| 1. |
- Duan, Shengchao, et al.
(författare)
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Evolution of nonmetallic inclusions in 80-t 9CrMoCoB large-scale ingots during electroslag remelting process
- 2024
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Ingår i: International Journal of Minerals, Metallurgy and Materials. - : University of Science and Technology Beijing. - 1674-4799 .- 1869-103X. ; 31:7, s. 1525-1539
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Tidskriftsartikel (refereegranskat)abstract
- In combination with theoretical calculations, experiments were conducted to investigate the evolution behavior of nonmetallic inclusions (NMIs) during the manufacture of large-scale heat-resistant steel ingots using 9CrMoCoB heat-resistant steel and CaF2–CaO–Al2O3–SiO2–B2O3 electroslag remelting (ESR)-type slag in an 80-t industrial ESR furnace. The main types of NMI in the consumable electrode comprised pure alumina, a multiphase oxide consisting of an Al2O3 core and liquid CaO–Al2O3–SiO2–MnO shell, and M23C6 carbides with an MnS core. The Al2O3 and MnS inclusions had higher precipitation temperatures than the M23C6-type carbide under equilibrium and nonequilibrium solidification processes. Therefore, inclusions can act as nucleation sites for carbide layer precipitation. The ESR process completely removed the liquid CaO–Al2O3–SiO2–MnO oxide and MnS inclusion with a carbide shell, and only the Al2O3 inclusions and Al2O3 core with a carbide shell occupied the remelted ingot. The M23C6-type carbides in steel were determined as Cr23C6 based on the analysis of transmission electron microscopy results. The substitution of Cr with W, Fe, or/and Mo in the Cr23C6 lattice caused slight changes in the lattice parameter of the Cr23C6 carbide. Therefore, Cr21.34Fe1.66C6, (Cr19W4)C6, Cr18.4Mo4.6C6, and Cr16Fe5Mo2C6 can match the fraction pattern of Cr23C6 carbide. The Al2O3 inclusions in the remelted ingot formed due to the reduction of CaO, SiO2, and MnO components in the liquid inclusion. The increased Al content in liquid steel or the higher supersaturation degree of Al2O3 precipitation in the remelted ingot than that in the electrode can be attributed to the evaporation of CaF2 and the increase in CaO content in the ESR-type slag.
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| 2. |
- Duan, Shengchao, et al.
(författare)
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Manufacturing an ultra-low-sulfur CoCrFeMnNi high-entropy alloy by slagging through induction melting with ferroalloys feedstock
- 2022
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 928, s. 167080-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Duan, Shengchao, et al.
(författare)
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Novel applications of ferroalloys for manufacturing of ultra-clean CoCrFeMnNi high-entropy alloy by slagging method
- 2023
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 939
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Fang, Xing, et al.
(författare)
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Effects of the superheating degree and cooling intensity on the as-cast microstructure of CP780 thin slab
- 2023
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Ingår i: International Journal of Cast Metals Research. - : Informa UK Limited. - 1364-0461 .- 1743-1336. ; 36:1-3, s. 9-17
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Tidskriftsartikel (refereegranskat)abstract
- This paper studied the effects of the superheating degree and cooling intensity on the solidification structure of CP 780 slab. The results indicated that the equiaxed crystal ratio decreases with the increase of superheating degree and the cooling intensity. When the superheating degree increases from 15 to 25°C, the equiaxed crystal ratio drops sharply. While the equiaxed crystal ratio decreases slightly with an increasing superheating degree from 25°C to 55°C. It is further revealed that the superheating degree has a greater effect on the equiaxed crystal ratio compared with the influence of cooling intensity. Quantitative analysed the relationship among the equiaxed crystal ratio, the superheating degree and cooling intensity is in line with the Extreme 2D model. The accuracy of the model performance can reach 97.6% when predicting the equiaxed crystal ratio of CSP-CP 780 during CSP process.
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| 5. |
- Huang, Shuo, et al.
(författare)
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Magnetocaloric properties of melt-spun MnFe-rich high-entropy alloy
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 119:14
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Tidskriftsartikel (refereegranskat)abstract
- High-entropy functional materials are of great interest in materials science and engineering community. In this work, ab initio electronic structure calculations of the phase stability and magnetic transition temperature of AlxCr0.25MnFeCo0.25-yNiy (x = 0-0.5, y = 0-0.25) alloys were performed to screen for compositions showing promising magnetocaloric properties in the vicinity of room temperature. The selected Al0.44Cr0.25MnFeCo0.05Ni0.2 alloy was synthesized via a rapid solidification technique and systematically characterized with respect to its structural and magnetocaloric properties. The results indicate that this alloy possesses a homogeneous microstructure based on an underlying body-centered cubic lattice and has a Curie temperature of & SIM;340 K. The temperature dependence of the adiabatic temperature change was evaluated using both direct and indirect methods. The ab initio-assisted design of 3d-metal-based high-entropy alloys, explored here, is intended to contribute to the development of magnetic refrigerators for room-temperature applications.
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| 6. |
- Li, Rongbin, et al.
(författare)
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Nonlinearity in mass spectrometry for quantitative multi-component gas analysis in reaction processes
- 2022
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Ingår i: Analytica Chimica Acta. - : Elsevier BV. - 0003-2670 .- 1873-4324. ; 1194, s. 339412-
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Tidskriftsartikel (refereegranskat)abstract
- Quantitative mass spectrometry analysis for multi-component gas phase reaction processes is a typical multi-input and multi-output (MIMO) nonlinear problem. Conventional calibration and analytical methods that are based on the common hypothesis of linearity of the detected signal and gas parameters, could result in misjudgment of the reaction mechanism and inaccuracy in the determination of the reaction kinetics. In the present work, theoretical derivations based on equivalent characteristic spectrum analysis (ECSA (R)), discrete mode experiments and continuous mode experiments were performed, and the nonlinearity of mass spectrometry was confirmed. It is only possible to determine the physical parameters such as flow rate and/or concentrations of gases by properly handling the nonlinearity of mass spectrometry. In such case comprehensive reaction mechanisms and even the kinetics of the process can be accurately characterized. Well-handled nonlinear mass spectrometry analysis ensures a reliable and highly accurate identification for the multi-component gas phase reaction processes, and ensures high signal-to-noise ratio for detecting the small-flow gases at a wide range of carrier gas flow.
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| 7. |
- Li, Wang, et al.
(författare)
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Annealing parameters effect on microstructure evolution, tensile properties and deformation behaviors of direct-cold-rolled UNS S32101 duplex stainless steel with heterogeneous layered structure
- 2023
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 883
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Tidskriftsartikel (refereegranskat)abstract
- Microstructure evolution, strain-induced martensite transformation (SIMT) kinetics, tensile properties, deformation behaviors of UNS S32101 duplex stainless steel (DSS) with heterogeneous layered structure (HLS) were investigated. HLS composed of multiscale grains (spanning coarse, fine, and ultrafine grains) was prepared by direct cold rolling in combination with short-time annealing, being dominated by coarse-grained ferrite (CGed α) and fine-grained austenite (FGed γ). A quantitative SIMT kinetics model was established to predict the α′-martensite fraction at various strain/annealing parameters, indicating that increased average grain size (AGS) for γ not only contributed to the SIM formation but also promoted the monotonic increase of SIMT rate until annealing for 10 min. Relatively high stacking fault energy (SFE, 35.89∼39.34 mJ/m2) favored mechanical twinning as the dominant deformation mode of γ accompanied by SIMT and dislocation glide. And α deformation was mainly coordinated by wavy slip. Both SFE and Olson-Cohen parameters were strongly correlated with the γ AGS, which could reasonably interpret the dependence of SIMT on the AGS. The A and B values increased progressively with grain coarsening along with the rapid decline in SFE, facilitating the martensite formation. Further increasing the AGS beyond the peak region severely suppressed SIMT probably due to the low probability of martensite embryo generation at deformation twins (DTs) intersections, coinciding with the sharp decrease A value.
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| 8. |
- Li, Wang, et al.
(författare)
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Correlation of microstructure and dynamic softening mechanism of UNS S32101 duplex stainless steel during elevated temperature tensile testing
- 2022
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 855
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic substructural development and softening mechanism of UNS S32101 duplex stainless steel were comprehensively investigated by employing hot-tensile tests at various strain rates of 0.1-10 s(-1) at a fixed temperature of 1200 degrees C. Different flow behaviors were attributed to the microstructural evolution and restoration process under various hot-deformation conditions. The alternative restoration mechanisms of ferrite in the current alloy were closely associated with the evolution of the misorientation angle in the (sub)grains, depending on the applied strain rates. Therein, three distinct softening mechanisms were found in ferrite, i) subgrain coalescence (SC) at 0.1 s(-1), ii) continuous dynamic recrystallization (CDRX) at 1 s(-1) and iii) subgrain rotationassisted discontinuous dynamic recrystallization (SR-assisted DDRX) at 10 s(-1). During SR-assisted DDRX process, new DRX nuclei were preferentially formed at the high-angle grain boundaries/phase boundaries (HAGBs/PBs) through the growth of highly misoriented subgrains. In contrast to ferrite, the available dynamic softening behavior of austenite, unlike the classical DDRX mechanism characterized by strain-induced boundary migration (SIBM), is affected by a limited number of pre-existing HAGBs. At lower strain rates of 0.1 and 1 s(-1), the nucleation process of DRX in austenite is analogous to the CDRX behavior, whereas the growth characteristics conform to DDRX, thus, it can be called dynamic recovery-assisted DDRX (DRV-assisted DDRX). At a high strain rate of 10 s(-1), DRX nucleation mainly took place through the strain-induced twin boundaries (TBs) transformation into HAGBs, and then rapidly grew via SIBM, referred to as TB-assisted DDRX.
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| 9. |
- Li, Wang, et al.
(författare)
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New comprehension on the microstructure, texture and deformation behaviors of UNS S32101 duplex stainless steel fabricated by direct cold rolling process
- 2022
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 845, s. 143150-
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Tidskriftsartikel (refereegranskat)abstract
- The effect of cold deformation on the detailed microstructure evolution, texture development and deformation behaviors/mechanisms of UNS S32101 duplex stainless steel (DSS2101) during the direct cold rolling process was investigated. The results showed that throughout the cold deformation process, the negative texture of {001}<110> component was nonexistent in deformed ferrite, and most texture components were mainly concentrated on alpha/gamma-fibers. Detwinning in austenite was substantial responsible for the reorientation in {111}< 112> towards {111}<110> of gamma-fiber in ferrite rather than martensite transformation. Austenite texture were composed of {110}<100> Goss and {110}<115> Goss/Brass components at heavy deformation (50% and 70%). The refinement and deformation behavior in ferrite was attributed to microbands (MBs) subdivision and dislocation activities, whilst that of austenite mainly occurred through twinning, strain induced detwinning (SID) and strain induced martensite (SIM).
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| 10. |
- Li, Wang, et al.
(författare)
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Partitioning behavior of N and its effect on hot deformation behavior of duplex stainless steels 2101 and 2205
- 2022
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Ingår i: Journal of Materials Science. - : Springer. - 0022-2461 .- 1573-4803. ; 57:48, s. 22119-22139
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the N back-migration and restoration behavior of duplex stainless steels (DSSs) 2101 and 2205 (DSS2205) were studied. Experimental findings indicated that the Cr2N in the ferrite (α) persistently decreased for both steels during the cooling process from 1200 °C to 1000 °C, and the disappearance rate of Cr2N in DSS2205 was significantly faster than that of lean duplex stainless steel 2101 (LDX2101). On the one hand, due to the severe partitioning behavior of N atoms in α migrating back to austenite (γ), on the other hand, the enriched Mn in LDX2101 and the enriched Ni in DSS2205 exerted an impact on N migration. Also, the cumulative thermal deformation at 1200 °C contributed to the N migration back into γ with the assistance of high-density dislocations and thermal deformation energy. Furthermore, the softening mechanism of constituent phases was dominated by discontinuous dynamic recrystallization (DDRX) mechanism in both steels at a strain rate of 10 s−1, which was characterized by strain-induced boundaries migration from low-density dislocations to high ones.
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