الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
AISI 304 austenitic stainless steel (0.06%C – 22%Cr – 13% Ni) and steel 37 (equivalent to AISI standard- AISI 1020) (0.19%C – 0.55%Mn – 0.41%Si) were welded together by flux cored arc welding process (FCAW) using electrode E 309 L T1 (0.03%C – 20%Cr – 12%Ni) and friction stir welding (FSW) using a tungsten carbide tool with rotational speed, traverse welding speed and applied load were changed from 400 to 700 rpm, 40 & 50 mm/min and 900 to 2000 Kg respectively for FSW. Results of preliminary tests showed that using of 500 rpm as rotational speed, 40 mm/min as traverse welding speed and load 1300 Kg ±10% produced defect free welds, and these conditions could be considered as the optimum conditions to produce the desired joints. Metallography, electrochemical measurements, and mechanical tests including tensile, impact, bending and hardness were carried out to analyze the properties of joints. Microstructural observations and ferrite number determination indicated that the weld metal produced by FCAW consisted mainly of austenite and about 7% ferrite. The heat affected zone (HAZ) area at the carbon steel side was composed of three regions: partial-grain refining, grain refining, and coarse grain while coarse grains near fusion lines, as a result of high heat input, was detected on the AISI 304 side. While, the weld area of FSW consisted of two zones, the first zone was the stir zone (SZ) in the AISI 304 side characterized by refined grain structure. The second zone SZ in the St-37 side characterized by fine ferrite and pearlite. This could be attributed to hot deformation of the St-37 in the austenitic region producing small austenite grains and these grains transformed to fine ferrite and pearlite after cooling. Thermo mechanically-affected zone (TMAZ) was observed on the AISI 304 side with features of dynamic recovery while HAZ in the St-37 side showed two regions: partially and fully refined microstructures. Energy Dispersive X-ray (EDX) and X-ray Differential Analysis (XRD) showed that no chromium carbide in welds produced by either FCAW or FSW techniques. Tensile strength were 361 and 381 MPa for FCAW and FSW weld respectively (approximately the same as that of St-37) however, elongation of FCAW joint was higher than FSW weld by about 40%. Macro-hardness of the FCAW was less than FSW joint and the average impact energy of the joints were 22 and 26 J of the FCAW and FSW respectively. It should be mentioned that heat input for FCAW and FSW joint were 1027 and 610 J/mm, respectively and recrystallization in the SZ of AISI 304 side and phase transformations in the SZ at St-37 side which were occurred during FSW welding produced fine grain structure. The corrosion rate of FCAW and FSW joints as a whole were 12 and 9 mpy respectively. An economic comparison study indicated that using of FSW decreased the operating welding time by about 5 times than that needed for FCAW, consequently reduced operational costs.