All metals have different mechanical properties at different temperatures. Fracture toughness and strength are especially effected. Bumax fasteners can be custom made and, dependent on grade, handle operating temperatures between -200°C to 800°C.
It is important to understand what happens with the fastener material when operating at elevated temperatures for prolonged times. Properties such as thermal expansion, strength, ductility, corrosion resistance and fatigue resistance are affected by high temperatures and its effect on the jointed application must be considered from case to case. Property changes during prolonged service at elevated temperature must also be considered. Gas corrosion at high temperature is totally different compared to wet corrosion at lower temperatures. Furthermore, changes in mechanical properties might gradually change over time due to ageing and creep deformation. Ageing that occurs in all stainless steel material over time is enhanced by high stresses in the material in combination with high temperature or temperature fluctuations, and can lead to ductility losses in the material. Creep deformation is a slow plastic deformation under the influence of mechanical stresses. It can occur as a result of long-term exposure to stresses that are still under the yield strength of the material and the effect increases at higher temperatures. Bumax HE and Bumax HEP are high temperature resistant grades optimized for high temperature conditions and are much more stable against ageing, gas oxidation, creeping and strength losses compared to regular stainless steels.
An increased brittleness at subzero and especially cryogenic temperatures is characteristic of all steels and metals in general. Some steel grades become more brittle than others at cryogenic temperatures below -150°C. This depends mainly on microstructure, chemical composition and internal stress. Austenitc stainless steels has generally better impact strength at very low temperatures than Duplex, Ferritic and Martensitic stainless steel.
To understand the environment and application requirements is therefore crucial. Data about strength losses at elevated temperature, creep resistanceand high temperature corrosion are available on request. Your local Bumax sales representative will help you selecting the right material.
Only the special high temperature resistant grades Bumax HE and Bumax HEP are recomended for prolonged usage at temperatures above 300°C.
|Grade||Thermal expansion, mean values in temperature ranges (x10^-6) per °C|
|20 to 100ºC||20 to 200ºC||20 to 300ºC||20 to 400ºC||20 to 500ºC||20 to 600ºC|