treatment are properly controlled, 316Ti prevents intergranular chromium depletion and is a robust choice for welded plant components, heat-exposed assemblies and moderate chloride environments where post-weld annealing cannot be guaranteed.

Proper procurement, MTR verification, welding procedure control and periodic inspection are essential to realize the alloy’s advantages.

 

คำถามที่พบบ่อย

What is the difference between 316Ti and 316L?

316Ti is titanium-stabilized (Ti added to form TiC), while 316L is low-carbon (L = low C).

Both routes reduce sensitization risk; 316Ti is specifically selected when components will see intermediate-temperature exposure and post-weld anneal is impractical.

Does titanium make 316Ti more corrosion resistant than 316L?

Titanium’s role is to prevent intergranular corrosion after thermal exposure; 316Ti’s bulk pitting resistance is similar to 316/316L (Mo in all gives comparable localized corrosion resistance).

For harsher chloride environments, duplex or higher-PREN alloys are preferred.

Do I need different filler metals to weld 316Ti?

Not necessarily—matching filler alloys (เช่น, ER316L/ER316Ti where available) are used.

Ensure filler chemistry and welding procedure maintain stabilization in the HAZ and weld metal; consult welding codes and metallurgical guidance for critical parts.