WC含量对明弧堆焊奥氏体合金显微组织及耐磨性的影响

采用金属粉型药芯焊丝自保护明弧焊制备Cr9Mn6Nb2WVSi Ti奥氏体耐磨堆焊合金,借助XRD,SEM,EDS及光学显微镜研究外加WC颗粒对其显微组织及耐磨性的影响。结果表明,随焊丝药芯中WC增加,奥氏体晶粒细化,沿晶分布的多元合金化碳化物数量增加。初生γ-Fe相原位析出了(Nb,Ti,V)C相和残留WCx颗粒,起到晶内弥散强化作用,沿晶分布的(Nb,Ti,V)C和M_6C(M=Fe,Cr,Mn,V,W)相隔断了网状或树枝状的沿晶M_7C_3相,使其细化、断续分布而提高合金韧性,减轻沿晶碳化物数量增加的不利影响。硬度和磨损测试结果显示,明弧堆焊奥氏体合金洛氏硬度仅为40~47,但其磨损质量损失低于高铬铸铁合金,具有良好耐磨性;随外加WC含量提高,奥氏体合金晶内和晶界显微硬度差异显著减小,合金表面趋于均匀磨损而改善耐磨性。该奥氏体合金的磨损机制主要是磨粒显微切削,适用于带有一定冲击载荷磨粒磨损的工况下使用。     

Influence of La2O3 addition on microstructure and wear resistance of Fe-Cr-C cladding formed by arc surface welding

The Fe-Cr-C claddings formed by arc surface welding with different La2O3 additions were investigated. The microstructures were observed by optical microscopy (OM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The phase structures were measured by X-ray diffraction (XRD). The wear resistances of the claddings were tested by friction and wear experiment. On this basis, the carbide refinement mechanism by inclusion enriched with La was discussed theoretically. The results showed that, the microstructure of the Fe-Cr-C cladding consisted of primary (Cr,Fe)7C3 carbides and eutectic (γ-Fe+(Cr,Fe)7C3 ) structure. With La2O3 addition increasing, the primary carbides were refined, and the mass loss of the cladding decreased gradually. The Fe-Cr-C cladding with 4wt.% La2O3 addition had a best wear resistance behaviour. The RE inclusion LaAlO3 as heterogeneous nuclei of the primary M7C3 was medium effective, and could refine the M7C3 carbides. Besides, the wear resistance could be improved by adding La2O3 in the claddings.     

Effect of cerium on abrasive wear behaviour of hardfacing alloy

Hardfacing alloys with different amounts of ceria were prepared by self-shielded flux cored arc welding.The abrasion tests were carried out using the dry sand-rubber wheel machine according to JB/T 7705-1995 standard.The hardness of hardfacing deposits was meas-ured by means of HR-150AL Rockwell hardness test and the fracture toughness was measured by the indentation method.Microstructure characterization and surface analysis were made using optical microscopy,scanning electron microscopy(SEM) and energy spectrum analy-sis.The results showed that the wear resistance was determined by the size and distribution of the carbides,as well as by the matrix micro-structure.The main wear mechanisms observed at the surfaces included micro-cutting and micro-ploughing of the matrix.The addition of ceria improved the hardness and fracture toughness of hardfacing deposits,which would increase the resistance to plastic deformation and scratch,thus the wear resistance of hardfacing alloys was improved.     

Correlation of microstructure with the wear resistance and fracture toughness of hardfacing alloys reinforced with complex carbides

A correlation was made of the microstructure, wear resistance, and fracture toughness of hardfacing alloys reinforced with complex carbides. The hardfacing alloys were deposited twice on a low-carbon steel substrate by a submerged arc welding (SAW) method. In order to investigate the effect of complex carbides, different fractions of complex carbide powders included inside hardfacing electrodes were employed. Microstructural analysis of the hardfaced layer showed that cuboidal carbides, in which a TiC carbide core was encircled by a WC carbide, and rod-type carbides, in which W and Ti were mixed, were homogeneously distributed in the bainitic matrix. In the surface layer hardfaced with FeWTiC powders, more complex carbides were formed, because of the efficient melting and solidification during hardfacing, than in the case of hardfacing with WTiC powders. As the volume fraction of complex carbides, particularly that of cuboidal carbides, increased, the hardness and wear resistance increased. In-situ observation of the fracture process showed that microcracks were initiated at complex carbides and that shear bands were formed between them, leading to ductile fracture. The hardness, wear resistance, and fracture toughness of the hardfacing alloys reinforced with complex carbides were improved in comparison with high-chromium white-iron hardfacing alloys, because of the homogeneous distribution of hard and fine complex carbides in the bainitic matrix.     

Correlation of microstructure and fracture toughness in high-chromium white iron hardfacing alloys

A correlation is made of microstructure and fracture toughness in hypereutectic high-chromium white iron hardfacing alloys. In order to investigate the matrix effect of these alloys, in particular, four different matrices such as pearlite, austenite, and a mixture of pearlite and austenite were employed by changing the ratio of Mn/Si, while the total volume fraction of carbides was fixed. The hardfacing alloys were deposited twice on a mild steel plate by the self-shielding flux-cored arc-welding method. Fracture toughness was increased by increasing the volume fraction of austenite in the matrix, whereas hardness and abrasion resistance were nearly constant.In situ observation of the fracture process showed that cracks initiated at large primary carbides tended to be blocked at the austenitic matrix. This suggested that fracture toughness was controlled mainly by the amount of austenite in the matrix, thereby yielding the better toughness in the hardfacing alloy having the austenitic matrix. Considering both abrasion resistance and fracture toughness, therefore, the austenitic matrix was preferred for the high-chromium white iron hardfacing alloys.     

On the Microstructure and Wear Behavior of Fe–xCr–4Mn–3C Hardfacing Alloys

The present paper describes an investigation aimed at evaluating the microstructural and dry sliding adhesive wear characteristics of Fe–xCr–4Mn–3C hardfacing alloys applied through shielded metal arc welding. The effect of chromium addition on the microstructure of hardfacings was carried out by using optical microscope, field emission scanning electron microscope and X-ray mapping. Dry sliding wear tests were performed on a pin-on-disc wear tribometer. From the experimental results, it was observed that the primary carbides were refined and increased with the increase of chromium content. The morphology of carbides revealed that the primary carbides were rod shaped. The increased chromium content was also found to be beneficial to enhance hardness and wear resistance of hardfacings. The correlation between hardness and wear resistance exhibited the reliability of hardness as an indicator of the wear performance of hardfacings.     

Microstructural and microhardness characteristics of laser-synthesized Fe-Cr-W-C Coatings

The effects of laser-processing parameters on the microstructure and microhardness of Fe-Cr-W-C quaternary alloy coatings were investigated experimentally. The coatings were developed by laser processing a powder mixture of Fe, Cr, W, and C at a weight ratio of 10:5:1:1 on a low-carbon steel substrate using a 10 kW continuous wave CO₂ laser. Depending on the processing parameters, either hypoeutectic or hypereutectic microstructures were produced. The hypoeutectic microstructures comprised primary dendrites of nonequilibrium face-centered cubic (fcc) austenite γ phase and eutectic consisting of pseudohexagonal close-packed (hcp) M₇C₃ (M = Cr, Fe, W) carbides and fcc γ phase. The hypereutectic microstructures consisted of hcp M₇C₃ primary carbides and eutectic similar to that in the hypoeutectic microstructures. The formation of hypoeutectic or hypereutectic microstructures was influenced by the alloy composition, particularly the C concentration, which depends on the amount of powder delivered into the melt pool and the extent of substrate melting. The enhancement of the lattice parameter of the γ phase is associated with the significant dissolution of alloying elements and lattice strains resulting from rapid quenching. The higher hardness of the hypereutectic microstructures is principally attributed to the formation of hcp M₇C₃ primary carbides. The relatively lower hardness of the hypoeutectic microstructures is related to the presence of y phase in the primary dendrites, excessive dilution from the base material, and relatively low concentrations of Cr and C. The results provide insight into the significance of laser-processing conditions on the composition and hardness of Fe-Cr-W-C alloy coatings and associated solidification characteristics.     

Studies on the Effect of Alloying Element in Iron Base Hardfacing Alloy

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, two hardfacing electrodes having different chemical compositions have been selected with addition of alloying elements and their hardness and microhardness responses were compared with that of mild steel. The emphasis has been to realize the effect of microstructure and chemical composition on the hardness and microhardness response of the hardfacing material with respect to mild steel. It has been observed that the hardness of hardfacing alloys is varied with addition of alloying elements compared to that without addition of alloying elements.     

Effects of presetting ferro- silicon content on microstructure and abrasion resistance of high- chromium hardfacing alloys

The morphology of the eutectic carbides in the high- chromium alloys has an effect on their embrittlement. High- chromium hardfacing alloys were deposited by the method of flux- cored wire self- shielded open arc welding with presetting alloying powders on weld beads. The effects of presetting ferro- silicon content on their microstructure and abrasion resistance were investigated by optical microscopy (OM), X- ray diffractometer (XRD) together with scanning electron microscopy (SEM). The results show that, with the continuous addition of ferro- silicon powders, the shape of primary M7C3 carbides transits from rod- like shape to hexagonal block- like shape in dispersion distributing state, M represents such element as Fe, Cr, Mn. Those surrounding eutectic carbides change from strip shape into granular shape, which is deliberately different from conventional eutectic one. On the condition of invariable weld input gross heat, presetting alloying powders on weld beads with the unit amount in equivalence with 40% to 60% of the mass of flux- cored wire deposited metals in need, can reduce 28% to 38% heat input on unit deposited metals and decrease the residual heat stress of weld beads. Presetting alloying powders not only leads to the 36% to 55% boosting of hardfacing deposition efficiency, but also improves the morphology of the eutectic carbides. Their wear mass loss reduces continuously with the increase of ferro- silicon powders and the abrasion resistance improves by at least 40%. Their wearing mechanism includes the micro- cutting and micro- spalling. The micro- spalling amount is reduced persistently for the improvement of the morphology of eutectic carbides.     

Correlation of microstructure with the wear resistance and fracture toughness of duocast materials composed of high-chromium white cast iron and low-chromium steel

The objective of this study is to investigate the correlation of microstructure with wear resistance and fracture toughness in duocast materials that consisted of a high-chromium white cast iron and a low-chromium steel as the wear-resistant and ductile parts, respectively. Different shapes, sizes, volume fractions, and distributions of M₇C₃ carbides were employed in the wear-resistant part by changing the amount of chromium and molybdenum. In the alloys containing a large amount of chromium, a number of large hexagonal-shaped primary carbides and fine eutectic carbides were formed. These large primary carbides were so hard and brittle that they easily fractured or fell off from the matrix, thereby deteriorating the wear resistance and fracture toughness. In the alloys containing a smaller amount of chromium, however, a network structure of eutectic carbides having a lower hardness than the primary carbides was developed well along solidification cell boundaries and led to the improvement of both wear resistance and toughness. The addition of molybdenum also helped enhance the wear resistance by forming additional M₂C carbides without losing the fracture toughness. Under the duocasting conditions used in the present study, the appropriate compositions for wear resistance and fracture toughness were 17 to 18 pct chromium and 2 to 3 pct molybdenum.     

Fe—Cr—O体系碳还原产物的形态

研究了不同温度和不同时间条件下C还原Fe-Cr-O体系所得产物的形态,样品主要包括FeCr₂O₄+C和Fe₂O₃+2Cr₂O₃+C两种体系.两种样品的还原度均随温度升高而升高,反应接近平衡时还原率均在90%以上.C还原FeCr₂O₄和Fe₂O₃-Cr₂O₃的过程大致相同,且最终还原产物基本组成均为Fe-Cr-C合金和金属碳化物（主要为Cr₇C₃）.针对最终还原产物中Fe-Cr-C合金和金属碳化物的含量提出了一种估算方法,其估算结果与理论计算结果基本吻合.结果显示,最终产物中Fe-Cr-C合金量随温度升高而升高,碳化物含量随温度升高而降低,且不同温度条件下所获得的Fe-Cr-C合金成分不同.      

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Hardfacing layer including NbC particles was produced by using automatic welding machine with Fe- Cr- C flux cored wire containing Nb- Fe powder. The effect of NbC on the microstructure and property of Fe- Cr- C hardfacing layer was studied. The results show that the size of M7C3 in Fe- Cr- C hardfacing layer is bigger and the distribution and size of Fe- Cr- Nb- C hardfacing layer are more uniform. The hardness of Fe- Cr- Nb- C hardfacing layer is 61. 4HRC, while that of Fe- Cr- C hardfacing layer is 52. 8HRC. The former is higher than the latter by about 16. 29%. Meanwhile the relative wear resistance of the former is higher than that of the latter by 43%. The hardness of hard phase NbC is 2237HV. The shape of section of NbC is an irregular polygon and its distribution is cluster and not uniform.     

钛合金固相渗硼-稀土渗硼机理研究

表面强化处理可以大幅提升钛合金的耐磨性， 也有利于钛合金在高温环境中应用。 钛合金高温固相渗硼是 重要的表面强化方式， 添加稀土提高渗硼效率是重要技术手段。 为深入研究稀土的渗硼催化机制， 本文开展了 900~1050℃渗硼试验， 重点分析了渗硼剂在试验后的相组成变化。 结果表明， 稀土可通过与硼源、 氧发生化学反 应， 生成熔点较低的稀土硼酸盐。 本文对该硼酸盐发挥的作用进行了解释， 论述了稀土在渗硼反应过程中的作用。 经过渗硼的钛合金表面形成了 TiB/TiB2 双相渗层， 显微组织分析表明该渗层与基材结合紧密、 无孔洞缺陷。 本文 还对渗硼钛合金的拉伸性能、 表面摩擦系数、 维氏硬度、 高温洛氏硬度、 结合力等基础力学性能进行了测试， 结 果表明， 渗硼钛合金具有优良的综合力学性能。     

Some observations of the influence of δ-ferrite content on the hardness,galling resistance,and fracture toughness of selected commercially available iron-based hardfacing alloys

Iron-based weld hardfacing deposits are used to provide a wear-resistant surface for a structural base material. Iron-based hardfacing alloys that are resistant to corrosion in oxygenated aqueous environments contain high levels of chromium and carbon, which results in a dendritic microstructure with a high volume fraction of interdendrite carbides which provide the needed wear resistance. The ferrite content of the dendrites depends on the nickel content and base composition of the iron-based hardfacing alloy. The amount of ferrite in the dendrites is shown to have a significant influence on the hardness and galling wear resistance, as determined using ASTM G98 methods. Fracture-toughness (K _IC) testing in accordance with ASTM E399 methods was used to quantify the damage tolerance of various iron-based hardfacing alloys. Fractographic and microstructure examinations were used to determine the influence of microstructure on the wear resistance and fracture toughness of the iron-based hardfacing alloys. A crack-bridging toughening model was shown to describe the influence of ferrite content on the fracture toughness. A higher ferrite content in the dendrites of an iron-based hardfacing alloy reduces the tendency for plastic stretching and necking of the dendrites, which results in improved wear resistance, high hardness, and lower fracture-toughness values. A NOREM 02 hardfacing alloy has the most-optimum ferrite content, which results in the most-desired balance of galling resistance and high K _IC values.     

TiC含量对激光熔覆TiC增强双相不锈钢复合涂层性能的影响

采用激光熔覆技术在40 Cr Ni Mo基材上制备了TiC增强双相不锈钢复合熔覆层,熔覆层物相主要由奥氏体、马氏体、M₇C₃型碳化物和TiC组成。其中M₇C₃型碳化物主要包括Fe₇C₃、Cr₇C₃或者(Fe、Cr)₇C₃三种,TiC按尺寸可分为熔解后析出的微米级TiC以及粗大的未熔TiC颗粒。析出的TiC颗粒为方块状,随着TiC添加量增加,呈花瓣状长大。未熔TiC颗粒与基材形成了扩散界面,具有很好的界面结合性。当加入30 wt.%TiC时,熔覆层具有最好的耐磨性,硬度可达55.26 HRC,磨损体积为2.54×10^-2 mm³,耐磨性是基材的3.37倍。     

Wear Resistant Steels and Casting Alloys containing Niobium Carbide

Niobium, like titanium and vanadium, forms superhard MC carbides that remain relatively pure in technical alloys on account of their low solubility for other metallic alloying elements. However, because they have a greater hardness than the precipitated chromium carbides commonly used in wear‐resistant alloys, they are suitable as alternative hard phases. This contribution deals with new wear‐resistant steels and casting alloys containing niobium carbide. These include a secondary hardening hardfacing alloy, a composite casting alloy for wear applications at elevated temperatures, a white cast iron as well as two variants of a corrosion‐resistant cold‐work tool steel produced by melt metallurgy and by powder metallurgy. A heat‐resistant casting alloy is also discussed. Based on equilibrium calculations the microstructures developing during production of the alloys are analysed, and the results are discussed with respect to important properties such as abrasive wear and corrosion resistance.     

Ballistic impact behavior of multilayered armor plates processed by hardfacing

Hardfacing is a type of surface treatment for the extension of service life of worn parts or structures and the improvement of the surface properties through deposition of the alloys using arc welding or laser cladding.^[1,2] Among the hardfacing alloys, the high chromium hardfacing alloys have been used most extensively for dies or parts in various industrial areas because of their excellent hardness, corrosion resistance, and wear resistance as well as inexpensiveness.^[2-6] These properties are obtained from the large volume fraction of hard chromium carbides.^[3-8] The recent works on these alloys have focused on the property enhancement, the microstructural modification, and the high-temperature application.^[1,7,8]     

Microstructure and Wear Behavior of Solidification Sonoprocessed B390 Hypereutectic Al-Si Alloy

The hypereutectic Al-Si alloys constitute an important family of alloys because of their excellent wear resistance and low thermal expansion. However, the optimal microstructure and hence the optimal service performance of these alloys cannot be achieved by the conventional melt treatments used in industry today, because of the chemical incompatibility between the primary-Si refiners and the eutectic-Si modifiers used in microstructure control. The current study aimed at using ultrasonic vibrations to improve the microstructure and the properties of these alloys. The results of the current study showed that for the B390 Al-Si alloy (i) the ultrasonic treatment has potential refining effect on the primary Si and Fe intermetallic phases, (ii) the primary Si particles become finer as the pouring temperature decreases from 1033 K (760 °C) to 938 K (665 °C), (iii) pouring and ultrasonic treatment at temperatures below the start of primary Si precipitation result in the coexistence of large and fine Si particles in microstructure, (iv) phosphorous additions of 50 ppm did not show any substantial effect in the ultrasonically treated ingots, (v) ultrasonic-treated samples have uniform hardness over the surface while the untreated samples show large scattering (high standard deviation) in hardness levels and (vi) ultrasonic-treated samples showed better wear resistance in the absence of phosphorous.