Austenitic Steels
Austenitic steels are steels which have been alloyed with a range of different alloying elements to make them suitable for use in a variety of critical applications such as jet engines, ships, nuclear power plants and cryogenic applications. Austenitic steels are among the most widely used alloys in engineering applications. This is due to their combination of corrosion resistance, strength, workability, weldability and ductility which allow them to be used in the most demanding of environments.
The metallurgical classification of Austenitic Steels is that of the particular alloying elements which have been added. These alloying elements are titanium, chromium, nickel and molybdenum. In general, it is unalloyed or low alloy Austenitic Steels which contain 0.1-2.0% of alloying elements; medium and high alloy Austenitic Steels contain 2-10% of alloying elements; and super alloys Austenitic Steels contain >10% of alloying elements.
The chemical composition of Austenitic Steels is very important in order to identify the suitability of the type of Austenitic Steel for a given application. The austenitic compositions can range from as low as 0.08% Carbon and 17.5-19.5% Chromium up to as much as 8% Carbon and 26-30% Chromium. This can range further in the case of specific alloys, with some super alloys containing up to 35% Chromium and 7.5-8.5% Nickel. There can also be other additional elements present, such as Molybdenum, Titanium and Manganese, depending on the particular alloy used.
In order to determine the composition of an Austenitic Steel, a specific heat treatment procedure must be followed. For example, a sample is first heated to a specified temperature, and then maintained at that temperature for a period of time in order for the alloying elements to be accurately determined. It is at this point that the composition can be measured via a process known as “fusion analysis”. This involves melting a sample of the steel, and then analyzing the metal droplets which are produced. This is done by measuring the melting point of each metal particle, and then comparing this to reference values in order to determine the corresponding metal content of the sample. The results of the fusion analysis will then be used to determine the exact proportions of the different alloying elements present, as well as whether or not the alloy meets the specifications required for the particular application in question.
Austenitic Steels are widely used in many critical applications due to their excellent mechanical properties, corrosion resistance and weldability. The composition of the alloys can be tailored to achieve optimum performance in a given application. In order to accurately determine the composition of the Austenitic Steels, a fusion analysis process should be used. This will give an accurate description of the metal content of the steel, and allow for the selection of the particular alloy for the given application.
