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Stainless Steel Types and Properties

Chromium is the key ingredient in stainless steel

Stainless steel mill finishes

Stainless steel is first rolled to size and thickness and then annealed. Standard mill finishes are applied directly by the rollers and/or later with abrasives.

  • No. 0 - Hot Rolled Annealed, thicker plates
  • No. 1 - Hot rolled, annealed and passivated
  • No, 2D - Cold rolled, annealed, pickled and passivated
  • No, 2B - Cold rolled, annealed, pickled and passivated, with an additional pass through polished rollers
  • No, 2BA - Bright Anealed (BA) same as above with highly polished rollers
  • No. 3 - Coarse abrasive finish
  • No. 4 - Fine abrasive finish
  • No. 6 - Matte finish
  • No. 7 - Reflective finish
  • No. 8 - Mirror finish

Adding more than 12% chromium, by weight, to certain iron-alloys results in the formation of a non-corrosive oxide, a "passive film," which serves as a protective barrier between the steel and its environment. This passive film keeps the steel shiny and will re-form if the steel is scratched. Adding various elements to the alloy result in different properties. Nickel is added for better corrosion resistance, ductility and weldability. Molybdenum is added to resist pitting. Carbon is added for higher strength and hardness. Aluminum and silicon are added for improved oxidation reststance.

Austenitic (non heat treatable) stainless steel grades

The austenitic grades, known as the 300 series are iron-nickel-chromium composites. They are non-magnetic in the annealed state and are non-heat treatable. They can be hardened by cold-working only. The retain their austenitic structure at all temperatures and are generally the most weldable stainless steels. Here are some of the more common types in the 300 series.

Martensitic (heat treatable) stainless steel grades

The Martensitic grades are strong, highly machinable, heat-treatable, and magnetic, but are not as corrosion reststant as the 300 series stainless steels. They are often used in bearings and cutlery. Here are some of the more common types.

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