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We report the chemical-composition-dependent precipitation of Cr-rich BCC particles and their role in the hardening of Fe-Cr-Ni medium entropy alloys (MEAs). Three alloys with different chemical compositions: 33Fe-32Cr-35Ni MEA (33Fe), 40Fe-30Cr-30Ni MEA (40Fe), and 45Fe-30Cr-25Ni MEA (45Fe) (at%), were investigated. After annealing at 800 and 950 degrees C, all three alloys had a heterogeneous grain size distribution, except for 40Fe annealed at 950 degrees C. The samples annealed at 800 degrees C showed a more heterogeneous grain size distribution, smaller average grain size, and lower degree of recrystallization than the samples an-nealed at 950 degrees C. This difference is ascribed mainly to the contents and precipitation kinetics of Cr-rich BCC particles at the two temperatures. The hardness decreased with the increase in annealing temperature for all the samples. The 33Fe sample exhibited higher hardness than 40Fe and 45Fe because of the joint effect of grain boundary strengthening and precipitation strengthening by the Cr-rich BCC particles. Different peak -load-dependent hardness behaviors were observed in 33Fe-A80 0 with relatively coarse BCC particles and 40Fe-A80 0 with fine BCC particles. The fine particles led to higher local hardness, whereas coarse particles resulted in higher microhardness owing to the hetero-deformation-induced strengthening effect. These results provide new insights into the strength optimization of medium-and high-entropy alloys through the dispersion of coarse Cr-rich BCC particles., QC 20221205

Lab-scale alloying experiments were carried out by first adding commercial low-carbon ferrochrome (LCFeCr) alloys and then adding ferroniobium (FeNb) alloys in 316-grade austenitic stainless steel in this study. The inclusion and precipitation characteristics in LCFeCr and FeNb were evaluated as well as in a 316 austenitic stainless steel after the alloy additions by using two- and three-dimensional characterization methods in combination with thermodynamic calculations. The results showed that MnCr2O4 spinels and pure Al2O3 were the main types of inclusions in LCFeCr alloys, while pure TiOx, Al2O3 inclusions and complex TiOx-Al2O3 aggregates were mainly found in FeNb alloys. After the addition of LCFeCr alloy to the steel, the SiO2 contents in liquid inclusions decreased to some extent, while more inclusions containing higher MnO contents were observed. Some MnCr2O4 spinel inclusions can be reduced by Si in steel and form liquid inclusions. Some MnCr2O4 spinel and Al2O3 inclusions from LCFeCr alloy can remain in the steel melt, which decreased the steel cleanliness. After the addition of FeNb alloy, pure TiOx inclusions present in this alloy can hardly be found in the steel melt. The inclusion types in steel were not changed so much but high Nb-containing phases were found around the inclusions and coarse Laves phases were formed in the matrix. Overall, this work aims to understand the impurity particle behavior during the alloying process when using ferroalloys to produce high-performance stainless steels., QC 20230822

The present study provides a benchmark of a sustainable solution utilizing ferroalloys to prepare ultra-clean CoCrFeMnNi high-entropy alloy (HEA). The designed CaO-MgO-Al2O3 slags saturated with CaAl2O4-MgAl2O4 (CA-MA, Slag A) and CaO-MgO (C-M, Slag M) were used to refine the HEA in Al2O3 and MgO refractory in an induction furnace under high-purity Ar atmosphere at 1773 K. The characteristics of non-metallic inclusions in the sampled HEA at different time intervals were quantitatively investigated. The results showed that three types of inclusions, i.e., sulfide (MnS), oxide, and complex type (oxide+sulfide), were found in the HEA regardless of refractory and slag types. The oxide inclusions such as MnAl2O4 and MgAl2O4 spinel particles can exist stably in the HEA melted in Al2O3 and MgO refractories with slag A and slag M, respectively. This fact is also confirmed not only by the electrolytic extraction method with elimination of the alloy matrix affection but also by the thermodynamic stability diagram for the HEA. For the structure of the complex inclusions, the core of oxide inclusions usually can act as the subsequent nucleation site for MnS since the precipitation temperature of the oxide inclusions (above the liquidus temperature of the HEA, TL approximately equal to 1623 K) is higher than that of MnS (below the solidus temperature of the HEA, TS approximately equal to 1573 K). The HEA melted in the MgO refractory with slag M had a higher cleanliness compared with that melted in the Al2O3 refractory with slag A, indicating that the MgO refractory with C-M saturated CaO-MgO-Al2O3 slag is suitable for producing an ultra-clean CoCrFeMnNi HEA prepared by the ferroalloys feedstock as the raw materials., QC 20230321

Commercial ferroalloys are used in the manufacturing of a CoCrFeMnNi high-entropy alloy (HEA) due to their price advantage and the productivity of the manufacturing process. However, elemental impurities such as sulfur in ferroalloys can undermine the mechanical properties of HEAs. Therefore, the desulfurization behavior of a CoCrFeMnNi HEA using the CaO-MgO-Al2O3 (CAM) slagging method with alumina or magnesia refractories and ferroalloys raw material feedstock was investigated in an induction melting furnace at 1773 K to determine how to control the cleanness of the HEA. The resulting desulfurization ratios of the alloy were approx. 47% when refined by the CaAl2O4-MgAl2O4(CA-MA)-saturated slag in an Al2O3 refractory, whereas 94% when refined by the CaO-MgO(C-M)-saturated slag in a MgO refractory. The overall mass transfer coefficients of sulfur for the HEA refined by the CA-MA- and C-M-saturated slags at 1773 K were ko = 1.4 x 10 6 m/s and ko = 2.0 x 10 6 m/s, respectively, which are lower than the coefficients of iron- and nickel-based alloys at the same experimental conditions. The MnS inclusion particles can precipitate in the mushy zone rather than the liquid region when the solid fraction is close to 1.0, i.e., at the final stage of the solidification. The theoretical radius of MnS increases from 0 to 1.6 mu m when the sulfur content rises from 3 ppm to 60 ppm, according to the hypothesis that the mass transfer of sulfur in the HEA is the rate-controlling step., QC 20221111

Co-based duplex entropic alloy is designed very recently to replace pure Co as a major component of the binder phase for cemented carbide cutting tools. This work aims to provide a fundamental study of oxide inclusion characteristics in the duplex fcc + hcp Co-based entropic alloys. It is found that the Co85-xCrxFe7.5Ni7.5 (x = 15, 30 at.%) alloys hold the highest liquidus (T-liq) and solidus (T-sol) temperatures, compare with the Co85-xCrxMn7.5Ni7.5 (x = 15, 30 at.%) and Co77.5-xCrxFe7.5Mn7.5Ni7.5 (x = 15, 30 at.%) alloys. For each grade, the increasing Cr content leads to a decrease of T-sol and T-liq temperatures. It is also noted that there is an approximate 100 degrees C of undercooling exists in each grade during the solidification. The stable oxide inclusion in the Co85-xCrxMn7.5Ni7.5 and Co77.5-xCrxFe7.5Mn7.5Ni7.5 alloys is the MnCr2O4 type, while Cr2O3 is the main stable inclusion in the Co85-xCrxFe7.5Ni7.5 alloy. Furthermore, the size range of the MnCr2O4 particles is larger than that of Cr2O3. The theoretical calculation shows that MnCr2O4 has a higher coagulation coefficient than Cr2O3 does. This is due to the influence of the thermo-physical parameters, i.e. the interfacial energy between the oxide and the alloy and the viscosity of liquid alloy. The theoretical calculation fits well with the experimental findings., QC 20220309