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Biljana Savić Research Assistant College of Technical Vocational Studies, Čačak Physical Model of the Friction Welded Joint of Different Types of Steel The paper comprises the phenomena encountered in the friction rotation welding process with a continual drive of different types of steel. The rotation friction welding with a continual drive of the HSS steel M2 was carried out with carbon steel 1060. Characterization of the phenomena, taking place within the welded joint over the friction phase
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  © Faculty of Mechanical Engineering, Belgrade. All rights reservedFME Transactions (2008) 36, 93-97 93  Received: July 2008, Accepted: September 2008Correspondence to: Dr Svetislav Markovi ć  College of Technical Vocational Studies,Svetog Save 65, 32000 Č a č ak, SerbiaE-mail: svetom@nadlanu.com Biljana Savi ć   Research AssistantCollege of Technical Vocational Studies, Č a č ak Svetislav Markovi ć   Professor College of Technical Vocational Studies, Č a č ak Radovan Ć iri ć   Professor College of Technical Vocational Studies, Č a č ak Physical Model of the Friction WeldedJoint of Different Types of Steel The paper comprises the phenomena encountered in the friction rotationwelding process with a continual drive of different types of steel. Therotation friction welding with a continual drive of the HSS steel M2 wascarried out with carbon steel 1060. Characterization of the phenomena,taking place within the welded joint over the friction phase was determined through direct measurement, made of the temperature cycles followed byexamining the structure and analytical procedure. Thorough studiesenabled setting up of the model of the friction welded joint of different types of steel with characteristic zones.  Keywords: HSS steel, carbon steel, friction welding, microstructure,model. 1. INTRODUCTION The process of rotation friction welding with continuousdrive (FW) is carried out through the following five phases: (i) initial friction, (ii) unstable friction, (iii) stablefriction, i.e. quasi-stationary phase, (iv) breaking and (v) pressing-upsetting [1,2]. The phase of stable friction(phase III) begins when the layer of considerable plasticity and small strength is spread along the wholefriction plane. Plastic deformation in this phase ischaracterized by transition from plastic deformation tothe deformation of thin layers of base metals (BM). It isconsidered that in this phase the heat exchange isestablished, which is characterized by the dynamic heat balance between the extend heat and the heat which istransferred to BM and the environment [3-5].However, close to friction plane, the viscous layer of metal is formed, and its shape, size and the path of flowof metal particles layers, either qualitatively or quantitatively have not been described yet [6-8].The purpose of this study is to establish a model of the friction welded joint of these steels withcharacteristic zones in the third phase of FW process, onthe basis of analysis of the flowing of the matter and thedistribution of carbide phase in friction plane area. 2. EXPERIMENT2.1 Material and experimental data HSS Steels M2 and carbon heat treatable steel 1060 (the bars of 10 mm in diameter), Table 1, were welded bythe procedure of rotation friction welding withcontinuous drive (FW). The basic parameters of FW process in the phase of friction are: friction pressure P f   [MPa], friction time V  f  [s] and the number of revolutions n (in the experiment n = const = 2850 min -1 ). The parameters in the phase of upsetting are the pressure P u [MPa] and time V  u [s]. Only the sample of steel M2 was rotated. Variable parameters in theexperiment were P f  , V  f  and P u .Quantitative and qualitative analysis of layers in thefriction plane, high plasticity zone and in the viscouslayer was carried out on the experimental samples.Processes occurring in the viscous layer andneighbouring zones were investigated duringexperiments by the optical, quantitative opticalmicroscopy and electron microscopy as well as by theanalysis of rheological appearances [9]. 3. RESULTS AND DISCUSSION3.1 The shape of the flowing of matter in frictionplane area Detailed analysis of microstructure and phasecomposition of the welded joint, particularly the viscouslayer and viscoplastic layer was performed by theoptical and quantitative optical microscopy and electronmicroscopy. The analysis covers mostly by phenomenaoccurring in phase III of the FW process.As reported in studies [7,8] and according to theauthors’ investigation result, a viscous metal layer isformed in phase III of the FW process.Electron microscopy (JEOL microscope JSM 5300,Japan) revealed the friction plane and the viscous layer formed in the third (III) phase of friction.The viscous layer is formed on both sides of thefriction plane. In that layer, the displacement of theviscous mass of metal and of the solid carbide particlesoccur, according to the mechanism of the rotational, both luminary or local turbulent flow, Fig. 1.This complex current circuit falls into the class of multi phase (multi-component) flows of non-Newtonfluids, which have not still been investigated enough, sothat the results obtained cannot not be compared withthe data from the literature.Regarding the mechanism of flowing, it is obviousthat during the process of rotational FW steel M2 with1060 the dominant shape of the flowing of matter islaminar. Also, in the first and the second phase of friction, the secondary flow occur (transition of laminar into turbulent movement, formation of whirls of different dimensions and structures, twirl-like flowingwith recirculating zones), Fig. 2.    94 ▪ VOL. 36, No 2, 2008 FME Transactions   Table 1. Chemical compositions and hardness of basic materials M2 and 1060 in agreement to AISI Content of elements, wt. %SteelC Si Mn Cr W Mo V S PHardness, HB2.5/62.5/20StateM2 0.86 – – 4.07 6.03 4.75 1.82 0.0036 0.0137 260 – 2721060 0.63 0.194 0.82 0.0036 0.00273 – – – – – Softannealed   Figure 1. Local turbulent flow in friction plane area duringthe FW process of steel M2 with 1060 ; SEM, 1500X According to Figure 2a, the influence of frictiontime V  f  on the shape of the joint line (shape of theflowing of matter) depends greatly on thermal-deformation conditions realized during the FW process.During short friction times ( V  f    ≈ 1 s), the transferred parts of both metals (BM) are heated at lower temperatures and they are deformed with a smaller degree of deformation. Along with rising of  V  f  ,temperature rises too, and the deformation of contactlayers is bigger. When friction times are sufficientlylong ( V  f    ≈ 13 s), contact layers are in highly plastic andviscous state, so the process of deformation is reducedto the deformation of thin surface layers.According to Figure 2a, the shape of the secondaryflows (mixing of particles of both BMs) in friction planearea is the following: when V  f  is shorter, besides thedominating laminar flowing, the secondary turbulentflows appear, as well as whirl. When V  f  is longer, theflowing of the highly plastic and viscous metal islaminar. 3.2 Distribution of carbide phase in friction area On the basis of the analysis of microstructure, it wasdetermined that the process of deformation of metal inthe third phase of friction ( V  h   ≈ 13 s) is characterized bytransition from the plastic deformation along bigger depth onto the deformation of thin surface layers BM.Content, size and location of carbide particles affectthe character of the process in the characteristic zonesand vice versa. Thus, non-dissolved carbides, i.e. solid particles in solid-liquid metal (viscous layer) and inhigh-plasticity zones (outside the layer), may have asubstantial effect on the character of metaldisplacement, Fig. 3. At the same time, thermal-deformation conditions have a substantial effect on thedissolution phenomena and mechanical fractures of thecarbide phase, etc. These occurrences cause changing of the shape and size of carbide phase.The volume content of non-dissolved carbide particles after FW without upsetting was measured at adistance of 1 mm from the rotational axis in the viscouslayer, zone of mixing of both BM, HAZ metal in steelM2 and in steel 1060 outside the HAZ. The mean V  f    ≈ 1 s V  f  [s], r  [mm] V  f    ≈ 13 s r    ≈ 1 mm r    ≈ 2.5 mm V  f    ≈ 1 s V  f  [s], r  [mm] V  f    ≈ 13 s r    ≈ 1 mm r    ≈ 2.5 mm Figure 2. The shape of the line of joint steel M2 with 1060 (a) and characteristic shapes of mixing of particles of both BMs,magnification 50X (b) in the function axial distance from time of friction plane and radial distance from the rotation axis; M2(light spots), 1060 (dark spots). Regime FW: P  f  = 80 MPa, n  = 2850 min -l , FW without upsetting and after that cooled in the air,magnification 500X (a)(b)  FME Transactions   VOL. 36, No 2, 2008 ▪   95   Figure 3. Displacement of the carbide phase in the joint area in the steel M2Table 2. Volume content and the average size of the carbide particles in the area of FW joint between steel M2 and steel 1060 Zone Content of non-dissolved carbides [vol. %] Mean average of carbide particles [mm]Friction plane 24.05 0.93829Viscous layer (outside friction plane) 5.70 0.63780Zone of mixing of both BM 9.38 0.97125HAZ in steel M2 10.43 0.91381Steel M2 26.90 0.63597 0.00.30.60.91.21.51.82.12.42.73.005101520    R  e   l .   F  r  e  q . ,   % Intercept, µ m 0204060801000.00.30.60.91.21.51.82.12.42.73.0    C  u  m .   F  r  e  q . ,   %   Figure 4. Function and histogram (probability) of carbideparticles distribution per sizes in the friction plane measured content of the carbide phase and average sizeof the carbide particles in characteristic zones are givenin Table 2. The probability density of size distributionon the carbide particles in the friction plane is shown inFigure 4.In literature [9] the adapted physical-mathematicalmodel was established, which explains the movement of carbide particles in viscous environment.The measurement was carried out by linear methodon the automatic device for the analysis of the picture“Quantimet 500 MC” manufactured by the Leicacompany, with the help of the optical microscope.According to Table 2 the lowest share by volume of carbides is measured in the viscous layer out of thefriction plain (5.70 %). The volume share of carbides inthe carbide layer itself which is formed along thefriction plane is 24.05 %; it is almost at the level of share in M2 and it is considerably higher than in other characteristic zones.The phenomenon of appearance of significantdifferences in the concentration of carbide phase in thecharacteristic zones in steel M2 in the area of friction plane can be explained by the analysis of the field of tension of pressure and in the viscous metalimmediately near the friction plane. 3.3 Physical model of the friction welded joint of HSS steel and carbon steel Based on detailed microstructure investigation, the physical model of the friction welded joint of HSS steeland carbon steel with characteristic zones wasestablished, Fig. 6. Microstructure in the area of welded joint is presented in Figure 5, and the microstructures of metal in the characteristic zones in Figures 6-10 in thethird phase of FW process. 1 – Viscous layer; 2 – Carbide layer; 3 – Layer M2 surfacedonto 1060; 4 – Viscoplastic layer; 5 – Particles of steel 1060in M2; 6 – Steel 1060; 7 – Line of joint; 8 – HAZ in M2; 9 –HAZ in 1060Figure 5. The microphotograph of the characteristic zonesof the vicinity of the friction plane in third friction phase of the process FW of M2 with 1060    96 ▪ VOL. 36, No 2, 2008 FME Transactions   1 – Viscous layer (Fig. 7); 2 – Carbide layer (Fig. 8); 3 –Layer M2 surfaced onto 1060 (Fig. 9); 4 – Viscoplastic layer (Fig. 10); 7 – Line of joint; 8 – HAZ in M2; 9 – HAZ in 1060Figure 6. The model of the FW joint HSS steel and carbonsteel with the characteristic zones in the vicinity of thefriction planes in the third friction phase of the process FWFigure 7. Viscous layer Figure 8. Carbide layer  Viscous layer 1 in Figures 5 and 6 is formed in thethird phase of FW immediately near the friction plane.In the friction phase, the matter in this zone is asuspension of the viscous solution of steel M2 and solidcarbide particles [9]. After cooling, the content of theundissolved carbides in this layer is lower in relation tothe adjoining zones, Fig. 7.During the FW process, carbide layer is formed onthe front of the rotational steel bar M2. On thelongitudinal cross-section, the layer is seen in the shapeof the line of carbides, Fig. 8. The content of carbide inthis layer is significantly higher in relation to theadjoining zones. The phenomenon of forming of thislayer is explained in literature [9] on the basis of theanalysis of rheological occurrences. Figure 9. Layer M2 surfaced onto 1060Figure 10. Viscoplastic layer  Due to the difference in thermal-physical properties between BMs at the very beginning of the friction process, the steel M2 is surfaced onto the 1060, Fig. 9.The result of this is that the friction plane is moved intoM2 (friction is done between the two layers of steelM2).Viscoplastic layer is most frequently formed in layer M2 surfaced onto 1060. During the friction phase, thiszone is heated at the temperatures higher than those of the standard plastic deformation. In this layer, thethermal-deformation conditions necessary for therealization of the process of dynamic recrystallizationand obtaining of a very tiny grain, Fig. 10, are reached.The mixing zone of particles of both BMs, 5 inFigure 5, is formed in the first and second friction phase. Along with the prolonging of  V  f  , this undesirablezone is most frequently extruded out of the friction plane. Characteristic shapes of the mixing of particles of  both BMs are given in Figure 2.The areas 8 and 9 in Figures 5 and 6 represent theheat-affected zones (HAZ) in steels M2 and 1060. 4. CONCLUSIONS ã   On the basis of the tests performed, the physicalmodel of the friction-welded layer withcharacteristic zones is established (viscous layer,
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