铌、钛微合金化仿晶界型铁素体/粒状贝氏体复相钢的形变诱导铁素体相变的研究

以仿晶界型铁素体型/粒状贝氏体复相钢为对象,研究了铌、钛微合金化对其形变诱导铁素体相变的影响以及以仿晶界铁素体/粒状贝氏体为基本组织的复相钢形变诱导铁素体相变规律.研究表明,仿晶界铁素体/粒状贝氏体复相钢进行微合金化,会使其形变诱导铁素体相变受到抑制而推迟;同时因为微合金元素的加入,细化了相变中诱导析出的铁素体晶粒,有利于复相钢中粒状贝氏体的形成.形变参数对相变过程有着显著的影响,奥氏体化温度决定了奥氏体原始晶粒尺寸同样影响着形变诱导铁素体相变过程.采用合适的形变参数和奥氏体温度都可以促进形变诱导铁素体相变的进行从而细化铁素体晶粒.     

0.02%Nb空冷仿晶界型铁素体/粒状贝氏体复相钢的相变及强韧性

采用Gleeble-1500D热模拟机进行热模拟实验和轧制实验,研究了添加0.02%Nb对仿晶界型铁素体(F_(GBA))/粒状贝氏体(B_G)复相空冷钢相变及力学性能的影响.结果表明,0.02%Nb使该钢的连续冷却转变曲线右移,淬透性增加;0.02%Nb抑制了γ→α相变,细化了仿晶界铁素体,促进了粒状贝氏体转变,细化了粒状贝氏体及其内部的铁素体片条及马氏体-奥氏体(M-A)岛.与不含Nb的F_(GBA)/B_G复相钢相比,由于组织细化及强化相体积分数的提高,含0.02%Nb的复相钢经轧后空冷后抗拉强度上升了157 MPa,屈服强度增加了93 MPa,强化效果显著.分析了添加0.02%Nb使复相钢的组织细化及强化相体积分数增加的原因.     

显微组织对SA508 Gr.3钢断裂方式的影响

采用光学显微镜、扫描电镜和电子背散射衍射等手段研究了具有铁素体+贝氏体、粒状贝氏体、板条贝氏体+马氏体和板条马氏体4种显微组织的核电压力容器用SA508 Gr.3钢的低温(-196℃)冲击吸收能量和二次裂纹扩展行为。结果表明:低温冲击吸收能量随实验钢中硬相增多而升高。铁素体+贝氏体混合组织的实验钢中,裂纹大多在晶界形核,二次裂纹数量较少,但易于扩展;粒状贝氏体组织的实验钢因含有大量的马氏体/奥氏体岛,能提供大量的形核位置,致使二次裂纹呈现多而短的特征;裂纹在板条贝氏体组织中比在马氏体中更容易扩展,这是因为高密度的大角度界面能有效阻止裂纹扩展,故板条马氏体组织实验钢的冲击性能最好。     

球墨铸铁强韧化的组织设计及其热处理工艺

根据球墨铸铁断裂过程中石墨及石墨-基体界面的微观力学行为,为提高其强韧性,对球墨铸铁组织进行优化设计：以强相（马氏体）或强韧相（奥氏体-贝氏体）环包围石墨,基体组织为马氏体或奥氏体-贝氏体,加上适量的铁素体,并通过适当的热处理工艺实现。结果表明,优化组织球墨铸铁具有很高的强韧性,其原因是石墨周围的强（韧）相有效抑制了石墨-基体界面的开裂及界面裂纹向基体的扩展,而基体中以强相（马氏体或奥氏体-贝氏体组织）提高强度,以韧相（铁素体或奥氏体）提高韧性,从而提高了球墨铸铁的强韧性。     

淬火温度对高强海洋平台钢组织和低温韧性的影响

研究了淬火温度对高强海洋平台用钢组织和低温韧性的影响。结果表明,760℃加热保温时沿粒状贝氏体晶界呈网状分布的奥氏体在淬火后转变为孪晶马氏体,回火过程中发生分解,对韧性造成损害。790℃加热保温时所生成的奥氏体在随后的淬火过程中转变为贝氏体岛,回火稳定性较强。未奥氏体化的粒状贝氏体在加热过程中发生再结晶,生成软相组织多边形铁素体,有助于钢板低温韧性的提高。     

奥氏体形变对仿晶界型铁素体/粒状贝氏体复相钢组织和强韧性能的影响

通过Gleeble-1500热力模拟实验机对仿晶界型铁素体／粒状贝氏体复相钢进行了Ar3以上不同温度、不同形变量的平面应变压缩实验．SEM和TEM观察表明，奥氏体形变不仅细化仿晶界型铁素体，而且促进先共析铁素体在原奥氏体晶内形核，从而有利于细化粒状贝氏体晶团及其内部的铁素体片条和MA岛．给出的组织变化模型可阐述形变对粒状贝氏体精细结构的影响．经过780℃下30％形变，即使在形变后空冷的条件下也获得了平均长度小于5μm、平均宽度小于2．5μm的仿晶界型铁素体晶粒、平均粒径小于3μm的晶内铁素体．与未经过形变的试样相比，CVN常温冲击韧性值从未形变的43J提高到108J，Vickers硬度从242提高到312，为工业生产工艺的改进提供了重要根据．     

两步贝氏体转变对中碳微纳结构钢韧性的影响

采用一步(300℃等温6 h)和两步(300℃等温2 h+250℃等温24 h)低温贝氏体转变工艺,研究了残留奥氏体对中碳微纳结构钢冲击韧性的影响,对不同热处理试样的显微组织、各相体积分数、大小角度晶界、有效晶粒尺寸与冲击性能进行表征和分析。结果表明,与一步贝氏体转变相比,两步贝氏体转变试样的冲击性能明显提高,-40℃冲击功从31 J提高到42 J,主要原因是第二步贝氏体转变时新形成的贝氏体铁素体分割细化块状未转变奥氏体,减少贝氏体等温后淬火过程中块状马氏体形成,在冲击过程中能够更好地使裂纹分叉甚至阻止裂纹的扩展,显著提高样品的韧性。     

960MPa级熔敷金属组织及冲击韧性分析

研制开发了960 MPa级高强韧性气体保护焊丝,利用金相显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM),并通过低温示波冲击等试验研究了熔敷金属微观组织和冲击韧性. 结果表明,熔敷金属金相组织为粒状贝氏体(GB)+低碳马氏体(M),马氏体的出现可能和合金元素的成分偏析有关. 贝氏体铁素体(BF)板条晶界形核并向晶内生长,BF片条间有呈薄膜状分布的残余奥氏体(γ'),对韧性有利. 该贝氏体-马氏体型混合组织冲击韧性较好,热输入为13.7 kJ/cm时,熔敷金属裂纹扩展功和冲击吸收总功分别为63和75 J.     

低碳低合金钢中粒状贝氏体的断裂特性

本文研究了一种低碳低合金钢中粒状贝氏体的室温机械性能和低温韧性,讨论了不同奥氏体化温度下连续冷却的粒状贝氏体和等温形成的粒状贝氏体的断裂特性,并与板条马氏体作比较。结果表明粒状贝氏体的脆性转折温度与奥氏体晶粒直径d和平均单位断裂路径Lc之间分别具有VTrs—logd~(-1/2)舌和vTrs-10gLc~(-1/2)形式的直线关系。晶粒粗大的粒状贝氏体,转折温度显著升高,韧性恶化。连续冷却(空冷)下的粒状贝氏体对解理裂纹扩展的阻力主要取决于奥氏体晶粒度和铁素体领域尺寸。已分解后的小岛对裂纹扩展的阻碍极小,其脆性作用也不大。等温形成的粒状贝氏体,出现岛状马氏休,脆性急剧增加。     

热处理工艺对35CrMo钢组织及性能的影响

利用SEM、金相显微镜、冲击试验机研究了淬火+回火、贝氏体等温淬火两种热处理工艺对35CrMo钢组织及性能的影响。结果表明,随回火温度提高或贝氏体含量的增加,材料的强度降低、塑韧性增加;回火索氏体组织的冲击断口表现为塑性韧窝状,而贝氏体/马氏体复相组织的冲击断口的纤维区表现为塑性韧窝状,放射区表现为脆性解理断裂;在等强度、塑韧性条件下,回火索氏体裂纹形成功低于贝氏体/马氏体复相组织,当裂纹形成后,回火索氏体组织裂纹扩展功高于贝氏体/马氏体复相组织。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。