ISSN (print) 1995-2732
ISSN (online) 2412-9003




Problem Statement (Relevance): The article focuses on the peculiarities of the thermal expansion of Fe-Ni-C invars alloyed with vanadium and molybdenum. The addition of carbon and strong carbide-forming elements can result in invars of higher strength compared with conventional invars due to the hardening effect produced by carbides. At the same time the coefficient of thermal expansion (CTE) of such invars remains low, which significantly expands the application scope of high-strength alloys within the precision instrument domain. Objectives: This research aimsto study the effect of heat treatment on the CTE of the Fe-Ni-C-V (32NF) and Fe-Ni-C-V-Mo (34NFM) invars. Methods Applied: The research involved physical modelling of heat treatment processes, dilatometry and the CTE determination realized with the Pocket Jaw module within Gleeble 3500. The samples used were 10 mm in diameter and 80 mm in length. As part of the heat treatment process, the samples were quenched in water with the start temperatures of 1200 and 1250 °C, which enabled the solid solution to be saturated with carbon and carbide-forming elements. After that the quenched samples were heated to 700 °C to induce the decomposition of the supersaturated solid solution. Originality: The study helped identify the patterns of changing CTE in the Fe-Ni-C-V and Fe-Ni-C-V-Mo invars as a result of heat treatment. Findings: The CTE values were determined for different heat treatment scenarios. It was found that the above alloys showed the lowest CTE values (for 32NF α30–150 = 1.26·10–6К–1; for 34NFM α30–150 = 2.14·10–6К–1) after they were quenched in water with the start temperature of 1250 °C and heated to 700 °C and soaked at this temperature for one hour. Practical Relevance: The study proved that the heat treatment of invars results in the lowest CTE values (0.5 × 10-6 to 3.0 × 10-6 K-1) which meet the high-strength industrial invar specification requirements.


High-strength invars, heat treatment, dilatometry, coefficient of thermal expansion.


Natalia V. Koptseva – D.Sc. (Eng.), Professor Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Dmitry M. Chukin – Ph.D. Student Nosov Magnitogorsk State Technical University, Magnitogorsk, Russia. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Manuele Dabala – Associate Professor Industrial Engineering Department, University of Padua, Padua, Italy. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

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