This product group includes a wide variety of alloys, e.g. soft magnetic iron-cobalt alloys for applications in solenoid control valves, but also iron-nickel (cobalt) alloys with temperature-dependent, low thermal expansion for use in measurement and control technology, for metal-glass connections and thermobimetals as well as alloys with shape memory.
Soft magnetic steels react to even weak magnetic fields with high polarisation. This is characterised by a narrow hysteresis curve with low coercive field strength Hc and high saturation polarisation Js. Typical materials with such properties are pure iron, FeNi and FeCo alloys for use in switching relays and as magnetic cores in measuring and control devices.
Alloys based on Fe-Ni can be used to set very different coefficients of thermal expansion. By varying the Ni content and adding Co and Cr, an approximation to the coefficient of thermal expansion of other materials can be achieved. Low thermal expansion is required for master measures, measuring tapes, balance beams and measuring instruments. Some alloys exhibit a thermal expansion comparable to that of glass and are used as electrical current feedthroughs, e.g. in light bulbs
Alloys with low thermal expansion can be positively bonded to materials with greater thermal expansion, resulting in thermobimetals for thermometers and temperature controllers.
Certain alloy systems, e.g. Fe-Ni-Co alloys with martensitic transformation, exhibit a certain temperature-dependent shape memory and can be used as actuators in control systems, for example.
Fe-Ni alloys with other alloying elements, e.g. Cr or Mo, exhibit a largely temperature-independent modulus of elasticity and are used as balance springs in watches, springs in spring balances and elements in load cells.