Classification of Stainless Steel Grades

Stainless steel can be classified into five major categories: coil, sheet, structural sections, pipes, and fabricated components. Among these, coil and sheet are the most important.

Structural profiles are materials of various shapes manufactured from sheet metal, including angle steel, flat bar, I-beam, and channel steel.

Steel pipes primarily refer to seamless steel pipes, as opposed to welded steel pipes. The key difference between the two lies in whether they are formed in a single step.

Components primarily refer to small parts such as elbows and flanges.

Coil stock and sheet stock are essentially the same; the difference lies in their form as processed at the factory: coil stock is supplied in rolls, while sheet stock is supplied in sheets. At the point of manufacture, both are classified as sheet stock, also referred to as “raw sheets.” Due to their relatively greater thickness, they are typically thick plates; if the thickness exceeds 16 millimeters, they generally can no longer be rolled into coils.

There are both roll‑form and sheet‑form materials, with sheets being the more common type. The pricing for rolls and sheets also differs: rolls are billed based on actual weight, resulting in a higher price, whereas sheets are priced according to theoretical dimensions, making them relatively cheaper. This price disparity arises because of inherent tolerances—for example, a nominal thickness of 10 mm may measure only 9.6 mm in practice, leading to a corresponding price difference.

Stainless steel sheets are classified into hot-rolled and cold-rolled grades, depending on the rolling process employed by the mill (a mill is equipment used for sheet rolling).

Hot-rolled steel is typically designated as NO.1, while cold-rolled steel is marked as 2B or BA (with BA having a smoother, brighter surface that closely resembles a mirror finish; among these, BA offers the best mirror effect, though sheets in this condition are not commonly stocked and require further processing). For example, 304 stainless steel sheet is often purchased in this form, meaning the material must be passed through a specialized leveling machine to achieve a flat, plate‑like shape—this equipment is known as a leveler.

It can be uncoiled to various lengths using a leveling machine. When the length is non‑standard, it is referred to as fixed‑length uncoiling, meaning the coil’s dimensions are predetermined, as customers often specify different lengths based on their specific requirements. In such cases, coiled material becomes particularly critical, and conventional sheet stock can no longer meet the corresponding needs.

Domestically produced cold-rolled sheet typically has a thickness of 3 mm or less, while hot-rolled sheet generally exceeds 3 mm. A thickness of 3 mm may refer to either hot-rolled or cold-rolled sheet; in contrast, imported cold-rolled sheet can be as thin as below 4 mm, and in some cases even below 6 mm.

Hot-rolled steel plates with thicknesses ranging from 3 mm to 12 mm are referred to as medium‑thick plates, while those exceeding 12 mm in thickness are classified as thick plates. Some may even surpass 120 mm in thickness and are accordingly called hot‑rolled medium‑thick plates; by contrast, cold‑rolled steel sheets are known as cold‑rolled thin sheets.