Lecture 5: Carbon and Low Alloy Steel

Carbon and Low Alloy Steel The most widely used materials in power-producing systems including nuclear are the steels, which are basically alloys of iron and carbon but which may also contain o...

Carbon and Low Alloy Steel The most widely used materials in power-producing systems including nuclear are the steels, which are basically alloys of iron and carbon but which may also contain other metals as minor or major alloying elements. The alloying elements impart desired properties such as strength, hardness or corrosion resistance to the steel. 1 Nuclear Power Plants Materials Map 2 3 4 5 6 7 8 9 10 11 12 Alloying elements Metals other than iron may be added to steel to impart desired mechanical properties or corrosion resistance - particularly useful for service at high temperature. The atoms of alloying metals are generally in substitutional solid solution, If the metal addition is less than 5 % what is commonly called a low-alloy steel results, while additions greater than 5 % produce the intermediate and high-alloy steels. The plain carbon steels often contain small amounts of elements such as manganese, phosphorus or sulphur - generally less than 1 % - as residuals from the steelmaking process or added. Manganese in particular can impart desirable mechanical properties to steel and in fact may be added deliberately to form low-alloy manganese steel with a marked resistance to wear. 13  Plain carbon steel and manganese steel are used extensively for general construction steelwork in power systems and in non-nuclear boiler construction for tubing and components that experience temperatures below about 500°C. They are also employed in the secondary or steam-raising systems of nuclear power plants and constitute a major proportion of the piping in the primary coolant systems of heavy water reactors such as the APR 1400 and CANDU reactor, which operate below about 320°C. As the service temperature increases the amount of alloying is necessarily increased to impart resistance to creep and scaling. 14 15 16 17 18 19 20 21 22 23 24 25