Laser cladding microstructure and properties of die steel

(4) Organizational structure. Regardless of whether or not the alloy powder is added, the microstructure of the cladding layer is very similar, and it is divided into two types: a mixed structure of a granular, short rod-like distribution on a nickel-chromium-silicon solid solution and a low-melting-point nickel-based eutectic matrix near the bottom of the molten pool. It is a typical planar epitaxial growth structure; the other is the dendritic structure in the middle of the molten pool and the surface growing along the direction of the heat flow, and the entire cladding layer is a mixed structure of planar crystals and dendrites. Under the scanning electron microscope, the eutectic structure of the cladding layer is more obvious, and the fine dendrites are arranged neatly. The addition of tungsten carbide did not change the structure and no desired tungsten carbide superhard spots were observed. During the cladding cooling process, a part of tungsten forms a composite phase with chromium, boron, etc., and a small portion is solid-dissolved in the eutectic matrix. Spectral analysis between the branches and dendrites shows that the branch zone is a nickel-based solid solution and contains a certain amount of chromium, while the tungsten content is low, but the tungsten content between the dendrites is high, indicating that the tungsten carbide is at high temperature. After being melted and cooled, the tungsten carbide disappears and is distributed between the dendrites in the form of other second phases such as W3.2Cr1.8B3.