Hot extrusion characteristics and technique optimization for superalloy 617B tube

Nickel-base superalloy 617B is one of the most promising candidates for superheater and reheater pipes of advanced ultra-supercritical (AUSC) power plants.Hot extrusion is a key process during the manufacturing of superalloy 617B pipes.However, the high content of alloying elements in superalloy 617B makes microstructure control difficult during the hot extrusion process.Furthermore, to date, no systematical theoretical investigation has been conducted in the hot extrusion process control of superalloy 617B.Hence, in this work, the hot extrusion process of superalloy 617B tube was studied by finite element simulation using DEFORM-2D finite element software.The microstructure evolution during hot extrusion was considered by combining the microstructure evolution model of superalloy 617B and finite element simulation software.The microstructure evolution model was programmed using FORTRAN language and was developed using the finite element simulation software.The hot extrusion characteristics of superalloy 617B were systematically analyzed by the simulation.As a result, the evolution of temperature, grain size, and loading could be predicted quantitatively.At the same time, to optimize the hot extrusion parameters, microstructure-based hot extrusion control principles, including temperature principle, loading principle, precise microstructure control principle, were proposed considering practical hot extrusion process.Moreover, the control mechanism and application process of these principles were elaborated in detail in this paper.The hot extrusion parameters of superalloy 617B tube were optimized based on the proposed microstructure-based hot extrusion control principles.Under the guidance of the microstructure-based hot extrusion control principles, superalloy 617B tube with uniform axial dimension and good surface quality was extruded successfully in the factory.The practical extrusion result agrees well with the simulated one.Therefore, the establishment and validation of the simulation method and microstructure-based hot extrusion control principles can provide theoretical guidance for the hot extrusion process optimization of nickel-base superalloy tube in practical applications.