The corrosion of hydraulic support has brought huge economic losses to coal enterprises. Using laser cladding stainless steel coating on the surface can improve its wear resistance and corrosion resistance. However, dense corrosion pits appeared on the hydraulic support coated 304 stainless steel after 25 days use in a coal mine. At present, there are few studies on the corrosion effect of this laser cladding layer under the actual mine. In this work, the oxide scales are characterized by 3D Optical Microscope (OM), Scanning Electron Microscopy (SEM) equipped with X-ray Energy Spectrometer (EDS), X-ray Photoelectron Spectrometer (XPS) and X-ray Diffraction (XRD) techniques. Based on the results, the localized corrosion mechanism is discussed. It was found that the corrosion products were mainly a mixture of (Fe,Cr)2O3 and CaCO3. The maximum pitting rate calculated from the depth data of pits. which were collected by ultra-depth of field optical microscopy, was 2.32 mm/a. The mechanism of corrosion of hydraulic support was discussed form perspectives of the under-deposit corrosion and corrosive ions (i.e. Cl- and S2)- in the environment.

Excellent resistance to steam oxidation is a key required property for heat-resistant alloys used in next-generation fossil power plants. In order to clarify the degradation mechanism of Ni-Fe-Cr alloys in high temperature steam, four kinds of Ni-Fe-Cr model alloys with various Cr content were prepared and their long-term steam oxidation were investigated at 650 °C and 700 °C. The microstructure and composition of oxide scales were characterized by SEM equipped with EDS, and the oxide phases were identified by XRD. The results showed significant dependence of temperature and Cr content in alloys on the oxidation kinetics, cross-section morphology and elemental section-distribution. For Ni-Fe-Cr alloys with low Cr contents (12∼16 wt.%), the increase of temperature made the oxide scale change from breakaway scale morphology (nodule-crater microstructure with external exfoliation) to protective scale morphology (uniform layer and internal oxidation). For Ni-Fe-Cr alloy with 18wt.% Cr, the effect of temperature was greatly reduced. The oxidation mechanism was discussed from the perspectives of selective oxidation and the effect of alloying elements.