Friction stir welding of AISI 304 austenitic ... - Wiley Online Library

Mat.-wiss. u. Werkstofftech. 2007, 38, No. 10

DOI: 10.1002/mawe.200700214

Friction stir welding of AISI 304 austenitic stainless steel Das Ru¨hrreibschweißen AISI 304 des austenitischen rostfreien Stahls C. Meran, V. Kovan, A. Alptekin

The objective of this work is to demonstrate the feasibility of friction stir welding (FSW) AISI 304 austenitic stainless steels. The tool used was formed of a tungsten-based alloy. The specimens were welded on an 11 kW vertical milling machine. Defect-free welds were produced on 2.5 mm plates of hot-rolled AISI 304 austenitic stainless steels at travel speeds ranging from 40 to 100 mm/ min with a constant rotating speed of 1000 rpm. Tensile strengths and hardness values of the weld interface were determined and microstructure features of these samples were investigated. Keywords: Friction stir welding, steel, AISI 304, mechanical properties, hardness

Die Zielsetzung dieser Arbeit war es, die Mo¨glichkeit des Ru¨hrreibschweißens (FSW) AISI 304 von austenitischem rostfreien Stahls zu demonstrieren. (Die Proben aus einer Wolframlegierung wurden in einer 11 Kilowatt Fra¨smaschine verschweißt.) Die Werkzeuge wurden aus einer Wolframlegierung geschmiedet. Die Proben wurden in einer vertikalen 11 Kw Fra¨smaschine geschweißt. Die fehlerfreien Schweißungen wurden aus 2,5 Millimeter Pla¨ttchen aus warmgewalztem AISI 304 austenitischen rostfreien Stahl mit einer Verfahrgeschwindigkeit von 40 bis 100 mm/min mit einer konstanten Rotationsgeschwindigkeit von 1000 U/min hergestellt. Zugbelastung und Ha¨rtewerte der Schweißschnittstelle wurden bestimmt und die mikrostrukturellen Eigenschaften untersucht. Schlu¨sselworte: Ru¨hrreibschweißen, Stahl, AISI 304, mechanische Eigenschaften, Ha¨rte

1 Introduction

blems - encountered in traditional melting welding - will be reduced [3]. One of the important aspects of joining stainless steel with FSW is that the involved high temperatures can soften the metal. FSW ferrous and nonferrous alloys require a tool that can withstand temperatures of approximately 900 – 1000 C at high Z and X axis loads. A critical issue is identifying the choice of suitable steel tool materials for FSW. Another essential requirement for FSW is maintaining a suitable differential between the hardness and elevated-temperature properties of the tool and of the workpiece material. Because steels have much higher hardness and elevated temperature properties, it is important to select tool materials with good wear resistance and toughness at temperatures of 1000 C or higher [4]. The high hardness values of PCBN (polycrystalline cubic boron nitride) limit tool abrasion during the FSW process. The other commonly used tool material for friction stir welding is tungsten carbide (WC) because it has the required properties, Table 1. High temperature resulted when friction developed between the tool and the welded metal. High temperature can pass to the head of the machine by convection and cause overheating and corruption for the bearing that holds the tool. In order to solve this problem, water cooled tool holders were introduced. In addition, by increasing resistance against corrosion in the welding area, a protective gas flow can be provided by using special tools [4]. Some FSW studies were recently conducted on austenitic stainless steel 304L [5, 10 – 13] and 316L [13], superaustenitic stainless steel Al 6XN [10,14]. These studies resulted in the following important observations. First, generally argon was used as the shielding gas to protect both the tool and the weld area from oxidation in the FSW of steels [6, 9, 12 – 15]. Secondly, it was reported that the temperature of the tool shoulder

Friction stir welding (FSW) is a solid state joining technique, invented in 1991 by TWI (The Welding Institute), Cambridge. It involves the joining of metals without fusion or filler materials. The process is most suitable for components that are flat and long (plates and sheets) but it can be adapted for pipes, hollow sections and positional welding. The welds are created by the combined action of frictional heating and mechanical deformation produced by a rotating tool. The maximum temperature reached is on the order of 0.8 of the melting temperature of the metal [1, 2]. The microstructure of a friction stir weld mainly depends on the details of the tool design, the rotation and traveling speeds of the tool, the applied impression force, and the characteristics of the materials being joined. Stainless steels are indispensable materials in industry and their use is growing. Their areas of application will expand because there are many types and kinds of stainless steel. Morever, these steels can be shaped easily and can be successfully welded with the improved welding methods. All stainless steels can be joined by any arc welding method, but the welder must be careful about decreasing corrosion resistance at the welding bead and the heat-effected zone, residual stress, crack formation at the bead, and distortion after welding. Three main problems encountered in the welding of austenitic stainless steel stand out. These are sensitive structure developing after the formation of chrome carbide on the surface that is being heated, the formation of “hot fracture”, and the formation of “sigma phase” risks encountered at high working temperatures. Although the workpiece does heat up during friction stir welding, the temperature does not reach the melting point of the welded metal. For this reason, when joining austenitic stainless steels with FSW, these three welding proF 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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Table 1. Properties of friction stir welding tools [4] Tabelle 1. Eigenschaften der Ru¨hrreibschweißwerkzeuge [4] Property

Units

PCBN

WC

4340 Steel

Coefficient of friction

-

0.10 – 0.15

0.20

0.78

-6

Coefficient of thermal expansion

10 / C

4.6 – 4.9

4.9 – 5.1

11.2 – 14.3

Thermal conductivity

W/mK

100 – 250

95

48

Compressive Strength

MPa

2700 – 3500

6200

690

Tensile Strength

MPa

-

1100

620

Hardness

HV

2600 – 3500

1300 – 1600

280

was over 1000 C and that of the ensuing weld track behind the trailing edge of the rotation tool was 900 – 1000 C. Similarly, a peak temperature of over 1000 C was observed by Lienert et al. just above the tool shoulder by using both thermocouples and infrared cameras. Based on extrapolation of the measured temperature and the microstructural evidence, Lienert et al. suggested that the peak temperature of the stirred zone exceeded 1100 C and likely surpassed 1200 C [7, 9]. Furthermore, the thermal modelling done by Lienert and Gould [8] also predicted that temperature throughout the weld zone exceeded 1000 C. Thirdly; most of 6.4 mm thick 304L steel plate can be successfully welded in a single pass. Welds of steel plates thicker than 6.4 mm were usually made with two passes from two sides because the range of influence of the tool is relatively small in steels compared to aluminum alloys [6, 7 – 13]. Fourthly, generally, the TMAZ (Thermomechanically effected zone) typically observed in FSW aluminum alloys is not evident in FSW steels due to transformations during the FSW thermal cycle [9, 15, 17]. However, Park et al. [12] and Johnson and Threadgill [13] identified an existence of the TMAZ in FSW 304 and 316L. Park et al. [12] reported that the TMAZ in FSW 304 was characterized by recovered microstructure, whereas Johnson and Threadgill [13] observed the evidence of partial recrystallization in the TMAZ of FSW 304L and 316L. Fifthly, the microstructural evolution of steels during FSW is more complicated than that of aluminum alloys due to the occurrence of transformation, recrystallization, and grain growth at the high temperature of 1000 C or above. These changes are significantly influenced by alloy chemistry. For austenitic stainless steels [10], it was reported that equiaxed grain structure developed within the weld nugget with significant grain refinement of up to one order of magnitude relative to the base metal. Sixthly, in general, the friction stir welds exhibited satisfactory hardness, transverse tensile properties, bend properties, and Charpy Vnotch toughness [7 – 9, 11, 14 – 16]. An essential requirement for FSW is maintaining a suitable differential between the hardness and elevated temperature properties of the tool and the work piece material. Because steels have much higher hardness and increased temperature properties, it is important to selected tool materials with good wear resistance and toughness at temperatures of 1000 C or higher. Tungsten alloy, molybdenum alloy, and polycrystalline cubic boron nitride (PCBN) were used as tool materials by some investigators [6, 9 – 12, 14 – 16]. Lienert and Gould [8] and Lienert et al. [9] reported that most of the tool wear appeared to occur during the initial plunge period at the start of each weld, and that both rubbing wear and deformation of 830

C. Meran, V. Kovan and A. Alptekin

the tool were suggested as the origin of the changes in tool dimensions. Furthermore, Lienert and Gould [8] reported that the tools were replaced once; they produced 1.5 – 2.0 m of weld. However, Sterling et al. [17] reported that a PCBN FSW tool exhibited very little wear after 6 m of welding of quenched and tempered C–Mn steel. Clearly, more research efforts should be directed at tool wear and identification/development of suitable tool materials/geometries. Furthermore, Thomas et al. [7] have determined that preheating of workpieces before welding should be beneficial for improving travel speed and minimizing tool wear. It may be simpler and more practical to preheat the initial plunge region of the workpieces before plunging the pin into the workpieces because tool wear mainly occurs during the initial plunge period at the start of each weld [8, 9]. Some experimental studies and their details on FSW of stainless steels are given below. Six mm thick AISI 304L stainless steel was successfully joined by FSW with 550 rpm and 1.3 mm/s travel speed, and 3.5 tool angle. A PBCN tool was successfully used in this study [18]. Reynold [19] investigated the friction stir weldability of 3.2 mm thick AISI 304 stainless steel with a 19 mm diameter tungsten alloy tool. He welded with 1.7 mm/s travel speed and 300 – 500 rpm rotation speed in his study. At the welding center made with low rotation speed, he obtained fine grain and high resisting structure. Uzun et. al. [20] studied joining aluminum alloy (AA 6013-T4) and stainless steel (X5CrNi18 – 10) dissimilar plates by friction stir welding. They successfully joined 4 mm thick materials at 800 rpm rotation and 80 mm/min travel speed. The progression of fatigue characteristics of welding joints was studied, and with AA 6013-T4 joining it was determined that welding bead fatigue strength was 30 % lower. Kimapogon et. al. [21] studied stirrer pin diameter and length in relation to the properties of FSW welding. In their work, they obtained the best bead strength at 0.2 mm distance from the pin’s base to the pin length. In their studies they specified that the diameter of the stirrer pin must be kept to a minimum. The best results were obtained when the diameter of the pin is 2 – 4 mm. Orhan [22] showed in his experiments that AISI 430 stainless steel sheet metal at 50 mm/min welding and 540 rpm rotation speed can confidently be joined with FSW. When he applied tensile testing to the welded bead, he saw that breaking materialized outside the welding area. The explanation of this result is that the strength of the bead was higher than that of the base metal. Feng et. al. [23] applied FSW to stainless steel pipes using 25 mm diameter, 5.5 mm length PCBN tools. In their work, they welded at 500 – 600 rpm rotating and 100 – 150 mm/min travel speed. Unlike other Mat.-wiss. u. Werkstofftech. 2007, 38, No. 10

studies, they performed joining by keeping the impression force at 10 KN, which is a very effective parameter for FSW. They used a special apparatus to fasten and join pipes. To prevent the welding area from oxidizing, they also applied argon gas to the welding bead. In tensile experiments on the joined specimens, breaking occurred in the base metal area. In a study at Brigham Young University, the feasibility of using FSW on AISI 304 stainless steel of 6 mm thickness was investigated. The experimenters used a PBCN tool having a 15 mm shoulder diameter, a 2 mm pin length, 800 – 900 – 1000 – 1100 rpm rotating speeds, and 50 – 75 – 100 – 130 mm/min travel speeds in their studies. In the work, in which successful beads were obtained, it was determined that PCBN is the best tool material for this method due to its very low wear [24]. This paper presents the results of a feasibility study on AISI 304 austenitic stainless steel. The main objective of this work was to demonstrate the feasibility of FSW for joining austenitic stainless steel by characterizing the process, microstructures, and mechanical properties of friction stir welds on austenitic stainless steel. The goal of the study was to explore the following: (1) the feasibility of applying FSW to austenitic stainless steel; (2) the possibility of using tungsten carbide tool materials for the FSW of austenitic stainless steel, and (3) the tensile properties and optical microstructure of two friction stir welds in 304 stainless steel.

2 Experimental Procedure 2.5 mm-thick AISI 304 (X5CrNi18 – 10) austenitic stainless steel plates were used in this work. The chemical composition (% wt) of the plates was 18.20 Cr, 8.42 Ni, 0.80 Si, 1.15 Mn, 0.080 C, 0.045 P, and 0.03 S. All of the welding trials were carried out on a manual vertical heavy duty-milling machine with 11 KW spindle drive motor power as per the TWI procedure described in the patent [2]. The machine frame was robust. Thus, it did not deflect significantly during the FSW trials. The steel workpiece plates were secured with work holding fixtures on the machine traverse table. A pilot hole with a diameter smaller than the probe was drilled between the abutting plates at the start of the weld seam. Traversing was initiated after a period of time sufficient to plasticize the workpiece material which was in contact with the shoulder and the probe The friction stir welding operation was carried out at ambient temperature with no auxiliary preheating or interpass heating of the workpiece. The shoulder diameter of the tool was 20 mm, and the threaded pin was changed conically 3.5 and 6 mm in diameter. The length of the pin is a very critical dimension for FSW. In order to form the FSW bead in the proper shape, the tool should pass very close to workbench plate. For this reason, the length of the pin was selected to be 2.3 mm, slightly shorter than the thickness of the plates. In cases where the pin is longer than needed, it was canalised on the workbench plate and softened metal was translated to this canal. In this case, insufficient penetration of the welding bead occurred. In order to decrease the fragility resulting from using tungsten carbide tools, the sharp corner of the pin and the shoulder part were rounded off and the pin was shaped to be conical towards the tip as shown Figure 1. At the beginning of the experiment, the tool was made by special cold working of steel X155CrVMo12 – 1 (EN ISO 4957, material number 1.2379) as shown in Figure 2a. Then, a hard nitride layer was obtained on the surface by covMat.-wiss. u. Werkstofftech. 2007, 38, No. 10

Fig. 1. Geometry and dimensions of tool Abb. 1. Geometrie und Abmessungen des Werkzeugs

ering it with titanium nitride. Also, for all tools an M5 right screw was threaded to the stirrer tip as specified in the literature [25]. However, these screws started to lose their hardness due to friction and progress movement on frictioned shoulder part inflation. One can observe breakage of the stirrer screw, Figure 2b. The broken stirrer was plastered into the metal at the screw part welding threshold. Then the FSW tool was made of tungsten carbide with 1650 HV hardness. The tungsten-based tool material has excellent toughness and hardness over a temperature range from ambient to a minimum of 1200 C. The tool material was very forgiving of unexpected sudden temperature and load changes during the welding trials. These changes would have led to premature failure of other tool materials under similar conditions. Before the start of welding, in order to get the welding plates face-to-face, a hole of 5.5 mm diameter was drilled. FSW was started by preheating; centering the tool pin, which was rotating at 1000 rpm in the hole; and dipping the tool shoulder into the material at a definite value. The rotating speed was kept at 1000 rpm during all experiments. The travel speeds used in this study were 40, 50, 63, 80, and 100 mm/ min. No elaborate attempt was made to optimize the process conditions in this phase of the study. The specimens’ sizes were 2.5x60x120 mm. The oxide layer was removed prior to processing and the plates were secured to a flat anvil. Due to a lack of equipment that measures impression force applied to the welded part’s surface by the tool’s shoulder between experiment set-ups, the aim was to keep impression force constant during experiments by providing the dipping tool’s shoulder to the specimen at the same proportion at all times.

Fig. 2. The view of tool used at the beginning of experimental works a) Before welding b) after welding Abb. 2. Ansicht des am Anfang der experimentellen Arbeiten verwendeten Werkzeugs a) vor dem Schweißen b) nach dem Schweißen Friction stir welding of AISI 304 austenitic stainless steel

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Fig. 3. The changes on welding bead at different tool dipping angles a) dipping angle 0 b) dipping angle 1 c) dipping angle 1.45 Abb. 3. Auswirkungen auf die Schweißnaht bei verschiedenen Eintauchwinkeln des Werkzeugs a) Eintauchen des Winkels 0 b) Eintauchen des Winkels 1 c) Eintauchen des Winkels 1.45

ments were made at the middle of the welding area of approximately 25 mm length with 0.5 mm spaces by using a 200 g weight.

3 Results and Discussion

Fig. 4. The dipping amount of tool depends on tool dipping angle for 20 mm diameter tool Abb. 4. Die Eindringtiefe des Werkzeugs ha¨ngt vom Eintauchwinkel des Werkzeugs fu¨r einen Durchmesser von 20 mm ab

Preheating continued until adequate heating was reached. At 1000 rpm, preheating was performed after waiting 45 seconds. During this time fumes were observed from the touching area and from the tool shoulder. Also, progress wear was observed between red and orange colors (approximately 900 – 1000 C). Plates were sectioned and polished for optical metallography. The sections were fine polished with 3 lm diamond paste and etched for 45 seconds with a solution of 10 grams of oxalic acid in 100 ml of distilled water. Micro hardness measure-

Unlike aluminum and most non-ferrous materials, which show little or no visible change during FSW due to increases in temperature, a color change occurred when stainless steel was welded. The tool shoulder reached a bright orange color within a few seconds of making contact with the plate. This indicated an approximate temperature of over 1000 C. The tool shoulder maintained its bright orange color throughout the weld. The temperature was dependent on rotational speed: temperature increased with increasing speed. During the studies, it was observed that the tool dipping angle has an important effect on the welding bead. To this end, many experiments were performed to find the best tool dipping angle for a welding bead. When welding was performed by keeping the part perpendicular to the surface, cracks were observed at bead length Figure 3a. By increasing the angle, the cracks formed on the bead decreased Figure 3b. At a 1.45 angle there were no cracks, Figure 3c. The best welds were obtained when the tool dipping angle was 1.45 . After this stage, it was not necessary to increase the tool dipping angle. At this point, with the tool dipping angle at 1.45 , the dipping amount was 0.35 mm, as in Figure 4. The closest distance of the tip part to the workbench was found to be 0.05 mm. Because the welding bead improved by changing the dipping angle while the dipping tool progressed through the angled tool, it seems that it was leaving a clean and smooth surface by applying an impression to the area left behind.

Table 2. Friction stir welding parameters for the square groove butt welding for AISI 304 Tabelle 2. Ru¨hrreibschweiß-Parameter fu¨r das quadratische Nutkolbenschweißen fu¨r AISI 304 Specimens Number

Rotation speed (rpm)

Travel speed (mm/min)

Angle of tool submersion ( )

Quantity of tool submersion (mm)

1,2, 3

1000

40

1.45

0.35

4,5, 6

1000

50

1.45

0.35

7,8,9

1000

63

1.45

0.35

10,11,12

1000

80

1.45

0.35

13,14,15

1000

100

1.45

0.35

832



Fig. 5. The appearance of upper surface and root side of welding beads produced with various travel speeds (1000rpm constant rotation speed) a) 40 mm/min, 1000 rpm b) 50 mm/min, 1000 rpm c) 63 mm/min, 1000 rpm (upper surface) d) 63 mm/ min, 1000 rpm (root part) e) 80 mm/min, 1000 rpm f) 100 mm/min, 1000 rpm Abb. 5. Darstellung der Oberfla¨che, sowie der Unterseite der Schweißnaht, hergestellt mit unterschiedlichen Fahrgeschwindigkeiten (1000U/min konstante Rotationsgeschwindigkeit)

Fig. 6. Dimensions and view of tensile test samples a) Technical dimensions of test samples b) Prepared tensile test samples Abb. 6. Abmessungen und Aussehen der Zugproben a) Probengeometrien b) Vorbereitete Zugproben

The welds were made on one side using two combinations of tool rotation speed and travel speed as shown in Table 2. By keeping the parameters of rotation speed, tool dipping angle, and tool dipping amount (which affects welding quality), the relation to travel speed, the last variable, was investigated. The macroscopic view of welding beads obtained by the welding parameters given in Table 2 is seen in Figure 5. A good welding penetration was not produced at 40 mm/min travel speed due to overheating and at 100 mm/min travel speed due to insufficient heating. Welding done at 40 mm/min travel speed formed cracks on the whole length of the welding bead. It is thought that the reason for this crack formation is high heat input due to a travel speed that is lower than the rotation speed. The appearance of welding beads made at 50 and 80 mm/min travel speed is not bad, but some cracks and insufficient penetration were observed. As shown in Figure 5, welding beads with the best appearance and penetration were obtained at 63 mm/min travel speed. At 100 mm/min travel speed, because of high speed, the intended heat input was not obtained in the welding Mat.-wiss. u. Werkstofftech. 2007, 38, No. 10

bath and, as a result, insufficient penetration occurred. Meanwhile, during welding additional metal and shielding gas were not used. If shielding gas had been used, it is obvious that the macroscopic view of welding bead would have improved. Tensile and hardness measurements were made with mechanical tests. To determine the strength of the welded joint, tensile testing samples were prepared from the welded specimens as shown in Figure 6. The test results in Table 3 were obtained from the average of three tensile tests. Average tensile strength, yield strength, and elongation are given in Table 3 where they are matched with properties of the base metal. Tensile experiments done showed that welding done at 40 and 100 mm/min travel speeds did not have enough strength. Likewise, even if their macroscopic views were not bad, welding beads obtained at 50 and 80 mm/min travel speeds, did not have strength that reached the intended level. The elevated strength of the welded metals relative to the base metal (particularly for the 1000 rpm and 63 mm/min welds) is consistent with the observation of refined grains in the weld nuggets. Based on the specimen size, and consisFriction stir welding of AISI 304 austenitic stainless steel

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Table 3. Tensile test results of friction stir welded plates Tabelle 3. Zugbelastungsergebnisse der ru¨hreibgeschweißten Platten Sample Number

Rotation speed (rpm)

Travelling Speed (mm/min)

Base Metal

Ultimate Tensile Strength, Rm (MPa)

‰.2 Yield Strength, Percent Elongation Rp0.2 (MPa) A (%)

505

215

20

1,2,3

1000

40

210

110

2

4,5,6

1000

50

325

175

10

7,8,9

1000

63

485

350

16

10,11,12

1000

80

320

195

12

13,14,15

1000

100

290

140

4

Fig. 7. The appearance of inner structure of various welding zone (x200) at 1000 rpm and 63 mm/min a) Base Metal b) Thermomechanically affected zone c) Nugget or stir zone Abb. 7. Innere Struktur der verschiedenen Schweißzonen (x200) bei 1000 U/min und 63 mm/min a) metallischer Grundwerkstoff b) Thermomechanisch betroffene Zone c) Nugget- oder Ru¨hrzone

tent with the observed yield strengths of the welded metal specimens, it is assumed that the residual stress in the tensile specimens was relieved when the specimens were cut from the welded plate. Breakage occurred for all welded beads, except those made at 63 mm/min travel speed. However, at the welding done at 63 mm/min travel speed, breaking occurred on the thermomechanically affected zone between the base material and the welding bead. The strength of welding done at the 63 mm / min travel speed was obtained compared to base material. Optical investigation showed three different microstructure zones, which are base material (BM), stir zone (SZ) or nugget,

and a thermomechanically affected zone (TMAZ). The SZ and TMAZ had finer grain sizes than the base metal zone, Figure 7. The SZ displayed somewhat lower hardness than the TMAZ, but generally higher than that of the base material as shown in Figure 8. From perspective of micro-hardness, it can be seen that the measurement of welding bead hardness is close to that of base material hardness, except at transition areas from the welding bead to the base material, where hardness increased a bit. It is thought that of the increase in hardness results from thermo-mechanical deformation at the area touching the tool shoulder.

4 Conclusion l

l

l

Fig. 8. The results of micro hardness (63 mm/min, 1000 rpm) Abb. 8. Mikroha¨rteuntersuchung (63 mm/min, 1000 U/min) 834


The mechanical and microstructural evolution of a 304 stainless steel weld during FSW was examined. Three different welding microstructure zones were found: base materials (BM), stirrer zone (SZ), and a thermomechanically affected zone (TMAZ). The heat affected zone was not in friction stir welding of aluminium and its alloys. Cold working steel is not suitable for the FSW of stainless steels. Using tungsten carbide tools for the FSW of stainless steels gave good results. Also, the best welding appearance was obtained when the tool dipping angle was 1.45 . The least waiting time for pre-heating was determined to be 45 second for the welding conditions of 1000 rpm rotating speed, 63 mm/min travelling speed, and 1.45 tool dipping angle. Mat.-wiss. u. Werkstofftech. 2007, 38, No. 10

l

l

l

The strength of welding done at the 63 mm/min travel speed and 1000 rpm rotating speed was found equally compared to base material. Welding bead hardness was obtained close to base material hardness. Also, at the transition area from the welding bead to the base material, hardness increased a bit. These studies showed that welding is safe if suitable conditions for austenitic stainless steels are provided.

References 1. Bhadeshia, H. K. D. H., http://www.msm.cam.ac.uk/phasetrans/2003/FSW/aaa.html, Friction Stir Welding, University of Cambridge, 2003. 2. W.M., Thomas, E.D., Nicholas, J.C., Needham, M.G., Murch, P., Templesmith, C.J., Dawes, Improvements relating to friction welding, European Patent EP 0 615 480 B1; 1992. 3. Z., Feng, High strength weight reduction materials, FY 2003 Progress Report, Friction stir processing of advanced materials principal investigator, 2003. 4. S., Packer, R., Steel, M., Matsunaga, Friction Stir Welding of High Melting Temperature Materials, Megastir, 2005. 5. S. Gourder, E.V. Konopleva, H.J. McQueen, F. Montheillet, Mater. Sci. Forum 1996, 441, 217 – 222. 6. R.H. Bricknell, J.W. Edington, Acta Metall. 1991, A 22, 2809. 7. W.M. Thomas, P.L. Threadgill, E.D. Nicholas, Sci. Tech. Weld. Joining 1999, 4, 365. 8. T.J. Lienert, J.E. Gould, in: Proceedings of the First International Symposium on Friction Stir Welding, Thousand Oaks, CA, USA, June 1999. 9. T.J. Lienert, W.L. Stellwag Jr., B.B. Grimmett, R.M. Warke, Weld. J. 2003, 82 (1), 1s. 10. 10] A.P. Reynolds, M. Posada, J. Deloach, M.J. Skinner, J. Halpin, T.J. Lienert, in: Proceedings of the Third International Symposium on Friction Stir Welding, Kobe, Japan, September 2001. 11. M. Posada, J. Deloach, A.P. Reynolds, M. Skinner, J.P. Halpin, in: K.V. Jata, M.W. Mahoney, R.S. Mishra, S.L. Semiatin, D.P. Filed (Eds.), Friction Stir Welding and Processing, TMS, Warrendale, PA, USA, 2001, p. 159. 12. S.H.C. Park, Y.S. Sato, H. Kokawa, K. Okamoto, S. Hirano, M. Inagaki, Scripta Mater. 2003, 49, 1175.


13. R. Johnson, P.L. Threadgill, in: S.A. David, T. DebRoy, J.C. Lippold, H.B. Smartt, J.M. Vitek (Eds.), Proceedings of the Sixth International Conference onTrends inWelding Research, Pine Mountain, GA, ASM International, 2003, pp.88 – 92. 14. M. Posada, J. Deloach, A.P. Reynolds, J.P. Halpin, in: S.A. David, T. DebRoy, J.C. Lippold, H.B. Smartt, J.M. Vitek (Eds.), Proceedings of the Sixth International Conference on Trends in Welding Research, Pine Mountain, GA, ASM International, 2003, pp. 307 – 312. 15. P.J. Konkol, J.A. Mathers, R. Johnson, J.R. Pickens, in: Proceedings of the Third International Symposium on Friction Stir Welding, Kobe, Japan, September 2001. 16. A.P. Reynolds, W. Tang, M. Posada, J. Deloach, Sci. Technol. Weld. Joining 2003, 8 (6), 455. 17. C.J. Sterling, T.W. Nelson, C.D. Sorensen, R.J. Steel, S.M. Packer, in: K.V. Jata, M.W. Mahoney, R.S. Mishra, S.L. Semiatin, T. Lienert (Eds.), Friction Stir Welding and Processing II, TMS, 2003, pp. 165 – 171. 18. W.M. Thomas, P.L. Threadgill, E.D. Nicholas, Sci. Tech. Weld. Joining 1999, 4, 365. 19. A.P. Reynolds, W. Tang, T. Gnaupel-Herold, H. Prask, Structure, properties and residual stress of 304L stainless steel friction stir welds, Scripta Materialia, 2003, 48, pp.1289 – 1294. 20. H. Uzun, Friction stir welding of dissimilar AA 6013-T4 to X5CrNi18 – 10 stainless steel, Materials and Design, 2005, 26, pp.41 – 46. 21. K. Kimapong, T. Watanabe, Friction stir welding of aluminium alloy to steel, Welding Journal , 2004, pp. 277 – 282. 22. N. Orhan, B. Kurt, E. Ertugrul, AISI 430 Ferritik paslanmaz celigin surtunme karistirma kaynagina devir sayisinin etkisi, 11. Uluslararasi Malzeme Sempozyumu, 2006, pp.12 – 15. 23. Z. Feng, R. Steel, S. Packer, S.A. David, Friction stir welding of API grade X65 steel pipes, Brigham University, 2005. 24. C. D. Sorensen, Progress in friction stir welding high temperature materials, Brigham Young University, 2004. 25. C. Meran, The joint properties of brass plates by friction stir welding, Materials and Design, 2006, 277, pp. 719 – 726. Coressponding author: Asst. Prof. Dr. Cemal Meran, Pamukkale University, Engineering Faculty, Denizli, Turkey, E-mail: [email protected]

Received in final form: August 8, 2007

Friction stir welding of AISI 304 austenitic stainless steel

[T 214]

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