Study on Solidification Structure Control and Heat Transfer Behavior of Up‐Drawing Continuous Casting Superalloy Tubes

It is difficult to produce heat‐resistant superalloy tubes with a consistent microstructure and superior performance because of the significant radial heat flow and declining solidification rates from the surface to the core in conventional water‐cooled castings. A super‐long heat‐resistant superalloy furnace tube with an outer diameter of 120 mm and a wall thickness of 15 mm is developed based on the numerical simulation analysis of the vertical continuous casting technology for hollow tubular materials. The yield strength of the alloy is 340 MPa, the tensile strength is 586 MPa, the elongation is 10.4%, and the average hardness is 221.2HV, the uniformity and performance of the cross‐sectional structure are superior to those of centrifugal casting. The findings show that the cross‐sectional grain structure of the tube at lower casting temperatures and drawing speeds is composed of columnar grain zones, outside surface equiaxed fine‐grain zones, and internal mixed grain zones. Increasing the cooling water flow rate improves the heat transfer rate between the melt and the crystallizer, increasing the drawing rate and casting temperature decreases the thickness of the tube's solidification wall. These factors speed up the growth of oriented solidification grains, and form columnar grains that grow uniformly from the outer surface to the inner surface, increasing the columnar grainsarea. Ultimately, casting temperature of 1650 °C, cooling water flow rate of 120 L h −1 , and drawing speed of 40 cm min −1 are all optimized to produce a consistent columnar grain structure with ongoing growth.