Flow characteristics and hot workability of a typical low-alloy high-strength steel during multi-pass deformation

Heavy components of low-alloy high-strength(LAHS) steels are generally formed by multi-pass forging. It is necessary to explore the flow characteristics and hot workability of LAHS steels during the multi-pass forging process, which is beneficial to the formulation of actual processing parameters. In the study, the multi-pass hot compression experiments of a typical LAHS steel are carried out at a wide range of deformation temperatures and strain rates. It is found that the work hardening rate of the experimental material depends on deformation parameters and deformation passes, which is ascribed to the impacts of static and dynamic softening behaviors. A new model is established to describe the flow characteristics at various deformation passes. Compared to the classical Arrhenius model and modified Zerilli and Armstrong model, the newly proposed model shows higher prediction accuracy with a confidence level of 0.98565. Furthermore, the connection between power dissipation efficiency(PDE) and deformation parameters is revealed by analyzing the microstructures. The PDE cannot be utilized to reflect the efficiency of energy dissipation for microstructure evolution during the entire deformation process, but only to assess the efficiency of energy dissipation for microstructure evolution in a specific deformation parameter state.As a result, an integrated processing map is proposed to better study the hot workability of the LAHS steel, which considers the effects of instability factor(IF), PDE, and distribution and size of grains. The optimized processing parameters for the multi-pass deformation process are the deformation parameters of 1223–1318 K and 0.01–0.08 s^(-1). Complete dynamic recrystallization occurs within the optimized processing parameters with an average grain size of 18.36–42.3 μm. This study will guide the optimization of the forging process of heavy components.

Recent progress in visualization and digitization of coherent transformation structures and application in high-strength steel

High-strength steels are mainly composed of medium-or low-temperature microstructures,such as bainite or martensite,with coherent transformation characteristics.This type of microstructure has a high density of dislocations and fine crystallographic structural units,which ease the coordinated matching of high strength,toughness,and plasticity.Meanwhile,given its excellent welding perform-ance,high-strength steel has been widely used in major engineering constructions,such as pipelines,ships,and bridges.However,visual-ization and digitization of the effective units of these coherent transformation structures using traditional methods(optical microscopy and scanning electron microscopy)is difficult due to their complex morphology.Moreover,the establishment of quantitative relationships with macroscopic mechanical properties and key process parameters presents additional difficulty.This article reviews the latest progress in microstructural visualization and digitization of high-strength steel,with a focus on the application of crystallographic methods in the development of high-strength steel plates and welding.We obtained the crystallographic data(Euler angle)of the transformed microstruc-tures through electron back-scattering diffraction and combined them with the calculation of inverse transformation from bainite or martensite to austenite to determine the reconstruction of high-temperature parent austenite and orientation relationship(OR)during con-tinuous cooling transformation.Furthermore,visualization of crystallographic packets,blocks,and variants based on actual OR and digit-ization of various grain boundaries can be effectively completed to establish quantitative relationships with alloy composition and key process parameters,thereby providing reverse design guidance for the development of high-strength steel.

Deep decalcification of factory-provided freezing acidolysis solution to achieveα-high-strength gypsum

The freezing acidolysis solution of the nitric acid-phosphate fertilizer process has a high calcium content,which makes it difficult to produce fine phosphate and high water-soluble phosphate fertilizer products.Here,based on the potential crystallization principle of calcium sulfate in NH_(4)NO_(3)-H_(3)PO_(4)-H_(2)O,the deep decalcification(i.e.calcium removal)technology to achieveα-high-strength gypsum originated from freezing acidolysis-solutions has been firstly proposed and investigated.Typically,calcium can be removed from the factory-provided freezing acidolysis-solution by neutralizing it with ammonia,followed by the addition of ammonium sulfate solution.As a result,the formation of calcium sulfate in the reaction system undergoes the nucleation and growth of CaSO_(4)·2H_(2)O(DH),as well as its dissolution and crystallization into short columnarα-CaSO_(4)·0.5H_(2)O(α-HH).Remarkably,with the molar ratio of SO_(4)^(2-)/Ca^(2+)at 1.8,the degree of neutralization(NH_(3)/HNO_(3) molar ratio)at 1.7,the reaction temperature of 94℃,and the reaction time of 300 min,the decalcification rate can reach 86.89%,of which the high-strengthα-CaSO_(4)·0.5H_(2)O(α-HH)will be obtained.Noteworthy,the deep decalcification product meets the standards for the production of fine phosphates and highly water-soluble phosphate fertilizers.Consequently,the 2 h flexural strength ofα-HH is 5.3 MPa and the dry compressive strength is 36.8 MPa,which is up to the standard of commercialα-HH.

Study on Fracture Delay of High-Strength Bolts in Road Bridge Maintenance

In the maintenance work of highway and bridge engineering structures,the fracture delay of high-strength bolts is a content that needs to be focused on and researched.Based on this,the paper analyzes the fracture delay of high-strength bolts in highway bridge maintenance,including an overview of the fundamental research on fracture delay and related specific studies.It is hoped that this study can provide scientific reference for the reasonable maintenance of high-strength bolts,so as to ensure the overall maintenance effect of highway bridge projects.

Effect of traveling-wave magnetic field on dendrite growth of high-strength steel slab: Industrial trials and numerical simulation

The dendrite growth behavior of high-strength steel during slab continuous casting with a traveling-wave magnetic field was studied in this paper. The morphology of the solidification structure and composition distribution were analyzed. Results showed that the columnar crystals could deflect and break when the traveling-wave magnetic field had low current intensity. With the increase in current intensity, the secondary dendrite arm spacing and solute permeability decreased, and the columnar crystal transformed into an equiaxed crystal. The electromagnetic force caused by the traveling-wave magnetic field changed the temperature gradient and velocity magnitude and promoted the breaking and fusing of dendrites. Dendrite compactness and composition uniformity were arranged in descending order as follows:columnar-toequiaxed transition (high current intensity), columnar crystal zone (low current intensity), columnar-to-equiaxed transition (low current intensity), and equiaxed crystal zone (high current intensity). Verified numerical simulation results combined with the boundary layer theory of solidification front and dendrite breaking–fusing model revealed the dendrite deflection mechanism and growth process. When thermal stress is not considered, and no narrow segment can be found in the dendrite, the velocity magnitude on the solidification front of liquid steel can reach up to 0.041 m/s before the dendrites break.

Hot deformation behavior of novel high-strength Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy

The hot compression behavior of as-extruded Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy was studied on a Gleeble-3500 thermal simulation machine.Experiments were conducted at temperatures ranging from 523 to 673 K and strain rates ranging from 0.001 to 1 s^(-1).Results showed that an increase in the strain rate or a decrease in deformation temperature led to an increase in true stress.The constitutive equation and processing maps of the alloy were obtained and analyzed.The influence of deformation temperatures and strain rates on microstructural evolution and texture was studied with the assistance of electron backscatter diffraction(EBSD).The as-extruded alloy exhibited a bimodal structure that consisted of deformed coarse grains and fine equiaxed recrystallized structures(approximately 1.57μm).The EBSD results of deformed alloy samples revealed that the recrystallization degree and average grain size increased as the deformation temperature increased.By contrast,dislocation density and texture intensity decreased.Compressive texture weakened with the increase in the deformation temperature at the strain rate of 0.01 s-1.Most grains with{0001}planes tilted away from the compression direction(CD)gradually.In addition,when the strain rate decreased,the recrystallization degree and average grain size increased.Meanwhile,the dislocation density decreased.Texture appeared to be insensitive to the strain rate.These findings provide valuable insights into the hot compression behavior,microstructural evolution,and texture changes in the Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy,contributing to the understanding of its processing-microstructure-property relationships.

Development of high-strength magnesium alloys with excellent ignition-proof performance based on the oxidation and ignition mechanisms: A review

High reactivity and ease of ignition are the major obstacles for the application of Mg alloys in aerospace.Thus,the ignition mechanisms of Mg alloys should be investigated systematically,which can guide the ignition-proof alloy design.This article concludes the factors influencing the ignition resistance of Mg alloys from oxide film and substrate microstructure,and also the mechanisms of alloying elements improving the ignition resistance.The low strength is another reason restricting the development of Mg alloys.Therefore,at the last section,Mg alloys with the combination of high strength and good ignition-proof performance are summarized,including Mg-Al-Ca based alloys,SEN(Mg-Al-Zn-Ca-Y)alloys as well as Mg-Y and Mg-Gd based alloys.Besides,the shortages and the future focus of theses alloys are also reviewed.The aim of this article is to promote the understanding of oxidation and ignition mechanisms of Mg alloys and to provide reference for the development of Mg alloys with high strength and excellent ignition-proof performance at the same time.

Microstructure Distribution Characteristics of High-Strength Aluminum Alloy Thin-Walled Tubes during Multi-Passes Hot Power Backward Spinning Process

The microstructure of the thin-walled tubes with high-strength aluminum alloy determines their final forming quality and performance. This type of tube can be manufactured by multi-pass hot power backward spinning process as it can eliminate casting defects, refine microstructure and improve the plasticity of the tube. To analyze the microstructure distribution characteristics of the tube during the spinning process, a 3D coupled thermo-mechanical FE model coupled with the microstructure evolution model of the process was established under the ABAQUS environment. The microstructure evolution characteristics and laws of the tube for the whole spinning process were analyzed. The results show that the dynamic recrystallization is mainly produced in the spinning deformation zone and root area of the tube. In the first pass, the dynamic recrystallization phenomenon is not obvious in the tube. With the pass increasing, the trend of dynamic recrystallization volume percentage gradually increases and extends from the outer surface of the tube to the inner surface. The fine-grained area shows the states of concentration, dispersion, and re-concentration as the pass number increases. .

宽带在片SOLT校准件研制及表征

针对在片S参数校准,设计制作GaAs衬底SOLT校准组件,通过计算方法对校准组件中直通、开路、短路和负载校准件中偏置传输线的时延和损耗进行定义,运用基于NIST muiline TRL校准的测量方法对校准组件中开路校准件电容和短路校准件电感参数进行提取,结合直流电阻测试法测试负载阻值大小,实现对SOLT校准组件的完整表征。最后用自行研制并表征的SOLT校准组件校准在片S参数测试系统,通过测量无源器件验证校准效果,将测量结果与NIST multilineTRL校准后的测量结果比较,在20 GHz内传输幅度最大偏差0.1 dB,传输相位最大偏差3.5°。

40GHz陶瓷衬底SOLT校准片研制与定标技术研究

在片测试系统在微波单片集成电路MMIC的设计建模及生产检验中有着必不可少的作用。由于测试参考面从矢网的同轴接口转移到微波探针,因此需要用共面波导校准片校准。设计制作了用于在片测试系统校准的陶瓷衬底的SOLT校准片,并对校准片进行了建模,提取出了1~40GHz频段内片上负载及短路件的等效电阻及寄生电感参量、直通件的延时参量。片上负载的电阻分量约为45Ω,回波损耗在1~30GHz小于-20dB;在30~40GHz小于-10dB。验证了SOLT校准片设计、制作及定标的整个工艺过程的有效性。

SOLT校准方法及其在射频测量中的应用

分析了矢量网络分析仪测试系统的误差来源,给出二端口SOLT校准的12项误差模型,由此推导了待测元件的真实S参数,并且详细讲述了SOLT校准件的制作方法,确定出开路件的边缘电容。最后,使用自制的PCB夹具测量了0603封装的电感和电容,对校准前后的测量数据进行了对比、分析,并成功地提取了封装后的模型参数,结果证明该方法可以用于射频夹具测量的校准。

一种用于在片器件直接测量的新型SOLT校准方法

介绍了一种“针尖前移”的在片SOLT校准方法,使用这种校准方法可以将测试参考面直接校准到内部被测件,从而可以进行无去内嵌(De-embedding)操作的直接测量。通过对在片平面螺旋电感的测试验证,证明这是一种精确高效的新校准方法。

Mechanical properties of calcium carbonate whisker-reinforced high-strength cement mortar

In order to improve the brittleness of high-strength cement mortar,calcium carbonate（CaCO3） whiskers are incorporated to strengthen and toughen the high-strength cement mortar.The compressive strength,flexural strength,split tensile strength and work of fracture are measured.Microstructures and micromechanical behaviors are investigated using scanning electron microscopy.The strengthening and toughening mechanisms and the efficiency of whisker-reinforced high-strength cement mortar are discussed.The results show that the addition of CaCO3 whiskers brings positive effects on the high-strength cement mortar.The strengthening and toughening mechanisms are whisker-cement coalition debonding,whisker peeling,whisker impact breakage and whisker bridging.Crack deflection is one efficient mechanism,but it is hard to be achieved in high-strength cement mortar.And the interfacial bonding strength between whiskers and the cement mortar matrix should be appropriately weak to introduce more crack deflection mechanisms to strengthen and toughen the cement mortar efficiently.

Effect of geometrical parameters on forming quality of high-strength TA18 titanium alloy tube in numerical control bending

The forming quality of high-strength TA18 titanium alloy tube during numerical control bending in changing bending angle β, relative bending radius R/D and tube sizes such as diameter D and wall thickness t was clarified by finite element simulation. The results show that the distribution of wall thickness change ratio Δt and cross section deformation ratio ΔD are very similar under different β; the Δt and ΔD decrease with the increase of R/D, and to obtain the qualified bent tube, the R/D must be greater than 2.0; the wall thinning ratio Δto slightly increases with larger D and t, while the wall thickening ratio Δti and ΔD increase with the larger D and smaller t; the Δto and ΔD firstly decrease and then increase, while the Δti increases, for the same D/t with the increase of D and t.

Development in oxide metallurgy for improving the weldability of high -strength low-alloy steel-Combined deoxidizers and microalloying elements

The mechanisms of oxide metallurgy include inducing the formation of intragranular acicular ferrite(IAF)using micron-sized inclusions and restricting the growth of prior austenite grains(PAGs)by nanosized particles during welding.The chaotically oriented IAF and refined PAGs inhibit crack initiation and propagation in the steel,resulting in high impact toughness.This work summarizes the com-bined effect of deoxidizers and alloying elements,with the aim to provide a new perspective for the research and practice related to im-proving the impact toughness of the heat affected zone(HAZ)during the high heat input welding.Ti complex deoxidation with other strong deoxidants,such as Mg,Ca,Zr,and rare earth metals(REMs),can improve the toughness of the heat-affected zone(HAZ)by re-fining PAGs or increasing IAF contents.However,it is difficult to identify the specific phase responsible for IAF nucleation because ef-fective inclusions formed by complex deoxidation are usually multiphase.Increasing alloying elements,such as C,Si,Al,Nb,or Cr,con-tents can impair HAZ toughness.A high C content typically increases the number of coarse carbides and decreases the potency of IAF formation.Si,Cr,or Al addition leads to the formation of undesirable microstructures.Nb reduces the high-temperature stability of the precipitates.Mo,V,and B can enhance HAZ toughness.Mo-containing precipitates present good thermal stability.VN or V(C,N)is ef-fective in promoting IAF nucleation due to its good coherent crystallographic relationship with ferrite.The formation of the B-depleted zone around the inclusion promotes IAF formation.The interactions between alloying elements are complex,and the effect of adding dif-ferent alloying elements remains to be evaluated.In the future,the interactions between various alloying elements and their effects on ox-ide metallurgy,as well as the calculation of the nucleation effects of effective inclusions using first principles calculations will become the focus of oxide metallurgy.

一种L~Ka波段可调MEMS SOLT校准件的设计

针对矢量网络分析仪(VNA)及其测试连接系统校准的宽频带、低功耗、易操作的需求,设计了一款适用于L~Ka波段的可调微机电系统(MEMS)SOLT校准件.该结构校准件以串联、并联式MEMS开关为基础,首先设计出一款串并联混合式MEMS开关,并将负载电阻与MEMS开关进行集成,结合校准件的SOLT原理,利用该开关对信号的选通功能实现短路、开路、负载和直通4种校准状态.该结构的校准件弥补了传统校准件操作复杂、人为误差较大的不足,具有体积小、精度高、易于操作的特点.利用HFSS仿真软件对器件性能进行优化仿真,在L~Ka波段范围内,器件在直通、开路及短路状态下的损耗分别优于1.89 dB,1.8 dB及0.33 dB,阻抗稳定在50.5Ω.

复方黄黛片对Solt-Farber原发性肝癌大鼠血管新生作用的影响

目的:研究复方黄黛片对Solt-Farber原发性肝癌大鼠血管新生作用的影响。方法:将50只SD大鼠随机分为正常组、模型组、复方黄黛片高剂量组、中剂量组及低剂量组,每组10只。采用Solt-Farber二步法对除正常组外各组大鼠进行原发性肝癌造模,高(280 mg/kg)、中(140 mg/kg)及低剂量组(70 mg/kg)大鼠同时灌胃给予相应剂量的复方黄黛片,正常组与模型组则给予等量生理盐水,连续灌胃18周。末次灌胃12 h后取血,分离血清,检测其中肝功能指标水平(ALT、AST及TBIL)。取血完成,取各组大鼠肝脏,平均分为4份,分别进行病理组织学观察,采用免疫荧光法检测HIF-1α、VEGF及VEGFR-2的表达情况,计算其相对表达量并进行4组比较。结果:与模型组[ALT,(163.74±16.45)IU/L;AST,(331.24±31.35)IU/L;TBIL,(86.11±8.51)IU/L]比较,各组大鼠中血清肝功能指标均明显降低,其差异具有统计学意义(P<0.05);各组指标分别为高剂量组[ALT,(71.43±7.83)IU/L;AST,(112.52±12.58)IU/L;TBIL,(34.23±3.23)IU/L],中剂量组[ALT,(105.32±10.13)IU/L;AST,(223.52±36.58)IU/L;TBIL,(42.93±4.02)IU/L],低剂量组[ALT,(122.34±12.11)IU/L;AST,(254.21±25.14)IU/L;TBIL,(51.27±5.26)IU/L]。高剂量组、中剂量组及低剂量组大鼠肝组织均出现不同程度的癌变,癌细胞呈梁状排列,但癌变程度均不及模型组。与模型组(HIF-1α,14.23±1.28;VEGF,11.52±1.10;VEGFR-2,16.34±1.65)比较,各组大鼠肝组织HIF-1α、VEGF及VEGFR-2的阳性表达情况均明显减轻,且相对表达量均明显降低,其差异具有统计学意义(P<0.05);各组指标分别为高剂量组(HIF-1α,3.92±0.29;VEGF,2.87±0.26;VEGFR-2,3.45±0.40)、中剂量组(HIF-1α,6.36±0.65;VEGF,5.34±0.51;VEGFR-2,5.87±0.60)及低剂量组(HIF-1α,8.53±0.81;VEGF,7.76±0.74;VEGFR-2,8.12±0.87)。结论:复方黄黛片用于Solt-Farber原发性肝癌大鼠,可有效改善肝功能,抑制HIF-1α、VEGF及VEGFR-2等血管新生相关蛋白的表达。

In-depth analysis of the fatigue mechanism induced by inclusions for high-strength bearing steels

A numerical study of stress distribution and fatigue behavior in terms of the effect of voids adjacent to inclusions was conducted with finite element modeling simulations under different assumptions.Fatigue mechanisms were also analyzed accordingly.The results showed that the effects of inclusions on fatigue life will distinctly decrease if the mechanical properties are close to those of the steel matrix.For the inclusions,which are tightly bonded with the steel matrix,when the Young’s modulus is larger than that of the steel matrix,the stress will concentrate inside the inclusion;otherwise,the stress will concentrate in the steel matrix.If voids exist on the interface between inclusions and the steel matrix,their effects on the fatigue process differ with their positions relative to the inclusions.The void on one side of an inclusion perpendicular to the fatigue loading direction will aggravate the effect of inclusions on fatigue behavior and lead to a sharp stress concentration.The void on the top of inclusion along the fatigue loading direction will accelerate the debonding between the inclusion and steel matrix.

Toughening mechanisms of a high-strength acicular ferrite steel heavy plate

An ultra-low carbon acicular ferrite steel heavy plate was obtained with an advanced thermo-mechanical control process-relaxed precipitation controlled transformation （TMCP-RPC） at Xiangtan Steel, Valin Group. The heavy plate has a tensile strength of approximately 600 MPa with a lower yield ratio. The impact toughness of the heavy plate achieves 280 J at ？40°C. The fine-grained mixed microstructures of the heavy plate mainly consist of acicular ferrite, granular bainite, and polygonal ferrite. The high strength and excellent toughness of the heavy plate are attributed to the formation of acicular ferrite microstructure. The prevention of blocks of martensite/retained austenite （M/A） and the higher cleanness are also responsible for the superior toughness.

Influence of pre-stretching on quench sensitive effect of high-strength Al-Zn-Mg-Cu-Zr alloy sheet

The influence of pre-stretching on quench sensitive effect of high strength Al-Zn-Mg-Cu-Zr alloy AA 7085 sheet was investigated by tensile testing at room temperature,transmission electron microscopy(TEM)and differential scanning calorimetry(DSC).The water-cooled and aged alloy exhibits higher strength than the air-cooled and aged alloy;2.5%pre-stretching of tensile deformation exerts little effect on strength of water-cooled and aged alloy but increases that of air-cooled and aged one,and therefore the yield strength reduction rate due to slow quenching decreases from about 3.8%to about 1.0%,reducing quench sensitive effect.For the air-cooled alloy,pre-stretching increases the sizes ofη'strengthening precipitates but also increases their quantity and the ratio of diameter to thickness,resulting in enhanced strengthening and higher strength after aging.The reason has been discussed based on microstructure examination by TEM and DSC.