| The oxidation behavior of the as-received and laser melted high chrome steels at 650 and 800 °C were studied. High chrome steel consists of tempering martensite and reticular carbides. Due to the high thermal stability and the low oxidation rate of carbides, at the beginning oxidation nucleates at the matrix-carbide interfaces and propagates in the matrix, giving rise to an uneven oxide scale. The surface of the as-received steel oxidized at 800 °C appears completely covered by the oxides, but maintains the irregular morphology. However, cracking was observed on the top layer due to growth stress and thermal stress. Laser surface melting leads to the dissolution of carbides and to the uniform distribution of carbon and alloying elements in the melted layer. The melted layer consists of fine austenite dendrites and granular M23C6 carbides. A homogenous oxidation occurred on the laser melted steel surface resulting in the formation of a compact and even oxide scale. The differences in the structure and the carbide volume fraction are responsible for the different oxidation mechanisms of the as-received and laser melted steels. |
full paper (pdf, 2656 Kb)