Heat Resistant Steels...

Heat Resistant Steels The properties of steel and its yield strength considerably decrease as the steel absorbs heat when exposed to high temperatures. Heat resistance means that the steel is resistant to scaling at temperatures higher than 500 deg C.  Heat resistant steels are meant for use at temperatures higher than 500 deg C since they have got good strength at this temperature and are particularly resistant to short and long term exposure to hot gases and combustion products at temperature higher than 500 deg C. These steels are solid solution strengthened alloy steels. As these steels are used over a certain broad temperature ranges, these steels are usually strengthened by hard mechanism of heat treatment, solid solution and precipitation. All the heat resistant steels are composed of several alloying elements for the purpose of achieving the desired properties and are used in applications where resistance to increased temperatures is critical. The level of the heat resistance of the heat resistant steels depends on the environment conditions in which they operate and cannot be characterized by a single testing method. Maximum service temperatures which can be extended to 1150 deg C depending on the alloy content can be severely reduced by the presence of some compounds such as sulphurous compounds, water vapour or ash. Resistance to molten metal and slag is also limited in these steels. In heat resistant steels, the two most important elements are chromium for oxidation resistance and nickel for strength and ductility. Other elements are added to improve these high temperature properties. The effect of various alloying elements is described below. Chromium – Chromium is the one element which is present in all the heat resistant steels. Besides imparting oxidation resistance, chromium adds to high temperature strength and carburization resistance. Chromium...