There are many stainless steel finishes for option, from mill finishes to further process finishes, these finishes have special surface appearance, smooth and bright surface will enhance long life usage and performance, different finishes has unique appearance of surface, knowing these finishes can help you choose right type for your application.
Stainless Steel Finishes
Stainless Steel Introduction
Stainless steel is an alloy group having special properties, they must contain minimum 10.5 Chromium content, that is necessary element to form stainless steel, stainless steel have Chromium film on the surface to resist corrosion, with addition of other elements, increasing the material properties make they have a wide range used for many applications.
Stainless steel is categorized in five groups, Austenitic, Ferritic, Martensitic, Duplex and Precipitation-hardening stainless steel.
Stainless Steel Finishes
There are many different finishes on stainless steel, some finishes generate from mill, like 2B finish, some can be achieved from fabrication process, main finishes include polished, brushed, blasted, etched and coloured finishes.
These finishes for sheet are stated conforming to ASTM A480.
|NO.1||Hot rolled, annealed, pickled, dull non reflective finish|
|NO.2D||Cold rolled, annealed, pickled, smooth non reflective finish|
|NO.2B||Cold rolled, annealed, pickled, smooth reflective finish, the most wide used finish|
|BA||Smooth, bright, reflective finish by annealing in the controlled atmosphere furnace|
|NO.3||non reflective finish, light polishing using grinding belt, 100 – 120 grit|
|NO.4||Reflective dull polishing, brushed finish, using 120 – 320 grit belt after light grinding|
|NO.6||Cold rolled, dull satin finish by tampico brushing a No.4 finish|
|NO.7||High reflective finish, by a finely ground surface, 320 grit is buffed|
|NO.8||High reflective, bright polishing, smooth surface, mirror finish|
|TR||Cold worked to obtain a specified properties|
Whether hot finishes or cold finishes, mill finishes are the basic surface of stainless steel flat products, without additional processing, hot rolled finishes are usually dark and dull surface, when in heat treated and hot rolling condition, mill finishes surface is pickled to remove scale.
2B is typical cold rolling, smooth surface, light reflective mill finish, heat treated, it is the most widely used finish, 2B finish is basic surface condition for many other polished finishes,
For welded tube production, it usually starts from 2B finish strip.
Mechanically process is common method to polish stainless steel, it is a rolling procedure using finer abrasives, this process can remove surface defects to achieve consistent surface quality, not only having a bright appearance but also resisting corrosion, wet and dry polishing types are available,
Mirror finishes are highly reflective surface by polishing, creating mirror like appearance.
Brushed finish has strong decorative surface, and not too reflective, it is one of the most popular finishes available, particularly kitchen appliances, there is light groove on the surface of stainless steel, so it is not suitable used corrosion environment, because this finish may lead to corrosion attack, it is applied in ornamental purpose in the most case.
Stainless Steel Finishes, Grit and Roughness
Metal surface roughness is measured using special means, Ra is a roughness unit, roughness of different finishes has different values.
There is no standard to specify stainless steel finishes relation with roughness value （Ra, in practice, they have roughly conversion.
|Common Name||Ra (µm)||Grit Number||USA Finish|
|Satin Sheet||1.75 max, 1-1.5||80||#2|
|1.3||100 to 120||#3|
|Sanitary/Dairy Finish||1.05 max, 0.75-0.875||150||#4|
|3A Sanitary Finish||0.8 max, 0.5-0.8||180||#4|
|Biotech Finish||0.625 max, 0.5-0.625||200 to 220||#4|
|Fine Satin Finish||0.375-0.5||240||#6|
|Semi-Bright Finish||0.3 max, 0.2-0.3||320||#7|
|Supermirror Finish||<0.1, 0.075-0.2||500||#8|