A Study on the Effect of the Interpass Temperatures in Properties and Microstructures of the Alloy 625 Dissimilar Fusion Zone

Abstract

The purpose of this study is to evaluate the effectiveness in the contribution of the interpass welding in the microstructures and properties of the dissimilar fusion zones produced with an alloy 625 and API 5L X65 steel pipes. Three multipass welded joints with v-groove, were made under the same welding parameters, therefore, changing only the interpass temperatures at: 150°C, 250°C and 450°C. The microstructural characterization was performed using the light microscopy and the scanning electron microscopy (SEM). The hardness test, charpy-V impact test and the transverse tensile test were conducted according to specific standards. The results have shown that all ruptures in the tensile tests occurred in the base metal. Both yield strengths and ultimate tensile strengths, have dropped to the 450°C interpass temperature. It was also observed a slight drop in the hardness with increasing interpass temperature. The Charpy-V impact test results showed no significant differences among the interpass temperatures. These said results indicated that the maximum interpass temperature for the alloy 625/X65 steel dissimilar welding is limited by the steel properties.

Mechanical Properties and Microstructural Characterization of Aged Nickel-based Alloy 625 Weld Metal

“…Notwithstanding Also for 100 and 200 h of exposure at 650 °C the presence of large blocks of NbC carbides and cubic NbTi complex were found, which remained from solidification. However, these particles probably have low or no effect on toughness, since in another study, carried out by Silva et al [48][49] evaluating the effect of the interpass temperature on mechanical properties in weld metal of 625 alloy, these particles were found. The results of the Charpy-V impact test at cryogenic temperature (-196 °C) showed no significant differences among the weld conditions and the level of energy absorbed was higher than 100 J.…”

“…It is possible that this was due to the formation of the orthorhombic  phase. Another works [49][50] has found that a reduction in Charpy impact energy to around 180 to J/cm 2 occurred as a result of intermediate temperature ageing, which was attributed primarily to the formation of the orthorhombic  phase.…”

“…As the analytical techniques used are not able to confidently identify other precipitates one should not assume the probable formation of ', " or Ni 2 (Cr,Mo) dispersion strengthening phases. Based on Kumar et al [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] , who studied a service tube of Inconel 625 alloy exposed to ~600 °C for ~60,000 h, a short duration aging at 650 ºC up to 10 h caused a dissolution of the Ni 2 (Cr,Mo) phase. When the alloy was aged at 850 ºC for 1 h, there was a complete dissolution of both '' and Ni 2 (Cr,Mo) precipitates.…”