【精品文档】39中英文双语外文文献翻译成品：球墨铸铁摩擦焊接过程中的微组织与质量传输

The microstructure and mass transport during friction welding of ductile cast ironMieczysaw KaczorowskiInstitute of Mechanics and Design, Warsaw University of Technology, Warsaw, Poland, andRadosaw WiniczenkoDepartment of Production Engineering, Warsaw University of Life Sciences, Warsaw, PolandAbstractPurpose The results of a study of friction welding of ductile cast iron using stainless steel interlayer are presented. Based on the microstructure evolution at the region close to the ductile cast iron-stainless steel interface, the phenomena accompanying the process of joining were evaluated. Therefore, the purpose of this paper is to take a closer look into metallurgical phenomena accompanying the friction welding of ductile cast iron.Design/methodology/approach In this paper, ductile cast iron and austenitic-stainless steel are welded using the friction welding method. The tensile strength of the joints was determined using a conventional tensile test machine. Moreover, the hardness across the interface ductile cast iron-stainless steel interface was measured on a metallographic specimen. The microstructure of the joints was examined using light metallography as well as electron microscopy. In this case, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied. Energy Dispersive X-ray analysis (EDS) was carried out across the section of friction welded ductile iron-stainless steel interface.Findings On the basis of careful analysis of experimental data it was concluded that the process of friction welding was accompanied with diffusion of Cr, Ni and C atoms across the ductile cast iron-stainless steel interface. This leads to an increase of carbon concentration in stainless steel where chromium carbides were formed, the size and distribution of which was dependent on the distance from the interface. Originality/value The main value of this paper is to contribute to the literature on friction welding of ductile cast iron.Keywords Friction welding, Ductile cast iron, Mass transport, Stainless steelPaper type Research paper1. IntroductionThe friction welding is a dynamic, thermodynamically activated process. According to Crossland (1971) and Healy et al. (1976), the friction welding is a metallurgical process, including the interaction of heat and force. It is accompanied by and coupled with a series of physical phenomena, heat generated by plastic deformation, cooling of high-temperature metal, dynamic stress-strain process and thermal effect for metal behaviour, etc. It is considered that a heat generation and sudden temperature increase, connected with it, a heat radiation, an abrasion of moving surfaces, plastic deformations, dynamic recovery and recrystallization processes and interdiffusion at the interface boundary of joined parts support that dynamic process (Francis and Craine, 1985; Lancaster, 1987; Suzalec, 1988; Fu and Duan, 1998). It is obvious that these metallurgical transformations and diffusion phenomena, occurring in the weld zone, commonly effect the service behaviour of joints. Especially important role is played by the diffusion processes activated by heat flow and stress with a high gradient (Vill, 1962). Diffusion relocation of alloying elements is directed toward the surface layer of the material. The rate and flow of the diffusion process are, apart from temperature, affected by many factors,The current issue and full text archive of this journal is available at /0036-8792.htmIndustrial Lubrication and Tribology65/4 (2013) 251 258q Emerald Group Publishing Limited ISSN 0036-8792 DOI 10.1108/00368791311331248such as crystal structure of coupled materials, nature and concentration of diffusion element and number of line and defects (Winiczenko, 2001). In the vicinity of the contact surface, in dislocation zones and area of metal discontinuity or change of the crystal structure, diffusion processes change. All the structural imperfections reduce activation energy, which contributes to the acceleration of the diffusion process (Richter and Palzkill, 1985; Dette and Hirsch, 1990).It can be doubted if and to what degree the diffusion appears when the process is on an atomic scale and friction welding lasts a few minutes.The friction welding technique is well known and used in practice. Many studies about the friction welding of dissimilar materials have been conducted by various researchers.Akata and Sahin (2003) investigated the effect of dimensional differences in friction welding of AISI 1040 specimens. Next year, Sahin and Akata (2004) conducted an experimental study on the friction welding of medium carbon and austenitic stainless steel components. Later, Akata et al. (2007) conducted an investigation into reutilizing of waste materials, using friction welding. Sahin (2009) joined stainless steel and copper materials with friction welding. Sunay et al. (2009) investigated the effects of casting and forging processes on joint properties in friction-welded AISI 1050 and AISI 304 steels.This work was supported by the Community of Scientific Investigation under Grant 7T08B05519. The authors would also like to thank Professors Eugeniusz Ranatowski and Stanislaw Dymski from the Faculty of Mechanics of Bydgoszcz Technical University for their valuable suggestions.251Friction welding of ductile cast ironMieczyslaw Kaczorowski and Radoslaw WiniczenkoThe phenomena, accompanying friction welding process are rather poorly documented in the literature: Michiura et al. (1998) studied friction welding of ductile cast iron pipes. Next year, Shinoda et al. (1999) joined cast iron and stainless steels with friction welding. Ogara et al. (2005) examined the relationship between tensile strength characteristics and the macrostructure of joint in friction-welded ductile cast iron. Ochi et al. (2007/2009) investigated the macrostructure and temperature distribution near the weld interface in the friction welding of FC250 grade cast iron. Song et al. (2008) investigated the strength distribution at the interface of rotary-friction-welded aluminium to nodular cast iron. Nakamura et al. (2010) investigated the influence of preheating temperature and welding speed in the light of the microstructure of joining zone used by friction stir welding (FSW) between ductile cast irons and stainless steels. So, the aim of these investigations was to take a closer look into metallurgical phenomena, accompanying the friction welding of ductile cast iron which is not a typical material for this joining method, because the graphite acts as lubricant and prevents the generation of heat sufficient for joining (AWS, 1989; Lebedev and Chernenko, 1992).2. ExperimentalThe ferritic ductile cast iron (nominal composition listed in Table I) was selected for the study. The specimens for friction welding were bars 20 mm in diameter and 100 mm in length. The surface for friction welding was prepared on the abrasive cut-off machine. The geometry of specimens used for friction welding and details of experiment was shown in Figure 1.Schematic drawings of the lap friction welding process are shown in Figure 1. Friction welding of ductile cast iron specimens was carried out, using X6CrNi18-10 stainless steel as an interface layer. The chemical composition of the stainless steel selected for the study is listed in Table II. The process of joining was carried out on a continuous drive friction machine of the ZT-14 type. Friction and forged pressures used in experiment lie in the range of 20-45 MPa. The spindle rotating speed was kept constant at 2,360 rpm. Because of graphite appearance, relative large friction time 150-180 s was applied. The tensile strength of the joints was determined using a conventional tensile test machine. Moreover, the hardness across the interface ductile of iron-stainless steel interface was measured on metallographic specimen. The Vickers tester using 5G load was applied for these hardness measurements.The microstructure of the joints was examined using either light metallography as well as electron microscopy. In this case, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied. The first one was performed with a Jeol JSM-5400 scanning electron microscope and the second one with Philips EM300 transmission electron microscope operating at 100 kV accelerating voltage. Energy dispersive X-ray analysis (EDS) was carried out across the section of friction welded ductile iron stainless steel interface. The surfaces of specimensTable I The chemical composition of ductile cast iron (ferritic of matrix) selected for the study according to EN-GJS 400-15Concentration (wt. %)CSiMnPSCrNiMgFe3.782.600.150.050.010.030.020.036BalIndustrial Lubrication and TribologyVolume 65 Number 4 2013 251 258were observed with a BEI COMPO microscope, mode using back scattered electrons (BSE). Thin foils technique was applied for TEM study. First 3 mm rods were cut perpendicularly to the joining interface at a half-radius distance from the axis of joined specimens. Then 0.1 mm discs were sliced from these rods, using “load-less” IF-07A wire saw. Finally, thin foils were thinned electrochemically, using STRUERS automatic equipment.3. Results3.1 Tensile testsThe mechanical testing of friction-welded specimen had only additional significance.Therefore, the specimens used in this experiment were not typical for mechanical testing and the authors wanted to get only very approximate information on the tensile strength of the joints and the parameters of friction welding, which would be useful in further experiments. The results of tensile tests are given in Table III. As can be seen from the table, the tensile strength of the friction-welded ductile cast iron with stainless steel interlayer is not satisfactory. The small values lying in the range of 132 and 293 MPa were obtained for ferritic ductile cast iron.The diagram of changes in experimental tensile strength as a function of friction time was shown in Figure 2. It is evident that along an increase in friction time the tensile strength of friction-welded joint increase.3.2 Hardness measurementsThe results of hardness measurements can be valuable mediate information on the structure in the given place of the specimen. These can also provide some extra information on the distribution of the heat produced during the process. The Vickers microhardness distribution in specimens on the both side of ductile cast iron-stainless steel interface is shown in Figure 3. The measurements were made either in the axis, or along the line located 2.5 mm from the periphery joined specimens. As it could be expected, its hardness reaches its maximum close to the interface and decreases very rapidly in the stainless steel region. In contrast with this, the decrease of hardness in ductile cast iron is much slower and exhibits some kind of plateau. This plateau extends approximately 5-8 mm from the interface, depends on the location of hardness measurements and then reaches the value of 200 mHV which is typical for parent material. It is obvious that the changes of hardness with the distance from the interface had to be caused by the microstructure evolution.3.3 The EDX spectrometry resultsEven in earlier papers: Michiura et al. (1998), Shinoda et al. (1999), Winiczenko (2001), Ogara et al. (2005), Ochi et al. (2007/2009), Song et al. (2008), Sunay et al. (2009) and Nakamura et al. (2010), the authors have paid attention to many phenomena, taking place during the friction welding of ductile cast iron with stainless steel. Mass transport across the interface is one of these phenomena. The second one is severe plastic deformation in both materials, but especially in stainless steel. The diffusion, as well as plastic deformation, is influenced by heat generated during friction welding, so it is very interesting, how the structure is changing in a joined zone. The results of EDS analysis are shown in Figure 4.The most outstanding result of Figure 4 analysis is that the chromium concentration which is high in stainless steel252Friction welding of ductile cast ironIndustrial Lubrication and TribologyMieczyslaw Kaczorowski and Radoslaw WiniczenkoVolume 65 Number 4 2013 251 258Figure 1 Shape and size of specimens (unit-mm) before friction weldingDuctile cast ironInterlayer20f 420ff2 452 4529595(a)Ductile cast ironDuctile cast ironInterlayerf 20f 4f 202 452 45239584 + 100(b)Notes: (a) Friction welding of ductile iron to stainless steel; (b) friction welding of ductileiron to ductile iron by interlayerTable IIThe chemical composition EN X6CrNi18-10 stainless steel selected for the studyConcentration (wt. %)CMnSiPCrNiTi0.082.00.80.04519105 x C 20.7Table IIIThe results of tensile testsFriction pressureForge pressureFriction timeStrength pressureTensile strengthAverage tensile strengthSpecimen numberPt (MPa)Psp (MPa)Tt (s)Fm (N)Rm (MPa)RmAV (MPa)1242418039,2401321582242418050,0311633242418053,7001804242424065,7272222365242424069,6512366242424073,5752497242427069,3002322518242427085,3472289242427087,309293gradually decreases in ductile iron. The depth of ductile cast iron enrichment with chromium extends to about 40-50 mm. Moreover, it should be noted that the distribution of chromium is very non-homogenous and typically the peaks of Cr correspond with the peaks of Fe. However, the analysis of Ni distribution is more difficult and risky; it might be suggested that the average level of concentration of nickel inductile cast iron close to the interface appears to be a little higher than in further regions.3.4 Structure investigationsFigure 5 shows an example of the stainless steel microstructure close to joining interface observed in SEM. It is very well visible that the grain boundaries are decorated with the carbides which253Friction welding of ductile cast ironIndustrial Lubrication and TribologyMieczyslaw Kaczorowski and Radoslaw WiniczenkoVolume 65 Number 4 2013 251 258Figure 2 Relationship between friction time and tensile strength of ductile cast iron jointsFigure 3 Hardness distributions of friction welded joints of ductile cast iron-stainless steelform almost continuous chains of precipitates. Such distribution of the carbides is very dangerous, because they are very hard and brittle, so precipitates can dramatically decrease the ductility of the material. As it can be suspected, these particles are most probably chromium carbides, which grew at the expense of Cr atoms in solid solution. This process involves mostly the grain boundary regions and results in chromium decrease much below the critical value. This, in turn, can lead to inter-granular corrosion and, in case of loading, to stress corrosion cracking.The next micrographs (Figure 6) show the results of TEM observations. First of them (Figure 6(a) presents the structure of stainless steel very close to the interface (x 0.25 mm). Very thin microtwins and high density dislocation loops are visible (note 120,000 magnification).The dislocation structure (Figure 6(b) and highly-magnified subgrain boundary (Figure 6(c) are shown in the next micrographs.Figure 6(b) shows dislocation trapped at very small precipitates and/or at subgrain boundaries. Dark field electron micrograph the Moire contrast (Thomas and Goringe, 1979), reveals many precipitates located at the subgrain boundary (Figure 6(c), which is a preferred place for diffusion, as well as for nucleation processes. Further, the dislocations were rearranged into a low energy structure (Figure 6(d).Three examples of the stainless steel structure close to ductile cast iron interface were shown in Figure 7.4. DiscussionAt the very beginning, the phenomena, accompanying the friction welding process will be considered. It should be discussed, what happened in stainless steel at the moment when forging was stopped (that means, at the moment when both materials: ductile cast iron and stainless steel, were plastically deformed). The severe plastic deformation was accompanied by formation of microtwins (Figure 6(a) and dislocations. The dislocations will tend to form low energy dislocation structure (Figure 6(b) because of very high temperature at the interface which, as followed from authors earlier observations, reached 1,1008C or even more. The high temperature at the interface means that the equilibrium vacancy concentration