Austenitic Stainless Steels...

Austenitic Stainless Steels Austenitic stainless steels are the most common and widely known types of stainless steels. They make up over 70 % of total stainless steel production. These steels contain around 16 % to 25 % chromium and sufficient nickel and/or manganese to retain an austenitic structure at all temperatures from cryogenic region to the melting point of the stainless steel. Austenitic stainless steels can also contain nitrogen in solution.  Although nickel is the alloying element most commonly used to produce austenitic stainless steels, nitrogen can also be used to produce austenitic stainless steels. The austenitic stainless steels are more easily recognized because of their non magnetic properties. Austenitic steels are non magnetic since the face centered cubic structure of austenite is non magnetic. They are extremely formable and weldable, and they can be successfully used from cryogenic temperatures to the jet engines and red hot temperatures of furnaces. The austenitic stainless steels can have compositions anywhere in the portion of the Schaeffer- Delong diagram labeled austenite shown in Fig. 1. Fig 1 Schaeffer- Delong diagram The family of austenitic stainless steels is shown in Fig 2. Fig 2 Family of austenitic stainless steels Austenitic stainless steels are mainly segregated into the following two series 200 series – Stainless steels with a low nickel and high nitrogen content are classified as 200 series. These are chromium-nickel-manganese austenitic stainless steels. Grade 201 is hardenable through cold working while the grade 202 is a general purpose stainless steel. Decreasing nickel content and increasing manganese results in weak corrosion resistance. 300 Series – The most common austenitic stainless steels are iron-chromium-nickel steels and are widely known as the 300 series. In this series the most widely used austenitic stainless steel is the grade 304, also known...

Austenitic Manganese Steel...

Austenitic Manganese Steel The first austenitic manganese steel was developed in 1882 by Robert Abbott Hadfield. Hadfield had done a series of test with adding ferro-manganese containing 80 % manganese and 7 % carbon to decarbonised iron. Increasing manganese and carbon contents led to increasing brittleness up to 7.5 % manganese. At manganese contents above 10 % however, the steel became remarkably tough. The toughness increased by heating the steel to 1000 deg C followed by water quenching, a treatment that would render carbon steel very brittle. The alloy introduced commercially contained 1.2 % carbon (C) and 12 % manganese (Mn) in a ratio of 1:10. This composition is used even today, and the austenitic manganese steel is still known as Hadfield steel. The steel was unique since it exhibited high toughness, high ductility, high work hardening ability and excellent wear resistance. Because of these properties Hadfield’s austenitic manganese steel (AMS) gained rapid acceptance as a useful engineering material. Austenitic manganese steels have a proven high resistance to abrasive wear including blows and metal-to-metal wear, even though they have a low initial hardness. These steels are supposed to work harden under use and thus give a hard wear resistant surface, but it has been reported that these steels have a good wear resistance in components even without heavy mechanical deformation. Hadfield`s austenitic manganese steel is still used extensively, with minor modifications in composition and heat treatment, primarily in the fields of earthmoving, mining, quarrying, oil well drilling, steelmaking, railroading, dredging, lumbering, and in the manufacture of cement and clay products. Austenitic manganese steel is used in equipment for handling and processing earthen materials (such as rock crushers, grinding mills, dredge buckets, power shovel buckets and teeth, and pumps for handling gravel and rocks). Other...

Stainless steels

                         Stainless steels  Stainless steel is a family of alloys of iron that contains at least 10.5% Chromium and a maximum of 1.2 % carbon which is essential of ensuring formation of a self healing surface passive layer. This passive layer provides the corrosion resistance. These characteristics make stainless steels totally different from mild steels. The stainless steel was discovered between 1900 and 1915. In 1904, Leon Guillet discovered alloys with composition similar to steel grades 410, 420, 442, 446 and 440-C. In 1906 he also discovered an iron-nickel-chromium alloy which was similar to the 300 series of stainless steel. In 1909 Giesen researched on the chromium-nickel (austenitic 300 series) stainless steels. In Germany, in 1908, Monnartz & Borchers found that a relationship exists between a minimum level of chromium (10.5%) on corrosion resistance as well as the importance of low carbon content and the role of molybdenum in increasing corrosion resistance to chlorides.  Stainless steel production process Stainless steel is produced in an electric arc furnace where carbon electrodes contact recycled stainless scrap and various alloys of chromium, nickel and molybdenum etc. depending on the type of stainless steel. A current is passed through the electrode and the temperature increases to a point where the scrap and alloys melt. The liquid steel can also be produced in LD converter using hot metal as a major input material. The liquid steel from the electric arc furnace or LD converter is then transferred into an AOD (Argon Oxygen Decarbonization) converter, where the carbon levels are reduced and the final alloy additions are carried out to achieve the desired chemistry.  The liquid steel is either cast into ingots or continually cast into slabs or billets. The slabs or billets are either hot rolled or forged into...