Stainless steels are alloys of iron base metals, highly resistant to acids, except sulfuric and hydrochloric acids. They are also resistant to oxidation and scaling at high temperatures and retain their physical properties well under heat. Stainless steels are used in the chemical, oil, dairy, food, paper and other industries requiring material with unusual resistance to corrosion and heat. The stainless steels are supplied in plates, sheets, bars, strip, tubing, bolts, nuts, rivets, and wire, and can be rolled, drawn, formed, or worked into almost any specific shape or apparatus, merely by following the correct procedure for the particular alloy at hand.
Usually, the resistance of stainless steels to corrosive attack is primarily due to chromium content, which is 10%or higher in most types of stainless steel. Nickel is also used as an alloying element, ranging in content from 2 to 35%. Consequently the stainless
steels are grouped into two main categories: straight chromium (or nearly so) and chromium-nickel (with the remainder essentially iron).
The straight chromium alloys contain about 12% chromium. Various others contain chromium in increasing amounts, but the majority are the austenitic class, consisting of iron alloyed with about 18% chromium and 8% or more of nickel.
In addition to the recognized corrosion resistance, certain types of stainless steels have a number of other useful properties, such as toughness at sub-zero temperatures, good strength at elevated temperatures, and the ability to remain nonmagnetic under a variety of conditions. Some alloys are hardened by simple, low temperature precipitation heat treatments, thus avoiding quenching operations. The reasons for selecting a stainless steel must justify its higher cost. However, when all aspects of fabricating, treating, and service performance are considered, stainless steel components are often incorporated in many kinds of welded construction.
Stainless steels in the form of castings have been given designations and composition limits by the Alloy Casting Institute (ACI), a division of Steel Founders Society of America (SFSA). Reference: Linnert, George E, Welding Metallurgy, Vol. 1, 4th Edition. American Welding Society, Miami, Florida. 1994.