The temperature coefficient of linear expansion (TCLR) is a characteristic that indicates how many times the linear dimensions or volume of the product will change with a constant pressure and an increase in temperature by 1°C. For steels with a given TCLR, this value is regulated, which makes it possible to accurately calculate the linear dimensions of parts made of precision alloys when used in certain temperature conditions.
Precision alloys with a given TKLR are divided into groups according to their magnetic properties: ferromagnetic metals and non-magnetic steels. Within groups, they are divided into subgroups according to the value of TCPR.
Ferromagnetic materials:
Non-magnetic alloys:
Regardless of TCLR, all precision non-magnetic materials are highly elastic and resistant to mechanical stress.
The main factors that affect the characteristics of alloys with a given TCLR are their chemical composition and production technology. To achieve the required temperature coefficient, tungsten, beryllium, cobalt, copper, titanium, manganese, chromium, aluminum, vanadium or molybdenum are added to the base metals.
The concentration of alloying elements directly affects the temperature coefficient of linear expansion. For example, copper and cobalt increase the temperature range of TCPR stability, while chromium, on the contrary, reduces it.
The required value of the coefficient in ferromagnetic steels is achieved by reducing or increasing the amount of nickel in the alloy. For example, invar, an iron-nickel alloy with a nickel content of 35-36% (36H steel), has an operating temperature range of −100... +100°C. Increasing the amount of nickel to 42% results in platinite (42H alloy), which retains its properties at temperatures as early as 300°C.
When manufacturing alloys with low TCLR, one of the post-processing methods is used to stabilize parameters over time:
In the production of metals with higher coefficients, hardening is used at 1,100... 1,150°C, followed by cooling in water. Annealing can also be used at temperatures up to 1,050°C.
Alloys with a specified temperature coefficient are produced in the form of a rod, wire, cold-rolled strip, strip and pipe.
The development of new precision alloys with specified thermal properties has had a high impact on the development of technologies in the field of radio and cryogenic engineering, as well as quantum electronics. Where even the minimal influence of magnetic fields of ferromagnetic materials was unacceptable, non-magnetic metals with minimal TCLR were widely used: steel grades 72TF, 75TM, 75NM-VI, 76NHVG93CT, 80NMV, 80HMBX3, 95HC and 96X.
Non-magnetic precision alloys with high TCLR (56DGNH, 70GNDH) are used in the manufacture of thermal bimetals.
Ferromagnetic materials with a minimum temperature coefficient are used in meteorology, geodesy, and in the construction of potentially dangerous pipelines.
Low and medium TCLR alloys are used for adhesion to ceramics and glass. For example, material such as Kovar (29NK) is manufactured on St. Petersburg Precision Alloy Plant in the form of a cold-rolled strip. It is used for vacuum-tight joints in metal-glass and metal-ceramic structures in the manufacture of parts for aircraft and space satellites.
