High-Purity Stainless Steel Coil Tube — Residual Element Controlled Series
Product Overview
The High-Purity Stainless Steel Coil Tube is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for applications demanding exceptional metallurgical purity. This product line addresses the critical challenge of residual element control in stainless steel metallurgy, where trace impurities such as phosphorus (P), sulfur (S), boron (B), and lead (Pb) can severely compromise mechanical integrity, corrosion resistance, and processability.
Unlike conventional coil tubes, this product series enforces stringent upper limits on residual and trace elements, ensuring the material meets the demanding requirements of high-purity applications across aerospace, chemical processing, pharmaceutical, and advanced energy sectors. The coil tube form factor offers continuous production efficiency while maintaining tight dimensional tolerances and superior metallurgical quality.
Material & Properties
Metallurgical Philosophy: Residual Element Control
In stainless steel metallurgy, residual elements refer to trace constituents that remain in the melt after primary deoxidation and refining. These elements — though present in minute quantities — exert a disproportionate influence on the material's behavior during hot working, welding, and long-term service. The key concerns include:
- Sulfur (S): Forms manganese sulfide (MnS) inclusions that act as stress concentrators during hot rolling and forging. Excessive sulfur causes hot shortness and transverse cracking at elevated temperatures.
- Phosphorus (P): Promotes intergranular segregation and sensitization, accelerating intergranular corrosion in austenitic grades. It also increases cold cracking susceptibility in welds.
- Boron (B): While beneficial in boron-bearing austenitic grades for solid solution strengthening, uncontrolled boron introduces embrittlement in non-intended applications and affects grain boundary cohesion.
- Lead (Pb): Segregates to grain boundaries, reducing creep strength and ductility at elevated temperatures. Lead is particularly detrimental in high-temperature applications.
Key Material Characteristics
- Ultra-Low Sulfur Content: S < 0.005% (50 ppm), significantly below industry-standard limits, minimizing MnS inclusion populations
- Controlled Phosphorus: P < 0.020% (200 ppm), reducing sensitization risk and improving weldability
- Refined Inclusion Morphology: Reduced and rounded oxide/sulfide inclusions through controlled refining
- Enhanced Hot Workability: Superior resistance to hot cracking during tube forming operations
- Improved Surface Quality: Fewer inclusion-related surface defects after pickling and passivation
Specifications
Residual Element Limits — High-Purity Grade
| Element | Symbol | Standard Limit (ASTM/EN) | High-Purity Limit (This Product) | Reduction Factor | Primary Benefit |
|---|---|---|---|---|---|
| Sulfur | S | ≤ 0.030% | < 0.005% | 6× | Prevents hot brittleness and MnS inclusion formation |
| Phosphorus | P | ≤ 0.045% | < 0.020% | 2.25× | Reduces sensitization and cold cracking susceptibility |
| Boron | B | Not typically specified | < 0.001% | — | Prevents uncontrolled grain boundary embrittlement |
| Lead | Pb | Not typically specified | < 0.001% | — | Maintains elevated-temperature creep strength |
| Nitrogen | N | ≤ 0.030% | ≤ 0.015% | 2× | Prevents nitride precipitation and age embrittlement |
| Oxygen | O | ≤ 0.020% | ≤ 0.010% | 2× | Reduces oxide inclusion content and improves fatigue life |
Typical Chemical Composition (304L/316L Base Grades)
| Grade | C | Mn | Si | Cr | Ni | Mo | N | Fe (balance) |
|---|---|---|---|---|---|---|---|---|
| 304L High-Purity | ≤ 0.020% | ≤ 2.00% | ≤ 1.00% | 18.0–20.0% | 8.0–11.0% | — | ≤ 0.015% | — |
| 316L High-Purity | ≤ 0.020% | ≤ 2.00% | ≤ 1.00% | 16.0–18.0% | 10.0–14.0% | 2.0–3.0% | ≤ 0.015% | — |
| 321 High-Purity | ≤ 0.080% | ≤ 2.00% | ≤ 1.00% | 17.0–19.0% | 9.0–13.0% | — | ≤ 0.015% | — |
| 347 High-Purity | ≤ 0.080% | ≤ 2.00% | ≤ 1.00% | 17.0–19.0% | 9.0–13.0% | — | ≤ 0.015% | — |
Dimensional Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Tube OD (Outer Diameter) | 6.0 mm – 102.0 mm | ASTM A269 / EN 10217-7 |
| Wall Thickness | 0.30 mm – 6.00 mm | ASTM A269 / EN 10217-7 |
| OD Tolerance | ±0.10 mm (≤ 25 mm); ±0.5% (＞ 25 mm) | ASTM A269 |
| Wall Thickness Tolerance | ±0.05 mm (≤ 1.5 mm); ±10% (＞ 1.5 mm) | ASTM A269 |
| Coil ID (Inner Diameter) | 152 mm (6") / 203 mm (8") | Standard coil configuration |
| Coil Weight | Up to 2,000 kg per coil | — |
| Surface Finish | 2B / BA / No. 4 / No. 8 / Mirror / Custom | ASTM A480 |
| Heat Treatment | Solution Annealed + Pickled & Passivated (P&H) | ASTM A269 |
Manufacturing Process
Process Flow for Residual Element Control
Achieving ultra-low residual element levels requires a tightly controlled metallurgical process chain from raw material selection through final coil forming:
-
Raw Material Selection & Pre-Treatment:
- Virgin nickel (Ni) and chromium (Cr) with certified trace element content
- Low-phosphorus and low-sulfur iron (Fe) scrap or remelted ingots
- Pre-weighed alloy additions with certified purity (≥ 99.95%)
-
Primary Melting (AOD/VOD):
- Arc Furnace (AF) melting with controlled electrode quality
- AOD (Argon Oxygen Decarburization) for carbon and chromium adjustment
- VOD (Vacuum Oxygen Decarburization) for deep sulfur and nitrogen removal
- Target: S < 0.010%, N < 0.020% after primary refining
-
Secondary Refining (LF + VD):
- LF (Ladle Furnace) for composition fine-tuning and temperature homogenization
- VD (Vacuum Degassing) for residual gas and light element removal
- Aluminum or calcium treatment for inclusion modification
- Target: S < 0.005%, O < 0.010%, P < 0.020%
-
Continuous Casting (CC):
- Single-strand continuous caster with controlled cooling rates
- Optimized casting speed to minimize centerline segregation
- Electromagnetic stirring (EMS) for homogenization
- Resulting billet/slab with uniform microstructure
-
Hot Rolling & Annealing:
- Hot rolling of ingots to produce seamless tube blanks or hot-rolled coil
- Interpass annealing to prevent hot cracking during deformation
- Temperature-controlled rolling to minimize grain boundary segregation
-
Cold Forming & Coil Tube Production:
- Strip slitting and cold reduction to precise dimensions
- Forming, welding (TIG/IG), and heat treatment
- Coiling on standard diameter cores with protective wrapping
-
Final Treatment:
- Solution annealing at 1050–1150°C in protective atmosphere
- Pickling and passivation (P&H) for surface oxide removal
- Full dimensional and chemical inspection prior to packaging
Critical Process Controls
| Process Stage | Control Parameter | Target Range | Monitoring Method |
|---|---|---|---|
| VOD Refining | Vacuum Pressure / Duration | ≤ 5 Pa / ≥ 30 min | Pressure gauge + timer |
| VD Treatment | Argon Flow Rate / Vacuum Level | 2,000–3,000 Nm³/h / ≤ 10 Pa | Flow meter + vacuum gauge |
| LF Refining | Deoxidizer Addition | Al wire: 0.02–0.05 kg/t | Automated wire feeding system |
| Continuous Casting | Casting Speed | 0.5–1.2 m/min | Encoder feedback |
| Hot Rolling | Fins Temperature | 1100–1200°C | Infrared pyrometer |
| Final Annealing | Temperature / Atmosphere | 1050–1150°C / H₂ or N₂ (Dew Point ≤ -50°C) |