Heat-resisting steels have special resistance, e.g. to the effects of gases and combustion products at temperatures above 550°C [1022.0°F]. The most important alloying element is chromium. Silicon and Aluminium also increase the resistance to scaling. The main areas of application are furnace construction and the cement and ceramics industries.
Steels are considered heat-resistant if they have good mechanical properties under short- and long-term stress and are particularly resistant to the effects of hot gases and combustion products as well as molten salts and metals at temperatures of approximately above 550°C. However, their resistance is very much dependent on the attack conditions and can therefore not be characterised exactly by values obtained in a single test method. At temperatures above 550°C, a reaction occurs between the steel surface and the gas atmosphere, during which oxide layers, the scale, are formed. While the affinity of the reaction partners plays a decisive role at the beginning of the scale formation, this process is subsequently influenced by diffusion and inhibited by special alloying elements if the adhesion and tightness of the scale layer is sufficient.
This is mainly achieved by the oxides of the alloying element chromium. Silicon and aluminium also increase the scale resistance.
A distinction is made between ferritic, ferritic-austenitic and austenitic steels; the ferritic and ferritic-austenitic steels are magnetisable, the austenitic steels are not.
The highest temperature stress in air up to about 1150°C can be achieved with special ferritic and austenitic heat-resistant steels. The highest resistance in sulphurous gases is achieved with ferritic steels. Austenitic steel types achieve the highest resistance in nitrogen and oxygen containing gases. Austenitic heat-resistant steels are more suitable for welding than ferritic and ferritic-austenitic steel types. For some steel types with particularly high chromium contents, there is a risk of embrittlement due to sigma phase in continuous operation in the temperature range from 600 to 850°C and due to coarse grain formation above 950°C.
Heat-resistant steels are usually melted in air.
Preferred fields of application for heat-resistant steels are furnace and boiler construction, the glass, porcelain, cement and ceramic industries, mechanical engineering, the oil and gas industry and power engineering.
Ferritic chromium-steel with additions of aluminium, good machineability and high temperature strength as well as scale resistant up to 800°C. Corrosion resistant in hot oxidizing and sulfuric gases and resistant to carburization. Furnace constrution and heat treatment shops.
Read MoreHeat treatment shops, Furnace and boiler construction, Glass, porcelain, enamel, cement and ceramic industries, Mechanical engineering, Petroleum industry
Read MoreBÖHLER H500RB (Alloy 800, 800HT) is an austenitic, high-temperature iron-nickel-chromium alloy with good creep rupture strength at temperatures above 600°C. This material also has good resistance in oxidising, carburising and sticking atmospheres with good workability. With a nickel content of more than 30%, this material has little tendency to precipitate sigma phase. In addition to the good mechanical long-term properties, BÖHLER H500RB is resistant to oxidation and carburisation up to approx. 1000°C. In certain temperature ranges, it shows resistance to sulphurous media. The original Alloy 800 is increasingly being replaced in the market by the variants 800H and HT. These can be solution annealed and therefore have improved creep rupture properties at high temperatures. The material BÖHLER H500RB fulfils the properties of Alloy 800 as well as Alloy 800H and 800HT by controlled contents of carbon, aluminium, titanium, silicon and manganese as well as controlled sum content of Al + Ti. In the case of Alloy 800H and HT, special solution annealing significantly increases the creep rupture strength at temperatures above 600°C.
Read MoreHeat treatment shops: Boxes and pots, muffles, retorts, crucibles and pans for all kinds of heat treatment processes. Heating cartridges and plates. Furnace and boiler construction: Grates and grate segments, fittings, conveyor components, supporting and walking beams, rams, rails, rollers, doors, gates and traps, housings, recuperators, fans, superheater suspensions, tube clamps, soot blower pipes. Glass, porcelain, enamel, cement and ceramic industries: Burner tips, rings, segments and components for rotary and lepol kilns. Mechanical engineering: Grid bars, valves and spindles, stirrer arms and teeth, sheath tubes for thermocouples, fittings, drums, bolts, nuts, rivets. Petroleum industry: Tubes und tubular components.
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