Phase Equilibria in FeS–XS and MnS–XS (X=Ti, Nb and V) Systems

Abstract

The phase equilibria in the FeS-XS and MnS-XS (X: Ti, Nb and V) pseudo-binary systems were investigated by using an X-ray diffraction and electron probe micro analyzer. In the FeS-TiS and FeS-VS systems, a mono-sulfide with the NiAs structure form a complete solid solution, while two-phase separation of the mono-sulfide with the NiAs structure is observed in the FeS-NbS system. In all MnS-XS systems, twophase region of a Mn-rich mono-sulfide and X-rich mono-sulfide exists widely. Solubility of each elements in the Mn-rich mono-sulfide and X-rich mono-sulfide is small, except that of Mn in Nb-rich mono-sulfide.KEY WORDS: iron sulfide; manganese sulfide; titanium sulfide; niobium sulfide; vanadium sulfide; phase equilibria.powder-synthesizing method using high purity iron, manganese, titanium, niobium, vanadium and sulfur powder. The mixed powders were uniaxially pressed at 250 MPa to form a green compacts with a cylinder shape in a diameter of 15 mm. The green compacts were sealed in evacuated quartz capsules and heat treated at 673 K for 72 h, and then elevated to 1 173 K and kept for 24 h to promote a chemical reaction of each powder. The prepared specimens were cut into four pieces and sealed again in evacuated quartz capsules. The small pieces in the quartz capsule were equilibrated at 1 173-1 573 K, and then the quartz capsule was dropped into ice water.Microstructure observation and composition analysis of the mirror-polished sections of the specimens were carried out by using an electron probe micro analyzer (EPMA). Xray diffraction (XRD) was used for the analysis of crystal structure of the equilibrated specimens ground to powder of the FeS-XS systems. Experimental Results FeS-XS SystemsTypical backscattering electron images (BEI) of (Fe 0.2 Ti 0.8 )S mixture annealed at 1 273 K for 10 h is shown in Fig. 1. Black and white color regions are void and metallic phases, respectively and the matrix in gray color is the sulfide phase. According to the EPMA analysis of sulfide phase at several points, the chemical composition of sulfide was almost the same value at every analyzed point. This result suggests that the sulfide phase in Fig. 1(a) is a homogeneous phase. Every samples of the FeS-TiS system showed the similar microstructure.Figures 2(a) and 2(b) show the typical XRD patterns obtained from (Fe 0.6 Ti 0.4 )S and (Fe 0.2 Ti 0.8 )S, respectively. The spectrum peaks of Figs. 2(a) and 2(b) can be identified as the NiAs and Ti 8 S 9 structure by Joint Committee on Powder Diffraction Standards of International Center for Diffraction Data (JCPDS-ICDD cards), respectively.22) The NiAs structure is observed a composition region from pure FeS to (Fe 0.4 Ti 0.6 )S and pure TiS, while several samples with high Ti content show the Ti 8 S 9 structure which is called NiAstype superstructure.23) This Ti 8 S 9 structure phase might be transformed from the NiAs structure phase during the cooling, because the phase transformation from the NiAs to the Ti 8 S 9 is very sensitive to the cooling rate.24) The lattice parameter...

Quantitative Analysis of Inclusions in Low Carbon Free Cutting Steel Using Small-angle X-ray and Neutron Scattering

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