大型支撑辊的堆焊修复工艺及应用

大型支撑辊重量大、辊径大、辊面长、耐磨层厚,采用传统的堆焊工艺修复Cr3~Cr5大型支撑辊难度大,母体金属与堆焊层容易在堆焊时发生相变,导致开裂。另外,传统的轧辊堆焊修复工艺不合理,修复的轧辊力学性能较差,限制了轧辊的使用寿命,大量报废的轧辊尤其是大型轧辊长期堆积在轧钢厂内,增加了生产成本,造成了极大浪费。为此,开展了大型热轧Cr3~Cr5支撑辊及大型冷轧Cr3支撑辊焊材制备、堆焊工艺及修复技术研究。技术实施表明,修复后的支撑辊使用寿命达到新轧辊的寿命,每支堆焊修复支撑辊上机使用至报废尺寸,至少可循环堆焊修复3次,使支撑辊单项辊耗成本在每个循环周期内降低40%~60%,同时解决了大型支撑辊焊接性能不稳定的难题。     

光内送丝激光熔覆修复砂光机轧辊

采用激光光内送丝法并利用多道搭接熔覆技术,对20钢砂光机轧辊的凹坑缺陷进行修复,结果表明,修复后的轧辊其几何尺寸复原,添加材料的组织性能优于基体,二者的界面达到了良好的冶金结合,修复层与凹坑周围基体的残余应力很小,无几何变形.     

半钢轧辊堆焊修复用隔离层材料的研制

依据半钢轧辊的成分特点和服役工况,设计开发半钢轧辊堆焊修复用的隔离层材料,研究采用隔离层材料打底,配合工作层材料修复半钢轧辊的可能性。结果表明,在半钢轧辊表面堆焊隔离层材料后,脆性高碳马氏体周围析出了韧性的珠光体组织,增加了隔离层的韧性储备,隔离层中无裂纹等冶金缺陷,且隔离层材料与工作层材料具有良好的相容性,解决了半钢轧辊不可堆焊修复的技术难题。     

高速钢轧辊表面氧化膜研究

借助Gleeble 3500模拟机模拟了高速钢轧辊服役时表面工作层温度的升高,得到了循环加热冷却30次、50次及100次后试样表面的氧化膜。为对比分析,对高铬铸铁轧辊进行了循环50次的试验。利用扫描电子显微镜、X射线衍射分析仪、原子力显微镜对循环氧化后的试样表面氧化产物及其形貌进行了分析。结果表明:随着循环次数增加,高速钢轧辊氧化程度加剧,氧化膜更加致密;同样循环次数下,高铬铸铁轧辊氧化程度要比高速钢严重且氧化膜的粗糙度也大于高速钢。     

轧辊的带板堆焊

选用国产焊接材料进行了轧辊带极堆焊试验研究,测试了焊接参数对堆焊层各参数及表面质量的影响,确定了最佳的焊接工艺参数,并堆焊完成了一个符合技术要求的轧辊,为轧辊的制造和修复提供了科学依据。     

轧辊的带极堆焊

选用国产接材料进行了轧辊带极堆焊试验研究,测试了焊接参数对堆焊层参数及表面质量的影响,确定了最佳的焊接工艺参数,并堆焊完成了一个符合技术要求的轧辊,为轧辊的制造和修复提供了科学依据。     

热轧板带轧机高速钢复合轧辊断裂失效分析

针对热轧板带工作辊在轧制过程中发生的断辊事故,对其失效原因进行了分析。通过对轧辊断口宏观形貌,材质化学成分、显微组织、工作层残余奥氏体含量及断口形貌的分析,认为轧辊断裂属于应力断裂.而造成轧辊断裂的主要原因是工作层残余奥氏体含量过高,轧辊在使用过程中残余奥氏体发生马氏体相变,巨大的内应力导致裂纹的产生;同时轧辊工作层显微组织中网状碳化物,芯部C、Mn含量不足以及铸造孔洞缺陷加速了裂纹扩展而造成的。为此,对轧辊的制造工艺、使用及维护提出了相应的措施,确保了轧辊的正常使用。     

离心铸造复合轧辊超声波探伤缺陷判定与质量改进措施

利用超声波探伤技术能够检测出离心铸造复合材料轧辊工作层与芯层冶金结合质量好坏，确定芯部有否缩松。阐述轧辊结合层超声探伤常见的典型回波形式和它们的形成原因，以及回波形式与结合层质量的关系。根据轧辊轴芯超声波穿透检查的不同结果，对轴芯区的质量分别作出技术判定，并介绍改进质量的相应措施。     

大型离心复合球墨铸铁轧辊的试验研究

本文确定了大型中厚板轧机离心复合球墨铸铁轧辊的化学成分,分析了各工艺因素对轧辊结合层质量的影响,并提出了相应的改进措施;同时,对大断面球墨铸铁的质量控制进行了探讨,取得了很好的技术效果。     

轧辊轴颈的激光熔覆修复

结合某轧钢厂轧辊轴颈的修复过程,分析轧辊轴颈的失效形式及原由,并介绍轧辊轴颈的激光熔覆修复工艺方法。实践证明,该工艺在轧辊轴颈的修复上优势明显,解决了传统工艺在修复过程易产生热应力和热变形、修复材料选用局限性、修复层与基体结合强度难以保证且晶粒粗大等矛盾,并为使用厂家节约了时间及资金成本。     

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。