Stainless steel surface finish is as important as the alloy grade in determining appearance, cleanability, corrosion resistance, and suitability for specific applications. From the utilitarian 2B mill finish to a mirror-polished No.8 architectural finish, each surface treatment carries its own cost, lead time, and performance characteristics. This guide covers the five most commonly specified finishes.
2B is the most widely produced stainless steel surface finish. After cold rolling, the steel is annealed, pickled to remove scale, and given a final light cold-rolling pass through polished rolls. The result is a smooth, matte grey surface with a typical roughness of Ra 0.1–0.5 µm.
2B is the default finish for industrial applications where appearance is secondary: chemical tanks, pressure vessels, heat exchangers, ductwork, and general fabrication. It provides a clean surface for welding and accepts subsequent polishing or painting. 2B is the most economical finish and the starting point for most fabricated stainless steel products.
Standard stock at Zunkai Stainless is held in 2B finish for 304, 316L, and 430 in thicknesses from 0.3 mm to 3.0 mm (cold-rolled sheet and coil) and 3.0 mm to 6.0 mm (hot-rolled, annealed, and pickled).
BA (Bright Annealed) finish is produced by annealing cold-rolled stainless steel in a controlled-atmosphere furnace that prevents oxidation. This preserves the reflective, bright surface from the final cold-rolling pass without the need for subsequent pickling. The result is a mirror-like but not optically flat surface, with Ra typically 0.05–0.10 µm.
BA finish is specified for applications where a bright, reflective appearance is required without the cost of mechanical polishing: kitchen appliances, architectural trim, automotive decorative parts, and consumer product housings. BA sheet is the preferred substrate for subsequent polishing to No.4 or mirror finishes because the smooth starting surface reduces polishing time and abrasive consumption.
BA finish is available in 304 and 430 grades at Zunkai Stainless, in thicknesses from 0.3 mm to 2.0 mm. The BA surface is sensitive to handling marks and is typically supplied with protective PVC film on one or both sides.
No.4 finish is the standard architectural brushed finish, produced by mechanically polishing 2B or BA sheet with 150–240 grit abrasive belts. The resulting surface shows a uniform, directional grain pattern with short parallel polishing lines. Surface roughness is typically Ra 0.2–1.0 µm, with the exact appearance depending on grit size and polishing technique.
No.4 is extensively specified for architectural cladding, elevator interiors, kitchen equipment, food processing surfaces, and medical device housings. It hides fingerprints and light scratches better than mirror finishes, reducing maintenance in high-touch applications.
The directional grain must be oriented consistently across adjacent panels in architectural installations, a requirement that should be clearly communicated in the purchase order. Zunkai Stainless supplies No.4 finish sheets in 304 and 316L, with protective PVC film applied after polishing.
HL (Hairline) finish is produced by continuous polishing with 150–240 grit abrasive to create a fine, continuous linear grain that is more uniform and finer than No.4. HL is essentially a refined No.4 finish, with longer, more continuous polishing lines and typically lower roughness (Ra 0.1–0.4 µm).
HL finish is the standard for architectural interior panels, column covers, wall cladding, and decorative applications where a consistent, elegant appearance is important. The fine grain is less prone to showing scratches during fabrication and installation than mirror finishes.
HL polishing is typically performed on coil-to-coil polishing lines for sheet products, ensuring consistent grain direction across the full coil length. Cut-to-length HL sheets should be specified with the grain direction noted if panel orientation matters for the installation design.
Mirror finish (No.8 under ASTM, 8K in commercial terminology) is the highest-reflectivity standard finish, produced by progressively polishing BA sheet with finer abrasives (typically 320–600 grit and beyond) followed by buffing with polishing compounds. The result is a highly reflective, distortion-free surface with Ra typically below 0.05 µm.
Mirror finish is specified for decorative architectural panels, mirror-polished column covers, cleanroom wall panels, pharmaceutical equipment surfaces, and high-end consumer product housings. The mirror surface shows every fingerprint, scratch, and dust particle, requiring careful handling throughout fabrication, transport, and installation.
Mirror polishing adds significant cost — typically 50–100% above No.4 finish, depending on sheet size and thickness. It is the most expensive standard finish and requires protective film plus careful packing for shipment.
When ordering surface-finished stainless steel, specify the finish designation per the applicable standard (ASTM A480, EN 10088-2, or JIS G4305) and note the required surface roughness Ra if critical for the application. For polished finishes, specify the grit range (e.g., "No.4, 180 grit") to ensure consistency between batches. Protect finished surfaces with PVC film and pack with interleaving paper or polyethylene to prevent transit abrasion.
Zunkai Stainless Steel supplies 2B, BA, No.4, HL, and mirror finish stainless steel sheet and coil. In-house polishing lines process sheet in standard dimensions up to 1,500 × 3,000 mm. Contact the sales team for finish availability by grade and thickness.
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