{"title":"Calorimetric Studies of Polymorphic Iron Transformation","authors":"S. V. Davydov, L. V. Spivak, N. E. Shchepina","doi":"10.3103/s0967091224700384","DOIUrl":null,"url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>Iron polymorphism, as a basic phase transformation in the industrial technology of iron-carbon alloys, manifests itself in three forms in iron heating and cooling. An analysis of the literature data revealed a lack of information about the mechanism of pure iron polymorphic transformation. In this work, an experimental verification of the second polymorphic transformation α-Fe ↔ γ-Fe is carried out using high-resolution differential scanning calorimetry (DSC). The object of the study are samples made from wire of technically pure iron (TPI–99.88% Fe) and high-purity zone-purified iron (ZPI–99.995% Fe). Heating and cooling are carried out in an argon atmosphere (99.9995% Ar). Based on the analysis of DSC curves, the following results are obtained: the value of hysteresis of the polymorphic transformation during thermal cycling is ~11°C; the iron polymorphic transformation is not reversible upon heating and cooling and occurs through different mechanisms; existing ideas about the reversible polymorphic phase transformation of α-Fe ↔ γ-Fe upon heating as phase recrystallization within the framework of a deformation (distortion) transition are untenable. It is experimentally proven that the pure iron polymorphic transformation under equilibrium conditions upon heating proceeds diffusion-free with a sequential change of three phase transformations of different origins. Jump in atomic volumes of polymorph phases α-Fe ↔ γ-Fe in the region of phase transformation is explained by indirect shear plastic transformation of the α-Fe polymorph crystal lattice into the γ-Fe polymorph crystal lattice, as is customary to date, but by the sequential destructuring of the α-Fe polymorph into a mixture of “paracluster” and amorphous phases. Within the framework of these studies, the following unsolved problems are identified: firstly, the process during which a significant amount of activation energy <i>G</i> is absorbed, is unclear: for TPI 2300 ± 150 kJ/mol, for ZPI 2400 ± 200 kJ/mol; secondly, there is no explanation for the mechanism of the iron crystal lattice transition to the amorphous state when heated; thirdly, the temperature of the polymorphic transformation range in carbon steel 20 does not coincide with the similar temperature range on the Fe–C diagram.</p>","PeriodicalId":21903,"journal":{"name":"Steel in Translation","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Steel in Translation","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.3103/s0967091224700384","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"Materials Science","Score":null,"Total":0}
引用次数: 0
Abstract
Iron polymorphism, as a basic phase transformation in the industrial technology of iron-carbon alloys, manifests itself in three forms in iron heating and cooling. An analysis of the literature data revealed a lack of information about the mechanism of pure iron polymorphic transformation. In this work, an experimental verification of the second polymorphic transformation α-Fe ↔ γ-Fe is carried out using high-resolution differential scanning calorimetry (DSC). The object of the study are samples made from wire of technically pure iron (TPI–99.88% Fe) and high-purity zone-purified iron (ZPI–99.995% Fe). Heating and cooling are carried out in an argon atmosphere (99.9995% Ar). Based on the analysis of DSC curves, the following results are obtained: the value of hysteresis of the polymorphic transformation during thermal cycling is ~11°C; the iron polymorphic transformation is not reversible upon heating and cooling and occurs through different mechanisms; existing ideas about the reversible polymorphic phase transformation of α-Fe ↔ γ-Fe upon heating as phase recrystallization within the framework of a deformation (distortion) transition are untenable. It is experimentally proven that the pure iron polymorphic transformation under equilibrium conditions upon heating proceeds diffusion-free with a sequential change of three phase transformations of different origins. Jump in atomic volumes of polymorph phases α-Fe ↔ γ-Fe in the region of phase transformation is explained by indirect shear plastic transformation of the α-Fe polymorph crystal lattice into the γ-Fe polymorph crystal lattice, as is customary to date, but by the sequential destructuring of the α-Fe polymorph into a mixture of “paracluster” and amorphous phases. Within the framework of these studies, the following unsolved problems are identified: firstly, the process during which a significant amount of activation energy G is absorbed, is unclear: for TPI 2300 ± 150 kJ/mol, for ZPI 2400 ± 200 kJ/mol; secondly, there is no explanation for the mechanism of the iron crystal lattice transition to the amorphous state when heated; thirdly, the temperature of the polymorphic transformation range in carbon steel 20 does not coincide with the similar temperature range on the Fe–C diagram.
期刊介绍：
Steel in Translation is a journal that represents a selection of translated articles from two Russian metallurgical journals: Stal’ and Izvestiya Vysshikh Uchebnykh Zavedenii. Chernaya Metallurgiya . Steel in Translation covers new developments in blast furnaces, steelmaking, rolled products, tubes, and metal manufacturing as well as unconventional methods of metallurgy and conservation of resources. Papers in materials science and relevant commercial applications make up a considerable portion of the journal’s contents. There is an emphasis on metal quality and cost effectiveness of metal production and treatment.
求助内容：
应助结果提醒方式：
京公网安备 11010802042870号
