Materials recovery carbide in openlca
The hot bending processes including reheating, water cooling, and tempering for the weld metal are similar to the postwar heat treatment (PWHT) of quenching and tempering. Accordingly, the effects of the reheating, water cooling, and tempering associated with the hot bending processes on impact toughness of the weld metal must be firstly considered. During the hot bending processes, the weld seam does not go through the bending deformation nevertheless, the weld metal must undergo reheating, spraying water cooling, and tempering. And yet for all that, the weld metal still has lower impact toughness than the pipe body. The microstructure and mechanical properties of the weld seam of LSAW steel pipes are different to the pipe body, and the acicular ferrite is obtained as an optimal microstructure to improve the impact toughness. The heavy-wall hot bends are usually made from longitudinal-seam submerged arc welding (LSAW) steel pipes by hot induction heated bending, on-line water cooling, and off-line tempering. Contemporaneously, heavy-wall hot bends have been developed. Recently, in order to maximize the transport efficiency and decrease the construction and transposition costs, the gas pipeline transmission develops toward a larger diameter and/or higher operation pressure thereby, the high strength X80 steel grade and heavy-wall pipe over 22 mm have been applied to many long-distance transmission pipeline projects, such as the Third West-to-East Gas Transmission Pipeline Project and the Sino-Russian Gas Transmission Pipeline Project.
Introductionīends are some of key parts of the pipeline projects. Addition of Ni to weld metals can refine the acicular ferrite and improve the impact toughness. With the increase of the tempering temperature, the carbide particles coarsen, which decreases the impact toughness of the weld metal of hot bends. The resulting carbide particles mainly distribute along the acicular ferrite grain boundaries. During tempering, the overlapping acicular ferrite microstructure is degenerated, and martensite/austenite (M/A) constituents in the acicular ferrite microstructure decompose into ferrites and carbides. So, the overlapping acicular ferrite microstructure is obtained in the weld metal after direct cooling from the reheating temperature. The results show that the nonmetallic inclusion particles in weld metals can become the nuclear core of acicular ferrite like in as-welded metal. In this study, three kinds of weld metals with different Ni contents were selected, and then the effects of tempering temperature on the microstructure impact toughness of weld metals for hot bends were investigated by simulation conducted on a Gleeble-3500 thermal simulator. Impact toughness of the weld metal is one of the important factors affecting the quality of hot bends, which is strongly dependent on the microstructure transformation during hot bending and tempering.