Theoretical Considerations on Transition Metals Sulphides Precipitation in Alloyed Steels
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retical Considerations on Transition Metals Sulphides Precipitation in Alloyed Steels Islam Moussaoui1, Abdelmalek Roula1,*, Mirsalim M. Asadov2,**, and Kamel Boudeghdegh1 1
2
Faculty of Science and Technology, Jijel University, Jijel, 18000 Algeria Institute of Catalysis and Inorganic Chemistry, Azerbaijan National Academy of Sciences, Baku, Azerbaijan *e-mail: [email protected] **e-mail: [email protected] Received September 1, 2019; revised September 18, 2019; accepted September 25, 2019
Abstract—Mechanical properties of alloyed steels parts may be improved by precipitation of simple and/or complex chemical combinations (carbides, nitrides, and/or carbonitrides) using thermal and/or thermo-chemical treatments. Nevertheless, the precipitation of transition metal sulphides (TMSs) is considered as an undesirable phenomenon because of the negative influence on the material properties. This phenomenon has been the object of several theoretical studies (phenomenological description, thermodynamical and/or kinetical approaches) and is still under focus. In this study, the theoretical approach to this phenomenon is carried out on the basis of the non-dimensional mathematical analysis (collection and mathematical modelling of specific data bank). We propose a relative ranking of sulphidising ability for transition metals (TMs) and models to compute any TMS amount and relative content in the metallic structure of Fe-C alloys. Keywords: transition metals, sulphides, Fe-C alloys, non-dimensional analysis DOI: 10.3103/S0025654420010173
1. INTRODUCTION Transition metal sulphides (TMSs) are a quasi-unavoidable and harmful impurity for Fe-C alloys. Steels may contain sulphur for several reasons (impurity of iron ore and all other chemical components used during the long and complex elaboration process). It is quite difficult to remove them and the exact process of the desulphurization is not completely known [1, 2]. The simultaneous existence of sulphur and transition metals (S and TMs = Ti, V, Cr, Mn, Co, Ni, Zr, Nb, and Mo are the most used) in the material chemical composition easily causes their combination as simple (MxSy) or complex (AxBySz) TMSs. The formation and the subsequent precipitation of these inclusions are promoted by the extremely low solubility of alkali and earth-alkali metals in Fe and Fe–C alloys [3–5]. The precipitation of these inclusions in low-carbon steels negatively affects their mechanical properties and significantly deteriorates their corrosion resistance [4–13]. The ascendancy of manganese sulphide (MnS) precipitation is often noticed; indeed, it seems that MnS is the preferential chemical combination despite the presence of others (even in higher contents than manganese) [4–14, 21–25]. As reported by Reformatskaya and co-authors [14], MnS inclusions precipitate in steels structure because these materials always contain manganese (as impurity or alloying element). In Cr-containing steels with very low Mn content, chromium sulphides are the most probable inclusions. In accordance with its
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