查看更多>>摘要：The effect of lanthanum on the characteristics of inclusions in the slab of non-oriented electrical steels was investigated through industrial trials and thermodynamic analysis.The number,size,and chemical composition of inclusions in the surface,one-quarter of thickness and the center of slabs with and without lanthanum addition were statistically analyzed using an automatic inclusion analysis system.In the lanthanum-free slab,inclusions were predominately MgO.Al2O3,MgO,and AlN as well as a small number of Al2O3-MgO-CaO and MgS.The number densities of oxide inclusions and AlN decreased from the surface to the center of the slab,which was ascribed to the difference in cooling intensity during the continuous casting.In the steel with lanthanum addition,inclusions were modified into LaAlO3 and La2O2S and gradually transformed into dual-phase MgO-La2S3 with an increasing distance from the slab surface due to the reaction between the lanthanum-containing inclusion and the steel matrix.The uneven distribution of oxide inclusions along the thickness of the slab was eliminated in the lanthanum-bearing slab because the dissolved oxygen was remarkably decreased by lanthanum.Lanthanum-bearing inclusions were more likely to agglomerate AlN by inducing the heterogeneous nucleation of AlN on their surface,while small-size MgO.Al2O3 inclusions hardly showed a coarsening effect on the size of AlN.
查看更多>>摘要：Metallographic microscopy,scanning electron microscopy and TiN growth thermodynamic and kinetic equations were used to investigate the morphology,quantity,and size of TiN in the center of high-titanium high-strength steels under different solidification cooling rates.The results showed that TiN in the center of the experimental steels mainly existed in three forms:single,composite(Al2O3-TiN),and multi-particle aggregation.TiN began precipitating at around 1497 ℃(solidification fraction of 0.74).From the end of melting to solidification for 180 s,the cooling rates in the center of the experimental steels for furnace cooling,air cooling,refractory mold cooling,and cast iron mold cooling tended to stabilize at 0.17,0.93,1.65,and 2.15 ℃/s,respectively.The size of TiN in the center of the experimental steel cooled using furnace cooling was mainly concentrated in the 5-15 pm range.In contrast,the size of TiN in the center of the experimental steels cooled using air cooling,refractory mold cooling,and cast iron mold cooling were mainly concentrated in the 1-5 pm range.In addition,their density of TiN in the center of the experimental steels is signif-icantly higher than that of the furnace-cooled experimental steel.Thermodynamic and kinetic precipitation models of TiN established predicted the growth size of TiN in a high-titanium high-strength steel when the solidification cooling rates are not below 0.93 ℃/s.
查看更多>>摘要：Surface morphology and roughness are important parameters of surface quality of cold-rolled ultra-thin strip steel.In order to study the effect of Si3N4 ceramic work rolls on the surface roughness of SUS304 ultra-thin strip,ABAQUS finite element model calculation,3D laser profilometry,and other methods were adopted based on the physical characteristics of Si3N4 ceramic roll and 9Cr2MoV steel roll,like anti-flattening performance and oil wettability.The surface morphology and roughness of SUS304 ultra-thin strip rolled by different material work rolls under oil lubrication conditions were measured.The results showed that under the rolling force of 10 kN,the maximum flattening amount of Si3N4 ceramic roll was reduced by 35.14％compared to that of 9Cr2MoV steel roll.The reduction rate of SUS304 ultra-thin strip rolled by ceramic roll was 34.19％,while that rolled by steel roll was only 22％;Si3N4 ceramic roll can further increase the number of alternating convex peaks and concave valleys in the rolled thin strip,reduce the profile steepness,reduce surface roughness,and enhance the planarization effect of surface micro-convex bodies,with improving surface quality and surface glossiness.Finally,the mechanism of Si3N4 ceramic roll significantly improving the surface roughness of rolled SUS304 ultra-thin strip was proposed.
查看更多>>摘要：To overcome the inaccuracy problem of the traditional wedge evaluation of steel plates and strips caused by the ran-domness of the thicknesses of two local points and improve the reliability of the wedge index,the double-centroid method for the wedge evaluation was proposed,and a model based on the centroid theory was established.Meanwhile,an integral model for the discrete thickness values of the cross-section profiles was derived.The discussion focused on the distinct characteristics of the two-point method,asymmetric method,and double-centroid method in evaluating the asymmetric distribution of cross-sections.The three methods were employed to evaluate the wedge values of both the theoretical and measured cross-sections of steel plates and strips,and the accuracies of three wedge evaluation models were analyzed and discussed.The results showed that the double-centroid method objectively reflects the degree and variation characteristics of the wedge values of the cross-sections of steel plates and strips,and this method is feasible,reliable,and outstanding.
查看更多>>摘要：Multiphase microstructure significantly increases the strength,usually at the expense of flangeability because of lacking microstructure homogeneity.To further improve the strength-flangeability of multiphase steel,the microstructural homogeneity was advanced by adjusting the hard martensite/austenite(M/A)islands.The strength-flangeability was measured via uniaxial tensile tests and hole expansion tests.Their microstructures were characterized using a scanning electron microscope equipped with an electron backscatter diffraction detector and a transmission electron microscope.Nanoindentation tests were supplementally used to quantitatively reveal the microstructural homogeneity of the steels.Results show that the adjusted multiphase steel achieves an excellent ultimate tensile strength(～800 MPa)and flangeability(～135％hole expansion ratio).A promising homogeneous multiphase microstructure was obtained by controlling undercooled austenite transformed at about 600 ℃.This microstructure consists of soft polygonal ferrite,blocky bainitic ferrite,and hard M/A islands.The volume fraction of M/A islands is around 5％,and the average size is less than l pm.Detailed nanoindentation analysis indicated that the participation of M/A islands impressively influenced the microstructural homogeneity.Weakened strain partition and better mechanical compatibility were present in the adjusted multiphase steel since the plasticity initiation started late,which resulted in a positive flangeability.Moreover,avoiding M/A islands distributed in the chain along the rolling direction on the matrix hindered the possibility of voids coalescing into cracks and stabilized the flanging performance.
查看更多>>摘要：The high-strength low-alloy steel plates with varying Ni/Mo contents were manufactured using the thermos-mechanical control process.The investigation was conducted to explore the effect of Ni/Mo microalloying on microstructure evolution and mechanical properties of the steel.The results revealed that the increase in Ni content from 1 to 2 wt.％reduced the transition temperature of ferrite and the growth range of ferritic grain was narrowed,which promoted grain refinement.The optimized combination of grain size,high-angle grain boundaries(HAGBs),and martensite-austenite(M-A)islands parameter contributed to the excellent impact toughness of S1 steel at-100 ℃(impact absorbed energy of 218.2 J at-100 ℃).As the Mo increases from 0 to 2 wt.％,the matrix structure changes from multiphase structure to granular bainite,which increases the average effective grain size to～4.62 pm and reduces HAGBs proportion to～36.22％.With these changes,the low-temperature impact toughness of S3 steel is weakened.In addition,based on the analysis of the characteristics of crack propagation path,it was found that M-A islands with low content(～2.21％)and small size(～1.76 pm)significantly retarded crack propagation,and the fracture model of M-A islands with different morphologies was further proposed.Furthermore,correlation between behaviour of delamination and toughness was further analysed by observing delamination size and impact energy parameters.
查看更多>>摘要：To address the inhomogeneous microstructure and improve the mechanical properties of DT300 ultra-high strength steel specimens fabricated by laser powder bed fusion,different post-heat treatment schedules are performed.With the increase in austenitizing temperature and time,the migration rate of austenite grain boundaries continuously increases with the dissolution of nano-carbides,and the formation of nano-oxides and twin martensite is also inhibited accordingly.The rapid growth in the size of prior austenite grains and martensite laths,as well as the decrease in the content of nano-oxides and twin martensite,led to a rapid decrease in the strength(yield strength and ultimate tensile strength)from HT2 to HTF specimens.The HT1 specimens(austenitizing at 830 ℃ for 30 min,then oil quenching and tempering at 300 ℃ for 120 min and finally air cooling)display excellent mechanical properties of yield strength of 1572 MPa,ultimate tensile strength of 1847 MPa,elongation of 9.84％,and fracture toughness of 106 MPa m1/2,which are counterparts to those of conventional DT300 steel forgings after heat treatment.
查看更多>>摘要：To provide a new idea to reduce anisotropy for sheets in the thickness direction by microstructure modification and,mean-while,maintain or even enhance tensile performance,the in-situ ZrB2 particle/AA7085 composite sheets with thicknesses of 1,2,3,and 6 mm were investigated.The as-cast grain size was significantly refined by the heterogeneous nucleus of the ZrB2 particle.The microstructure results show that severe hot deformation converts as-cast disordered microstructure into a sequential microstructure by crushing the remanent phases and matrix into a fiber structure.After the solid solution and aging heat treatment,the composite sheets exhibit largely recrystallized grains compared with partially recrystallized grains in the matrix sheets,and weak or even free texture exists in the composite.The grain size in the composite sheets decreases with the increase in thickness reductions.For the thickness range of 1-3 mm,the composite sheets maintain a similar tensile per-formance as that in matrix sheets,while the strength and ductility in the 6-mm-thick composite sheet are improved.
查看更多>>摘要：The effects of V on microstructure,room temperature,and high-temperature(350 ℃)mechanical properties of Al-5Cu-1.5Ni alloy were investigated.The results show that Al-5Cu-1.5Ni-xV alloys mainly comprise α-Al,Al2Cu,Al3(Ni,Cu)2,Al3Ni,Al7Cu4Ni,and Al10V phases.The addition of V can signally refine α-Al dendritic structure,which improves the mechanical properties of the as-cast alloys at room and high temperatures.After T6 heat treatment(540 ℃/12 h/WC+170 ℃/8 h/AC),α-Al,network skeleton structure Al3(Ni,Cu)2,and Al10V phases all show coarsening,while the fine nano-θ'-Al2Cu precipitated from the matrix and dispersed distributed.The introduction of V promotes the quantity of precipitated θ'-Al2Cu particles.The ultimate tensile strength of the heat-treated alloys at room and high temperatures is greatly improved compared to that of the as-cast alloy.The highest high-temperature ultimate tensile strength of the alloys with V is 111.8 MPa,21.5％higher than that of the base alloy.The analysis shows that the improvement of high-temperature mechanical properties after heat treatment is mainly due to the introduction of V,increasing the precipitated quantity of nano-θ'-Al2Cu particles and improving its thermal stability.The dispersion strengthening effect of θ'-A12Cu particles exceeds the weakening effect of other adverse microstructures on the mechanical properties.
查看更多>>摘要：Mo element was added to cobalt-based alloy L605,and cold forging deformation was performed.The effects of the addition and cold forging deformation on the microstructure and mechanical properties of the alloy were studied by thermodynamic calculation,electron backscatter diffraction,transmission electron microscopy,and X-ray diffraction.The stacking fault energy(SFE)of the alloy decreased after the addition,and the formation of stacking faults and intersections were promoted to improve the strength and hardness.The tensile strength of the alloy with Mo increased from 1190 to 1702 MPa after 24％cold deformation,producing significant work hardening.The strengthening mechanism is strain-induced martensitic transformation(SIMT)and deformation twinning.The alloy,combined with Mo and after 24％deformation,had both high strength and ductility in comparison with the original cobalt-based alloy L605.This is attributed to the lower SFE which caused the increase in stacking fault density.During the tensile process,the ε-hcp phase was easily generated at the stacking fault to reduce the stress concentration and increase the ductility.Controlling SIMT by adjusting the density of stacking faults can improve the mechanical properties of cobalt-based alloys.The ε-hcp phase,the interaction between deformation twins and dislocations,and the interaction between e-hcp phases during cold forging deformation caused local stress concentration,lowering ductility and toughness.
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