Mill Finish Stainless Steel Welded Square Tube For Structural Concealed Applications
The Mill Finish Stainless Steel Welded Square Tube is manufactured from high-quality austenitic stainless steel coils, formed into a square profile, and longitudinally welded using TIG or ERW processes. The mill finish surface is the condition directly after welding and annealing, characterized by the presence of a thin oxide scale and the absence of any subsequent mechanical or chemical surface treatment. This economical finish is ideal for industrial applications where surface appearance is secondary to structural integrity and corrosion resistance. It serves as an excellent base material for further fabrication, painting, or coating.
| Parameter | Details |
|---|---|
| Standards | ASTM A554, A269; EN 10219-2; JIS G3446 |
| Available Grades | 304, 304L, 316, 316L, 201 |
| Square Sizes | 10 mm * 10 mm – 300 mm * 300 mm (3/8″ * 3/8″ – 12″ * 12″) |
| Wall Thickness | 0.5 mm – 6.0 mm (20 ga – 1/4″) |
| Length | 3m, 6m, or custom lengths upon request |
| Welding Process | TIG (GTAW) or ERW (high frequency) |
| Heat Treatment | Annealed after welding |
| Surface Finish | Mill finish (as-annealed, unpolished) |
| Corner Radius | As-rolled (typically 1.5* to 2.5* wall thickness) |
| End Finish | Plain ends, deburred |
| Grade | C ≤ | Si ≤ | Mn ≤ | P ≤ | S ≤ | Cr | Ni | Mo |
|---|---|---|---|---|---|---|---|---|
| 304 | 0.08 | 0.75 | 2.00 | 0.045 | 0.030 | 18.0-20.0 | 8.0-10.5 | – |
| 304L | 0.03 | 0.75 | 2.00 | 0.045 | 0.030 | 18.0-20.0 | 8.0-12.0 | – |
| 316 | 0.08 | 0.75 | 2.00 | 0.045 | 0.030 | 16.0-18.0 | 10.0-14.0 | 2.0-3.0 |
| 316L | 0.03 | 0.75 | 2.00 | 0.045 | 0.030 | 16.0-18.0 | 10.0-14.0 | 2.0-3.0 |
| 201 | 0.15 | 0.75 | 5.5-7.5 | 0.045 | 0.030 | 16.0-18.0 | 3.5-5.5 | – |
Composition per ASTM A554.
| Grade | Tensile Strength (MPa) min | Yield Strength (MPa) min | Elongation (%) min | Hardness (HRB) max |
|---|---|---|---|---|
| 304 | 515 | 205 | 35 | 92 |
| 304L | 485 | 170 | 35 | 92 |
| 316 | 515 | 205 | 35 | 95 |
| 316L | 485 | 170 | 35 | 95 |
| 201 | 515 | 275 | 35 | 100 |
Tested in accordance with ASTM E8 / E8M.
Mill finish refers to the surface condition of stainless steel immediately following the final manufacturing process (welding and annealing). Key characteristics include:
| Characteristic | Description |
|---|---|
| Appearance | Dull, matte gray with visible oxide scale |
| Surface Texture | Slightly rough; may show weld seam visibility |
| Oxide Layer | Heat tint and chromium oxide scale present |
| Reflectivity | Non-reflective |
| Consistency | May show minor variations along the tube length |
| Cost | Lowest among all finish options |
Note: Mill finish is not intended for decorative or sanitary applications without additional surface treatment.
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Lowest Cost Option – Most economical stainless steel square tube finish
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Full Corrosion Resistance – Inherent stainless steel protection (surface scale does not impair performance)
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Annealed Condition – Soft, ductile, and easy to fabricate
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Good Structural Integrity – Ideal for load-bearing applications
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Excellent Base for Fabrication – Easily welded, cut, drilled, and machined
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Ready for Surface Treatment – Can be pickled, polished, painted, or coated as needed
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No Decorative Requirements – Suitable where appearance is not critical
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Wide Size Range – Available from 10 mm to 300 mm
| Parameter | Tolerance |
|---|---|
| Outside dimensions | ±0.4 mm for sizes ≤ 50 mm; ±0.8% for larger sizes |
| Wall thickness | ±10% |
| Length | +0 / -3 mm for fixed lengths |
| Straightness | 0.15% of total length |
| Twist | 2 mm + 0.5 mm per meter |
| Concave / Convex | 0.8% of width |
| Squareness of corners | 90° ± 1° |
| Finish | Appearance | Corrosion Resistance | Relative Cost | Typical Use |
|---|---|---|---|---|
| Mill Finish | Dull, scale present | Full (after scale removal) | $ | Industrial structures, concealed |
| Pickled | Clean, matte gray | Excellent (scale removed) | $$ | Chemical, marine, visible industrial |
| Brushed / Satin | Grain direction, semi-bright | Good (passivated) | $$$ | Architectural, railings, furniture |
| Polished | Reflective, smooth | Good (passivated) | $$$$ | Food equipment, decorative |
| Mirror | Highly reflective | Good (passivated) | $$$$$ | Elevators, luxury architecture |
Mill finish tubes can be further processed to achieve desired surface characteristics:
| Process | Result |
|---|---|
| Pickling (acid bath) | Removes oxide scale, restores uniform matte finish |
| Mechanical Polishing | Achieves brushed, satin, or mirror finish |
| Abrasive Blasting | Creates uniform matte texture |
| Painting / Coating | Allows color matching or additional protection |
| Electropolishing | Smooths surface, enhances corrosion resistance |
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Equipment frames and supports
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Conveyor structures
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Machine guards and enclosures
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Storage racks and shelving
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Workbenches and platforms
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Material handling equipment
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Temporary structural supports
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Embedded components in concrete
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Hidden framework and bracing
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Utility supports and hangers
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Backing for architectural panels
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Greenhouse framing
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Livestock equipment
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Irrigation supports
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Fencing posts and rails
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Truck body frames (concealed areas)
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Trailer structural components
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Container frames
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Base material for welded assemblies
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Prototype and test structures
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Internal framework for enclosures
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Non-decorative welded products
| Process | Recommendation |
|---|---|
| Cutting | Band saw, abrasive wheel, or plasma cutter |
| Welding | TIG (GTAW) recommended; remove mill scale at weld zone |
| Drilling | Cobalt or carbide bits; use cutting fluid |
| Grinding | Use dedicated stainless steel abrasives to prevent contamination |
| Surface Prep for Welding | Grind or pickle to remove oxide scale at joint area |
| Post-Weld Cleaning | Pickle or wire brush to restore corrosion resistance |
For inquiries, technical datasheets, or custom sizes, please contact our sales team.
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