2B vs BA vs No.4 Surface Finish on 304 Stainless Steel Coils: Which One Your Fabrication Shop Actually Needs

Why the Surface Finish Question Matters at Receiving

Most purchasing orders for cold rolled stainless steel coils list 304 as the grade and stop there. The fabricator discovers at receiving inspection — sometimes after slitting has begun — that the surface finish was wrong for the application. The coil is either returned, repurposed for a lower-priority job, or shipped downstream and rejected by the end customer. The root cause is almost always the same: the spec sheet mentioned “304″ but never named the surface finish, or named it loosely (“mill finish”, “standard finish”) that the mill interpreted differently than the buyer expected.

Three finishes account for the overwhelming majority of 304 stainless steel coil orders: 2B, BA, and No.4. Each is produced by a fundamentally different sequence of mill operations, which is why they have different surface roughness values, different reflective behavior, different costs, and — most importantly for a fabrication shop — different behavior when welded, formed, or polished downstream. The British Stainless Steel Association surface-finish reference treats these as the three baseline finishes from which all other stainless surface treatments are derived.

This guide explains what each finish actually is, how it is produced, and how to match it to the work your fabrication shop is doing. The 304 grade is used as the reference because it is the most widely specified austenitic stainless steel — its mechanical behavior, corrosion resistance, and weldability are well documented in ASTM standards and ISO specifications, and the same finish designations apply to 316, 316L, 430, and other grades with only minor adjustments to processing parameters.

2B Finish — The Cold-Rolled Mill Default

2B is the default finish that most cold-rolled 304 coils leave the mill with. The “2″ denotes the second-generation cold-rolled surface category and the “B” denotes the specific processing route: cold-rolled, annealed, pickled, and skin-passed. It is the finish most buyers receive when they order “standard 304 coil” without specifying anything more.

How 2B is produced

The production sequence at a typical integrated stainless mill is:

1. Hot rolling to a starting gauge well above the final target thickness.
2. Cold rolling through a tandem mill to bring the strip close to final thickness and to work-harden the austenitic structure.
3. Annealing in a continuous atmosphere furnace to restore ductility by dissolving the work-hardened structure into equiaxed austenite.
4. Pickling in a mixed acid bath (typically nitric plus hydrofluoric) to remove the annealing scale and leave a clean passive surface.
5. Skin passing — a light final cold reduction of roughly 0.5-2% on a tension leveler or temper mill — to impart a controlled surface texture, set mechanical properties, and improve flatness.

The skin pass is what separates 2B from the older 2D finish (which is annealed and pickled but not skin-passed and therefore has a rougher, more matte appearance). 2B’s signature look — smooth, slightly reflective, dull-gray with a faint directional sheen — comes from the roll texture of the temper mill.

Typical Ra and surface behavior

2B surfaces typically measure Ra 0.2-0.5 micrometers (8-20 microinches). That is smoother than a typical machined surface but rougher than a BA or polished finish. The roughness is small enough that the surface still has reasonable cleanability for food handling and general industrial use, but the directional roll marks are visible at close range and can trap contaminants in applications with strict hygiene requirements.

Where 2B is the right answer

2B is the most fabrication-friendly of the three finishes. The surface accepts welding without unusual preparation, draws well in deep-drawing operations, and polishes uniformly when a downstream customer wants a #4 or mirror finish applied. It is the default feedstock for precision 304 stainless steel strips that will subsequently be slit, cut, formed, or coated.

Typical 2B applications include chemical-processing equipment, storage tanks, heat-exchanger shells, architectural components that will be painted or coated, and any fabrication where the surface is hidden or further processed after forming.

BA Finish — Bright Annealed, the Reflective Choice

BA (Bright Annealed) is the highest-reflectivity finish that ships directly from the cold-rolled mill without any mechanical polishing. It is also the most demanding to produce, which is why it commands a meaningful price premium over 2B.

How BA is produced

BA follows the same cold-rolling sequence as 2B but the annealing step is fundamentally different:

1. Cold rolling to near-final gauge, identical to 2B.
2. Bright annealing in a continuous furnace with a controlled hydrogen-nitrogen atmosphere that contains virtually no oxygen or water vapor. Because there is no oxidation during heating and soaking, no scale forms on the surface — the strip emerges with the reflective finish imparted by the cold-rolling rolls intact.
3. Cooling in the same protective atmosphere to prevent oxidation on the way out.
4. Light skin passing for flatness, with the rolls kept clean to preserve reflectivity.

The atmosphere control is the critical step. Even trace oxygen in the furnace atmosphere will form chromium oxide scale on the surface, which must then be removed by pickling — and once pickled, the surface is no longer BA. Mills that produce BA maintain atmosphere dew points below roughly -40°C and use hydrogen concentrations above 75% to keep the surface chemically clean throughout the heat cycle.

Typical Ra and surface behavior

BA surfaces typically measure Ra below 0.05 micrometers (below 2 microinches) — smoother than 2B by roughly an order of magnitude. The reflectivity is high enough that BA is used as a substrate for subsequent mirror polishing where an even higher finish is needed, and it has the cleanest, most uniform appearance of any as-rolled stainless surface.

Where BA is the right answer

BA is specified where appearance, reflectivity, and cleanability all matter simultaneously. The pharmaceutical industry uses BA for process vessels and piping because the smooth surface is easy to clean-in-place and easy to visually inspect for residual product. The dairy and beverage industries use BA for similar reasons. The semiconductor industry uses BA for gas-delivery tubing and process-chamber internals where surface roughness could shed particles.

Architectural interiors — elevator doors, decorative trim, high-end appliance panels — also specify BA where a mirror-like surface is the design intent. In these applications BA is sometimes called “mirror finish” informally, but the formal designation remains BA until additional polishing is performed.

No.4 Finish — The Brushed Architectural Standard

No.4 is a mechanically textured finish produced by abrasive belts, not by the rolling or annealing process. It is the finish most people picture when they hear “brushed stainless steel”.

How No.4 is produced

No.4 is applied to a coil or sheet that has already received a 2B or BA finish. The process:

1. Starting stock is typically 2B coil (sometimes BA for higher-end applications).
2. Abrasive belt polishing with a sequence of grits — typically starting at 80-120 grit to remove mill scale and surface defects, then progressing to 150-180 grit for the final No.4 texture. The belts run in a single direction, creating the unidirectional grain pattern that defines No.4.
3. Cleaning to remove abrasive residue and metal fines.
4. Optional PVC film application to protect the directional grain during downstream handling.

The grit sequence matters. A mill that uses 120 grit throughout produces a coarser No.4 than a mill that finishes with 180 grit. The EN 10088-2 standard defines No.4 with a Ra range of roughly 0.6-1.0 micrometers (24-40 microinches), but suppliers vary within that band.

Typical Ra and surface behavior

No.4 surfaces measure Ra 0.6-1.0 micrometers by design — much rougher than 2B or BA. The roughness is intentional: the texture scatters reflected light, hides minor scratches, and provides a uniform appearance across large panels even when individual coils have minor surface variation.

Where No.4 is the right answer

No.4 is the dominant finish for architectural applications — wall panels, column covers, elevator interiors, handrails, and signage — because the grain hides fingerprints and small scratches that would be obvious on a 2B or BA surface. Commercial kitchen equipment (work tables, range hoods, refrigerator doors) uses No.4 for the same reason: in a working environment, the surface will be touched constantly and the grain hides the wear.

No.4 is also widely used in food and beverage processing for visible customer-facing equipment where the brushed appearance is part of the brand identity. The grain direction must be specified consistently across a fabrication run — once established, all panels must have grain running the same way or the finished assembly will look visibly mismatched.

Side-by-Side Comparison: Ra, Process, Cost

The table below summarizes the practical differences a fabrication shop needs to weigh at order entry. Ra values are typical ranges for 304 cold-rolled coils; actual values vary by mill, thickness, and customer specification.

Standards reference

Surface-finish designations are defined in ASTM A480 (general requirements for flat-rolled stainless) and EN 10088-2 (stainless steel technical delivery conditions for sheet and strip). JIS G4305 covers the Japanese equivalent. These three standards converge on the same 2B, BA, and No.4 designations, so a coil ordered to any one of them will receive a comparable surface from a globally integrated mill. Reference the World Stainless Steel Association for additional international specification guidance.

Why the cost difference exists

2B is the cheapest because it is the natural output of the standard cold-rolled mill sequence — no extra processing beyond what every coil already receives. BA costs more because the bright-annealing furnace runs at lower throughput than a conventional anneal-and-pickle line and requires tight atmosphere control. No.4 costs more than 2B because the abrasive belt polishing line is a separate operation with its own inspection and handling costs. For very thin gauges (below 0.3 mm), No.4 polishing is particularly challenging and the premium increases noticeably.

How Each Finish Behaves on the Shop Floor

Surface finish is not just a cosmetic property — it determines how the coil behaves during slitting, forming, welding, and downstream finishing. Fabrication shops that order the wrong finish for the work discover this at the laser table or the press brake, not at receiving inspection.

Slitting and cut-to-length

All three finishes slit and shear cleanly. BA coils require the most careful handling: every die mark, roll mark, or scratch from the slitter shows up on the finished strip. 2B forgives minor handling marks. No.4 hides them as part of the existing grain pattern.

Welding

All three finishes weld with standard austenitic stainless procedures (typically TIG or laser for thin gauges). The difference is in post-weld cleanup:

• 2B welds receive a light pickle-passivation to restore the passive layer; the surrounding 2B surface tolerates the chemical treatment without visible mismatch.
• BA welds must be pickled AND the heat tint must be fully removed, otherwise the weld zone will be visibly duller than the surrounding BA surface. Many shops specify post-weld electropolishing on BA work to restore the original reflectivity.
• No.4 welds must be re-brushed with the same grit sequence to match the surrounding grain direction. A weld that is left unbrushed on No.4 stock is immediately obvious and is the most common cosmetic rejection reason for architectural stainless work.

Forming and deep-drawing

2B is the most formable because its surface roughness is small enough that the draw dies do not leave visible marks, and the lubricant film stays uniform during deep drawing. BA draws well in principle, but the mirror surface shows every die mark and minor orange-peel effect — many shops draw BA coils only when the formed part will be subsequently polished, or when the cosmetic requirements are critical. No.4 is generally not specified for deep drawing because the unidirectional grain distorts during forming and the finished part looks mottled.

Cleaning and passivation

2B and BA surfaces clean uniformly. No.4 surfaces trap contaminants in the directional grain if cleaned with the wrong direction of wiping — always wipe with the grain, never across it. For all three finishes, passivation in nitric or citric acid restores the chromium-oxide passive layer after welding or heavy fabrication, and is best done as a final step before shipment.

Decision Framework: Which Finish Your Shop Actually Needs

The fastest path to the right finish is to answer three questions in order:

Question 1 — Will the surface be visible in the finished product?

If no, or if it will be coated, painted, or covered by another component, specify 2B. It is the cheapest and most forgiving of fabrication marks. If yes, move to question 2.

Question 2 — Does the customer require reflectivity or a specific texture?

If the design calls for a near-mirror reflective surface (pharmaceutical, dairy, semiconductor, decorative elevator panels), specify BA. If the design calls for a brushed grain or for a surface that will be touched frequently and must hide fingerprints (kitchen equipment, architectural cladding, public-facing panels), specify No.4. If neither reflectivity nor grain is required, return to question 1 and use 2B.

Question 3 — What downstream operations will the coil see?

If the coil will be deep-drawn, heavily formed, or undergo significant plastic deformation, 2B is the safer choice. If the coil will be welded and the welds must match the surrounding finish, choose the finish whose post-weld restoration is most practical for your shop (typically 2B or No.4; BA requires electropolishing). If the coil will be polished further, 2B is the right starting surface.

Common scenarios

For a fabrication shop that runs mixed work, keeping a small inventory of 2B and No.4 coils in 304 covers most orders. BA is usually ordered to specific customer specifications rather than held in stock, because the cosmetic requirements are tighter and PVC film protection has a limited shelf life.

Buying Checklist: What to Confirm With the Mill

Surface finish is one of the most under-specified items on stainless coil orders. Confirming the following points at order entry eliminates most downstream disputes:

1. Standard reference. Confirm ASTM A480, EN 10088-2, JIS G4305, or equivalent — and which edition. Mills in different regions default to different standards.
2. Ra range, not just the finish name. “No.4″ without an Ra value allows the mill to deliver anywhere within the band. Specify Ra 0.6-1.0 micrometers if you need a coarse No.4, or Ra 0.4-0.6 micrometers for a finer No.4.
3. Grain direction for No.4. Parallel to coil length (the standard) or parallel to coil width (less common, used for specific architectural applications).
4. PVC film. Specify thickness (typically 50-80 micrometers), adhesive type, color, and which side(s) are coated.
5. Paper interleaving. Required for some BA applications to prevent surface scratching during coil handling.
6. Edge condition. Slit edge (from slitting) or mill edge (from the original hot-rolled edge) — affects downstream handling and welding.
7. Coil inner diameter and outer diameter. 508 mm (20 in) and 610 mm (24 in) are standard; confirm to match your decoiler.
8. Test reports. Mill test certificate to EN 10204 3.1 for chemical composition and mechanical properties; surface-roughness measurement report for Ra verification.

For shops that order 304 coils regularly, building a relationship with a mill that stocks the specific surface finishes you use allows faster turnaround than ordering to spec every time. Cold rolled stainless steel coils in 2B finish are the most readily available, with BA and No.4 typically requiring additional lead time.

If you are evaluating a new supplier or running a first-time order, contact a mill representative with the specific application in mind. Most technical-sales teams will recommend a finish based on your fabrication sequence rather than simply quoting what was ordered last time.

For more detail on the precision 304 grade that ships in 2B, BA, and No.4 finishes as standard options, the precision 304 stainless steel strips product page lists the available thickness, width, hardness, and edge-condition combinations.

Frequently Asked Questions