Study of Residual Stress on Inconel 690 Alloy Butt-Welded by GTAW and LBW Processes

Autor: Meng-Hsuan Lee, 李孟軒
Rok vydání: 2007
Druh dokumentu: 學位論文 ; thesis
Popis: 95
This study investigated the residual stress and corrosion resistance of Inconel 690 Alloy weldments by GTAW and Nd-YAG Laser Beam Welding processes. The residual stress of the weldments was measured by the high speed hold-drilling strain-gage method, and their corrosion resistance was evaluated by the U-Bend stress corrosion test. The temperature measurements showed that LBW process resulted in much higher heating rate (3020˚C/sec) and cooling rate (147~157˚C/sec)of the weldment than GTAW process. Compared to the temperature observations in the heat affected zone of both weldments, it only took 1.4~1.5 seconds to pass through the sensitization range in the LBW weldment, whereas 17 seconds period was needed in the GTAW counterpart. The high cooling rate is favourable for depressing Cr-carbides precipitation along the grain boundary, and hence to improve the corrosion resistance of weldments. Moreover, high tensile residual stresses were observed near the fusion line of all specimens. The maximum residual stress of LBW weldment is higher than that of GTAW counterpart, which value approaches to the yielding strength of 690 alloy. This may be attribute to the high temperature gradient of the LBW process. The residual stresses decrease with increasing distance from the fusion line, and LBW specimen has a compressive residual stress zone clearly following the tensile residual stress zone. From the comparison with metallography, residual stress of weldments and the results of corrosion tests, it was found that the welding microstructure is a major factor to affect the corrosion resistance of weldments, whereas the welding residual stress didn’t show an obvious effect to it. Keywords: Inconel 690 Alloy, GTAW, Laser Beam Welding, Residual Stress, Corrosion
Databáze: Networked Digital Library of Theses & Dissertations
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