Shakhnazarov K.Yu. Abnomal phisical and mechanical properties of iron resultant from transformations at ~650, ~450 and ~200°C

Abstract

Problem Statement (Relevance): The need for a thorough study of the relationship between the temperature and the properties of iron is due to the following: iron is the "main" base of the "main" industrial alloys (steels); the body-centered cubic lattice characteristic of iron at low temperatures is unique and theoretically impossible, but it still exists; the heat capacity of iron «is contradictory to» Debye theory not only when it reaches Curie point (~ 770°C), but also at ~ 200°C, ~ 450°C and ~ 650°C, which leads to the assumptions that transformations may occur in iron when it reaches the above temperatures. Objectives: The aim of the research is to use the literature and empirical data to justify the transformations that occur in iron at ~200°C, ~450°C and ~650°C in order to explain the properties of steels. Methods Appled: The specimens used in the research were almost pure iron (0.008% C). A 20°C step was used for the experiment, which included an x-ray diffraction analysis and identifying the resistance to sinking strain (with the help of Gleeble 3800). The methodology is based on the following propositions by B.G. Livshits: «Any property can be used for analyzing the phase equilibrium»; by А.А.Vertman, A.M. Samarin: «One can choose any from around 50 properties currently used in physical and chemical analysis as structure-sensitive properties»; by A.A. Bochvar: «As a measured physical property, one can be take hardness..., electrical conductivity…, density, linear expansion coefficient and so on». Originality: Based on the empirical and theoretical data on abnormal physical and mechanical properties of iron (and steel as its derivative) the article describes why transformations occur in iron at ~ 650°C, ~ 450°C, ~ 200°C. By recognizing the transformations that occur in iron at the above temperatures one can explain the nature of multiple abnormal properties of iron and steel. Findings: Using the following curves: «resistance to sinking strain» and «fine structure of iron depending on the temperature» – and abundant literary evidence describing the physical and mechanical properties of iron (and steel), the article states that transformations occur in iron at ~200°C, ~450°C and ~650°C. Practical Relevance: By recognizing that the suggested transformations do take place, one can find the explaination for multiple abnormal properties demonstrated by iron and steel, as well as predict the properties of steels that are exposed to the above mentioned temperatures as part of the heat treatment process.

Keywords

Iron, steel, polymorphism, transformation, TRIP effect, hardness, strength, ductility, heat capacity.

Karen Yu. Shakhnazarov – Ph.D. (Eng.), Associate Professor

St. Petersburg Mining University, St. Petersburg, Russia. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.. ORCID: http://orcid.org/0000-0001-7501-6590

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