that Haynes had already registered one. Brearley and Haynes pooled their funding and, with a group of investors, formed the American Stainless Steel Corporation, with headquarters in Pittsburgh, Pennsylvania. Rustless steel Brearley initially called his new alloy "rustless steel". The alloy was sold in the US under different brand names like "Allegheny metal" and "Nirosta steel". Even within the metallurgy industry, the name remained unsettled; in 1921, one trade journal called it "unstainable steel". Brearley worked with a local cutlery manufacturer, who gave it the name "stainless steel". As late as 1932, Ford Motor Company continued calling the alloy rustless steel in automobile promotional materials. In 1929, before the Great Depression, over 25,000 tons of stainless steel were manufactured and sold in the US annually. Major technological advances in the 1950s and 1960s allowed the production of large tonnages at an affordable cost: AOD process (argon oxygen decarburization), for the removal of carbon and sulfur Continuous casting and hot strip rolling The Z-Mill, or Sendzimir cold rolling mill The Creusot-Loire Uddeholm (CLU) and related processes which use steam instead of some or all of the argon Types There are five main families, which are primarily classified by their crystalline structure: austenitic, ferritic, martensitic, duplex, and precipitation hardening. Austenitic Austenitic stainless steel is the largest family of stainless steels, making up about two-thirds of all stainless steel production. They possess an austenitic microstructure, which is a face-centered cubic crystal structure. This microstructure is achieved by alloying steel with sufficient nickel and/or manganese and nitrogen to maintain an austenitic microstructure at all temperatures, ranging from the cryogenic region to the melting point. Thus, austenitic stainless steels are not hardenable by heat treatment since they possess the same microstructure at all temperatures. Austenitic stainless steels sub-groups, 200 series and 300 series: 200 series are chromium-manganese-nickel alloys that maximize the use of manganese and nitrogen to minimize the use of nickel. Due to their nitrogen addition, they possess approximately 50% higher yield strength than 300 series stainless sheets of steel. Type 201 is hardenable through cold working. Type 202 is a general-purpose stainless steel. Decreasing nickel content and increasing manganese results in weak corrosion resistance. 300 series are chromium-nickel alloys that achieve their austenitic microstructure almost exclusively by nickel alloying; some very highly alloyed grades include some nitrogen to reduce nickel requirements. 300 series is the largest group and the most widely used. Type