Stainless Steel - Rust and stain-resistant steel

Stainless Steel - Rust and stain-resistant steel:

The resistance of stainless steel to corrosion and staining, low maintenance, relative inexpensive and familiar luster make it an ideal base material for a host of commercial applications.Stainless steels are distinguished from carbon steel by their content of chromium and, in certain cases, nickel. Adding chromium to carbon steel makes it more rust and stain-resistant and adding nickel to chromium stainless steel enhances the mechanical properties of the steel.

Stainless steels are iron-base alloys containing Chromium. Stainless steels usually contain less than 30% Cr and more than 50% Fe. They attain their stainless characteristics because of the formation of an invisible and adherent chromium-rich oxide surface film. This oxide establishes on the surface and heals itself in the presence of oxygen. Some other alloying elements added to enhance specific characteristics include nickel, molybdenum, copper, titanium, aluminum, silicon, niobium, and nitrogen. Carbon is usually present in amounts ranging from less than 0.03% to over 1.0% in certain martensitic grades. Corrosion resistance and mechanical properties are commonly the principal factors in selecting a grade of stainless steel for a given application. The resistance of stainless steel to many corrosive factors, such as exposure to water, air, acid and alkalis, is provided by a transparent protective chromium oxide film that forms on its exterior.

Stainless steels are manufactured in different types of grade, but all types contain at least 10% chromium, along with other elements added to develop specific properties. Depending on the quantity of the various elements present in a stainless steel alloy, it has a metallurgical structure that is characteristic of one of three basic stainless steel groups – (a) Martenistic, (b) Ferritic and (c) Austenitic. There are over 150 grades of stainless steel, of which fifteen are most common. The alloy is milled into sheets, plates, bars, wire, and tubing to be used in cookware, cutlery, hardware, surgical instruments, major appliances, industrial equipment, a structural alloy in automotive and aerospace assembly and building material in skyscrapers and other large buildings.

There are a large number of stainless steels produced. Corrosion resistance, physical properties, and mechanical properties are generally among the properties considered when selecting stainless steel for an application. A more detailed list of selection criteria is listed below:

(i) Corrosion resistance;

(ii) Resistance to oxidation and sulfidation;

(iii) Toughness;

(iv) Cryogenic strength;

(v) Resistance to abrasion and erosion;

(vi) Resistance to galling and seizing;

(v) Surface finish;

(vi) Magnetic properties;

(vii) Retention of cutting edge;

(viii) Ambient strength;

(ix) Ductility;

(x) Elevated temperature strength;

(xi) Suitability for intended cleaning procedures;

(xii) Stability of properties in service;

(xiii) Thermal conductivity;

(xiv) Electrical resistivity;

(xv) Suitability for intended fabrication techniques