![]() ![]() In addition, a higher heat input (increased energy density) during welding enhances the efficiency of melting and therefore increases the amount of molten zone (weld bead) (Ref 15). Especially for welding large components with large wall thickness and a high number of weld seams, welding with higher heat input might offer the possibility to increase the productivity as it enables welding of larger volumes with fewer weld beads. A high heat input during SAW causes larger sized weld beads and thus slower cooling rates, leading to differences in the weld metal’s bead sequence and microstructure, compared to welding with lower heat input (Ref 12, 14). The most important ones are the filler metal (i.e., the combination of flux and wire), the applied welding current and voltage, the deposition rate as well as the interpass and preheat temperature (Ref 7, 8, 9, 10, 11).įor the process of SAW, where the thermal efficiency factor is close to 1, the product of welding current and voltage multiplied by 60 and divided by the welding speed equals approximately the heat input (Ref 9, 12, 13). There are many factors which directly influence the process of SAW and in further consequence possess an impact on the microstructure and mechanical properties of the resulting welded component. SAW is an established manufacturing process with a continuous wire feed and a welding flux which shields the weld pool from the surrounding atmosphere and has numerous functions such as deoxidation, supply of alloying elements and slag formation. For the application in thick walled reactors, the 2.25Cr-1Mo-0.25V steel is commonly joined with submerged-arc welding (SAW) (Ref 5). As these reactors might be operated under creep conditions, the applied 2.25Cr-1Mo-0.25V welding consumables require a beneficial combination of strength and toughness as well as enhanced creep rupture strength (Ref 3, 4, 5, 6). Typical applications are, e.g., hydrocracking and desulfurization reactors, which are exposed to elevated temperatures of 400 to 450 ☌ and high pressures (Ref 4). It is commonly used for reactors in power stations or in petroleum and chemical plants (Ref 1, 2, 3). The alloy 2.25Cr-1Mo-0.25V was developed in the early 90s by combining the properties of 2.25Cr-1Mo-type with the ones of 1CrMoV-type steels. In contrast to the stress rupture time and the toughness, the weld metal’s strength, ductility and macro-hardness remain nearly unaffected by changes of the heat input. This is assumed to be linked to a lower number of weld layers, and therefore, a decreased amount of fine grained reheated zone if the multilayer weld metal is fabricated with higher heat input. Furthermore, it was determined that a higher heat input during SAW causes an increase in the stress rupture time and a decrease in Charpy impact energy. The heat input was found to increase the primary and secondary dendrite spacing as well as the bainitic and prior austenite grain size of the weld metal. ![]() This study deals with the influence of the heat input during submerged-arc welding (SAW) on the solidification structure and mechanical properties of 2.25Cr-1Mo-0.25V multilayer metal. The mechanical properties are known to be influenced by several welding parameters. As these reactors are operated at elevated temperatures and high pressures, the 2.25Cr-1Mo-0.25V welding consumables require a beneficial combination of strength and toughness as well as enhanced creep properties. The alloy 2.25Cr-1Mo-0.25V is commonly used for heavy wall pressure vessels in the petrochemical industry, such as hydrogen reactors.
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