A novel Nb–V–Ce multi-microalloyed low-alloy cast steel for offshore platform nodes was investigated to achieve the properties similar to X80 pipeline steel,including high yield strength and low-temperature impact e...A novel Nb–V–Ce multi-microalloyed low-alloy cast steel for offshore platform nodes was investigated to achieve the properties similar to X80 pipeline steel,including high yield strength and low-temperature impact energy.The experimental results demonstrate that the addition of elements such as Nb,V and Ce can markedly improve the strength of the low-alloy cast steel.Maintaining a constant level of elements such as Nb,V and Ce,while reducing the content of Si to 0.28 wt.%,leads to substantial enhancements in impact energy at−40℃,meeting the mechanical properties criteria of X80 pipeline steel.The excellent mechanical properties of the multi-microalloyed low-alloy cast steel result from the reason that the multi-addition of microalloying elements refines the grains and facilitates the formation of nanoprecipitates like NbC.Moreover,decreasing Si content can enhance the recovery of martensitic laths in cast steel during the tempering process,reducing stress from dislocation movement and improving plasticity.展开更多
To develop a melting-based larger-scale fabrication process for oxide dispersion strengthened(ODS)steel,this study proposed a method of zone melting with built-in precursor powder(ZMPP),followed by hot forging and agi...To develop a melting-based larger-scale fabrication process for oxide dispersion strengthened(ODS)steel,this study proposed a method of zone melting with built-in precursor powder(ZMPP),followed by hot forging and aging treatments.A 50 kg ingot was successfully prepared,highlighting the scalability of this innovative process.Microstructural analysis revealed a predominantly lath martensite matrix with a small amount of ferrite in the hot-forged ODS steel,without oxide particle aggregation.Aging at 750℃ resulted in the formation of sub-micron-sized Cr_(23)C_(6) particles at grain boundaries and martensitic lath interfaces,accompanied by a high-density(7.64×1023 m^(-3))nano-scale(~6 nm)Y-Si-O complex oxides after 25 h.Additionally,the hot-forged sample exhibited a high yield strength(871 MPa)but limited ductility(5.0%).Aging treatments led to an increase in ductility but a decrease in yield strength.Notably,prolonged aging maintained the strength level of steels while enhancing ductility,with a 23.3% total elongation observed after 25 h.The novel ZMPP method,preparing high-quality ODS steels with uniform microstructure and good mechanical properties,provided a new avenue for large-scale production of ODS steels.展开更多
Precipitation strengthening of nano-scale TiC is a promising method to improve mechanical properties of Fe–16Mn–9Al–0.8C(wt.%)low-density steel.This work attempted to introduce nano-scale TiC precipitates by adding...Precipitation strengthening of nano-scale TiC is a promising method to improve mechanical properties of Fe–16Mn–9Al–0.8C(wt.%)low-density steel.This work attempted to introduce nano-scale TiC precipitates by adding 1 wt.%Ti element.The experimental results show that these precipitates with the total fraction of about 2 vol.%were formed and no coarse precipitates were observed despite the high Ti addition.It was interesting that the polygonal and needle-shaped TiC precipitates were observed inγ-austenite andδ-ferrite,respectively.Ti addition also decreased the volume fraction ofγ-austenite significantly.Correspondingly,the yield strength was increased,but the elongation was significantly decreased due to the significant decrease ofγ-austenite.Comparing with the Ti-free steel,the formation of TiC precipitates was the main reason for the increase in yield strength of Ti-bearing steel,and TiC precipitates also led to a higher strain hardening index at the first deformation stage.TiC precipitates promoted the Orowan strengthening,resulting in a higher strain hardening capability than Ti-free steel reinforced by shearableκ-carbide.展开更多
In order to investigate the modification behavior and regularity of inclusions in X80 pipeline steel by Mg-treatment, the comparative industrial experiments of Mg-treatment and Ca-treatment in X80 pipeline steel were ...In order to investigate the modification behavior and regularity of inclusions in X80 pipeline steel by Mg-treatment, the comparative industrial experiments of Mg-treatment and Ca-treatment in X80 pipeline steel were carried out. Mg and Ca were added to the steel in the form of cored wire after RH (Ruhrstahl-Hereaeus vacuum degassing) process. After adding Ca-containing cored wire, the inclusions were transformed into CaO–Al_(2)O_(3) in the steel. With the progress of smelting, the cleanliness of molten steel became worse, and the equivalent diameter of inclusions was at a higher level. Mg-treatment had a good effect on the modification of inclusions. After Mg-containing cored wire was added to the steel, Al_(2)O_(3) and CaO–Al_(2)O_(3) in the steel were transformed into MgO, MgO·Al_(2)O_(3), and CaO–MgO–Al_(2)O_(3) inclusions, which were basically spherical. The initial precipitated MgO became the core of other inclusions in the steel, which promotes the precipitation of MgO·Al_(2)O_(3). After Mg-treatment, almost no unmodified calcium aluminate inclusions existed in the hot rolled plate, and the cleanliness of the steel was improved. The effect of Ca and Mg on the transformation of inclusions in pipeline steel was studied by thermodynamic calculation, the result of which is consistent with the experimental results.展开更多
Te treatment is an effective method for modifying sulfide inclusions,and MnTe precipitation has an important effect on thermal brittleness and steel corrosion resistance.In most actual industrial applications of Te tr...Te treatment is an effective method for modifying sulfide inclusions,and MnTe precipitation has an important effect on thermal brittleness and steel corrosion resistance.In most actual industrial applications of Te treatment,MnTe precipitation is unexpected.The critical precipitation behavior of MnTe inclusions was investigated through scanning electron microscopy,transmission electron microscopy,machine learning,and first-principles calculation.MnTe preferentially precipitated at the container mouth for sphere-like sulfides and at the interface between MnS grain boundaries and steel matrix for rod-like sulfides.The MnS/MnTe interface was semicoherent.A composition transition zone with a rock-salt structure exhibiting periodic changes existed to maintain the semicoherent interface.The critical precipitation behavior of MnTe inclusions in resulfurized steels involved three stages at varying temperatures.First,Mn(S,Te)precipitated during solidification.Second,MnTe with a rock-salt structure precipitated from Mn(S,Te).Third,MnTe with a hexagonal NiAs structure transformed from the rock-salt structure.The solubility of Te in MnS decreased with decreasing temperature.The critical precipitation behavior of MnTe inclusions in resulfurized steels was related to the MnS precipitation temperature.With the increase in MnS precipitation temperature,the critical Te/S weight ratio decreased.In consideration of the cost-effectiveness of Te addition for industrial production,the Te content in resulfurized steels should be controlled in accordance with MnS precipitation temperature and S content.展开更多
The high-temperature dissolution behavior of primary carbides in samples taken from GCr15 continuous-casting bloom was observed in-situ by confocal laser scanning microscopy.Equations were fitted to the dissolution ki...The high-temperature dissolution behavior of primary carbides in samples taken from GCr15 continuous-casting bloom was observed in-situ by confocal laser scanning microscopy.Equations were fitted to the dissolution kinetics of primary carbides during either heating or soaking.Dissolution of carbides proceeded in three stages(fast→slow→faster)as either temperature or holding time was increased.During the heating process and during the first and third stages of the soaking process,the original size of the carbides determined the steepness of the slope,but during the middle(“slow”)stage of the soaking process,the slope remained zero.The initial size of the carbides varied greatly,but their final dissolution temperature fell within the narrow range of 1210-1235℃,and the holding time remained within 50 min.Fractal analysis was used to study the morphological characteristics of small and medium-sized carbides during the dissolution process.According to changes in the fractal dimension before and after soaking,the carbides tended to evolve towards a more regular morphology.展开更多
Electric current heat treatment is an innovative technique to improve microstructures and mechanical properties of metallic materials.The microstructures and mechanical properties of a powder metallurgy high-speed ste...Electric current heat treatment is an innovative technique to improve microstructures and mechanical properties of metallic materials.The microstructures and mechanical properties of a powder metallurgy high-speed steel(PM-HSS)treated by electric current heat treatment and traditional heat treatment are comparatively investigated.Results showed that after austenitizing at 1130°C,the structure of PM-HSS sample composed of ferrite matrix,M_(6)C,M_(23)C_(6),and MC carbides,transformed into a martensite matrix accompanied by M_(6)C and MC carbides.Compared to the traditional austenitizing at 1130℃ for 30 min,the electric current austenitizing at 1130℃ for 5 min dissolved more carbides,resulting in a greater solid solution of alloying elements in the matrix.Further traditional triple tempering led to carbide coarsening,whereas electric current triple tempering promoted the carbide dissolution.Notably,the dissolution of more carbides resulted in a higher C content in the martensite matrix of HSS treated by electric current,significantly promoting the formation of nanotwins(5-20 nm in width).The electric current triple tempering sample exhibited a yield strength of 3097 MPa,compressive strength of 5016 MPa,and a fracture strain of 30.0%,outperforming the traditional triple tempering sample by nearly 600 MPa in yield strength.Analysis revealed that this significant strengthening was primarily attributed to nanotwin formation and solid solution strengthening caused by carbide dissolution.展开更多
Fe-28Mn-(10-12)Al-(0.8-1.4)C(wt.%)steels were designed to investigate the influence of varying Al and C content on precipitation behavior ofκ-carbide and its contribution to the strength of high-Mn low-density steels...Fe-28Mn-(10-12)Al-(0.8-1.4)C(wt.%)steels were designed to investigate the influence of varying Al and C content on precipitation behavior ofκ-carbide and its contribution to the strength of high-Mn low-density steels.Results reveal that both Al and C elements promoteκ-carbide precipitation,with C having a more pronounced effect.In near-rapidly solidified 10Al steel strips,increasing C content from 0.8wt.%to 1.4wt.%raises theκ-carbide size from 9.6 nm to 38.2 nm,accompanied by volume fraction increase from 10.2vol.%to 29.8vol.%.In comparison,the average size and volume fraction ofκ-carbides in 12Al0.8C steel are only 11.4 nm and 17.8vol.%,respectively.Higher Al and C content reduces the lattice mismatch between austenite andκ-carbides,thus promoting nucleation ofκ-carbides.Notably,the increase in C content results in a greater reduction in the Gibbs free energy ofκ-carbide,leading to a stronger driving force forκ-carbide formation.Consequently,as the C content increases from 0.8wt.%to 1.4wt.%,the interaction betweenκ-carbides and dislocations transforms from particle cutting to bypassing,and the maximum precipitation strengthening ofκ-carbides reaches 583 MPa.The construction of the relationship between Al and C content andκ-carbide precipitation in this study would provide valuable insights for alloy design of high-Mn steels.展开更多
Cleanliness control of advanced steels is of vital importance for quality control of the products.In order to understand and control the inclusion removal during refining process in molten steel,its motion behaviors a...Cleanliness control of advanced steels is of vital importance for quality control of the products.In order to understand and control the inclusion removal during refining process in molten steel,its motion behaviors at the multiple steel/gas/slag interfaces have attracted the attention much of metallurgical community.The recent development of the agglomeration of non-metallic inclusions at the steel/Ar and steel/slag interfaces has been summarized,and both the experimental as well as theoretical works have been surveyed.In terms of in situ observation of high-temperature interfacial phenomena in the molten steel,researchers utilized high-temperature confocal laser scanning microscopy to observe the movement of more types of inclusions at the interface,i.e.,the investigated inclusion is no longer limited to Al_(2)O_(3)-based inclusions but moves forward to rare earth oxides,MgO-based oxides,etc.In terms of theoretical models,especially the model of inclusions at the steel/slag interface,the recent development has overcome the limitations of the assumptions of Kralchevsky-Paunov model and verified the possible errors caused by the model assumptions by combining the water model and the physical model.Last but not least,the future work in this topic has been suggested,which could be in combination of thermal physical properties of steels and slag,as well as utilize the artificial intelligence-based methodology to implement a comprehensive inclusion motion behaviors during a comprehensive metallurgical process.展开更多
The mechanical properties of an austenite-based Fe-Mn-Al-C lightweight steel were improved by co-precipitation of nanoscale Cu-rich andκ-carbide particles.The Fe-28Mn-9Al-0.8C-(0,3)Cu(wt.%)strips were near-rapidly so...The mechanical properties of an austenite-based Fe-Mn-Al-C lightweight steel were improved by co-precipitation of nanoscale Cu-rich andκ-carbide particles.The Fe-28Mn-9Al-0.8C-(0,3)Cu(wt.%)strips were near-rapidly solidified and annealed in the temperature range from 500℃to 700℃.The microstructure evolution and mechanical properties of the steel under different annealing processes were studied.Microstructural analysis reveals that nanoscaleκ-carbides and Cu-rich particles precipitate in the austenite and ferrite of the steel in this annealing temperature range.Co-precipitation of nanoscale Cu-rich particles andκ-carbides provides an obvious increment in the yield strength.At the annealing temperature of 600℃,both the yield strength and ultimate tensile strength of Fe-28Mn-9Al-0.8C-3Cu(wt.%)steel strip are the highest.The total elongation is 25%,which is obviously higher than that of Cu-free steel strips,for the addition of Cu reduces the large sizedκ-carbides precipitated along austenite/ferrite interfaces.When the annealing temperature rises to 700℃,the strength and ductility of the two steel strips deteriorate due to the formation of massive intergranularκ-carbides precipitated along austenite/ferrite interfaces.It can be concluded that a proper co-precipitation of Cu-rich particles andκ-carbides would improve the properties of austenite-based Fe-Mn-Al-C steel.展开更多
With the rapid development of high-strength low-alloy(HSLA)steel,Nb as an important microalloying element has received more and more attention in recent years.The application and behavior of Nb in HSLA steel,including...With the rapid development of high-strength low-alloy(HSLA)steel,Nb as an important microalloying element has received more and more attention in recent years.The application and behavior of Nb in HSLA steel,including microstructures optimization,refining grain size,and precipitation behavior of Nb-containing phases,were reviewed.Nb could play an important role in following manners:(1)Nb-containing phases promote ferrite formation,and Nb solute promotes bainite formation.(2)Nb solute atoms and Nb-containing phases can inhibit the growth of austenite grains and austenite recrystallization.(3)Nb(C,N)that precipitates in ferrite/bainite can provide more significant strengthening contribution(more than 300 MPa)than that in austenite(about 100 MPa).Some reasonable suggestions for the production of Nb-bearing HSLA steel with excellent mechanical properties were put forward.展开更多
The morphology and distribution of manganese sulfide(MnS)inclusions have a significant influence on the comprehensive performance,which is an important research field for resulfurized steels.Based on the experiments o...The morphology and distribution of manganese sulfide(MnS)inclusions have a significant influence on the comprehensive performance,which is an important research field for resulfurized steels.Based on the experiments of non-aqueous electrolyte and scanning electron microscope observation,the fractal theory was employed to study the three-dimensional morphologies of MnS inclusions.The results showed that the edge fractal dimension of MnS inclusions was between 1.59 and 1.88.In addition,similar morphology of MnS inclusions had a close fractal dimension.The MnS edge fractal dimension is highly positively correlated with the morphological parameters.The multifractal spectrums of MnS inclusions on two-dimensional plane of as-cast and as-rolled resulfurized free-cutting steels were calculated.The large-size MnS inclusions belong to large probability subset,while the small-size MnS inclusions belong to small probability subset.The multifractal spectrum can truly and effectively reflect the difference and non-uniformity of distribution of MnS inclusions on 2D plane.On the premise of similar content of MnS,with the refinement of MnS inclusions,the multifractal spectrum width and the multifractal spectrum symmetry parameter were decreased.The multifractal spectrum provides a new method for studying the second phase in materials.展开更多
Submerged entry nozzle(SEN)clogging is a major problem affecting the production quality of rare earth steel,and finding a suitable refractory outlet can significantly reduce production costs.To explore the relationshi...Submerged entry nozzle(SEN)clogging is a major problem affecting the production quality of rare earth steel,and finding a suitable refractory outlet can significantly reduce production costs.To explore the relationship between refractory composition and interface interaction,unprotected coated Al_(2)O_(3)–MgO refractories and SiO2-coated Al_(2)O_(3)–MgO refractories were added to rare earth high-carbon heavy rail steel under laboratory conditions,and the Al_(2)O_(3)–MgO refractory was found to be more suitable.The results show that,from the epoxy resin side to the refractory side,the contour of the refractory interface reaction layer can be divided into two main layers:an iron-rich reaction layer and an iron-poor reaction layer.Calculations based on the spherical model suggest that the adhesion force is proportional to the size of the refractory particles and inclusions,and the same result applies to the surface tension.Controlling the inclusions at a smaller size has a specific effect on alleviating the erosion of refractories.Combined with the erosion mechanism of Al_(2)O_(3)–MgO refractories,the interface reaction mechanism between Al_(2)O_(3)–MgO refractories and molten steel was proposed,which provides ideas for solving SEN clogging.展开更多
An aging method assisted by electric current was applied to a Fe-18Mn-9Al-1C(wt.%)low-density steel.It improves the microstructure and therefore significantly increases both the yield strength and ductility of the ste...An aging method assisted by electric current was applied to a Fe-18Mn-9Al-1C(wt.%)low-density steel.It improves the microstructure and therefore significantly increases both the yield strength and ductility of the steel.This current-assisted aging method can increase the yield strength by 178 MPa and elongation by 1.16 times in only 0.5 min at 450℃.However,the yield strength is increased only 90 MPa by the traditional aging method(heat conduction)at 450℃for 180 min,and the elongation is even decreased from 42.0%to 31.6%.The obvious improvement in yield strength by the current-assisted aging for a short time is resulted from the fact that the current-assisted aging promotes a rapid precipitation of nano-scaleκ-carbides inγ-austenite by reducing the thermodynamic barrier and accelerating the atomic diffusion.This work demonstrates that this current-assisted aging method is significantly time saving and cost-effective for low-density steels,with potential for various industrial applications.展开更多
Steels. the most widely used metals in the world, play fundamental and crucial roles in various industries as well as our daily life. It is well known that the performance of materials is correlated with designed comp...Steels. the most widely used metals in the world, play fundamental and crucial roles in various industries as well as our daily life. It is well known that the performance of materials is correlated with designed composition and achieved structures that are controlled by process procedures and parameters, and thus the employment of proper procedures and parameters is essential for the properties and quality of final steel products.展开更多
基金supported by the National Natural Science Foundation of China(No.52071195)Key Project of the National Natural Science Foundation of China(No.52130109).
文摘A novel Nb–V–Ce multi-microalloyed low-alloy cast steel for offshore platform nodes was investigated to achieve the properties similar to X80 pipeline steel,including high yield strength and low-temperature impact energy.The experimental results demonstrate that the addition of elements such as Nb,V and Ce can markedly improve the strength of the low-alloy cast steel.Maintaining a constant level of elements such as Nb,V and Ce,while reducing the content of Si to 0.28 wt.%,leads to substantial enhancements in impact energy at−40℃,meeting the mechanical properties criteria of X80 pipeline steel.The excellent mechanical properties of the multi-microalloyed low-alloy cast steel result from the reason that the multi-addition of microalloying elements refines the grains and facilitates the formation of nanoprecipitates like NbC.Moreover,decreasing Si content can enhance the recovery of martensitic laths in cast steel during the tempering process,reducing stress from dislocation movement and improving plasticity.
基金financially supported by the National Natural Science Foundation of China(Nos.52271034,52301058 and 52471042)the National MCF Energy R&D Program of China(No.2018YFE0306102)+1 种基金the China Postdoctoral Science Foundation(No.2023M732183)the Postdoctoral Fellowship Program of CPSF(No.GZB20230399).
文摘To develop a melting-based larger-scale fabrication process for oxide dispersion strengthened(ODS)steel,this study proposed a method of zone melting with built-in precursor powder(ZMPP),followed by hot forging and aging treatments.A 50 kg ingot was successfully prepared,highlighting the scalability of this innovative process.Microstructural analysis revealed a predominantly lath martensite matrix with a small amount of ferrite in the hot-forged ODS steel,without oxide particle aggregation.Aging at 750℃ resulted in the formation of sub-micron-sized Cr_(23)C_(6) particles at grain boundaries and martensitic lath interfaces,accompanied by a high-density(7.64×1023 m^(-3))nano-scale(~6 nm)Y-Si-O complex oxides after 25 h.Additionally,the hot-forged sample exhibited a high yield strength(871 MPa)but limited ductility(5.0%).Aging treatments led to an increase in ductility but a decrease in yield strength.Notably,prolonged aging maintained the strength level of steels while enhancing ductility,with a 23.3% total elongation observed after 25 h.The novel ZMPP method,preparing high-quality ODS steels with uniform microstructure and good mechanical properties,provided a new avenue for large-scale production of ODS steels.
基金the National Natural Science Foundation of China(No.51974184)National MCF Energy R&D Program of China(No.2018YFE0306102)Independent Research Project of State Key Laboratory of Advanced Special Steel and Shanghai Key Laboratory of Advanced Ferrometallurgy,Shanghai University.
文摘Precipitation strengthening of nano-scale TiC is a promising method to improve mechanical properties of Fe–16Mn–9Al–0.8C(wt.%)low-density steel.This work attempted to introduce nano-scale TiC precipitates by adding 1 wt.%Ti element.The experimental results show that these precipitates with the total fraction of about 2 vol.%were formed and no coarse precipitates were observed despite the high Ti addition.It was interesting that the polygonal and needle-shaped TiC precipitates were observed inγ-austenite andδ-ferrite,respectively.Ti addition also decreased the volume fraction ofγ-austenite significantly.Correspondingly,the yield strength was increased,but the elongation was significantly decreased due to the significant decrease ofγ-austenite.Comparing with the Ti-free steel,the formation of TiC precipitates was the main reason for the increase in yield strength of Ti-bearing steel,and TiC precipitates also led to a higher strain hardening index at the first deformation stage.TiC precipitates promoted the Orowan strengthening,resulting in a higher strain hardening capability than Ti-free steel reinforced by shearableκ-carbide.
基金funded by the National Natural Science Foundation of China(Nos.52104334,51874195 and 52074179)Center for Advanced Solidification Technology(CAST)and State Key Laboratory of Advanced Special Steel.
文摘In order to investigate the modification behavior and regularity of inclusions in X80 pipeline steel by Mg-treatment, the comparative industrial experiments of Mg-treatment and Ca-treatment in X80 pipeline steel were carried out. Mg and Ca were added to the steel in the form of cored wire after RH (Ruhrstahl-Hereaeus vacuum degassing) process. After adding Ca-containing cored wire, the inclusions were transformed into CaO–Al_(2)O_(3) in the steel. With the progress of smelting, the cleanliness of molten steel became worse, and the equivalent diameter of inclusions was at a higher level. Mg-treatment had a good effect on the modification of inclusions. After Mg-containing cored wire was added to the steel, Al_(2)O_(3) and CaO–Al_(2)O_(3) in the steel were transformed into MgO, MgO·Al_(2)O_(3), and CaO–MgO–Al_(2)O_(3) inclusions, which were basically spherical. The initial precipitated MgO became the core of other inclusions in the steel, which promotes the precipitation of MgO·Al_(2)O_(3). After Mg-treatment, almost no unmodified calcium aluminate inclusions existed in the hot rolled plate, and the cleanliness of the steel was improved. The effect of Ca and Mg on the transformation of inclusions in pipeline steel was studied by thermodynamic calculation, the result of which is consistent with the experimental results.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.52104335,51874195 and 52074179)the Shanghai“Super Postdoctoral”Incentive Plan(No.2020194).
文摘Te treatment is an effective method for modifying sulfide inclusions,and MnTe precipitation has an important effect on thermal brittleness and steel corrosion resistance.In most actual industrial applications of Te treatment,MnTe precipitation is unexpected.The critical precipitation behavior of MnTe inclusions was investigated through scanning electron microscopy,transmission electron microscopy,machine learning,and first-principles calculation.MnTe preferentially precipitated at the container mouth for sphere-like sulfides and at the interface between MnS grain boundaries and steel matrix for rod-like sulfides.The MnS/MnTe interface was semicoherent.A composition transition zone with a rock-salt structure exhibiting periodic changes existed to maintain the semicoherent interface.The critical precipitation behavior of MnTe inclusions in resulfurized steels involved three stages at varying temperatures.First,Mn(S,Te)precipitated during solidification.Second,MnTe with a rock-salt structure precipitated from Mn(S,Te).Third,MnTe with a hexagonal NiAs structure transformed from the rock-salt structure.The solubility of Te in MnS decreased with decreasing temperature.The critical precipitation behavior of MnTe inclusions in resulfurized steels was related to the MnS precipitation temperature.With the increase in MnS precipitation temperature,the critical Te/S weight ratio decreased.In consideration of the cost-effectiveness of Te addition for industrial production,the Te content in resulfurized steels should be controlled in accordance with MnS precipitation temperature and S content.
基金supported by Independent Research Project of State Key Laboratory of Advanced Special Steel,Shanghai Key Laboratory of Advanced Ferrometallurgy,Shanghai University(SKLASS-2023-Z13)the Science and Technology Commission of Shanghai Municipality(No.19DZ2270200)+1 种基金A portion of the work was performed at US National High Magnetic Field Laboratory,which is supported by the National Science Foundation(Cooperative Agreement No.DMR-1157490 and DMR-1644779)the State of Florida.Thanks also to Mary Tyler for editing.
文摘The high-temperature dissolution behavior of primary carbides in samples taken from GCr15 continuous-casting bloom was observed in-situ by confocal laser scanning microscopy.Equations were fitted to the dissolution kinetics of primary carbides during either heating or soaking.Dissolution of carbides proceeded in three stages(fast→slow→faster)as either temperature or holding time was increased.During the heating process and during the first and third stages of the soaking process,the original size of the carbides determined the steepness of the slope,but during the middle(“slow”)stage of the soaking process,the slope remained zero.The initial size of the carbides varied greatly,but their final dissolution temperature fell within the narrow range of 1210-1235℃,and the holding time remained within 50 min.Fractal analysis was used to study the morphological characteristics of small and medium-sized carbides during the dissolution process.According to changes in the fractal dimension before and after soaking,the carbides tended to evolve towards a more regular morphology.
基金financially supported by the National Natural Science Foundation of China(Nos.52271034,52301058 and 52471042)China Postdoctoral Science Foundation(No.2023M732183)Postdoctoral Fellowship Program of CPSF(No.GZB20230399).
文摘Electric current heat treatment is an innovative technique to improve microstructures and mechanical properties of metallic materials.The microstructures and mechanical properties of a powder metallurgy high-speed steel(PM-HSS)treated by electric current heat treatment and traditional heat treatment are comparatively investigated.Results showed that after austenitizing at 1130°C,the structure of PM-HSS sample composed of ferrite matrix,M_(6)C,M_(23)C_(6),and MC carbides,transformed into a martensite matrix accompanied by M_(6)C and MC carbides.Compared to the traditional austenitizing at 1130℃ for 30 min,the electric current austenitizing at 1130℃ for 5 min dissolved more carbides,resulting in a greater solid solution of alloying elements in the matrix.Further traditional triple tempering led to carbide coarsening,whereas electric current triple tempering promoted the carbide dissolution.Notably,the dissolution of more carbides resulted in a higher C content in the martensite matrix of HSS treated by electric current,significantly promoting the formation of nanotwins(5-20 nm in width).The electric current triple tempering sample exhibited a yield strength of 3097 MPa,compressive strength of 5016 MPa,and a fracture strain of 30.0%,outperforming the traditional triple tempering sample by nearly 600 MPa in yield strength.Analysis revealed that this significant strengthening was primarily attributed to nanotwin formation and solid solution strengthening caused by carbide dissolution.
基金supported by the National Natural Science Foundation of China(Nos.52301058 and 52271034)the China Postdoctoral Science Foundation(No.2023M732183)+3 种基金the Postdoctoral Fellowship Program of CPSF(No.GZB20230399)the Key scientific and technological project in Ningbo City(No.2022Z056)supported by the Independent Research Project of State Key Laboratory of the Advanced Special Steel,Shanghai Key Laboratory of Advanced Ferrometallurgy,Shanghai University(SKLASS 2023-Z12)the Science and Technology Commission of Shanghai Municipality(No.19DZ2270200).
文摘Fe-28Mn-(10-12)Al-(0.8-1.4)C(wt.%)steels were designed to investigate the influence of varying Al and C content on precipitation behavior ofκ-carbide and its contribution to the strength of high-Mn low-density steels.Results reveal that both Al and C elements promoteκ-carbide precipitation,with C having a more pronounced effect.In near-rapidly solidified 10Al steel strips,increasing C content from 0.8wt.%to 1.4wt.%raises theκ-carbide size from 9.6 nm to 38.2 nm,accompanied by volume fraction increase from 10.2vol.%to 29.8vol.%.In comparison,the average size and volume fraction ofκ-carbides in 12Al0.8C steel are only 11.4 nm and 17.8vol.%,respectively.Higher Al and C content reduces the lattice mismatch between austenite andκ-carbides,thus promoting nucleation ofκ-carbides.Notably,the increase in C content results in a greater reduction in the Gibbs free energy ofκ-carbide,leading to a stronger driving force forκ-carbide formation.Consequently,as the C content increases from 0.8wt.%to 1.4wt.%,the interaction betweenκ-carbides and dislocations transforms from particle cutting to bypassing,and the maximum precipitation strengthening ofκ-carbides reaches 583 MPa.The construction of the relationship between Al and C content andκ-carbide precipitation in this study would provide valuable insights for alloy design of high-Mn steels.
基金the National Natural Science Foundation of China(Grant No.52074179)for the financial supportNational Key Research and Development Program of China(2024YFB3713705)is also acknowledged.
文摘Cleanliness control of advanced steels is of vital importance for quality control of the products.In order to understand and control the inclusion removal during refining process in molten steel,its motion behaviors at the multiple steel/gas/slag interfaces have attracted the attention much of metallurgical community.The recent development of the agglomeration of non-metallic inclusions at the steel/Ar and steel/slag interfaces has been summarized,and both the experimental as well as theoretical works have been surveyed.In terms of in situ observation of high-temperature interfacial phenomena in the molten steel,researchers utilized high-temperature confocal laser scanning microscopy to observe the movement of more types of inclusions at the interface,i.e.,the investigated inclusion is no longer limited to Al_(2)O_(3)-based inclusions but moves forward to rare earth oxides,MgO-based oxides,etc.In terms of theoretical models,especially the model of inclusions at the steel/slag interface,the recent development has overcome the limitations of the assumptions of Kralchevsky-Paunov model and verified the possible errors caused by the model assumptions by combining the water model and the physical model.Last but not least,the future work in this topic has been suggested,which could be in combination of thermal physical properties of steels and slag,as well as utilize the artificial intelligence-based methodology to implement a comprehensive inclusion motion behaviors during a comprehensive metallurgical process.
基金financially supported by the National Natural Science Foundation of China(No.51974184)the National MCF Energy R&D Program of China(No.2018YFE0306102)。
文摘The mechanical properties of an austenite-based Fe-Mn-Al-C lightweight steel were improved by co-precipitation of nanoscale Cu-rich andκ-carbide particles.The Fe-28Mn-9Al-0.8C-(0,3)Cu(wt.%)strips were near-rapidly solidified and annealed in the temperature range from 500℃to 700℃.The microstructure evolution and mechanical properties of the steel under different annealing processes were studied.Microstructural analysis reveals that nanoscaleκ-carbides and Cu-rich particles precipitate in the austenite and ferrite of the steel in this annealing temperature range.Co-precipitation of nanoscale Cu-rich particles andκ-carbides provides an obvious increment in the yield strength.At the annealing temperature of 600℃,both the yield strength and ultimate tensile strength of Fe-28Mn-9Al-0.8C-3Cu(wt.%)steel strip are the highest.The total elongation is 25%,which is obviously higher than that of Cu-free steel strips,for the addition of Cu reduces the large sizedκ-carbides precipitated along austenite/ferrite interfaces.When the annealing temperature rises to 700℃,the strength and ductility of the two steel strips deteriorate due to the formation of massive intergranularκ-carbides precipitated along austenite/ferrite interfaces.It can be concluded that a proper co-precipitation of Cu-rich particles andκ-carbides would improve the properties of austenite-based Fe-Mn-Al-C steel.
文摘With the rapid development of high-strength low-alloy(HSLA)steel,Nb as an important microalloying element has received more and more attention in recent years.The application and behavior of Nb in HSLA steel,including microstructures optimization,refining grain size,and precipitation behavior of Nb-containing phases,were reviewed.Nb could play an important role in following manners:(1)Nb-containing phases promote ferrite formation,and Nb solute promotes bainite formation.(2)Nb solute atoms and Nb-containing phases can inhibit the growth of austenite grains and austenite recrystallization.(3)Nb(C,N)that precipitates in ferrite/bainite can provide more significant strengthening contribution(more than 300 MPa)than that in austenite(about 100 MPa).Some reasonable suggestions for the production of Nb-bearing HSLA steel with excellent mechanical properties were put forward.
基金The authors gratefully express their appreciation to National Key Research and Development Program of China (Grant No.2018YFB0704400)National Natural Science Foundation of China (Grant Nos.51874195 and 52074179)for supporting this work+1 种基金support from the Youth Program of National Natural Science Foundation of China (Grant No.52104335)Shanghai "Super Postdoctoral"Incentive Plan (Grant No.2020194).
文摘The morphology and distribution of manganese sulfide(MnS)inclusions have a significant influence on the comprehensive performance,which is an important research field for resulfurized steels.Based on the experiments of non-aqueous electrolyte and scanning electron microscope observation,the fractal theory was employed to study the three-dimensional morphologies of MnS inclusions.The results showed that the edge fractal dimension of MnS inclusions was between 1.59 and 1.88.In addition,similar morphology of MnS inclusions had a close fractal dimension.The MnS edge fractal dimension is highly positively correlated with the morphological parameters.The multifractal spectrums of MnS inclusions on two-dimensional plane of as-cast and as-rolled resulfurized free-cutting steels were calculated.The large-size MnS inclusions belong to large probability subset,while the small-size MnS inclusions belong to small probability subset.The multifractal spectrum can truly and effectively reflect the difference and non-uniformity of distribution of MnS inclusions on 2D plane.On the premise of similar content of MnS,with the refinement of MnS inclusions,the multifractal spectrum width and the multifractal spectrum symmetry parameter were decreased.The multifractal spectrum provides a new method for studying the second phase in materials.
基金the State Key Laboratory of Rare Earth Resources Research and Comprehensive Utilization of Baiyun Obo for the open project(Grant No.2022(Kehe)00281)the Central Government Guidance Local Science and Technology Development Fund Project(Grant No.2022ZY0124)for supporting this worksupported by the National Natural Science Foundation of China(Grant No.52074179).
文摘Submerged entry nozzle(SEN)clogging is a major problem affecting the production quality of rare earth steel,and finding a suitable refractory outlet can significantly reduce production costs.To explore the relationship between refractory composition and interface interaction,unprotected coated Al_(2)O_(3)–MgO refractories and SiO2-coated Al_(2)O_(3)–MgO refractories were added to rare earth high-carbon heavy rail steel under laboratory conditions,and the Al_(2)O_(3)–MgO refractory was found to be more suitable.The results show that,from the epoxy resin side to the refractory side,the contour of the refractory interface reaction layer can be divided into two main layers:an iron-rich reaction layer and an iron-poor reaction layer.Calculations based on the spherical model suggest that the adhesion force is proportional to the size of the refractory particles and inclusions,and the same result applies to the surface tension.Controlling the inclusions at a smaller size has a specific effect on alleviating the erosion of refractories.Combined with the erosion mechanism of Al_(2)O_(3)–MgO refractories,the interface reaction mechanism between Al_(2)O_(3)–MgO refractories and molten steel was proposed,which provides ideas for solving SEN clogging.
基金financially supported by the National MCF Energy R&D Program of China(No.2018YFE0306102)the National Natural Science Foundation of China(No.51974184)the Joint Fund of Iron and Steel Research(No.U1660103)
文摘An aging method assisted by electric current was applied to a Fe-18Mn-9Al-1C(wt.%)low-density steel.It improves the microstructure and therefore significantly increases both the yield strength and ductility of the steel.This current-assisted aging method can increase the yield strength by 178 MPa and elongation by 1.16 times in only 0.5 min at 450℃.However,the yield strength is increased only 90 MPa by the traditional aging method(heat conduction)at 450℃for 180 min,and the elongation is even decreased from 42.0%to 31.6%.The obvious improvement in yield strength by the current-assisted aging for a short time is resulted from the fact that the current-assisted aging promotes a rapid precipitation of nano-scaleκ-carbides inγ-austenite by reducing the thermodynamic barrier and accelerating the atomic diffusion.This work demonstrates that this current-assisted aging method is significantly time saving and cost-effective for low-density steels,with potential for various industrial applications.
文摘Steels. the most widely used metals in the world, play fundamental and crucial roles in various industries as well as our daily life. It is well known that the performance of materials is correlated with designed composition and achieved structures that are controlled by process procedures and parameters, and thus the employment of proper procedures and parameters is essential for the properties and quality of final steel products.
