Compared with the traditional atm ospheric carburization, low-pressure carburization has the benefits of producing no surface oxidation and leaving fine, uniformly dispersed carbides in the carburized layer. However, ...Compared with the traditional atm ospheric carburization, low-pressure carburization has the benefits of producing no surface oxidation and leaving fine, uniformly dispersed carbides in the carburized layer. However, the process param eters for low-pressure carburization of 16Cr3NiWMoVNbE steel have yet to be optimized. Thus, we use the saturation-value method to optimize these parameters for aviation-gear materials. Toward this end, the m icrostructure and properties of 16Cr3NiWMoVNbE steel after different carburization processes are studied by optical microscopy, scanning electron microscopy, transm ission electron microscopy, and electron probe microanalysis. Considering the saturated austenite carbon concentration, we propose a model of carbon flux and an alloy coefficient for low -pressure carburization to reduce the carbon concentration in austenite and avoid the surface carbide network. At the early stage of carburization (30 s), the gas-solid interface has a higher concentration gradient. The averaging method is not ideal in practical applications, but the carbon flux measured by using the segm ented average m ethod is 2.5 times that measured by the overall average method, which is ideal in practical applications. The corresponding carburization tim e is reduced by 60%. By using the integral average method, the actual carburization time increases, which leads to the rapid form ation of carbide on the surface and affects the entire carburization process. Nb and Wcombine with C to form carbides, which hinders carbon diffusion and consumes carbon, resulting in a sharp decrease in the rate of C diffusion in austenite (the diffusion rate is reduced by 52% for 16Cr3NiWMoVNbE steel). By changing the diffusion coefficient model and comparing the hardness gradient of different processes, the depth of the actual layer is found to be very similar to the design depth.展开更多
There is currently a gap in our understanding of mechanisms that contribute to high strength and high plasticity in high strength UFG ferritic steel with nano-size Fe3 C carbides in situations that involve combination...There is currently a gap in our understanding of mechanisms that contribute to high strength and high plasticity in high strength UFG ferritic steel with nano-size Fe3 C carbides in situations that involve combination of various strain rates and high temperature.In this regard,we describe the mechanistic basis of obtaining high strength-high plasticity combination in an ultrafine-grained(UFG)(~500±30 nm)ferritic steel with nano-size carbides,which sustained large plastic deformation,exceeding 100%elongation at a temperature significantly below 0.5 of the absolute melting point(Tm).To address the missing gap in our knowledge,we conducted a series of experiments involving combination of strain rate and temperature effects in conjunction with electron microscopy and atom probe tomography(APT).Strain rate studies were carried out at strain rates in the range of 0.0017-0.17 s^(-1)and at different temperatures from 25℃to 600℃.Dynamic recrystallization occurred at 600℃,resulting in a significant decrease in yield and tensile strength.Nevertheless,the UFG ferritic steels had an advantage in tensile strength(UTS)and elongation-to-failure(εf)at 600℃,especially at strain rate of 0.0017 s^(-1),with high UTSof 510 MPa and excellent low temperature(<0.42 Tm)superplasticity(εf=110%).These mechanical properties are significantly superior compared to similar type of steels at identical temperature.A mechanistic understanding of mechanical behavior of UFG ferritic steels is presented by combining the effect of strain rate,temperature,and nano-size carbides.展开更多
This research explores the prospect of fabricating a face-centered cubic(fcc) Ni-base alloy cladding(Inconel 690) on an fcc Fe-base alloy(316 L stainless-steel) having improved mechanical properties and reduced sensit...This research explores the prospect of fabricating a face-centered cubic(fcc) Ni-base alloy cladding(Inconel 690) on an fcc Fe-base alloy(316 L stainless-steel) having improved mechanical properties and reduced sensitivity to corrosion through grain boundary and microstructure engineering concepts enabled by additive manufacturing(AM) utilizing electron-beam powder bed fusion(EPBF). The unique solidification and associated constitutional supercooling phenomena characteristic of EPBF promotes[100] textured and extended columnar grains having lower energy grain boundaries as opposed to random, high-angle grain boundaries, but no coherent {111} twin boundaries characteristic of conventional thermo-mechanically processed fcc metals and alloys, including Inconel 690 and 316 L stainless-steel.In addition to [100] textured grains, columnar grains were produced by EPBF fabrication of Inconel 690 claddings on 316 L stainless-steel substrates. Also, irregular 2–3 μm diameter, low energy subgrains were formed along with dislocation densities varying from 108 to 109 cm^2, and a homogeneous distribution of Cr_(23)C_6 precipitates. Precipitates were formed within the grains(with ~3 μm interparticle spacing),but not in the subgrain or columnar grain boundaries. These inclusive, hierarchical microstructures produced a tensile yield strength of 0.527 GPa, elongation of 21%, and Vickers microindentation hardness of 2.33 GPa for the Inconel 690 cladding in contrast to a tensile yield strength of 0.327 GPa, elongation of 53%, and Vickers microindentation hardness of 1.78 GPa, respectively for the wrought 316 L stainlesssteel substrate. Aging of both the Inconel 690 cladding and the 316 L stainless-steel substrate at 685?C for50 h precipitated Cr_(23)C_6 carbides in the Inconel 690 columnar grain boundaries, but not in the low-angle(and low energy) subgrain boundaries. In contrast, Cr_(23)C_6 carbides precipitated in the 316 L stainless-steel grain boundaries, but not in the low energy coherent {111} twin boundaries. Consequently, the Inconel690 subgrain boundaries essentially serve as surrogates for coherent twin boundaries with regard to avoiding carbide precipitation and corrosion sensitization.展开更多
Gradient boosting decision tree(GBDT)machine learning(ML)method was adopted for the first time to automatically recognize and conduct quantitative statistical analysis of boundaries in bainitic microstructure using el...Gradient boosting decision tree(GBDT)machine learning(ML)method was adopted for the first time to automatically recognize and conduct quantitative statistical analysis of boundaries in bainitic microstructure using electron back-scatter diffraction(EBSD)data.In spite of lack of large sets of EBSD data,we were successful in achieving the desired accuracy and accomplishing the objective of recognizing the boundaries.Compared with a low model accuracy of<50%as using Euler angles or axis-angle pair as characteristic features,the accuracy of the model was significantly enhanced to about 88%when the Euler angle was converted to overall misorientation angle(OMA)and specific misorientation angle(SMA)and considered as important features.In this model,the recall score of prior austenite grain(PAG)boundary was~93%,high angle packet boundary(OMA>40°)was~97%,and block boundary was~96%.The derived outcomes of ML were used to obtain insights into the ductile-to-brittle transition(DBTT)behavior.Interestingly,ML modeling approach suggested that DBTT was not determined by the density of high angle grain boundaries,but significantly influenced by the density of PAG and packet boundaries.The study underscores that ML has a great potential in detailed recognition of complex multi-hierarchical microstructure such as bainite and martensite and relates to material performance.展开更多
This work aims to elucidate the impact of aluminum-content on microstructure and deformation mechanisms of transformation-induced plasticity（TRIP） steels through macroscale and nanoscale deformation experiments comb...This work aims to elucidate the impact of aluminum-content on microstructure and deformation mechanisms of transformation-induced plasticity（TRIP） steels through macroscale and nanoscale deformation experiments combined with post-mortem electron microscopy of the deformed region.The solid-state transformation-induced mechanical deformation varied with the Al contents,and influenced tensile strength-ductility combination.Steels with 2–4 wt% Al were characterized by TRIP effect.In contrast to 2 Al-TRIP and 4 Al-TRIP steels,twinning-induced plasticity（TWIP） was also observed in conjunction with strain-induced martensite in 6 Al-TRIP steel.This behavior is attributed to the increase in stacking fault energy with the increase of Al content and stability of austenite,which depends on the local chemical variation.The study addresses the knowledge gap with regard to the effect of Al content on austenite stability in medium-Mn TRIP steels.This combination is expected to potentially enable cost-effective alloy design with high strength-high ductility condition.展开更多
In this study, two types of as-cast microstructure produced by strip casting were cold rolled and annealed to investigate the effect of initial microstructure on the textural evolution and magnetic properties of non-o...In this study, two types of as-cast microstructure produced by strip casting were cold rolled and annealed to investigate the effect of initial microstructure on the textural evolution and magnetic properties of non-oriented silicon steel. The results indicated that the cold-rolled sheets of coarse-grained strip with pronounced {100} components exhibited stronger 入 fiber(<100>//ND) and weaker γ fiber(<111>//ND)texture as composed to the fine-grained strip with strong Goss({110}(001)) texture. After annealing, the former was dominated by η fiber(<001>//RD) texture with a peak at {110}<001)orientation, while the latter consisted of strong {111}(112) and relatively weak {110}(001) texture. In addition, a number of precipitates of size ～30-150 nm restricted the grain growth during annealing, resulting in recrystallization of grain size of ～46 μm in the coarse-grained specimen and ～41μm in the fine-grained specimen.Ultimately, higher magnetic induction(～1.72 T) and lower core loss(～4.04 W/kg) were obtained in the final annealed sheets of coarse-grained strip with strong {100} texture.展开更多
The structure-property relationship in heat-affected zone (HAZ)of a low-carbon steel bearing V-N subjected to gasshielded arc welding was explored.The microstructural characteristics of base metal (BM),coarse-grained ...The structure-property relationship in heat-affected zone (HAZ)of a low-carbon steel bearing V-N subjected to gasshielded arc welding was explored.The microstructural characteristics of base metal (BM),coarse-grained HAZ (CGHAZ),fine-grained HAZ,and intercritical HAZ were significantly different.The effect of grain-refinement strengthening and transformation hardening on HAZ contributed to equivalent hardness of 260.8-278.5 HV in comparison with BM hardness of 272.0 HV.Moreover,excellent impact toughness at -20 ℃ was obtained because of high resistance to crack propagation by high-misorientation boundaries,leading to impact fracture consisting of dimples.In CGHAZ,free N was partly fixed by V(C,N)precipitates,such that the deterioration effect of N on toughness was considered to be nearly eliminated.In comparison with CGHAZ,weld metal contained higher fraction of acicular ferrite with fine plates,while the impact toughness was inferior because of the detrimental influence of coarse inclusions from the welding wire.The nanoscale V(C,N)precipitates in CGHAZ had weak effect on toughness because of small size.展开更多
Advanced bainitic steels with the multiphase structure of bainitic ferrite,retained austenite and martensite exhibit distinctive fatigue crack initiation behavior during high cycle fatigue/very high cycle fatigue(HCF/...Advanced bainitic steels with the multiphase structure of bainitic ferrite,retained austenite and martensite exhibit distinctive fatigue crack initiation behavior during high cycle fatigue/very high cycle fatigue(HCF/VHCF)regimes.The subsurface microstructural fatigue crack initiation,referred to as“non-inclusion induced crack initiation,NIICI”,is a leading mode of failure of bainitic steels within the HCF/VHCF regimes.In this regard,there is currently a missing gap in the knowledge with respect to the cyclic response of multiphase structure during VHCF failure and the underlying mechanisms of fatigue crack initiation during VHCF.To address this aspect,we have developed a novel approach that explicitly identifies the knowledge gap through an examination of subsurface crack initiation and interaction with the local microstructure.This was accomplished by uniquely combining electron microscopy,three-dimensional confocal microscopy,focused ion beam,and transmission Kikuchi diffraction.Interestingly,the study indicated that there are multiple micro-mechanisms responsible for the NIICI failure of bainitic steels,including two scenarios of transgranular-crack-assisted NIICI and two scenarios of intergranular-crack-assisted NIICI,which resulted in the different distribution of fine grains in the crack initiation area.The fine grains were formed through fragmentation of bainitic ferrite lath caused by localized plastic deformation or via local continuous dynamic recrystallization because of repeated interaction between slip bands and prior austenite grain boundaries.The formation of fine grains assisted the advancement of small cracks.Another important aspect discussed is the role of retained austenite(RA)during cyclic loading,on crack initiation and propagation in terms of the morphology,distribution and stability of RA,which determined the development of localized cyclic plastic deformation in multiphase structure.展开更多
High-strength pipeline steel was subjected to friction stir welding(FSW)at rotation rates of 400-700 rpm,and the grain refinement mechanism of the nugget zone(NZ)was determined.The thermomechanical process during FSW ...High-strength pipeline steel was subjected to friction stir welding(FSW)at rotation rates of 400-700 rpm,and the grain refinement mechanism of the nugget zone(NZ)was determined.The thermomechanical process during FSW in the NZ was simulated by multi-pass thermal compression,thereby achieving the austenitic non-recrystallization temperature(T_(nr)).The austenitic non-recrystallization in the NZ at the lowest rotation rate of 400 rpm caused a significant grain refinement.Furthermore,the reduced rotation rate also resulted in the formation of a high ratio of island-like martensite-austenite(M-A)constituent.The toughness of the NZs was enhanced as the rotation rate decreased,which is attributed to the fine effective grains and homogeneously distributed fine M-A constituents dramatically inhibiting crack initiation and propagation.展开更多
The corrosion behavior of high-strength steel used for flexible riser exposed to CO_(2-)saturated saline solution and CO_(2-) saturated vapor environments was studied through immersion experiment and electrochemical c...The corrosion behavior of high-strength steel used for flexible riser exposed to CO_(2-)saturated saline solution and CO_(2-) saturated vapor environments was studied through immersion experiment and electrochemical corrosion experiment. The corrosion behavior and mechanism of the tested steel were analyzed on the basis of corrosion kinetics, nature of corrosion products, corrosion product morphology, elemental distribution and polarization curves. The experimental results showed that the microstructure of the tested steel was bainitic microstructure. The corrosive activity of the tested steel exposed to CO_(2-) saturated vapor environment was significantly lower than that exposed to CO_(2-) saturated saline solution environment.On prolonging the exposure time, the corrosion rate gradually decreased, the corrosion heterogeneity increased, and the dimensions of FeCO_3 crystals gradually became small. At later stages of corrosion, the corrosion current density decreased significantly and the anodic Tafel slope increased, indicating that the corrosion process was strongly inhibited. The corrosion mechanism of low-alloy steel with bainitic microstructure was proposed based on experimental results.展开更多
Hot deformation behavior of a high Al-low Si transformation-induced plasticity（TRIP） steel was studied by an MMS-300 thermo-simulation machine at the temperature range of 1050–1200℃ and strain rate range of 0.01–...Hot deformation behavior of a high Al-low Si transformation-induced plasticity（TRIP） steel was studied by an MMS-300 thermo-simulation machine at the temperature range of 1050–1200℃ and strain rate range of 0.01–10s^（-1）. The constitutive equations of the TRIP steel were established at high temperature by fitting the strain factor with a sixth-order polynomial. The instability during hot rolling was discussed using processing maps. The results reveal that two types of flow stress curves（dynamic recrystallization and dynamic recovery） were observed during the hot compression of the high Al-low Si TRIP steel. Flow stress decreased with increasing deformation temperature and decreasing strain rate. The predicted flow stress of experimental TRIP steel is in agreement with the experimental values with an average absolute relative error of 4.49% and a coefficient of determination of 0.9952. According to the obtained processing maps, the TRIP steel exhibits a better workability at strain rate of 0.1s^（-1） and deformation temperature of 1200℃ as compared to other deformation conditions.展开更多
The infuences of cold-rolling deformation and annealing on the damping capacity of Fe-19Mn-8Cr alloy were investigated.It was observed that the cold-rolled Fe-19Mn-8Cr alloy with a reduction of 10%showed the relativel...The infuences of cold-rolling deformation and annealing on the damping capacity of Fe-19Mn-8Cr alloy were investigated.It was observed that the cold-rolled Fe-19Mn-8Cr alloy with a reduction of 10%showed the relatively excellent damping capacity because of the relatively moreε-martensite and lower dislocation density,and the reduction of slopes of diferent damping curves increased along with increasing the cold-rolling reduction.Besides,the subsequent annealing process can further enhance the damping capacity.After 70%cold-rolling deformation,the austenite grain would grow up with the increase in the annealing temperature,which resulted in a signifcant change in the content and morphology ofε-martensite infuencing the damping capacity of the experimental steel.The damping capacity was optimum when annealed at 800°C for 30 min,displaying that the size ofε-martensite has a vital infuence on the damping capacity of the experimental alloy.This study may enrich the fundamental knowledge about how to ameliorate the damping capacity of Fe-Mn-Cr damping steels.展开更多
A copper-bearing Ti-6Al-4V-5Cu alloy was processed and subjected to different heat treatments to explore the relationship among microstructure, antibacterial performance, and cytocompatibility. Characterization of mic...A copper-bearing Ti-6Al-4V-5Cu alloy was processed and subjected to different heat treatments to explore the relationship among microstructure, antibacterial performance, and cytocompatibility. Characterization of microstructure revealed that the solution treated alloy consisted of α phase, α＇ phase and β phase, while besides these phases, the aged alloy also contained the precipitations of intermetallic Ti2Cu compound. The solution treated alloy showed better antibacterial performance with increasing the solution temperature. The Cu ions released from Ti-6AI-4V-5Cu alloy could effectively inhibit the formation of bacterial biofilm on the surface of alloy, and do not induce any cytotoxicity. The optimal heat treatment for Ti-6AI-4V-5Cu alloy was solution treated at 930 ℃, at which it could exhibit both promising antibacterial performance and no cvtotoxicity.展开更多
A high-performance Ti-Ni-B alloy with good tensile properties and reduced mechanical anisotropy was developed by promoting the columnar to equiaxed transition(CET)of prior-βgrains and modifyingα-laths to equiaxed gr...A high-performance Ti-Ni-B alloy with good tensile properties and reduced mechanical anisotropy was developed by promoting the columnar to equiaxed transition(CET)of prior-βgrains and modifyingα-laths to equiaxed grains.Both Ni and B contributed to the refinement of columnar prior-βgrains during the L→βphase transformation by generating constitutional undercooling.Compared with Ni,B had a su-perior capability of generating constitutional undercooling,which not only replaced a significant amount of Ni with a minor addition to reduce the formation of brittle eutectoid,but also reacted with Ti to form TiB to promote heterogeneous nucleation ofα-Ti grains during theβ→αphase transformation.Together with the restricted growth ofα-laths induced by the refinement of prior-βgrains,a fully equiaxedα-Ti structure was obtained.The competition between the negative effect of brittle eutectoid and the positive role ofα-lath to equiaxed grain transition on the ductility of as-printed Ti-Ni-B alloys was fundamen-tally governed by the morphology of eutectoid and technically dependent on the Ni-B content.When the addition was 1.2Ni-0.06B(wt.%)or less,the positive effect ofα-lath on equiaxed grain transition can effectively mitigate the issue of reduced ductility caused by brittle eutectoid.In contrast,at 1.8Ni-0.09B or greater,the negative effect of eutectoid dominated.New insights into microstructural design obtained through the aforementioned approach were presented and discussed.展开更多
The cellular structured titanium alloys have attracted significant attention for implants because of their lower Young’s modulus,which is comparable to human bone and has the capability of providing space for bone ti...The cellular structured titanium alloys have attracted significant attention for implants because of their lower Young’s modulus,which is comparable to human bone and has the capability of providing space for bone tissue in-growth.However,there is a gap in the knowledge in regard to the relationship between the pore characteristics and the electrochemical performance of open-cellular structured titanium alloys.In this study,we elucidate the influence of pore characteristics on the electrochemical performance of open-cellular structured Ti-6Al-4V alloys produced by electron beam melting(EBM).Intriguingly,the passive film formed on cellular structured Ti-6Al-4V alloy with a larger pore size was more stable and protective,and the corrosion performance was superior compared to the samples with a smaller pore size in phosphate buffered saline(PBS),mainly because of relatively smaller exposed surface area and unlimited flow of electrolyte.However,in acidic PBS containing fluoride ions,the pore characteristics did not play an important role in the corrosion resistance.It was considered that the protective film breaks down such that the corrosion performance of cellular structured alloys was comparable to each other in this harsh environment.展开更多
In the endeavor to maximize the refinement effect of primary Si and alleviate the inherent brittleness of hypereutectic Al-Si alloy,the approach of coating P as a modifier on powder was adopted.The ultimate aim was to...In the endeavor to maximize the refinement effect of primary Si and alleviate the inherent brittleness of hypereutectic Al-Si alloy,the approach of coating P as a modifier on powder was adopted.The ultimate aim was to create more heterogeneous fine Al P nucleus and enhance the nucleation efficiency of primary Si on Al P to refine the coarse primary Si to nano-scale during 3D printing.In the combination of large undercooling and high density of nucleation sites,the size of primary Si was successfully refined to 200–300 nm and the divorced eutectic was also induced to modify the microstructure of matrix.In the presence of nano-scale primary Si,the melting pool boundary(MPB)feature disappeared and the fracture mechanism also changed from load transfer to interfacial fracture.Compared with the pristine alloy,the ductility was increased four times without significantly changing the ultimate tensile strength(UTS)and wear resistance.The improvement of ductility is attributed to the refinement of primary Si,the disappearance of MPB features and the formation of divorced eutectic.The optimal tensile properties were:UTS-482 MPa,yield strength-320 MPa and ductility of 8.1%at 0.05 wt.%P.These are comparable to those for high-strength Al alloys.展开更多
The corrosion behavior and mechanism of 3Ni weathering steel in a simulated oceanic atmospheric environment are investigated in order to comprehend the impacts of La,as determined through electrochemical analysis and ...The corrosion behavior and mechanism of 3Ni weathering steel in a simulated oceanic atmospheric environment are investigated in order to comprehend the impacts of La,as determined through electrochemical analysis and rust layer characterization.The results of this study demonstrate that the addition of La enhances the corrosion resistance of 3Ni weathering steel in the marine atmospheric environment,thereby reducing the corrosion rate and improving the protection of the rust layer.The influence of La on corrosion resistance can be attributed to two primary factors.Firstly,La functions as a grain refiner,minimizing the potential difference of the micro-regions on the substrate surface,thereby significantly reducing the corrosion of bare steel in the marine environment.Secondly,La inhibits the process of Fe_(3)O_(4) oxidation back toγ-FeOOH during corrosion at the local site,thus decreasing the formation ofγ-FeOOH and enhancing the charge transfer resistance.This research work may serve as a reference for expanding the application of rare earth elements in the field of weathering steel.展开更多
This paper focuses on the relationship between the microstructure and tensile properties of Fe-Mn-Al-C low-density high-strength steel processes by hot-rolling and air-cooling process. The microstructure analysis reve...This paper focuses on the relationship between the microstructure and tensile properties of Fe-Mn-Al-C low-density high-strength steel processes by hot-rolling and air-cooling process. The microstructure analysis reveals that the combination of hot-rolling and air-cooling results in the formation of heterogeneous structures comprising different-sized γ and B_(2) phases in the low-density steel with the addition of nickel (Ni). The addition of Ni promotes the formation of the B_(2) phase and induces the pinning of B_(2) phase particles at the γ grain boundaries. This pinning effect effectively hinders the growth of the γ grains, leading to grain refinement. The tensile test results demonstrate that LDS-5Ni (low-density steel, LDS) exhibits excellent high strength and ductility combination, e.g., a tensile strength of 1535 MPa, yield strength of 1482 MPa, and elongation of 23.3%. These remarkable mechanical properties are primarily attributed to the combined strengthening contributions of grain refinement and duplex nano-sized second-phase precipitation hardening.展开更多
Grain-oriented 4.5 wt% Si and 6.5 wt% Si steels were produced by strip casting, warm rolling, cold rolling, primary annealing, and secondary annealing. Goss grains were sufficiently developed and covered the entire su...Grain-oriented 4.5 wt% Si and 6.5 wt% Si steels were produced by strip casting, warm rolling, cold rolling, primary annealing, and secondary annealing. Goss grains were sufficiently developed and covered the entire surface of the secondary recrystallized sheets. The microstructure and texture was characterized by OM, EBSD, TEM, and XRD. It was observed that after rolling at 700 ℃, the 6.5 wt% Si steel exhibited a considerable degree of shear bands, whereas the 4.5 wt% Si steel indicated their rare presence. After primary annealing, completely equiaxed grains showing strong y-fiber texture were presented in both alloys. By comparison, the 6.5 wt% Si steel showed smaller grain size and few favorable Goss grains. Additionally, a higher density of fine precipitates were exhibited in the 6.5 wt% Si steel, leading to a ~ 30-s delay in primary recrystallization. During secondary annealing, abnormal grain growth of the 6.5 wt% Si steel occurred at higher temperature compared to the 4.5 wt% Si steel, and the final grain size of the 6.5 wt% Si steel was greater. The magnetic induction B8 of the 4.5 wt% Si and the 6.5 wt% Si steels was 1.75 and 1.76 T, respectively, and the high- frequency core losses were significantly improved in comparison with the non-oriented high silicon steel.展开更多
1.Introduction Advanced high-strength steels with good ductility are essen-tial to the manufacturing,structural safety,and light-weighting of load-bearing structures in many industries[1-3].Austenitic stain-less steel...1.Introduction Advanced high-strength steels with good ductility are essen-tial to the manufacturing,structural safety,and light-weighting of load-bearing structures in many industries[1-3].Austenitic stain-less steel(ASS)exhibits high ductility due to the TRIP and/or TWIP effect that can alleviate stress concentration,prevent void nucle-ation,enhance work hardening,and postpone necking[4-6].The yield strength of conventional ASS is generally low(∼200-500 MPa),and their deformation resistance is insufficient for many load-bearing applications[6].Previous studies reported the in-creased yield strength in various austenitic steels through grain refinement,dislocation strengthening,precipitation strengthening,and heterogeneous hardening[7-14].A single strengthening mech-anism,however,is typically insufficient to obtain ultrahigh yield strength over 1 GPa in austenitic steel[12].展开更多
基金financially supported by the National Key R&D Program of China (Grant No. 2016YFB0300600)the National Natural Science Foundation of China (Grant No. 51604074)
文摘Compared with the traditional atm ospheric carburization, low-pressure carburization has the benefits of producing no surface oxidation and leaving fine, uniformly dispersed carbides in the carburized layer. However, the process param eters for low-pressure carburization of 16Cr3NiWMoVNbE steel have yet to be optimized. Thus, we use the saturation-value method to optimize these parameters for aviation-gear materials. Toward this end, the m icrostructure and properties of 16Cr3NiWMoVNbE steel after different carburization processes are studied by optical microscopy, scanning electron microscopy, transm ission electron microscopy, and electron probe microanalysis. Considering the saturated austenite carbon concentration, we propose a model of carbon flux and an alloy coefficient for low -pressure carburization to reduce the carbon concentration in austenite and avoid the surface carbide network. At the early stage of carburization (30 s), the gas-solid interface has a higher concentration gradient. The averaging method is not ideal in practical applications, but the carbon flux measured by using the segm ented average m ethod is 2.5 times that measured by the overall average method, which is ideal in practical applications. The corresponding carburization tim e is reduced by 60%. By using the integral average method, the actual carburization time increases, which leads to the rapid form ation of carbide on the surface and affects the entire carburization process. Nb and Wcombine with C to form carbides, which hinders carbon diffusion and consumes carbon, resulting in a sharp decrease in the rate of C diffusion in austenite (the diffusion rate is reduced by 52% for 16Cr3NiWMoVNbE steel). By changing the diffusion coefficient model and comparing the hardness gradient of different processes, the depth of the actual layer is found to be very similar to the design depth.
基金financially supported by the Natural Science Foundation of China(No.51922026)the Fundamental Research Funds for the Central Universities(Nos.N2002013 and N2002005)the support from the National Science Foundation(Nos.DMR-1611180 and 1809640)with the program directors,Drs.G.Shiflet and D.Farkas。
文摘There is currently a gap in our understanding of mechanisms that contribute to high strength and high plasticity in high strength UFG ferritic steel with nano-size Fe3 C carbides in situations that involve combination of various strain rates and high temperature.In this regard,we describe the mechanistic basis of obtaining high strength-high plasticity combination in an ultrafine-grained(UFG)(~500±30 nm)ferritic steel with nano-size carbides,which sustained large plastic deformation,exceeding 100%elongation at a temperature significantly below 0.5 of the absolute melting point(Tm).To address the missing gap in our knowledge,we conducted a series of experiments involving combination of strain rate and temperature effects in conjunction with electron microscopy and atom probe tomography(APT).Strain rate studies were carried out at strain rates in the range of 0.0017-0.17 s^(-1)and at different temperatures from 25℃to 600℃.Dynamic recrystallization occurred at 600℃,resulting in a significant decrease in yield and tensile strength.Nevertheless,the UFG ferritic steels had an advantage in tensile strength(UTS)and elongation-to-failure(εf)at 600℃,especially at strain rate of 0.0017 s^(-1),with high UTSof 510 MPa and excellent low temperature(<0.42 Tm)superplasticity(εf=110%).These mechanical properties are significantly superior compared to similar type of steels at identical temperature.A mechanistic understanding of mechanical behavior of UFG ferritic steels is presented by combining the effect of strain rate,temperature,and nano-size carbides.
基金Support for this project was provided by US Department of Energy grant DE-SC0011826
文摘This research explores the prospect of fabricating a face-centered cubic(fcc) Ni-base alloy cladding(Inconel 690) on an fcc Fe-base alloy(316 L stainless-steel) having improved mechanical properties and reduced sensitivity to corrosion through grain boundary and microstructure engineering concepts enabled by additive manufacturing(AM) utilizing electron-beam powder bed fusion(EPBF). The unique solidification and associated constitutional supercooling phenomena characteristic of EPBF promotes[100] textured and extended columnar grains having lower energy grain boundaries as opposed to random, high-angle grain boundaries, but no coherent {111} twin boundaries characteristic of conventional thermo-mechanically processed fcc metals and alloys, including Inconel 690 and 316 L stainless-steel.In addition to [100] textured grains, columnar grains were produced by EPBF fabrication of Inconel 690 claddings on 316 L stainless-steel substrates. Also, irregular 2–3 μm diameter, low energy subgrains were formed along with dislocation densities varying from 108 to 109 cm^2, and a homogeneous distribution of Cr_(23)C_6 precipitates. Precipitates were formed within the grains(with ~3 μm interparticle spacing),but not in the subgrain or columnar grain boundaries. These inclusive, hierarchical microstructures produced a tensile yield strength of 0.527 GPa, elongation of 21%, and Vickers microindentation hardness of 2.33 GPa for the Inconel 690 cladding in contrast to a tensile yield strength of 0.327 GPa, elongation of 53%, and Vickers microindentation hardness of 1.78 GPa, respectively for the wrought 316 L stainlesssteel substrate. Aging of both the Inconel 690 cladding and the 316 L stainless-steel substrate at 685?C for50 h precipitated Cr_(23)C_6 carbides in the Inconel 690 columnar grain boundaries, but not in the low-angle(and low energy) subgrain boundaries. In contrast, Cr_(23)C_6 carbides precipitated in the 316 L stainless-steel grain boundaries, but not in the low energy coherent {111} twin boundaries. Consequently, the Inconel690 subgrain boundaries essentially serve as surrogates for coherent twin boundaries with regard to avoiding carbide precipitation and corrosion sensitization.
基金financially supported by the National Key Research and Development Program of China(No.2017YFB0304900)。
文摘Gradient boosting decision tree(GBDT)machine learning(ML)method was adopted for the first time to automatically recognize and conduct quantitative statistical analysis of boundaries in bainitic microstructure using electron back-scatter diffraction(EBSD)data.In spite of lack of large sets of EBSD data,we were successful in achieving the desired accuracy and accomplishing the objective of recognizing the boundaries.Compared with a low model accuracy of<50%as using Euler angles or axis-angle pair as characteristic features,the accuracy of the model was significantly enhanced to about 88%when the Euler angle was converted to overall misorientation angle(OMA)and specific misorientation angle(SMA)and considered as important features.In this model,the recall score of prior austenite grain(PAG)boundary was~93%,high angle packet boundary(OMA>40°)was~97%,and block boundary was~96%.The derived outcomes of ML were used to obtain insights into the ductile-to-brittle transition(DBTT)behavior.Interestingly,ML modeling approach suggested that DBTT was not determined by the density of high angle grain boundaries,but significantly influenced by the density of PAG and packet boundaries.The study underscores that ML has a great potential in detailed recognition of complex multi-hierarchical microstructure such as bainite and martensite and relates to material performance.
基金supported financially by the National Science Foundation,USA (No.#DMR-MRI 1530891)
文摘This work aims to elucidate the impact of aluminum-content on microstructure and deformation mechanisms of transformation-induced plasticity（TRIP） steels through macroscale and nanoscale deformation experiments combined with post-mortem electron microscopy of the deformed region.The solid-state transformation-induced mechanical deformation varied with the Al contents,and influenced tensile strength-ductility combination.Steels with 2–4 wt% Al were characterized by TRIP effect.In contrast to 2 Al-TRIP and 4 Al-TRIP steels,twinning-induced plasticity（TWIP） was also observed in conjunction with strain-induced martensite in 6 Al-TRIP steel.This behavior is attributed to the increase in stacking fault energy with the increase of Al content and stability of austenite,which depends on the local chemical variation.The study addresses the knowledge gap with regard to the effect of Al content on austenite stability in medium-Mn TRIP steels.This combination is expected to potentially enable cost-effective alloy design with high strength-high ductility condition.
基金support from the National Natural Science Foundation of China(Nos.51674080,51404155 and U1260204)the National Key R&D Program of China(No.2017YFB0304105)
文摘In this study, two types of as-cast microstructure produced by strip casting were cold rolled and annealed to investigate the effect of initial microstructure on the textural evolution and magnetic properties of non-oriented silicon steel. The results indicated that the cold-rolled sheets of coarse-grained strip with pronounced {100} components exhibited stronger 入 fiber(<100>//ND) and weaker γ fiber(<111>//ND)texture as composed to the fine-grained strip with strong Goss({110}(001)) texture. After annealing, the former was dominated by η fiber(<001>//RD) texture with a peak at {110}<001)orientation, while the latter consisted of strong {111}(112) and relatively weak {110}(001) texture. In addition, a number of precipitates of size ～30-150 nm restricted the grain growth during annealing, resulting in recrystallization of grain size of ～46 μm in the coarse-grained specimen and ～41μm in the fine-grained specimen.Ultimately, higher magnetic induction(～1.72 T) and lower core loss(～4.04 W/kg) were obtained in the final annealed sheets of coarse-grained strip with strong {100} texture.
基金the National Natural Science Foundation of China (Grant No.51604072)the Fundamental Research Funds for the Central Universities (Grant No.N170704016)the National High-Tech R&D Program (863 Program)of China (Grant No.2015AA03A501).
文摘The structure-property relationship in heat-affected zone (HAZ)of a low-carbon steel bearing V-N subjected to gasshielded arc welding was explored.The microstructural characteristics of base metal (BM),coarse-grained HAZ (CGHAZ),fine-grained HAZ,and intercritical HAZ were significantly different.The effect of grain-refinement strengthening and transformation hardening on HAZ contributed to equivalent hardness of 260.8-278.5 HV in comparison with BM hardness of 272.0 HV.Moreover,excellent impact toughness at -20 ℃ was obtained because of high resistance to crack propagation by high-misorientation boundaries,leading to impact fracture consisting of dimples.In CGHAZ,free N was partly fixed by V(C,N)precipitates,such that the deterioration effect of N on toughness was considered to be nearly eliminated.In comparison with CGHAZ,weld metal contained higher fraction of acicular ferrite with fine plates,while the impact toughness was inferior because of the detrimental influence of coarse inclusions from the welding wire.The nanoscale V(C,N)precipitates in CGHAZ had weak effect on toughness because of small size.
基金the funding by National Key Technologies Research and Development Program of China(2017YFB0304500)the support from National Natural Science Foundation of China(No.51771014)Joint Funds of National Natural Science Foundation of China(No.U1834202)。
文摘Advanced bainitic steels with the multiphase structure of bainitic ferrite,retained austenite and martensite exhibit distinctive fatigue crack initiation behavior during high cycle fatigue/very high cycle fatigue(HCF/VHCF)regimes.The subsurface microstructural fatigue crack initiation,referred to as“non-inclusion induced crack initiation,NIICI”,is a leading mode of failure of bainitic steels within the HCF/VHCF regimes.In this regard,there is currently a missing gap in the knowledge with respect to the cyclic response of multiphase structure during VHCF failure and the underlying mechanisms of fatigue crack initiation during VHCF.To address this aspect,we have developed a novel approach that explicitly identifies the knowledge gap through an examination of subsurface crack initiation and interaction with the local microstructure.This was accomplished by uniquely combining electron microscopy,three-dimensional confocal microscopy,focused ion beam,and transmission Kikuchi diffraction.Interestingly,the study indicated that there are multiple micro-mechanisms responsible for the NIICI failure of bainitic steels,including two scenarios of transgranular-crack-assisted NIICI and two scenarios of intergranular-crack-assisted NIICI,which resulted in the different distribution of fine grains in the crack initiation area.The fine grains were formed through fragmentation of bainitic ferrite lath caused by localized plastic deformation or via local continuous dynamic recrystallization because of repeated interaction between slip bands and prior austenite grain boundaries.The formation of fine grains assisted the advancement of small cracks.Another important aspect discussed is the role of retained austenite(RA)during cyclic loading,on crack initiation and propagation in terms of the morphology,distribution and stability of RA,which determined the development of localized cyclic plastic deformation in multiphase structure.
基金supported by the National Nature Science Foundation of China(No.51774085)Liaoning Province Excellent Youth Foundation(2020-YQ-03)+1 种基金the Open Research Fund from the State Key Laboratory of Rolling and AutomationNortheastern University(NEU)(2020RALKFKT009)。
文摘High-strength pipeline steel was subjected to friction stir welding(FSW)at rotation rates of 400-700 rpm,and the grain refinement mechanism of the nugget zone(NZ)was determined.The thermomechanical process during FSW in the NZ was simulated by multi-pass thermal compression,thereby achieving the austenitic non-recrystallization temperature(T_(nr)).The austenitic non-recrystallization in the NZ at the lowest rotation rate of 400 rpm caused a significant grain refinement.Furthermore,the reduced rotation rate also resulted in the formation of a high ratio of island-like martensite-austenite(M-A)constituent.The toughness of the NZs was enhanced as the rotation rate decreased,which is attributed to the fine effective grains and homogeneously distributed fine M-A constituents dramatically inhibiting crack initiation and propagation.
基金financial support from the National High Technology Research and Development Program of China (Grant No. 2015AA03A501)Doctoral Scientific Research Foundation of Jiangsu University of Science and Technology (1062931702)
文摘The corrosion behavior of high-strength steel used for flexible riser exposed to CO_(2-)saturated saline solution and CO_(2-) saturated vapor environments was studied through immersion experiment and electrochemical corrosion experiment. The corrosion behavior and mechanism of the tested steel were analyzed on the basis of corrosion kinetics, nature of corrosion products, corrosion product morphology, elemental distribution and polarization curves. The experimental results showed that the microstructure of the tested steel was bainitic microstructure. The corrosive activity of the tested steel exposed to CO_(2-) saturated vapor environment was significantly lower than that exposed to CO_(2-) saturated saline solution environment.On prolonging the exposure time, the corrosion rate gradually decreased, the corrosion heterogeneity increased, and the dimensions of FeCO_3 crystals gradually became small. At later stages of corrosion, the corrosion current density decreased significantly and the anodic Tafel slope increased, indicating that the corrosion process was strongly inhibited. The corrosion mechanism of low-alloy steel with bainitic microstructure was proposed based on experimental results.
基金financially supported by the National Program on Key Basic Research Project (Grant No. 2011CB606306-2)the National Natural Science Foundation of China (Grant No. 51775102)
文摘Hot deformation behavior of a high Al-low Si transformation-induced plasticity（TRIP） steel was studied by an MMS-300 thermo-simulation machine at the temperature range of 1050–1200℃ and strain rate range of 0.01–10s^（-1）. The constitutive equations of the TRIP steel were established at high temperature by fitting the strain factor with a sixth-order polynomial. The instability during hot rolling was discussed using processing maps. The results reveal that two types of flow stress curves（dynamic recrystallization and dynamic recovery） were observed during the hot compression of the high Al-low Si TRIP steel. Flow stress decreased with increasing deformation temperature and decreasing strain rate. The predicted flow stress of experimental TRIP steel is in agreement with the experimental values with an average absolute relative error of 4.49% and a coefficient of determination of 0.9952. According to the obtained processing maps, the TRIP steel exhibits a better workability at strain rate of 0.1s^（-1） and deformation temperature of 1200℃ as compared to other deformation conditions.
基金This work was financially supported by the National Key R&D Program of China(Grant No.2016YFB0300303)。
文摘The infuences of cold-rolling deformation and annealing on the damping capacity of Fe-19Mn-8Cr alloy were investigated.It was observed that the cold-rolled Fe-19Mn-8Cr alloy with a reduction of 10%showed the relatively excellent damping capacity because of the relatively moreε-martensite and lower dislocation density,and the reduction of slopes of diferent damping curves increased along with increasing the cold-rolling reduction.Besides,the subsequent annealing process can further enhance the damping capacity.After 70%cold-rolling deformation,the austenite grain would grow up with the increase in the annealing temperature,which resulted in a signifcant change in the content and morphology ofε-martensite infuencing the damping capacity of the experimental steel.The damping capacity was optimum when annealed at 800°C for 30 min,displaying that the size ofε-martensite has a vital infuence on the damping capacity of the experimental alloy.This study may enrich the fundamental knowledge about how to ameliorate the damping capacity of Fe-Mn-Cr damping steels.
基金financial supports from the National Basic Research Program of China(No.2012CB619101)the National Natural Science Foundation of China(No.81271957)the Basic Research Project of Shenzhen City(No.JCYJ20120616142847342)
文摘A copper-bearing Ti-6Al-4V-5Cu alloy was processed and subjected to different heat treatments to explore the relationship among microstructure, antibacterial performance, and cytocompatibility. Characterization of microstructure revealed that the solution treated alloy consisted of α phase, α＇ phase and β phase, while besides these phases, the aged alloy also contained the precipitations of intermetallic Ti2Cu compound. The solution treated alloy showed better antibacterial performance with increasing the solution temperature. The Cu ions released from Ti-6AI-4V-5Cu alloy could effectively inhibit the formation of bacterial biofilm on the surface of alloy, and do not induce any cytotoxicity. The optimal heat treatment for Ti-6AI-4V-5Cu alloy was solution treated at 930 ℃, at which it could exhibit both promising antibacterial performance and no cvtotoxicity.
基金This work was supported by the National Natural Science Foun-dation of China(Nos.52074254,51874271,and 52174349)the Key Projects of International Cooperation(No.122111KYSB20200034)+3 种基金the Project of Key Laboratory of Science and Technology on Par-ticle Materials(No.CXJJ-22S043)the CAS Project for Young Scientists in Basic Research(No.YSBR-025)This work was finan-cially supported by the Selection of Best Candidates to Undertake Key Research Projects(No.211110230200)This research work was also financially supported by the OU Master Plan Implementation Project promoted under Osaka University.
文摘A high-performance Ti-Ni-B alloy with good tensile properties and reduced mechanical anisotropy was developed by promoting the columnar to equiaxed transition(CET)of prior-βgrains and modifyingα-laths to equiaxed grains.Both Ni and B contributed to the refinement of columnar prior-βgrains during the L→βphase transformation by generating constitutional undercooling.Compared with Ni,B had a su-perior capability of generating constitutional undercooling,which not only replaced a significant amount of Ni with a minor addition to reduce the formation of brittle eutectoid,but also reacted with Ti to form TiB to promote heterogeneous nucleation ofα-Ti grains during theβ→αphase transformation.Together with the restricted growth ofα-laths induced by the refinement of prior-βgrains,a fully equiaxedα-Ti structure was obtained.The competition between the negative effect of brittle eutectoid and the positive role ofα-lath to equiaxed grain transition on the ductility of as-printed Ti-Ni-B alloys was fundamen-tally governed by the morphology of eutectoid and technically dependent on the Ni-B content.When the addition was 1.2Ni-0.06B(wt.%)or less,the positive effect ofα-lath on equiaxed grain transition can effectively mitigate the issue of reduced ductility caused by brittle eutectoid.In contrast,at 1.8Ni-0.09B or greater,the negative effect of eutectoid dominated.New insights into microstructural design obtained through the aforementioned approach were presented and discussed.
基金partial support from the National Key Research and Development Program of China(Nos.2017YFC1104902,2016YFC1100502 and 2018YFC1105503)the National Natural Science Foundation of China(Nos.51871220 and 51631007)+3 种基金the Key Research Program of Frontier Sciences,CAS(No.QYZDJ-SSW-JSC031-02)the Natural Science Foundation of Liaoning Province of China(No.2019-MS-327 and 2020-KF-14-01)the State Key Laboratory of Light Alloy Casting Technology for Highend Equipment(No.LACT-007)the Shenyang Talents Program(No.RC200230)。
文摘The cellular structured titanium alloys have attracted significant attention for implants because of their lower Young’s modulus,which is comparable to human bone and has the capability of providing space for bone tissue in-growth.However,there is a gap in the knowledge in regard to the relationship between the pore characteristics and the electrochemical performance of open-cellular structured titanium alloys.In this study,we elucidate the influence of pore characteristics on the electrochemical performance of open-cellular structured Ti-6Al-4V alloys produced by electron beam melting(EBM).Intriguingly,the passive film formed on cellular structured Ti-6Al-4V alloy with a larger pore size was more stable and protective,and the corrosion performance was superior compared to the samples with a smaller pore size in phosphate buffered saline(PBS),mainly because of relatively smaller exposed surface area and unlimited flow of electrolyte.However,in acidic PBS containing fluoride ions,the pore characteristics did not play an important role in the corrosion resistance.It was considered that the protective film breaks down such that the corrosion performance of cellular structured alloys was comparable to each other in this harsh environment.
基金financially supported by the National Key Research and Development Program of China(No.2018YFB1105100)the Scientific Instrument Developing Project of the Chinese Academy of Sciences(No.YJKYYQ20190011)。
文摘In the endeavor to maximize the refinement effect of primary Si and alleviate the inherent brittleness of hypereutectic Al-Si alloy,the approach of coating P as a modifier on powder was adopted.The ultimate aim was to create more heterogeneous fine Al P nucleus and enhance the nucleation efficiency of primary Si on Al P to refine the coarse primary Si to nano-scale during 3D printing.In the combination of large undercooling and high density of nucleation sites,the size of primary Si was successfully refined to 200–300 nm and the divorced eutectic was also induced to modify the microstructure of matrix.In the presence of nano-scale primary Si,the melting pool boundary(MPB)feature disappeared and the fracture mechanism also changed from load transfer to interfacial fracture.Compared with the pristine alloy,the ductility was increased four times without significantly changing the ultimate tensile strength(UTS)and wear resistance.The improvement of ductility is attributed to the refinement of primary Si,the disappearance of MPB features and the formation of divorced eutectic.The optimal tensile properties were:UTS-482 MPa,yield strength-320 MPa and ductility of 8.1%at 0.05 wt.%P.These are comparable to those for high-strength Al alloys.
基金G.Niu,R.Yuan,H.B.Wu,C.J.Shang,and X.P.Mao appreciate the support from the National Key R&D Program of China(No.2021YFB3701700)G.Niu appreciates the support from the National Natural Science Foundation of China(No.52304389)the China Postdoctoral Science Foundation(No.2022M720402).
文摘The corrosion behavior and mechanism of 3Ni weathering steel in a simulated oceanic atmospheric environment are investigated in order to comprehend the impacts of La,as determined through electrochemical analysis and rust layer characterization.The results of this study demonstrate that the addition of La enhances the corrosion resistance of 3Ni weathering steel in the marine atmospheric environment,thereby reducing the corrosion rate and improving the protection of the rust layer.The influence of La on corrosion resistance can be attributed to two primary factors.Firstly,La functions as a grain refiner,minimizing the potential difference of the micro-regions on the substrate surface,thereby significantly reducing the corrosion of bare steel in the marine environment.Secondly,La inhibits the process of Fe_(3)O_(4) oxidation back toγ-FeOOH during corrosion at the local site,thus decreasing the formation ofγ-FeOOH and enhancing the charge transfer resistance.This research work may serve as a reference for expanding the application of rare earth elements in the field of weathering steel.
基金funding from the National Key Technologies Research and Development Program of China(No.2021YFB3703500)the National Natural Science Foundation of China(No.51771014).
文摘This paper focuses on the relationship between the microstructure and tensile properties of Fe-Mn-Al-C low-density high-strength steel processes by hot-rolling and air-cooling process. The microstructure analysis reveals that the combination of hot-rolling and air-cooling results in the formation of heterogeneous structures comprising different-sized γ and B_(2) phases in the low-density steel with the addition of nickel (Ni). The addition of Ni promotes the formation of the B_(2) phase and induces the pinning of B_(2) phase particles at the γ grain boundaries. This pinning effect effectively hinders the growth of the γ grains, leading to grain refinement. The tensile test results demonstrate that LDS-5Ni (low-density steel, LDS) exhibits excellent high strength and ductility combination, e.g., a tensile strength of 1535 MPa, yield strength of 1482 MPa, and elongation of 23.3%. These remarkable mechanical properties are primarily attributed to the combined strengthening contributions of grain refinement and duplex nano-sized second-phase precipitation hardening.
基金inancially supported by the National Natural Science Foundation of China(Nos.51174059,51404155,and U1260204)the Fundamental Research Funds for the Central Universities(N130407003)+1 种基金the Program for New Century Excellent Talents in University(NCET-130111)the Program for Liaoning Excellent Talents in University (LR2014007)
文摘Grain-oriented 4.5 wt% Si and 6.5 wt% Si steels were produced by strip casting, warm rolling, cold rolling, primary annealing, and secondary annealing. Goss grains were sufficiently developed and covered the entire surface of the secondary recrystallized sheets. The microstructure and texture was characterized by OM, EBSD, TEM, and XRD. It was observed that after rolling at 700 ℃, the 6.5 wt% Si steel exhibited a considerable degree of shear bands, whereas the 4.5 wt% Si steel indicated their rare presence. After primary annealing, completely equiaxed grains showing strong y-fiber texture were presented in both alloys. By comparison, the 6.5 wt% Si steel showed smaller grain size and few favorable Goss grains. Additionally, a higher density of fine precipitates were exhibited in the 6.5 wt% Si steel, leading to a ~ 30-s delay in primary recrystallization. During secondary annealing, abnormal grain growth of the 6.5 wt% Si steel occurred at higher temperature compared to the 4.5 wt% Si steel, and the final grain size of the 6.5 wt% Si steel was greater. The magnetic induction B8 of the 4.5 wt% Si and the 6.5 wt% Si steels was 1.75 and 1.76 T, respectively, and the high- frequency core losses were significantly improved in comparison with the non-oriented high silicon steel.
基金the support from the National Natural Science Foundation of China (Nos.51774033 and 51474031)。
文摘1.Introduction Advanced high-strength steels with good ductility are essen-tial to the manufacturing,structural safety,and light-weighting of load-bearing structures in many industries[1-3].Austenitic stain-less steel(ASS)exhibits high ductility due to the TRIP and/or TWIP effect that can alleviate stress concentration,prevent void nucle-ation,enhance work hardening,and postpone necking[4-6].The yield strength of conventional ASS is generally low(∼200-500 MPa),and their deformation resistance is insufficient for many load-bearing applications[6].Previous studies reported the in-creased yield strength in various austenitic steels through grain refinement,dislocation strengthening,precipitation strengthening,and heterogeneous hardening[7-14].A single strengthening mech-anism,however,is typically insufficient to obtain ultrahigh yield strength over 1 GPa in austenitic steel[12].
