BB503钢气电立焊工艺及其组织性能研究

采用气电立焊工艺以及CO2气体保护焊工艺对50mm厚的BB503钢进行焊接,对焊接接头进行拉伸、侧弯、冲击等力学性能测试,采用光学显微镜对焊接接头热影响区组织进行观察分析.结果表明,气电立焊工艺连接BB503所得到的焊接接头抗拉强度高于CO2气体保护焊;BB503钢焊接能够更好的适应单位质量热输入较小的焊接工艺.     

9Ni钢焊接HAZ晶粒长大数值模拟

用Monte Carlo模拟方法研究了超低温用9Ni钢焊接热影响区(HAZ)的晶粒长大。结合焊接试验,建立了9Ni钢焊接HAZ晶粒长大模型,模拟了晶粒生长过程。模拟结果表明,HAZ奥氏体晶粒尺寸平均为70~85μm,与实际对应焊接工艺参数条件下的晶粒尺寸测量结果相吻合。并给出了HAZ存在很陡的温度梯度对晶粒长大起阻碍作用的"热钉扎"效应。研究了焊接工艺参数(焊接热输入和预热温度)对HAZ晶粒尺寸的影响,得出热输入是影响HAZ晶粒尺寸的主要因素。为获得优良的HAZ韧性,在焊接实际生产中需采用较小的热输入。     

大线能量焊接用FH500高强船板钢的研制与焊接试验

采用复合微合金化的成分设计,通过TMCP(热机械处理)工艺开发了适应大线能量焊接的FH500高强船板钢。运用埋弧焊和垂直气电立焊对FH500船板钢进行了焊接试验,对两种焊接方式的焊接接头分别进行了拉伸、弯曲、冲击等力学试验,研究了不同热输入值对接头力学性能的影响;运用透射电镜对焊接热影响区组织析出物进行了分析。结果表明:FH500高强船板钢组织以针状铁素体为主,具有良好的强韧性匹配;两种焊接方式接头力学性均能满足船级社标准。焊接热影响区(HAZ)组织为针状铁素体和贝氏体组织,晶内含有大量纳米级析出物,能谱显示,其成分为钛铌的复合析出物。     

20MnTiB钢与调质45钢焊接工艺

本文通过理论分析与试验结合的方法,对调质45钢与20MnTiB钢异种钢接头的焊接工艺进行了研究.分析表明:2种材料的碳当量都大于0.4％,钢材淬硬性和冷裂倾向较大,20MnTiB钢的HAZ区域极易因焊接热输入大而软化.要确保焊接质量,必须采取合理的焊前预热、道间保温、焊后热处理以及控制热输入等工艺措施.试验结果表明,本文拟定的工艺方案完全达到了设计要求,并已投入焊接生产.     

热输入对00Cr12NiTi不锈钢焊接HAZ组织及性能的影响

研究了铁道车辆用铁素体不锈钢00Cr12NiTi在MAG焊时,焊接热输入对HAZ的组织及性能的影响.结果表明,该钢种对焊接热输入非常敏感,须控制在1 kJ/mm以下,多道焊时,热输入会随着焊道的增加而增加.焊接热输入越大,接头HAZ的金相组织和力学性能越差.最后,总结了热输入及多道焊对HAZ的组织与力学性能的影响规律,并提出了焊接该不锈钢的优化工艺措施.     

EH40船用高强钢双丝气电立焊接头组织与性能

对板厚68 mm的EH40船用高强钢进行了热输入分别为382、440和450 kJ/cm的双丝气电立焊试验,借助焊接接头的拉伸试验、冲击试验、硬度测试及显微组织分析等方法,研究了热输入对EH40钢大厚板双丝气电立焊接头组织和性能的影响。结果表明,大热输入焊接主要通过控制针状铁素体形核长大、改变晶界铁素体形貌及奥氏体晶粒大小来影响EH40钢焊接接头的组织和性能。随着热输入增加,接头强度降低,热影响区软化倾向增大。热输入过大或过小都对焊缝金属韧性不利,纵观焊接接头整体力学性能的变化,在坡口角度20°、间隙8 mm条件下,其最佳的热输入为400~440 kJ/cm。     

热输入对1Cr18Mn8Ni5N奥氏体不锈钢接头热影响区裂纹的影响

进行了1Cr18Mn8Ni5N不锈钢平板对接刚性拘束焊试验,研究焊接热输入对热影响区(HAZ)裂纹的影响,采用SEM、EDS、XRD等分析了接头热影响区显微组织及裂纹特点。结果表明:该钢HAZ组织为单一的奥氏体。热输入为250~290 J/mm时,接头上下表面出现微裂纹;热输入增加至396.7 J/mm则无裂纹。裂纹自紧邻熔合区一侧的HAZ启裂,沿奥氏体晶界扩展,甚至在紧邻HAZ的母材区也分布着裂纹。这是由于接头HAZ显微组织沿厚度方向上存在差异所致。热输入为250~290 J/mm时,接头上部和下部HAZ的晶粒尺寸大于中部的尺寸,且尺寸均匀性差;当热输入为396.7 J/mm时,整个接头HAZ晶粒充分长大,沿厚度方向的晶粒尺寸趋于一致。     

焊接热输入对N80/45异种钢焊接接头组织性能的影响

本文采用CO_2气体保护焊,在不同焊接热输入作用下焊接异种材料N80钢和45钢,并对其HAZ组织和性能进行了研究,结果表明:N80/45异种钢在焊接热循环的作用下HAZ晶粒明显长大,随着焊接热输入的增大,晶粒长大的趋势显著。N80钢一侧过热区组织由铁素体和马氏体组成,随着焊接热输入的增加出现了少量贝氏体,45钢一侧过热区组织由马氏体和贝氏体组成。不同的焊接热输入下由于产生了淬火马氏体,在焊接热影响区均存在一定的硬化现象,随着焊接热输入的增加,HAZ的硬度呈逐渐降低的趋势。     

热输入对Q500CF钢板焊接热影响区组织和冲击性能的影响

通过埋弧焊试验和Gleeble热模拟试验研究了热输入对Q500CF钢热影响区(HAZ)组织和冲击性能的影响.埋弧焊结果表明,热输入为15～ 50 kJ/cm时,HAZ的-20℃冲击吸收功大于等于146 J;HAZ中熔合线(FL)处冲击吸收功最低且随热输入增大而减小.组织观察表明,随热输入增加,粗晶区组织由15 kJ/cm时的板条贝氏体(LB)和粒状贝氏体(GB)转变为50 kJ/cm时的GB组织;临界粗晶区在晶界上出现了大量l ～7 μm的M-A组元,导致低温冲击韧性恶化.Gleeble热模拟结果表明,热输入为50 ～ 70 kJ/cm时,粗晶区GB组织粗化并导致该区冲击韧性恶化.因此为确保多道焊焊接接头HAZ低温冲击韧性,焊接热输入应限制在15～50 kJ/cm之间.     

大热输入焊接DH36钢焊接粗晶区组织与性能分析

利用焊接热模拟的方法,对比研究了大热输入焊接DH36钢焊接粗晶区的组织与性能.结果表明,低碳、低锰及低碳当量+微钛处理的合金设计可显著改善钢大热输入焊接粗晶区的组织与性能.随着t8/5的增大,大热输入焊接DH36钢粗晶区的组织由细小(尺寸1μm)的板条状马氏体-奥氏体岛(M-A岛)组织转变为大尺寸块状M-A岛组织,同时组织中先共析铁素体数量增多,尺寸增大.降低钢中的Mn元素含量可显著促进先共析铁素体的形成,抑制硬质相M-A岛的产生,但过多的粗大先共析铁素体形成会降低HAZ的低温韧性.M-A岛和先共析铁素体共同作用决定着大热输入HAZ的性能.     

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.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.