Gas nitriding of h13 tool steel used for extrusion dies: Numerical and experimental Investigation

Gas nitriding under controlled nitriding potential represents one of the most important factors in enhancing the service life of dies used in the hot aluminum extrusion industry. Nitriding of complex-shaped extrusion dies, which is a very sensitive process with regard to achieving a nitride layer with uniform quality, may result in nonuniform nitride layers; therefore, required hardness may not be achieved in some regions of the bearing area. The focus of this chapter is to investigate the influence of various factors like surface texture, multiple nitriding, and die geometry on the kinetics of the nitrided layer developed during the gas nitriding process under controlled nitriding potential. Both experimental and numerical results are presented and compared. In experimental parts, the nitride layers are characterized using different techniques, including optical microscopy, scanning electron microscopy, X-ray diffraction analysis, microhardness analysis, and energy dispersive spectrometry techniques. A sequentially coupled heat-diffusion analysis of nitriding treatment is also conducted numerically using a finite element code, ABAQUS. The numerically predicted results are in close agreement with experimental results in terms of nitride layer growth and nitrogen concentration distribution in the diffusion zone.