Effect of molybdenum on oxide scale of martensitic stainless steel 40Cr13Mo after full hydrogen batch annealing
The oxide scale samples of full hydrogen batch annealing steel coil of 40Cr13Mo and 40Cr13 pro-duced by the same process were analyzed by scanning electron microscopy(SEM),X-ray energy dispersion spectrum(EDS)and X-ray diffraction(XRD).The results showed that the oxide scale of stainless steel 40Cr13Mo was dense with low peeling degree due to the addition of Mo.Only few small defects were ob-served inside.There was pressure stress in some parts and the strength was slightly higher than that of ox-ide scale.The bonding regions with matrix were colloidal,and there were"small wedge prominences"of 2FeO·SiO2(fayalite)with pinning depth of 0.81 μm.The oxide scale thickness was small but the range was large,and the bonding surface with matrix was uneven.The energy distribution trend of Cr was con-sistent with O in EDS surface scanning.The high-level regions accounted for above 90％,which were dis-tributed in middle and lining of oxide scale.The middle-level regions of 10％were distributed in periphery of oxide scale,and there were no low-level regions.In the bonding regions with matrix,Si showed contin-uous middle-level stripes with width of 3 μm,and there were 3 μm high-level spots in stripes.The reduc-tion process of oxide scale with hydrogen lagged behind seriously.The phases were mainly FeCr2O4 and FeO.Their contentsaccounted for 90.2％(mass fraction,the same above),and the contents of Fe,Cr and Cr0.7Fe0.3 were only 9.6％.
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