| 1. |
- Deng, Biao, et al.
(författare)
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Effects of Austenitizing Temperature on Tensile and Impact Properties of a Martensitic Stainless Steel Containing Metastable Retained Austenite
- 2021
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 14:4
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Tidskriftsartikel (refereegranskat)abstract
- Austenitizing temperature is one decisive factor for the mechanical properties of medium carbon martensitic stainless steels (MCMSSs). In the present work, the effects of austenitizing temperature (1000, 1020, 1040 and 1060 degrees C) on the microstructure and mechanical properties of MCMSSs containing metastable retained austenite (RA) were investigated by means of electron microscopy, X-ray diffraction (XRD), as well as tensile and impact toughness tests. Results suggest that the microstructure including an area fraction of undissolved M23C6, carbon and chromium content in matrix, prior austenite grain size (PAGS), fraction and composition of RA in studied MCMSSs varies with employed austenitizing temperature. By optimizing austenitizing temperature (1060 degrees C for 40 min) and tempering (250 degrees C for 30 min) heat treatments, the MCMSS demonstrates excellent mechanical properties with the ultimate tensile strength of 1740 +/- 8 MPa, a yield strength of 1237 +/- 19 MPa, total elongation (ductility) of 10.3 +/- 0.7% and impact toughness of 94.6 +/- 8.0 Jcm(-2) at room temperature. The increased ductility of alloys is mainly attributed to the RA with a suitable stability via a transformation-induced plasticity (TRIP) effect, and a matrix containing reduced carbon and chromium content. However, the impact toughness of MCMSSs largely depends on M23C6 carbides.
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| 2. |
- Deng, B., et al.
(författare)
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Toughness Improvement in a Novel Martensitic Stainless Steel Achieved by Quenching–Tempering and Partitioning
- 2021
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Nature. - 1073-5623 .- 1543-1940. ; 52:11, s. 4852-4864
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, a novel medium carbon martensitic stainless steel (MCMSS) with an excellent combination of strength, ductility, and impact toughness was designed on the basis of quenching-tempering and partitioning (Q–T&P) technology. Q–T&P is an identical heat treatment with a standard quenching and tempering (Q–T) process but has the same role with quenching and partitioning (Q&P) on microstructure control, i.e., promoting carbon-rich retained austenite via inhibiting carbide precipitation. Results show that, without compromise on strength, the total elongation and room temperature impact toughness, i.e., 9.6 pct and 90 J cm−2, of the proposed alloy (23Cr13MnSi) increase by 14 and 110 pct, respectively, as compared to those of the commercial AISI 420. The significant improvement of ductility and impact toughness in the proposed alloy is mainly a result of the gradual transformation induced plasticity (TRIP) effects, which are caused by carbon-rich retained austenite with heterogeneous stability and carbide-free martensite formed in the Q–T&P process
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| 3. |
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| 4. |
- Hou, Ziyong, 1986-, et al.
(författare)
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Coarsening of cementite during tempering of a martensitic steel
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Coarsening of cementite (M3C) in a martensitic steel alloy Fe–1C–1Cr (wt. %) during tempering at 700 °C was investigated by electron microscopy and kinetic modelling. It is shown that the large M3C carbides are mostly located at high-angle grain boundaries in the coarsening stage and simple kinetic simulations predict the experimentally observed mean size evolution well when grain boundary diffusion of Cr is taken into account. However, the particle size distribution of M3C maintain a log-normal distribution throughout the whole extended tempering process (5000 h at 700 °C), which indicates that a modified LSW distribution , as predicted by classical steady-state coarsening theory , is not fully adequate for practical purposes in tempering of martensitic steels.
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| 5. |
- Hou, Ziyong, 1986-, et al.
(författare)
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Early stages of cementite precipitation during tempering of 1C-1Cr martensitic steel
- 2019
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Ingår i: Journal of Materials Science. - : Springer. - 0022-2461 .- 1573-4803. ; 54:12, s. 9222-9234
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Tidskriftsartikel (refereegranskat)abstract
- The precipitation of cementite (M3C) from as-quenched martensite during tempering at 500 and 700 degrees C was investigated in a Fe-1C-1Cr (wt%) alloy. Tempering for a short duration at 700 degrees C results in a Cr/Fe ratio in the core region of M3C precipitates which is equal to the bulk alloy composition, while a shell on the surface of the precipitates exhibits a higher Cr concentration. With a prolonged tempering up to 5h, the shell concentration gradually increases toward the equilibrium value, but the core region has not yet reached the equilibrium value. After tempering for 5s at 500 degrees C, there is no Cr enrichment found at the M3C-matrix interface, while a transition to partitioning of Cr is found during the first 5min of tempering at 500 degrees C. These experimental results indicate that M3C grows without significant partitioning of substitutional elements at both temperatures initially, i.e., growth is carbon diffusion controlled. This stage is, however, very short, and soon after 5s at 700 degrees C and 5min at 500 degrees C, Cr diffusion becomes important. Calculations using the diffusion simulation software DICTRA and precipitation simulation software TC-PRISMA were performed. The diffusion simulations using the local equilibrium interface condition show excellent agreement with experiments concerning Cr enrichment of the particles, but the size evolution is overestimated. On the other hand, the precipitation simulations underestimate the size evolution. It is suggested that a major improvement in the precipitation model could be achieved by implementing a modified nucleation model that considers nucleation far from the equilibrium composition.
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| 6. |
- Hou, Ziyong, 1986-, et al.
(författare)
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Early stages of cementite precipitation during tempering of 1C-1Cr martensitic steel
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The precipitation of cementite (M3C) from as-quenched martensite during tempering at 500 and 700 °C was investigated in a Fe–1C–1Cr (wt. %) alloy. Tempering for a short duration at 700 °C results in a Cr/Fe ratio in the core region of M3C precipitates which is equal to the bulk alloy composition, while a shell on the surface of the precipitates exhibit a higher Cr concentration. With a prolonged tempering up to 5 hours, the shell concentration gradually increases towards the equilibrium value but the core region has not yet reached the equilibrium value. After tempering for 5 seconds at 500 °C, there is no Cr enrichment found at the M3C/matrix interface, while a transition to partitioning of Cr is found during the first 5 minutes of tempering at 500 °C. These experimental results indicate that M3C grows without significant partitioning of substitutional elements at both temperatures initially, i.e. growth is carbon diffusion controlled. This stage is, however, very short, and soon after 5 seconds at 700 °C and 5 min at 500 °C, Cr diffusion becomes important. Calculations using the diffusion simulation software DICTRA and precipitation simulation software TC-PRISMA were performed. The diffusion simulations using the local equilibrium interface condition show excellent agreement with experiments concerning Cr enrichment of the particles, but the size evolution is overestimated. On the other hand, the precipitation simulations underestimate the size evolution. It is suggested that a major improvement in the precipitation model could be achieved by implementing a modified nucleation model that considers nucleation far from the equilibrium composition.
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| 7. |
- Hou, Ziyong, 1986-, et al.
(författare)
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Enhanced Grain Growth Behavior of Ferritic Steel during Continuous Cyclic Annealing
- 2018
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Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 89:11
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Tidskriftsartikel (refereegranskat)abstract
- Microstructural characterization as well as mechanical property determination of a cold-rolled ferritic steel subjected to isothermal and cyclic non-isothermal annealing, has been carried out by utilizing comprehensive experimental analysis. The findings show that the variables of cyclic annealing, that is, amplitude, ramp rate, and intermediate holding time exhibit a great effect on the grain growth kinetics and the evolution of grain boundaries. The resulting grain size of the cyclic annealed steel is mainly attributed to the following factors: 1) the accelerating effect in the grain growth behavior caused by the additional driving force available during cyclic annealing, which increases with increasing amplitude; 2) the retarding effect due to the low equivalent isothermal temperature. Furthermore, the formation of low sigma- coincidence site lattice (sigma CSL) boundaries and the strength of gamma-fiber texture are enhanced through the cyclic annealing compared to the isothermal annealing. The potential advantages of continuous cyclic annealing in the steel industry are explored, in comparison with the conventional isothermal and cyclic annealing with an intermediate soaking time.
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| 8. |
- Hou, Ziyong, 1986-, et al.
(författare)
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Evaluating magnetic properties of composites from model alloys – Application to alternative binder cemented carbides
- 2019
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Ingår i: Scripta Materialia. - : Acta Materialia Inc. - 1359-6462 .- 1872-8456. ; 168, s. 96-99
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of 85Ni-15Fe model alloys containing Co, W and C have been studied with the intent to isolate the influence of alloy chemistry on quality control measurements of alternative binder cemented carbides. The results show a strong influence of dissolved W on the Curie temperature and the saturation magnetization. The amount of dissolved C, and the presence of WC precipitates, on the other hand, is shown to have negligible effect. Furthermore, the magnetic coercivity is indicated to be entirely dominated by the microstructural features and quite insensitive to composition.
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| 9. |
- Hou, Ziyong, 1986-, et al.
(författare)
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Importance of Microstructure on Precipitation in Tempering of Martensitic Steels
- 2022
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Ingår i: 42Nd Riso International Symposium On Materials Science. - : IOP Publishing.
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Konferensbidrag (refereegranskat)abstract
- Precipitation hardening is one of most effective strengthening mechanisms in steels, and much research has been performed in the past. To evaluate the contribution of precipitates, the quantitative features of precipitates including mean size and particle size distribution etc., are vital and needed. However, the predictive modeling of precipitation is still a challenge so far, especially on a quantitative level. Thus, in the present work, precipitation of carbides after tempering of martensitic FeCr-C alloys, consisting of hierarchically arranged substructures within the prioraustenite grains, namely packets and blocks of individual laths, up to 1000h has been investigated. Experimental measurements using electron microscopy and modeling using a Langer-Schwartz theory with the Kampmann-Wagner -Numerical (KWN) method have been conducted. The importance of a proper definition of the initial microstructure for predictive modeling is discussed, in terms of the comparison of calculated and experimental results.
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| 10. |
- Hou, Ziyong, 1986-, et al.
(författare)
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Microstructure evolution during tempering of martensitic Fe-C-Cr alloys at 700 A degrees C
- 2018
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Ingår i: Journal of Materials Science. - : SPRINGER. - 0022-2461 .- 1573-4803. ; 53:9, s. 6939-6950
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure evolution of two martensitic alloys Fe-0.15C-(1.0 and 4.0) Cr (wt%) was investigated, using X-ray diffraction, electron backscatter diffraction, electron channeling contrast imaging and transmission electron microscopy, after interrupted tempering at 700 A degrees C. It was found that quenching of 1-mm-thick samples in brine was sufficient to keep most of the carbon in solid solution in the martensite constituent. The high dislocation density of the martensite decreased rapidly during the initial tempering but continued tempering beyond a few minutes did not further reduce the dislocation density significantly. The initial martensitic microstructure with both coarse and fine laths coarsened slowly during tempering for both alloys. However, a clear difference between the two alloys was distinguished by studying units separated by high-angle boundaries (HABs). In the low-Cr alloy, M3C precipitates formed and coarsened rapidly, thus they caused little hindrance for migration of HABs, i.e., coarsening of the HAB units. On the other hand, in the high-Cr alloy, M7C3 precipitates formed and coarsened slowly, thus they were more effective in pinning the HABs than M3C in the low-Cr alloy, i.e., coarsening of HAB units was minute in the high-Cr alloy.
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