Sdudy On Welding Process And Heat Treatment After Bending Of Fine Grained SUPER304H Tube

The ultra supercritical(USC) power plants were developed quickly in recently years in China. When the USC technology was imported, many types of new materials were used for USC boiler fabrication at the same time. Super304H steel was one of the new materials, which was widely used for the reheater and superheater fabrication. Welding process and heat treatment after tube bending was the key technology in the boiler fabrication factory. Thus both welding process and heat treatment after tube bending were found in the literatures. Taking serious steam oxidation into consideration, fine grain Super304H steel was widely used recently. Therefore, the welding process and heat treatment are studied for fabrication of USC boiler in this thesis.With the utilization of Gleeble thermal-mechanical simulator, optical microscope and other equipments, and post the welding thermal simulation experiment, bending head heat treatment experiment, and testing of grain size and mechanical properties, the effect of welding process with water cooling on microstructure and the effect of different solid solution temperature on grain size and mechanical properties of bending head have been conducted. Experimental results showed that water cooling added in welding process can effectively control the grain size of weld heat affecting zone. With the heat treatment of 950℃×30min, water cooling or air cooling, the internal stress can be released, and the hardness and grain grade of bending head can meet the requirement of ASME Code Case 2328 specification. The welding process and bending head heat treatment adapted from author's research results was successfully applied to the fabrication of tube equipments.