Heat-resistant steels are widely used for casting of components for many industries such as the oil and gas, petrochemical and power generation. The properties of these steels provide them with good thermal and oxidation resistance to high temperature environments, coupled with good strength and high hardness.
The mechanical properties of heat-resistant steels depend on their composition and heat treatment. They usually consist of a combination of chromium, nickel and molybdenum as the main alloying elements, with additional elements such as manganese, silicon, aluminium and titanium added. The main purpose of this alloying is to improve the oxidation and creep resistance, as well as forming an austenite matrix. The greater the amount of chromium, the better the oxidation and creep resistance, the addition of nickel increases the strength of the material and molybdenum helps with the hardening of the steels.
Heat treatments are necessary to obtain the required mechanical properties. These include solution heat treatment, which is performed to stabilise the as cast microstructure, followed by hardening treatments such as quenching and tempering. The temperature and duration of the heat treatments will depend on the properties required of the castings.
The application of heat-resistant steels for casting can provide components with good oxidation and creep resistance, and improved strength and high hardness. The alloying and heat treatment of these steels is of particular importance for their performance in service.
Heat-resistant steels are used for a number of purposes in a number of industries. In the oil and gas industry, the high-temperature resistance and strength of the steels allow them to be used in wellhead equipment, downhole tubing and other components exposed to high temperatures. The steels are also used extensively in petrochemical plants, power generation and the nuclear industry.
Heat-resistant steels are available in a variety of shapes and sizes, with most found in cast form. The selection of the grade of steel will depend on the operating temperature of the component. Higher-alloyed grades with improved high-temperature creep resistance are normally selected for components exposed to higher operating temperatures.
Heat-resistant steels can provide good thermal and oxidation resistance, coupled with good strength and high hardness. The alloying elements, along with the heat treatments applied, are of particular importance for their application in service. Careful consideration needs to be given to select the correct grade of steel for specific applications.
