查看更多>>摘要：After cooling in the hot rolling process,the metallographic structure of microalloyed dual-phase steel is nonuniform along the rolling direction,while the thickness fluctuation of microalloyed dual-phase steel with a nonuniform metallographic structure will occur during cold rolling.The mechanism of nonuniform phase transformation of microalloyed dual-phase steels was studied during the cooling process after hot rolling,and the nonuniform phase transformation of microalloyed dual-phase steel was regulated during the cooling process after hot rolling through process optimization.First,the empirical equation of phase transformation temperature was measured by a dilatometer considering thermal expansion.Then,the phase field and temperature field of laminar cooling process were calculated to provide initial boundary conditions for the finite element model.After that,the coupling finite element model of the temperature phase transfor-mation of the strip steel in coiling transportation process was established.The simulation results show that the different thermal contact conditions of the microalloyed dual-phase steel during coil transportation lead to uneven cooling of the coil,which leads to nonuniform transformation of the coil along the rolling direction.In addition,by prolonging the time interval from coiling to unloading,the phenomenon of nonuniform phase transformation of microalloyed dual-phase steel can be effectively controlled.The simulation results are applied to industrial production.The application results show that prolonging the time interval from coiling to unloading can effectively improve the nonuniform phase transformation of microalloyed dual-phase steel in the cooling process after hot rolling.
查看更多>>摘要：Surface defects can affect the quality of steel plate.Many methods based on computer vision are currently applied to surface defect detection of steel plate.However,their real-time performance and object detection of small defect are still unsatisfactory.An improved object detection network based on You Only Look One-level Feature(YOLOF)is proposed to show excellent performance in surface defect detection of steel plate,called DLF-YOLOF.First,the anchor-free detector is used to reduce the network hyperparameters.Secondly,deformable convolution network and local spatial attention module are introduced into the feature extraction network to increase the contextual information in the feature maps.Also,the soft non-maximum suppression is used to improve detection accuracy significantly.Finally,data augmentation is performed for small defect objects during training to improve detection accuracy.Experiments show the average precision and average precision for small objects are 42.7％and 33.5％at a detection speed of 62 frames per second on a single GPU,respectively.This shows that DLF-YOLOF has excellent performance to meet the needs of industrial real-time detection.
查看更多>>摘要：Regular TiN is harmful to the toughness of steel,and its shape and size need to be controlled.Understanding the behavior of TiN precipitation on CeAlO3 surfaces is critical for controlling the morphology and formation process of CeA1O3-TiN composite inclusions in the steel.Experimental results showed that TiN had a square morphology on the CeA1O3 surface,and electron backscatter diffraction phase identification results revealed the orientation relationship between CeAlO3 and TiN as follows:(001)CeA1O3//((1)10)TiN,(100)CeAlO3//(00(1))TiN,and[010]CeAlO3//[110]TiN.The CeA1O3 crystal structure was studied using the first-principles calculation method,and the adsorption and growth process of TiN on the CeA1O3 surface were investigated from the atomic scale.The calculation results indicate that there is no metallic bonding present in the CeAlO3 system.Among the low-index crystal planes of CeAlO3,the(110)planes terminated with O and CeAlO have the highest and lowest surface energies,respectively,with values of 0.373 and 0.051 eV/A2.On the high surface energy plane of CeAlO3,the TiN atomic permutation structure is consistent with the arrangement of Ti and N atoms in TiN(100)or(110).For the low surface energy plane of CeAlO3,the Ti and N atoms are arranged in a ring-like structure.
查看更多>>摘要：The grain boundary(GB)damage of long-term crept HR3C(25Cr-20Ni-Nb-N)austenitic steel with solid solution state was investigated by nanoindentation test accompanied with in-situ electron back-scattered diffraction.The corresponding microstructure was characterized by scanning electron microscopy and transmission electron microscopy.Results show that the increase in nanoindentation hardness at the GBs and triple grain junctions may be related to the dislocation accumulation and carbide growth during the creep.Coarsened M23C6 and dislocations piling-up at the GB accelerate the nucleation and coalescence of creep cavity along the GB.The nanoindentation hardness in grains varies with orientation of the stress axis.The orientation difference of neighbor grains may induce local high geometrically necessary dislocation densities and strain gradients near the GB,consequently causing stress concentration and subsequent crack growth at specific GBs.
查看更多>>摘要：Static recrystallization(SRX)behaviors and corresponding recrystallization mechanisms of 7Mo super-austenitic stainless steel were studied under different deformation conditions.The order of influence of deformation parameters on static recrystallization behaviors,from high to low,is followed by temperature,first-stage strain and strain rate.Meanwhile,the effect of holding time on static recrystallization behaviors is significantly controlled by temperature.In addition,with the increase in temperature from 1000 to 1200 ℃,the static recrystallization mechanism evolves from discontinuous static recrystallization and continuous static recrystallization(cSRX)to metadynamic recrystallization and cSRX,and finally to cSRX.The cSRX exists at all temperatures.This is because high stacking fault energy(56 mJ m-2)promotes the movement of dislocations,making the deformation mechanism of this steel is dominated by planar slip of dislocation.Large undissolved sigma precipitates promote static recrystallization through particle-stimulated nucleation.However,small strain-induced precipitates at grain boundaries hinder the nucleation of conventional SRX and the growth of recrystallized grains,while the hindering effect decreases with the increase in temperature.
查看更多>>摘要：Hydrogen embrittlement of pipelines depends on the hydrogen-induced cracking behavior of the pipeline steel microstructure.Based on molecular dynamics analysis,the ferrite-cementite(α-Fe/Fe3C)lamellar atomic structure with the Bagaryatskii orientation relationship was established,and stepwise relaxation of the conjugate gradient energy mini-mization and constant-temperature and constant-pressure relaxation were performed under NPT(the isothermal-isobaric)conditions.The mechanical property curves of the α-Fe/Fe3C models were obtained under different cementite terminal plane structures,and the evolution of the atomic structure was analyzed in detail.In addition,the influence of different hydrogen concentrations,different temperatures,different strain rates,changes in voids,and different micro-degrees of freedom on the deformation and failure mechanism of the model was investigated,aiming to provide a reliable way to explore the micro-mechanism of macro-cracking behavior of pipeline steel.
查看更多>>摘要：The corrosion mechanism of 510L low alloy steel treated by acid-cleaned surface(ACS)and eco-pickled surface(EPS)techniques in three simulated solutions(S0:atmospheric environment;S1:soil environment;S2:industrial environment)and the influence of interaction between different corrosive anions on corrosion were investigated.The results show that the total corrosion rates of samples in three simulated solutions were in order of S2＞S0＞S1,which is simultaneously correlated with initial corrosion dissolution processes as well as after the formation of corrosion products.HCO3-will inhibit the initial corrosion owing to the formation of films,whereas HSO3-will accelerate the dissolutions of the matrix based on the synergistic action of HSO3-and Cl-.On the other hand,there is no significant difference in corrosion rates between the samples treated by ACS and EPS techniques.The EPS technique that is safe,reusable and environmentally friendly can be further widely used in future work.
查看更多>>摘要：Copper alloy composite bit matrix was prepared by pressureless vacuum infiltration,using at least one of the three kinds of tungsten carbide particles,for example,irregular cast tungsten carbide,monocrystalline tungsten carbide and sintered reduced tungsten carbide particles.The effects of powder particle morphology,particle size and mass fraction of tungsten carbide on the microstructure and mechanical properties of copper alloy composite were investigated by means of scanning electron micro-scopy,X-ray diffraction and abrasive wear test in detail.The results show that tungsten carbide morphology and particle size have obvious effects on the mechanical properties of copper alloy composites.Cast tungsten carbide partially dissolved in the copper alloy binding phase,and layers of Cu0.3W0.5Ni0.1Mn0.1C phase with a thickness of around 8-15 μm were formed on the edge of the cast tungsten carbide.When 45％irregular crushed fine cast tungsten carbide and 15％monocrystalline cast tungsten carbide were used as the skeleton,satisfactory comprehensive performance of the reinforced copper alloy composite bit matrix was obtained,with the bending strength,impact toughness and hardness reaching 1048 MPa,4.95 J/cm2 and 43.6 HRC,respectively.The main wear mechanism was that the tungsten carbide particles firstly protruded from the friction surface after the copper alloy matrix was worn,and then peeled off from the matrix when further wear occurred.
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