Characterization of microstructure, hardness, chemical composition and crystal structure of layers on steel surface

Steel and alloys are used as structural material for nuclear reactor components and supporting equipments of hot cells. During the operation of nuclear reactors or hot cell facilities, structural materials suffer from tensile, compressive, and frictional stresses in high radiation environments and thus reduce the life time of the components. One solution for this issue is surface coating of steel with materials having high hardness, corrosion and wear resistance. The aim of this research is to obtain the characteristics of microstructure, thickness, hardness, chemical composition and crystal structure of layers on steel surface. The method used was observation with optical microscope for microstructure, vickers microhardness tester for hardness, spark spectrometry for chemical composition and X-ray diffractometry for crystal structure. The results shows that the base metal microstructure consists of fine equi axial grains with ferrite and pearlite phases, where the metal-layer interface is clearly visible, and the compact and homogeneous layer has an average thickness of 624.071 μm. The hardness of the layer is 943 VHN. From the chemical composition it is identified that the base metal is S45C carbon steel, and the surface layer is a stable compound of chromium oxide (Cr₂O₃) with hexagonal crystal structure. (author)