Wyniki 1-1 spośród 1 dla zapytania: authorDesc:"Mateusz Kopuściański"

Thermal range of cementite occurrence in hypereutectoid alloys with controlled C, Cr and Mn content DOI:10.15199/28.2018.1.5

  1. INTRODUCTION Hypereutectoid steels are characterized by the high carbon content. High amount of the carbon, above the eutectoid point, resulted in the formation of the secondary carbides in microstructure. This precipitations in a great way influent on the mechanical properties [1÷4]. Cementite is a metastable iron carbide with the rhombic crystallographic structure and structural formula M3C. In cementite particles also could dissolve Cr, Mn, V, Mo, Ti, especially in the case of alloyed steels. It have been shown that the Cr and Mn dissolved in pure cementite increases the temperature of the cementite formation. Additionally, this elements increase the cementite hardness by approximately 3.5 GPa for the 20 mass % of Cr and by 5 GPa for 30 mass % of Mn. The thermal stability of cementite is more significant for the Cr addition than Mn. This alloying elements also increases the Young module of the cementite. It should be noted that with the increase of the alloying elements content also increase a linear expansion coefficient of cementite. Manganese increases resulted in a constant increase of α coefficient with temperature, in pure cementite this relation is opposite. Whereas the 20% mass Cr addition stabilized the α at value 25.5×10-6 K-1 at the temperature range from RT to 1273 K (for a pure cementite 16.2×10-6 K-1 above 481 K). Titanium addition to pure cementite resulted in its destabilization and formation of more thermodynamic stable titanium carbides [5÷7]. It should be noted that the relevant are thermodynamic correlations between the cementite and ferrite/austenite. Enthalpy of the cementite formation in a Fe-C system is about 27.0 kJ/mol [6]. In a Fe-C system in a traditionally used iron alloys, cementite is a part of the eutectoid mixture or could be formed as a precipitations from the liquid/austenite/ferrite. In a case of the eutectoid transformation two main mechanisms of the perlite formation were f[...]

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