Microstructure evolution and mechanical properties of multiple-layer laser cladding coating of 308L stainless steel

•Grain morphology transformations of 308L stainless steel multiple-layer are studied.•The cladding metals solidify in AF mode and consist of austenite and about 10.48% δ ferrite.•The ferrite content distributes into an increasing trend as the number of layers increase.•The distribution of hardness f...

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Veröffentlicht in:Applied surface science 2015-06, Vol.340, p.143-150
Hauptverfasser: Li, Kaibin, Li, Dong, Liu, Dongyu, Pei, Guangyu, Sun, Lei
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Sprache:eng
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Zusammenfassung:•Grain morphology transformations of 308L stainless steel multiple-layer are studied.•The cladding metals solidify in AF mode and consist of austenite and about 10.48% δ ferrite.•The ferrite content distributes into an increasing trend as the number of layers increase.•The distribution of hardness from the substrate to the coating is relatively uniform.•The cladding tensile sample shows good tensile properties, and the fracture mode is the ductile fracture. Multiple-layer laser cladding of 308L stainless steel was obtained by a fiber laser using a way of wire feeding to repair the surface scrapped or erosive parts of 316L stainless steel. The microstructure of the coating was measured by a metallographic microscope, and phase composition was determined by X-ray diffraction. The results show that good metallurgical bonding can be obtained between the 308L stainless steel coating and 316L stainless steel substrate. The coating is mainly composed of columnar dendrites, and there are also a few planar crystals and cellular dendrites distributed in the bonding zone. Meanwhile, some equiaxed grains and steering dendrites are distributed in the apex of the coating. Grains incorporate in epitaxial columnar dendrite's growth between different layers and tracks. It has been proved using XRD that the coating basically consists of austenite and a small amount of δ ferrite. The coating solidifies in FA mode according to the Creq/Nieq ratio and metallurgical analysis results. The average content of δ ferrite is about 10.48% and morphologies of the ferrite are mostly vermicular, skeletal and lathy. Due to heat treatment and different cooling rate, the δ ferrite content generally increases as the number of laser cladding layers increases. The coating and the substrate have equivalent microhardness, and softening zone does not appear in the heat affected zone. The tensile strength and elongation of the coating are 548MPa and 40%, about 86% and 74% of the substrate, respectively. Ductile fracture is proved by the emergence of obvious dimples in the fracture surface.
ISSN:0169-4332
1873-5584
DOI:10.1016/j.apsusc.2015.02.171