Ss310 Ss316 Hot Rolled Stainless Steel Sheet Hairline Surface Treatment

Why a hairline finish on hot rolled plate is unusual

Almost all hairline and brushed stainless on the market is cold rolled, because the process needs a flat, uniform, thin sheet to run through a polishing line and because cold rolled sheet has the dimensional consistency that a directional grain finish requires. Hot rolled plate is thicker, carries a wider thickness tolerance, and its surface is a pickled grey with a scale pattern that has to be removed before a grain can be laid down.

It is done anyway, for specific reasons. A furnace casing, a kiln shell or a large architectural feature may need 6 to 12 mm of material for temperature or structural reasons, and still be visible. On those jobs, the alternative to a hairline hot rolled plate is to buy pickled plate and grind it on site, which is slower, dirtier and usually less even.

The process here is: hot rolled plate, annealed and pickled, then ground to remove the pickle texture, then brushed with a controlled abrasive to lay a directional grain. The result is a plate with the thickness of hot rolled and the surface of cold rolled.

310S: the heat resistant case

310S carries 24 to 26 percent chromium and 19 to 22 percent nickel. That combination gives it the highest oxidation resistance of the common austenitic grades, roughly 1000 to 1100 C in continuous service, and it holds a tight, adherent oxide scale that protects the metal beneath. In a furnace or a kiln, that scale is the reason the part survives.

The surface finish interacts with this directly. A ground and brushed surface has a different oxide nucleation behaviour from a pickled one: it is smoother, it oxidises more evenly, and it spalls less in thermal cycling. On a radiant tube or a furnace liner that is cycled, a brushed finish can extend service life because the scale stays attached rather than flaking and exposing fresh metal to repeat oxidation.

What 310S is not good at: sulphur bearing atmospheres, where it suffers sulphidation, and chloride environments, where it is no better than 304 despite the higher alloy content. It is also expensive, and buying it for a part that only reaches 600 C is money wasted.

316: the corrosion case

316 and 316L at hot rolled thickness are used where the environment needs molybdenum and the section needs to be thick: chemical plant linings, tank shells, ductwork in a corrosive atmosphere, marine structures, and architectural soffits where a heavier section is specified for rigidity or fire performance.

At 6 mm and above, the low carbon version matters. A 316 plate welded into a tank shell will cool slowly enough that chromium carbides can precipitate in the heat affected zone unless the carbon is held at or below 0.03 percent. That is the whole reason 316L exists, and at plate thickness the distinction is not cosmetic.

Specification

Note the practical limit: above about 12 mm, a uniform hairline becomes difficult because the grinding head cannot follow a plate with a wider thickness tolerance without leaving waves. For thickness above 12 mm we normally quote a ground finish rather than a true hairline, and say so in the offer.

Grain direction, and why it is specified

A brushed surface has a direction. On a wall panel the convention is a vertical grain, so that water runs down along the grain rather than crossing it and so that the reflection lines read as vertical. On a horizontal surface such as a counter or a soffit, the grain usually runs along the long dimension.

Getting this wrong is a visible, expensive mistake, because the panels cannot be re oriented after fabrication if they have been cut with a grain direction. State the direction on the drawing, and mark the sheets on delivery so the fabricator does not mix them.

Fabrication and care

• Grinding and brushing generate heat; on 310S keep the surface cool to avoid local oxidation that will later read as a stain.
• Use dedicated stainless abrasives. A disc that has been used on carbon steel embeds iron and produces rust spots within weeks.
• After any welding, pickle and passivate the weld zone. A brushed surface next to an untreated weld will show a rust streak that runs with the grain.
• Clean with a neutral detergent. Chlorinated cleaners on 316 at elevated temperature are a stress corrosion risk.

Frequently asked questions

Can you supply 310S hairline in 20 mm?
Normally as a ground finish rather than a true hairline, because of thickness tolerance. Send the application and we will propose.

What is the maximum service temperature of 310S?
About 1100 C in continuous service, lower under thermal cycling or in sulphur bearing gas.

Is the grain direction guaranteed?
Yes, if it is stated on the order. Default is along the length.

Do you supply cut to size panels?
Yes, to a cutting list, with the grain direction marked on each piece.