Stainless steel 4B finish specifications

A. There is no relationship between a #4 (dairy) finish and a 4B mill finish. The #4 finish is a ground finish. There is little agreement on what it should look like and you will rarely find two #4 finishes that look or feel the same though the surface roughness numbers (Ra's) will be broadly similar. A 4B mill finish is produced by rolling the sheets of stainless steel between polished rollers. It commonly has a slightly matte or frosted appearance. The surface is usually very smooth but the Ra's can be all over the place and still meet the spec.. I did a survey of mills a few years back and got readings from 8 to 28 Ra. We most commonly see Ra's in the range of 8 to 20. Is there a 4A finish? It seems logically consistent but I must confess, I don't know.

A. To the best of my understanding there is no 4B finish.

Over time people have somehow combined a 2B and a #4 finish.And incorrectly called it a 4B finish.

Most of the time when referring to a 4B finish they actually want a #4 finish.

Sometimes however when referring to a 4B finish they want a #2B finish.

Its best to talk to them so you understand what they want.

Check out "Wikipedia" under "stainless steel finishes"
it list and explains industry standard finishes.

A. The previous response is correct. There is no "4B" finish recognized by ASTM and a colleague confirmed that there is no industry specific 4B. The relevant ASTM standard for stainless steel sheet and strip finishes is ASTM A480. Another potential source of confusion is that the Europeans and Japanese have two No. 4 finishes. The difference between them is surface roughness and surface roughness maximums are not uncommon in industry.

A. I do not understand why we call it 4B Finish as it is not mentioned in any Technical Standards Books related to Stainless Steel Surface Finish. If any such Code is available let me Know. But as far as I understand no such Code called 4B Finish exists.

Can anybody explain me with details about 4B Finish with Photograph?

A. The web site below gives an explanation of a "4B Dairy Finish":
www.arcabrasives.com/Metals/Stainless.html

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Ed. note: July 2018. Although that page is now gone, you can view it courtesy of the Internet Archive:
https://web.archive.org/web/20170228045231/http://arcabrasives.com/Metals/Stainless.html

A. Hi G.G.
Can we assume you are speaking of stainless steel railings?

A "mill finish" means no finishing after rolling at the steel mill. It's probably somewhat smooth from rolling, but few guarantees about anything. A 180-grit finish is probably a scratch-brush finish from passing through a machine which scratches it with an endless belt of 180-grit sandpaper.

The extra operation probably costs some amount of money. But you ought to be able to see samples rather than buying a pig in a poke. Good luck.

Regards,