Solution and Precipitation Behavior of Nb and Its Role in Medium Carbon Long Product Steels

Controlling of the solution and precipitation for microalloying additions of Nb,V,Ti and their combination is the basic building block of microalloyed steels.Among three microalloying elements,Nb has been regarded the most effective microalloying ingredient used for low carbon flat products due to marked strengthening effect of grain refinement and relatively weak precipitation strengthening effect by matching proper thermomechanical processing(TMP).However,Nb was not viewed as attractive as V for medium carbon long products in the past because of limited solubility during reheating process.What is more,hot working is usually carried out at high temperatures in the recrystallization regime,so it is difficult to exert conventional controlled rolling to obtain pancaked austenite,which has further affected the research and application of Nb in medium carbon long products.Because of these factors,studies of Nb in medium carbon long products were incomplete,and even some recognitions and conclusions are subjected to debate.In order to clarify the strengthening effects of Nb in medium carbon long products,the reinforcing bars have been chosen as experimental steels to clarify the role of Nb on microstructural changes along the whole hot working,cooling processes.In addition,qualitative and quantitative analyses of Nb’s state and distribution in reheating,rolling and cooling had been carried out to illustrate some singularities.

The development of 3D printing technology and the current situation of controlling defects in SLM technology

With unique manufacturing technology,the additive manufacturing technology divides the three-dimensional object into countless two-dimensional laminates.Compared with the traditional material reduction manufacturing method,it has the characteristics of saving materials,being fast,and especially suitable for single and small batch parts and the rapid manufacturing of parts with complex shapes and internal structures.In this paper,various methods of additive manufacturing technology are reviewed.This paper introduces the characteristics of selective laser melting technology and its forming equipment system.On this basis,the technical defects of selective laser melting technology are analyzed,and the status of controlling defects in SLM technology is explained.In the end,the prospects of additive manufacturing technology are described.

Effect of the feeding rate on microstructure and properties of plasma spheroidized GH4169 powder

The growing interest in additive manufacturing of GH4169 alloy was accompanied by the demand on spherical GH4169 powders with high performance.The powder particles were treated by radio frequency plasma with the different feeding rates.The microstructure and morphology,the particle size distribution of as-treated powders were studied by scanning electron microscopy and laser particle size analysis.It was demonstrated that GH4169 powders with extremely fine followability were obtained by radio frequency plasma spheroidization technology.With the same plasma parameters,the spheroidization efficiency of the particles varied with the feeding rates.When the rate of the powder feeding rates was too small,the excessive absorption of the heating by the powders caused vaporization,then the collection decreased.When the feeding rates was too large,the powder particles were insufficiently absorbed,resulting in defects in the powders.The microstructure of the as-treated spherical particles was mainly cell crystals,columnar crystals,and even microcrystals.Under the suitable plasma parameters,the resulting powders haved a slightly increased average particle size,excellent spheroidization,surface smoothness,followability,and bulk ratio.

Noise Suppression Effect of Composites Containing Glass-Covered Amorphous CoFeSiBCr Wires

The noise suppression effect and its mechanism are investigated for a composite sheet and a composite film made of glass-covered amorphous CoFeSiBCr wires.Both samples show a significant noise suppression effect.The power loss ratio of the composite sheet is above 80% from 1.6 GHz to 8.5 GHz,and that of the composite film is above 70% from 3.2 GHz to 8.5 GHz even if its thickness is only 0.20 mm.The composite sheet demonstrates high real and imaginary permittivity above 30.7 and low real and imaginary permeability below 1.2.The surface resistivities of the two composite samples are as high as about 3 × 10^(12) Ω/square.The power loss of the composite containing glass-covered wires should be mainly contributed by dielectric loss derived from electronic polarization and relaxation.

Metallurgical Design, Development and Strengthening Mechanisms for HRB600E Reinforcing Bar

High-strength,anti-seismic requirements represent the development tendency to hot-rolled ribbed bar used for the reinforcement of concrete.In this paper,metallurgical design,development and strengthening mechanisms for 600 MPa reinforcing bar with anti-seismic requirements have been studied and presented based on the production practice of 335 MPa,400 MPa and 500 MPa grades.Through trial and error,it was found that alloy design with niobium plus vanadium is the best way to achieve the optimum combination of yield strength and anti-seismic properties,especially,small amount niobium addition can improve upon tensile-to-yield ratio.In order to clarify the underlying theoretical principles for the strengthening effects,qualitative and quantitative analysis for microstructure had been conducted with the aid of optical microscopy,scanning electron microscopy,transmission electron microscopy and chemical extraction technique,together with the solution and precipitation behavior of niobium and vanadium during the hot-rolling and cooling processes.Based on analysis results,it was found strengthening effects of both niobium and vanadium demonstrate some additional strengthening effects apart from predominated precipitation strengthening and grain refinement strengthening respectively.Although adding high vanadium contents is indispensable to achieve needed yield strength through precipitation strengthening effects,but fine VN particles precipitated in relatively high temperature also bring grain refinement effects for austenite and ferrite.Equally,grain refinement is not overall to describe the effects of niobium in long products,small amount of niobium contents is marked to improve upon tensile-to-yield ratio due to transformation strengthening resulted from the niobium contents in solution.Through the development of HRB600E,strengthening mechanisms of vanadium and niobium in medium carbon long products had been enriched.

Continuous Cooling Transformation Behavior and Microstructure Control of Nb Microalloyed Reinforcing Bars

In this paper,CCT(continuous cooling transformation)diagrams are determined for Nb-containing reinforcing bars with different Nb,Mn additions,and initial austenite grain sizes by simulating industrial conditions via dilatometry tests.It was found that coarse austenite grain size,high Mn content and Nb remaining in solution all increase hardenability of Nb-containing rebars,namely lower Ar3 for acicular phase transformation products,which leads to continuous yielding during tensile deformation when the volume fraction of acicular ferrite or bainite microstructure reaches a certain volume fraction.By coupling with actual cooling rates for different size rebars,it can be explained why bainitic structure is prone to form in the center of rebars,especially for small size rebars.In order to achieve required ferrite-pearlite microstructure,cooling strategy is optimized for industrial production.

Study on tungsten sintering temperature field based on electromagnetic simulation and computational fluid dynamics

In order to study the influence of various sintering variables more intuitively and clearly,electromagnetic field analysis and computational fl uid dynamics are used to analyze the infl uence of gas flow,heating power and other process parameters on the temperature range of medium-frequency sintering in this paper.The results indicate that the uniformity of temperature fi eld is determined by the gas flow rate and heating power.When the heating power is 50 kW,the stable temperature drops about 10 K for every 1 m^(3)·h^(−1)increase of hydrogen flow.The peak value of the maximum temperature diff erence on the tungsten rods gradually increases with the increase of the hydrogen flow rate,and it appears slightly later.The temperature distribution of tungsten rods in furnace is similar with diff erent hydrogen flow rate.At the same time,the closer to the furnace wall,the higher the temperature of the tungsten rod.The temperature diff erence between tungsten rods mainly occurred within 1 h after the beginning of heating.Increasing the heating power can improve the stable temperature,but has little eff ect on the heating time.Increasing heating power can increase the peak value of the maximum temperature diff erence on the tungsten rods,but has little eff ect on the occurrence time of the peak value of the maximum temperature diff erence on the tungsten rods.Increasing the heating power will increase the temperature diff erence of a single tungsten rod,but the temperature diff erence of a single tungsten rod never exceeds 65 K.This study can be used to guide the process optimization design.Combined with numerical simulation calculation,the sintering parameters with low energy consumption and high temperature uniformity can be quickly and eff ectively found,thus improving the microstructure and properties of sintered tungsten products.

Formation mechanism of surface oxide layer of grain-oriented silicon steel

The surface oxide layer of grain-oriented electrical steels was investigated by scanning electron microscopy.The formation mechanism and the influence on the glass film of the surface oxide layer were analyzed by the calculation of thermodynamics and kinetics.The surface oxide layer with 2.3μm in thickness is mainly composed of SiO_(2),a small amount of FeO and Fe_(2)SiO_(4).During the formation of surface oxide layer,the restriction factor was the diffusion of O in the oxide layer.At the initial stage of the decarburization annealing,FeO would be formed on the surface layer.SiO_(2) and silicate particles rapidly nucleated,grew and formed a granular oxide layer in the subsurface.As the oxidation layer thickens,the nucleation of new particles decreases,and the growth of oxide particles would be dominant.A lamellar oxide layer was formed between the surface oxide layer and the steel matrix,and eventually formed a typical three-layer structure.During the high temperature annealing,MgO mainly reacted with SiO_(2) and Fe_(2)SiO_(4) in the surface oxide layer to form Mg2SiO_(4) and Fe_(2)SiO_(4) would respond first,thus forming the glass film with average thickness of 4.87μm.

Effect of process parameters on the morphology of aluminum/copper alloy lap joints by red and blue hybrid laser welding

In order to overcome the problems of many pores,large deformation and unstable weld quality of traditional laser welded aluminumcopper alloy joints,a red-blue dual-beam laser source and a swinging laser were introduced for welding.T2 copper and 6063 aluminum thin plates were lap welded by coaxial dual-beam laser welding.The morphology of weld cross section was compared to explore the influence of process parameters on the formation of lap joints.The microstructure characteristics of the weld zone were observed and compared by optical microscope.The results show that the addition of laser beam swing can eliminate the internal pores of the weld.With the increase of the swing width,the weld depth decreases,and the weld width increases first and then decreases.The influence of welding speed on the weld cross section morphology is similar to that of swing width.With the increase of welding speed,the weld width increases first and then decreases,while the weld depth decreases all the time.This is because that the red laser is used as the main heat source to melt the base metals,with the increase of red laser power,the weld depth increases.As an auxiliary laser source,blue laser reduces the total energy consumption,consequently,the effective heat input increases and the spatter is restrained effectively.As a result,the increase of red laser power has an enhancement effect on the weld width and weld depth.When the swing width is 1.2 mm,the red laser power is 550 W,the blue laser power is 500 W,and the welding speed is 35 mm/s,the weld forming is the best.The lap joint of T2 copper and 6063 aluminum alloy thin plate can be connected stably with the hybrid of blue laser.The effect rules of laser beam swing on the weld formation were obtained,which improved the quality of the joints.

Review on effect of applied internal cooling source and vibration on metal solidification process

Advancements in metallurgical technology have led to the emergence of high-performance requirements for metal materials,like high uniformity,high purity,and superfine crystallinity.This has resulted in the development and application of internal cooling source(ICS),vibrational,and vibrational internal cooling source methods in metal solidification processes to afford products with refined crystal grains and large proportions of equiaxed crystals.These methods have gradually been introduced into laboratories and some steel mills over the past few decades.However,there are few successful industrial applications of these methods,as there is no comprehensive understanding of their control theories and principles.Accordingly,the development,basic principles,and classifications of the three types of methods are summarized,and their impact on the solidification of molten metals and the morphology of solid products is discussed.In addition,experimental and numerical simulation-based researches on each type of method are reviewed and their prospects for applications are briefly discussed to control metal solidification.Finally,detailed future perspectives are provided on vibratory strip feeding,ICS,and pulsed magneto-oscillation methods.Hopefully,it will serve as a reference for future studies of the application of these and related methods in metal solidification processes.

BiAlO_(3)-modified BiFeO_(3)-BaTiO_(3) high Curie temperature lead-free piezoelectric ceramics with enhanced performance

BiFeO_(3)-BaTiO_(3)(BF-BT)lead-free piezoelectric ceramics have high piezoelectricity and high Curie temperature(T_(C)),but the mixed-valence Fe ions and Bi^(3+)volatilization would promote the formation of Bi_(25)FeO_(40)/Bi_(2)Fe_(4)O_9 and oxygen vacancy,which greatly degrade the insulation properties required for polarization.In this study,it was found that the modification of BiAlO_(3)(BA)in BF-BT ceramics could effectively solve these problems,reducing the leakage current to 1×10^(-9)A·cm^(-2)and transiting the space charge-limited conduction to ohmic conduction.Because of the enhanced insulation properties and appropriate rhombohedral-pseudocubic phase ratio(C_R/C_(PC)),BF-BT-xBA ceramics in an optimized composition obtain enhanced piezoelectric performance:piezoelectric charge coefficient(d_(33))=196 pC·N^(-1),planar electromechanical coupling coefficient(k_(p))=31.1%,T_(C)=487℃and depolarization temperature(T_d)=250°C;unipolar strain(S_(uni))=0.17%and piezoelectric strain coefficient(d_(33)^(*))=335 pm·V^(-1)at 100℃.Especially,d_(33)exceeds 283 pC·N^(-1)at 233℃and d_(33)^(*)is 335 pm·V^(-1)at100℃,showing an excellent high-temperature piezoelectricity and high depolarization temperature.The results are attributed to the domain structure of rhombohedral-pseudocubic phase coexistence and its high-temperature switching behavior.This work provides a feasible and effective approach to improve the high temperature piezoelectric properties of BF-BT-xBA ceramics,making them more suitable for high temperature applications.

Prior austenite grain boundary recognition in martensite microstructure based on deep learning

Grain size determination is essential in producing and testing iron and steel materials.Grain size determination of martensitic steels usually requires etching with picric acid to reveal the prior austenite grain boundaries.However,picric acid is toxic and explosive and belongs to hazardous chemicals,which makes it difficult for laboratories and testing institutions to obtain.A new experimental method was developed to use Nital etchant instead of picric acid.The deep learning method was used to recognize the prior austenite grain boundaries in the etched martensite microstructure,and the grain size could be determined according to the recognition result.Firstly,the polished martensite specimen was etched twice with Nital etchant and picric acid,respectively,and the same position was observed using an optical microscope.The images of the martensitic structure and its prior austenite grain boundary label were obtained,and a data set was constructed.Secondly,based on this data set,a convolutional neural network model with a semantic segmentation function was trained,and the accuracy rate of the test set was 87.53%.Finally,according to the recognition results of the model,the grain size rating can be automatically determined or provide a reference for experimenters,and the difference between the automatic determination results and the measured results is about 0.5 level.

纳米尺度非均匀性诱导自更新铁基非晶合金具有优异的长期反应活性（英文）

铁基非晶合金作为亚稳态新型零价铁,具有高活性亚稳态结构、较大的残余应力和高密度低配位点等特性,在催化和废水处理中引起了广泛的关注;但由于腐蚀产物沉淀覆盖活性位点,非晶合金的反应活性随着时间的推移而逐渐降低,导致耐用性差.腐蚀产物沉淀造成长期反应活性降低也是阻碍传统晶态零价铁技术在废水处理领域应用的主要问题之一.本文通过在铁基非晶合金中引入纳米尺度的化学不均匀性,有助于构成局部原电池效应,加速电子在降解过程中的转移,可以有效地克服这一问题.更重要的是,非晶合金中的零价铁被选择性腐蚀/脱合金,导致反应区域局部体积收缩和裂纹形成,裂纹扩展使沉淀腐蚀产物和反应区域自剥落.因此,可以连续提供新的低配位,消除质量传递和反应活性恶化的问题.本文所制备的具有成分不均匀的铁基非晶合金即使在中性溶液中也具有良好的长期反应活性和自更新性能.研究结果不仅为废水处理提供了一种新材料,而且为设计高活性零价铁材料提供了一种新思路.

Experimental study and industrial demonstration on utilization of Fe,Ti and V from vanadium-bearing titanomagnetite ore sands

In order to achieve highly efficient utilization of three valuable elements Fe,Ti and V simultaneously from vanadium-bearing titanomagnetite ore sands,an improved carbothermic reduction method was proposed and verified in both laboratory scale and industrial test-bed scale.The method combined the process of direct reduction and the process of further reduction and separation.Particularly,pulverized coal injection was introduced.In experimental tests,the effects of parameters such as carbon content in briquette,reduction duration and reduction temperature on the contents of metallic Fe and FeO as well as Fe metallization rate were analyzed.Experimental results indicated that Fe metallization rate in the carbon-containing briquette could reach 75.83%.In the industrial test-bed tests,the effects of carbon content in briquette,reduction duration and reduction temperature were also investigated,respectively.In addition,processes with and without pulverized coal injection were tested.The comparative analysis indicated that the content of TiO2 in titaniferous slag was increased by applying pulverized coal injection,and it can reach 82.5 wt.%.Meanwhile,the energy performance analysis showed that the equivalent electricity consumption of the test-bed dropped significantly to 2071 kWh per ton of slag,about 26.0%less than that of traditional method.Moreover,the investment payback of the test-bed is 3.4 years.Both experiments and industrial test-bed tests demonstrated that the proposed method has the advantages of highly efficient utilization,high energy efficiency as well as good economic performance.

Erratum to:Excellent long-term reactivity of inhomogeneous nanoscale Fe-based metallic glass in wastewater purification(vol 63,issue 3,pg 453-466,2020)

In the version of the article originally published in the volume 63,ssue 3,2020 of Sci China Mater(2020,63(3):453-46,https:/doi.org/10.1007/s40843-019-1205-5),the affiliations of the authors were incorrectly labeled.