高铬铸铁芯焊条堆焊层组织分析

基于焊芯过渡合金元素的技术思路,研制了高铬合金铸铁同质堆焊焊条．分析了不同药皮堆焊焊条的堆焊层组织及性能,定量表征了合金元素的过渡系数．结果表明,通过焊芯过渡合金元素的高铬合金铸铁堆焊焊条可获得组织和性能均匀的堆焊层．合金过渡系数高于85％．碱性药皮堆焊焊条堆焊层为亚共晶成分高铬合金铸铁,组织由奥氏体γ＋马氏体M＋碳化物Cr7C3组成．堆焊层硬度为44．5～56．5HRC．碱性石墨化型药皮堆焊焊条堆焊层组织由初生碳化物Cr7C3＋马氏体M＋碳化物Fe7C3＋少量石墨G组成,堆焊层硬度可达59～67HRC．     

碳化硼对电弧喷涂涂层性能的影响

将碳化硼(B4C)陶瓷粉末和其它合金元素与304L不锈钢带轧制成粉芯丝材,采用电弧喷涂技术制备金属陶瓷复合涂层.研究了B4C在电弧喷涂中的应用.利用XRD,SEM对涂层的形貌、相组成和磨损表面进行了分析.利用自行设计的高温磨粒磨损装置和高温冲蚀设备分别评价了B4C对涂层耐高温磨粒磨损性能和耐高温冲蚀性能的影响.结果表明,粉芯丝材喷涂工艺良好,B4C陶瓷与粉芯中其它组分反应,可以形成含Fe3B,CrB,FexN i23-xB6,Fe23(C,B)6,(Cr,Fe)7C3和Fe3C等硬质相的复合涂层,大幅度提高了涂层的硬度和耐磨耐冲蚀性能.     

纳米大理石对D600R堆焊焊条性能的影响

用粒径70～90nm大理石取代堆焊焊条D600R药皮中的微米大理石,制成纳米大理石焊条.利用汉诺威电弧质量分析仪对焊接过程中的电流电压和短路时间进行测试,获得微米大理石焊条和纳米大理石焊条的燃弧特征;通过焊接工艺试验、测氢试验、熔化温度测试、硬度试验、耐磨试验和微观分析,分别对两种焊条的工艺性能和力学性能进行分析.结果表明,用纳米大理石替代微米大理石可降低焊条药皮的熔化温度和堆焊层金属中的扩散氢含量;提高焊条的熔敷效率;降低焊条短路电压、短路电流概率密度和,在短路时间t12.05ms时间段内缩短累计短路时间;改善焊条操作性能;提高堆焊层金属硬度和耐磨性.     

X80管线钢焊条电弧焊接头组织与耐蚀性分析

利用双熔敷极焊条电弧焊技术对X80管线钢进行了焊接,并在焊接接头成分、组织及耐蚀性方面与传统焊条电弧焊进行了对比分析.结果表明,双熔敷极焊条电弧焊技术熔敷效率高,但受其结构及药皮重量系数的影响焊缝中合金元素的含量比普通焊接焊缝的低,且焊缝中多边形铁素体含量较高,另一方面由于对母材的热输入较低,使得其粗晶区组织较为细小,这有利于其性能的提高;对0.5 M Na₂CO₃-1 M NaHCO₃溶液及通饱和CO₂的NACE A溶液中的耐蚀性研究发现,焊缝及粗晶区耐蚀性均差于母材,且采用双熔敷极焊条电弧焊技术有利于提高焊缝及粗晶区的耐蚀性.     

Microstructure and properties of Fe–Cr–C hardfacing alloys reinforced with TiC–TiB2

Abstract

Different amounts of TiB₂ powder were added to flux cores of wear resistant hardfacing flux cored wires for the preparation of new flux cored wires. Fe–Cr–C hardfacing alloys reinforced with TiB₂ were produced by arc hardfacing. The microstructure, hardness and wear resistance behaviour of the hardfacing alloys were investigated using an optical micrograph, scanning electron micrograph (SEM), X-ray diffractometer, macrohardness tester, microhardness tester and abrasive wear tester. The results showed that, among the hardfacing alloys, a new hard phase, i.e. TiC–TiB₂ composite compound particles, was formed and dispersed in the primary carbides and matrix structures. The TiC–TiB₂ reinforced Fe–Cr–C hardfacing alloys imparted greater hardness and better wear resistance. The presence of TiC–TiB₂ hard phase particles is the main reason for the improvement in hardness and wear resistance of Fe–Cr–C hardfacing alloys.     

Coating composition,weld parameter and consumable conditioning effects on weld metal composition in shielded metal arc welding

Abstract

Pipeline construction has been moving towards the use of higher strength low carbon steels as these become available. In order to achieve the required high strength and toughness to match those of the parent pipe, girth weld metals have to rely mostly on their composition. The aim of the present study was to characterise the influence of the consumable chemistry and moisture content, and the welding parameters on the composition of weld metals produced by E8010 and E9010 shielded metal arc (SMA) cellulosic consumables. The alloying compounds in the consumable coating were isolated using a caustic soda solution, analysed with electron backscattered diffraction and identified as a variety of oxides. Making use of a mechanised SMA welding machine, the effect on weld metal alloying element contents of the welding conditions was evaluated. Smaller welding arc voltages and lower consumable coating moisture content produced weld metals with richer chemistry. The element transfer mechanisms from the consumable coating to the weld metal are also discussed.     

Arc-Sprayed Iron-Based Coatings for Erosion-Corrosion Protection of Boiler Tubes at Elevated Temperatures

Wire arc spraying is an economically attractive thermal spray process that is especially interesting for the protection of large-scale parts or constructions. This study presents the results of the development and investigation of a number of cored wires based on the Fe-Cr-Al system with minor addition of alloying elements (B, Mn, Ni, Si, Ti, Mg, etc.). The microstructure of the coatings, their electrochemical behavior, and isothermal oxidation performance over a temperature range of 20-700 °C were investigated. Erosion resistance at elevated temperatures was determined with a laboratory test unit under test conditions that have simulated the work conditions in fossil-fuel-fired boilers. It was established that the oxidation resistance and the gas-abrasive wear resistance of arc-sprayed coatings depend mostly on the coating microstructure and homogeneity of element distribution rather than on the general alloying level and microhardness of the coating. A new parameter for coating characterization, namely, the coefficient of chemical microheterogeneity, K _CMH, is introduced to quantify this influence. Formation of the coating microstructure at elevated temperatures and its influence on the protection ability of the coating are discussed.     

Assessing metal transfer stability and spatter severity in flux cored arc welding

Abstract

Five experimental basic type flux cored arc welding consumable wire electrodes were manufactured from the same base formulation. The composition of these electrodes was adjusted in an attempt to improve the operating performance. This involved additions of various ratios of alkali oxides, namely, lithium, magnesium, sodium, and potassium containing ingredients, in the flux formulations. The operating behaviours of these experimental electrodes and two reference products (i.e. one commercial basic T–5 and one commercial rutile T–1 electrode) were thoroughly investigated by recording welding arc signals using a high speed data acquisition system. By comparing these electrodes among themselves, the experimental electrodes were reported to exhibit extremely stable arcs, some showing electrical arc signals even smoother than those for the reference rutile grade electrode. Despite their improved metal transfer consistency, however, basic electrodes were characterised by somewhat higher spatter levels.     

风机叶轮用0Cr13Ni5Mo钢焊条的研制

根据风机叶轮焊接接头强韧性要求,利用组织匹配原则设计焊芯,用药皮过渡方法补充选用焊芯与设计焊芯成分间的差距,并通过金相分析、力学性能及工艺性能测试等方法,研制了0Cr13Ni5Mo钢专用焊条.结果表明,用药皮过渡方式补充选用焊芯与设计焊芯成分之差的方法,既可验证所设计焊芯能否达标,也可用于指导小批量生产特种焊条;1号、2号、3号焊条所得接头的焊缝区和HAZ组织均为回火索氏体+板条马氏体+残余奥氏体+二次析出相,其对应接头力学性能均高于4号传统焊条;2号焊条工艺性最好,3号综合性能最好,可作为0Cr13Ni5Mo钢专用焊条.     

The influence of welding condition on the microstructure of WC hardfacing coating on carbon steel substrate

Tungsten carbide (WC) hardfacing coating technique is widely used to improve the performance of carbon steel blade exposed to acidic and abrasive conditions during production. This paper deals with the influence of welding parameters on the microstructure and carbide distribution of WC. WC hardfacing was deposited onto carbon steel by shielded metal arc welding (SMAW). Welding parameters such as welding current, number of weld layers, electrode drying and base material preheat were the focus of this work. Coating hardness, microstructure and elemental composition were analysed in detail. The effects of the welding parameters on WC hardfacing coating microstructure and hardness value were characterized by scanning electron microscope (SEM) and micro-Vickers hardness tester respectively. The larger carbide growth in overall coating region is mainly dictated by high current (200 A), increased number of weld layers (3 layers) and presence of base material preheat due to sufficient heat energy initiating carbide growth. The investigation also revealed that high current affected the growth of smaller carbide particles in matrix region significantly. Meanwhile, number of weld layers and base material preheat influences were seen during hardfacing with lower welding current. The absence of electrode drying led to uniform smaller carbide distribution in matrix region. It was found that increased number of large carbides and uniformly distributed smaller carbides in WC hardfacing deposit increased the hardness value of the coating.     

Features of Coatings Obtained by Supersonic Laser Deposition

The three types of coatings that can be deposited by supersonic laser deposition, namely coatings built without the melting of the processed powder particles, coatings built from molten particles and coatings made from molten particles and with solid particles embedded in the coating, are discussed. For instance, with no melting of the powder material, a titanium alloy coating without transformation of the structure and with a uniform distribution of the chemical elements in the coating cross-section was obtained. Self-fluxing coatings (NiCrCBSiFe) with high hardness were achieved by melting the powder and mixing it with the substrate. The mixing of the coating metal with the substrate metal led to a significant increase in the concentration of the main alloying elements in the coating–substrate interface. X-ray diffraction analysis also showed that the mixing of the NiCrCBSiFe coating with a medium-carbon steel substrate led to the formation of new Fe_xNi phases, while their concentration decreased through coating thickness.     

FeAl and NbAl3 Intermetallic-HVOF Coatings: Structure and Properties

Transition metal aluminides in their coating form are currently being explored in terms of resistance to oxidation and mechanical behavior. This interest in transition metal aluminides is mainly due to the fact that their high Al content makes them attractive for high-temperature applications. This is also a reason to study their resistance to wear; they may be suitable for use in applications that produce a lot of wear in aggressive environments, thus replacing established coating materials. In this study, the microstructure, microhardness, and wear and oxidation performance of FeAl and NbAl₃ coatings produced by high-velocity oxy-fuel spraying are evaluated with two main aims: (i) to compare these two coating systems—a commonly studied aluminide (FeAl) and, NbAl₃, an aluminide whose deposition by thermal spraying has not been attempted to date—and (ii) to analyze the relationship between their microstructure, composition and properties, and so clarify their wear and oxidation mechanisms. In the present study, the higher hardness of niobium aluminide coatings did not correlate with a higher wear resistance and, finally, although pesting phenomena (disintegration in oxidizing environments) were already known of in bulk niobium aluminides, here their behavior in the coating form is examined. It was shown that such accelerated oxidation was inevitable with respect to the better resistance of FeAl, but further improvements are foreseen by addition of alloying elements in that alloy.     

Effect of microstructure and chemical composition of hardfacing alloy on abrasive wear behavior

Hardfacing, a surface modification technique, is used to rebuild the surface of a workpiece. The economic success of the process depends on selective application of hardfacing material and its chemical composition for a particular application. In this context, three hardfacing electrodes having different chemical compositions have been selected and their abrasive wear responses was compared with that of mild steel. The emphasis has been made to realize the effect of microstructure and chemical composition on the wear response of the hardfacing material with respect to mild steel. It has been observed that the wear rate of hardfacing alloys is lower than that of mild steel. The hardfacing alloy having the highest chromium content exhibits the lowest wear rate.     

超高硬度堆焊材料的硬度及耐磨性

通过在堆敷合金系统中添加多种强碳化物形成元素，在焊接热循环作用下或随后的回火过程中以弥散碳化物形式析出。弥散碳化物的析出既可以在强化堆敷金属的同时，提高堆敷层抗磨损的能力，又可以降低基体组织中的碳含量，增加基体的韧性。利用上述思想，以C、Cr、Mo、W、V作为基础合金系统，采用二次旋转回归设计方法设计试验方案，建立了超高硬度堆敷金属的硬度、耐磨性与合金元素间的数学模型，并研究了药芯焊丝中合金元素对堆敷金属硬度及耐磨性的定量影响规律。     

大型热轧定宽压力机出钢辊的堆焊复合

针对出钢辊长期在温度800℃以上、红热钢坯作用下产生严重的冷热疲劳龟裂和金属间磨损的现象,开发出采用N合金化的堆焊硬面药芯焊丝材料。其显微组织为马氏体+少量铁素体+合金化合物,堆焊层金属具有极高的抗高温软化性能、抗冷热疲劳性能和耐金属磨损性能。制定了合理的堆焊工艺规范,堆焊复合制造的出钢辊使用寿命可长达半年,无热疲劳裂纹的产生,金属间磨损小,满足使用要求。     

Surface modified long-life electrode for resistance spot welding of Zn-coated steel

In order to increase the life of conventional copper electrodes in resistance spot welding of Zn-coated sheet steel, a multi-layer Ni/(TiC_P/Ni)/Ni composite coating was deposited onto the copper electrode top surface by electro-spark deposition. Scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction and micro-hardness tests were employed to characterize the microstructure and property of the coating. The results showed that the copper electrodes with a dense Ni/(TiC_P/Ni)/Ni coating slightly increased the resistance of the weld system and hence the welding current could be reduced to produce a weld with the same button size as that made by uncoated electrodes at a high welding current. The coating was gradually cracked during welding under the action of welding force, forming Ni/(TiC_P/Ni)/Ni composite islands which were strongly adherent to and further, punched into copper substrate. The coating could significantly reduce the alloying between copper electrode substrate and molten Zn. As a result, coated electrode showed a much longer life than an uncoated electrode even though the welding current for coated electrode was lower than that for uncoated one.     

氟化物对自保护药芯焊丝焊接工艺性能的影响及熔敷金属中P、Si的控制

通过自制的5种药芯成分不同的自保护药芯焊丝，研究氟化钡和氟化钙的不同配比对焊接工艺性能、过渡熔滴、熔敷金属中P、Si的控制的影响。结果表明，随着：BaF2占氟化物总量的增加，立焊性能改善，焊接过程飞溅、烟尘减少，累积质量分数为50％时的熔滴的平均直径减小，而熔敷效率和Hmax／Bmax降低(Hmax为焊缝最大熔深，Bmax为焊缝最大熔宽)。BaF2比CaF2控制熔敷金属中P、Si含量的能力更强，并通过热力学分析解释了氟化物对熔敷金属中P、Si控制的机理。综合考虑焊接工艺性能和熔敷金属中P、Si的控制，药芯中选用BaF2占氟化物总量的75％～87．5％较为合适。     

Hardening rolling rolls by hardfacing with an alloyed strip electrode under a ceramic flux

The composition of 20KhN4MFB coldrolled strip for hardfacing rolling rolls was determined and production started. The deposited layer is characterized by high impact toughness, plasticity and resistance to cyclic heat changes. Additional alloying to increase the hardness and wear resistance of the metal is carried out through a ceramic flux. The composition of the new ceramic flux is characterized by improved welding and technological properties and relatively low chemical activity. Hardfacing of the hot rolling rolls increases the volume of rolled material per 1 mm of the reduction of the roll diameter.     

Synthetically Controlled,Carbon-Coated Co<Subscript>2</Subscript>SnO<Subscript>4</Subscript>/SnO<Subscript>2</Subscript> Composite Anode for Lithium-ion Batteries

The inherent drawbacks of Co₂SnO₄ in demonstrating the closer-to-theoretical capacity value behavior and the inadmissible volume-expansion-related capacity fade behavior have been surpassed by choosing a tailor-made material composition of Co₂SnO₄/SnO₂, prepared at two different temperatures such as 400°C and 600°C to obtain residual carbon-containing and carbon-free compositions, respectively. Among the products, carbon-coated Co₂SnO₄/SnO₂ composite exhibits better electrochemical performance compared with that of the carbon-free product mainly because of the beneficial effect of carbon in accommodating the volume-expansion-related issues arising from the alloying/de-alloying mechanism. A combination of conversion reaction and alloying/de-alloying mechanism is found to play a vital role in exhibiting closer-to-theoretical capacity values. In other words, an appreciable specific capacity value of 834 mAh g^?1 has been exhibited by Co₂SnO₄/SnO₂ anode containing carbon coating, thus, demonstrating the possibility to improve the electrochemical performance of the title anode through carbon coating, which is realized as a result of the addition of carefully manipulated synthesis conditions.     

Predicting steady state dilution in multipass hardfacing overlays - geometric approach

Abstract

A geometric model of steady state dilution in multipass hardfacing overlays deposited via self shielded flux cored arc welding is presented. In this model the steady state bead profile in cross-section and the shape of the fusion line are represented by parabolic functions. Without requiring empirical corrections, the model accurately predicts the steady state dilutions of eight high chromium white iron overlays that were each deposited on steel substrates under different welding conditions. Estimates for the surface smoothness of the overlay, or the peak to valley ripple, are also obtained from the model. Thus, the model provides the necessary information to predict the steady state composition and geometry of a multipass hardfacing overlay. Reference can then be made to studies relating composition and geometry to abrasive wear resistance in order to complete the link between the welding parameters used to deposit the overlay and its subsequent wear performance.