ASTM 321 Austenitic Heat-Resistant Stainless Steel Coil Tube
Product Overview
The ASTM 321 Stainless Steel Coil Tube, manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a premium austenitic heat-resistant alloy engineered for sustained service in high-temperature environments. This coil tube is distinguished by its titanium-stabilized microstructure, which provides exceptional resistance to intergranular corrosion (IGC) in temperature ranges between 450 °C and 900 °C — a critical performance window where conventional austenitic grades such as 304 and 304L are highly susceptible to chromium carbide precipitation and subsequent grain boundary degradation.
Delivered in coil form, this product offers superior formability, efficient downstream processing, and reduced material waste, making it an ideal feedstock for precision tube rolling, welding, and fabrication operations across aerospace, power generation, and process industries.
Material & Properties
The 321 grade is a titanium-stabilized variant of the austenitic stainless steel family (UNS S32100 / 1.4541 / 06Cr19Ni10Ti). The critical metallurgical requirement is that the titanium-to-carbon mass ratio satisfies:
Ti / C ≥ 5 × %C
This stoichiometric relationship ensures that titanium preferentially binds with carbon to form titanium carbides (TiC) rather than allowing chromium carbides (Cr₂₃C₆) to precipitate at grain boundaries. The result is a stable, chromium-rich grain boundary that maintains excellent resistance to intergranular attack even after prolonged exposure or thermal cycling within the sensitization range of 450–900 °C.
Mechanical Properties (Annealed Condition, Typical)
- Tensile Strength (Rm): ≥ 515 MPa (75 ksi)
- Yield Strength (Rp0.2): ≥ 205 MPa (30 ksi)
- Elongation (A₅₀): ≥ 40%
- Hardness: ≤ 200 HB (typical)
- Density: 7.93 g/cm³
Thermal Properties
- Thermal Conductivity at 100 °C: 16.3 W/(m·K)
- Thermal Conductivity at 500 °C: 21.5 W/(m·K)
- Thermal Expansion (20–1000 °C): 17.8 × 10⁻⁶ /K
- Maximum Continuous Service Temperature: 900 °C
- Maximum Intermittent Service Temperature: 980 °C
Corrosion Resistance Characteristics
- Intergranular Corrosion: Excellent — immune to sensitization in the 450–900 °C range due to Ti stabilization
- Oxidation Resistance: Superior scale formation (dense Cr₂O₃) at elevated temperatures
- Acid Resistance: Good in dilute sulfuric and phosphoric acids; moderate in oxidizing acids
- Chloride Stress Corrosion Cracking (Cl-SCC): Susceptible at temperatures above 60 °C in chloride-containing environments
Specifications
| Parameter | Specification / Value |
|---|---|
| Grade Designation | ASTM 321 / UNS S32100 / EN 1.4541 |
| Chemical Composition (wt%) | C ≤ 0.08; Si ≤ 1.00; Mn ≤ 2.00; P ≤ 0.045; S ≤ 0.030; Cr 18.0–20.0; Ni 9.0–13.0; Ti ≥ 5×C, min 0.50; N ≤ 0.10 |
| Ti/C Stabilization Ratio | Ti / C ≥ 5 × %C (mandatory) |
| Form | Coil Tube (盘管) — cold-rolled coil for tube rolling |
| Coil Dimensions (Typical) | Width: 150–1000 mm; Thickness: 0.3–3.0 mm; Coil ID: 508–610 mm; Coil OD: ≤ 1500 mm |
| Surface Finish | No. 1 (hot-rolled), 2B (cold-rolled, bright annealed), BA (bright annealed), No. 4 (hairline), or custom |
| Heat Treatment | Solution annealing at 1010–1150 °C followed by water or air quench |
| Weldability | Excellent — suitable for all standard fusion welding processes without pre/post-heat treatment |
| Formability | Excellent — cold workable to deep-draw and tube-rolling configurations |
| Standards Compliance | ASTM A240, ASTM A213, ASTM A312, EN 10088-1, EN 10216-5, GB/T 24511 |
| Applicable Standards (Coil) | ASTM A473, EN 10216-5, JIS G4305 |
Manufacturing Process
The production of ASTM 321 stainless steel coil tube at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage metallurgical process to ensure chemical homogeneity, mechanical integrity, and dimensional accuracy:
- Raw Material Preparation: Virgin stainless steel scrap and alloying elements (Cr, Ni, Ti, Mo) are carefully selected and analyzed to meet the required chemical composition within ASTM A240 tolerances.
- Melt Processing (AOD/VOD): Steel is melted in an Argon Oxygen Decarburization (AOD) converter to achieve precise carbon control. Vacuum Oxygen Decarburization (VOD) refining further reduces sulfur, nitrogen, and dissolved gases to ultra-low levels, ensuring a clean steel matrix.
- Continuous Casting: The refined molten steel is cast into slabs or billets via continuous casting (CC) technology, producing near-net-shape ingots with controlled cooling rates to minimize macro-segregation.
- Hot Rolling: Slabs are reheated to 1200–1250 °C and hot-rolled to intermediate gauge. This establishes the initial grain structure and reduces thickness to within ±0.5 mm of target.
- Pickle & Descale: Hot-rolled coils undergo acid pickling (HNO₃/HF or HNO₃/HCl) to remove mill scale and restore a clean, passive surface.
- Cold Rolling: The descaled coil is cold-rolled to final thickness with high reduction ratios (up to 80%), achieving tight dimensional tolerances (±0.02 mm) and improved surface finish.
- Solution Annealing: Cold-rolled coils are annealed at 1010–1150 °C in a controlled-atmosphere furnace (dew point ≤ –40 °C) to dissolve carbides, restore full austenitic structure, and eliminate cold-work hardening. Rapid quenching prevents re-precipitation.
- Coil Slitting & Edge Trimming: The annealed coil is slit to required widths and edges are trimmed to ensure flat, defect-free edges suitable for tube rolling.
- Quality Inspection & Packaging: Each coil undergoes ultrasonic testing (UT), positive material identification (PMI) via XRF spectroscopy, hardness testing, and dimensional verification before protective packaging and dispatch.
Applications
ASTM 321 coil tube is purpose-engineered for high-temperature service where intergranular corrosion resistance is paramount. Key application sectors include:
- Aerospace & Aviation: Aircraft exhaust system components, turbine casing linings, and hot-section structural elements where sustained temperatures exceed 500 °C and weight efficiency is critical.
- Power Generation: Boiler headers and collector tubes in supercritical and ultra-supercritical (USC) steam plants; furnace tubes in coal-fired and biomass boilers operating at 600–800 °C.
- Heat Exchangers: Shell-and-tube and plate heat exchangers in petrochemical refining, where thermal cycling and elevated temperatures demand reliable grain boundary stability.
- Petrochemical Processing: Crude oil fractionation columns, catalytic cracking unit transfer lines, and reformer tubes exposed to cyclic heating and corrosive media.
- Industrial Furnaces: Heat-treatment furnace components, radiant tubes, and muffles in continuous annealing lines and sintering furnaces.
- Food & Pharmaceutical Processing: High-temperature steam sterilization systems and hygienic heat exchangers requiring both corrosion resistance and sanitization capability.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that every batch of ASTM 321 coil tube meets international standards and customer-specific requirements:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing and supply chain processes.
- ISO 14001:2015 — Environmental Management System ensuring sustainable and responsible production practices.
- EN 10204 3.1 / 3.2 — Third-party inspection and material certification (Mill Test Certificates) issued by accredited inspection bodies (e.g., SGS, BV, TÜV, DNV).
- NACE MR0175 / ISO 15156 — Compliance for sour service applications where applicable.
- ASME Section II — Material compliance for pressure vessel and piping applications.
- Mill Test Reports (MTR): Each coil is accompanied by a full chemical analysis (spectrographic), mechanical test results (tensile, hardness, elongation), and heat treatment documentation traceable to the heat number.
Unique Selling Points
- Exceptional Grain Boundary Stability: The Ti/C ≥ 5×%C stabilization ratio provides a metallurgical guarantee against intergranular corrosion that surpasses 304L in elevated-temperature service — a decisive advantage for boiler and exhaust applications.
- Coil Form Advantage: Delivered as a continuous coil, this product enables seamless tube rolling, eliminates butt-weld seams in the parent material, and reduces processing waste by up to 30% compared to plate-based fabrication.
- Weldability Without Post-Weld Heat Treatment (PWHT): Unlike many high-alloy steels, 321 coil tube can be welded and formed without requiring post-weld annealing, significantly reducing fabrication costs and schedule time.
- Ultra-Low Carbon & High Cleanliness: AOD/VOD processing ensures sulfur ≤ 0.030% and nitrogen ≤ 0.10%, minimizing inclusion-related defects and ensuring long-term fatigue life in cyclic thermal service.
- Full Traceability: Every coil is heat-numbered and traceable through the entire production chain, from raw material to final delivery, meeting the stringent traceability requirements of aerospace and nuclear supply chains.