Analysis of inclusions and carbides in 102Cr17Mo bearing steel billet

102Cr17Mo steel belongs to high carbon and high chromium martensitic stainless steel. The morphology and distribution of inclusions and carbides in the steel have an important impact on its properties. The 102Cr17Mo mould billet modified by La-Ce composite rare earth in a factory,was analyzed with optical microscope,scanning electron microscope and three-dimensional etching of inclusions,Thermo-calc software. The results show that the equivalent diameter of inclusions in 102Cr17Mo slab is concentrated in 1-3 μm. The quantity density of inclusions is concentrated in 47-54 pieces/mm²,and the proportion of inclusion area is 0.025 3%-0.028 4%. The overall size of the inclusion is small and its distribution is dispersed. The difference between the quantity density and area proportion of the inclusion in different parts is small. The inclusions are mainly composed of O,Al,Ce,La and other small elements. The types of inclusions include rare earth oxide Ce-La-Al-O,rare earth oxide sulfide Ce-La-Al-O-S. No separate Al₂O₃ and MnS inclusions are found. The carbide morphology in the billet can be divided into three types, which are large granular carbide,aggregate carbide and network carbide. The size of large granular carbide is about 20 μm. The main elements are Fe,Cr,C and Mo,and the size of aggregate carbide is about 100 μm. The main elements are Fe,Cr,Mo and C,and the size of network carbide is about 80 μm. The main elements are Fe,Cr,Mo and C. From the edge to the center,the continuity of carbide increases gradually. The carbide phases in the billet are mainly bright white MC phase rich in niobium element, dark gray block M₇C₃ type carbide rich in chromium and iron, and light gray M₂₃C₆ type carbide rich in chromium and iron. In M₇C₃ carbide, the mass fractions of chromium, iron, and molybdenum elements are 62%, 28%, and 1%, respectively, and the mass ratio of Cr/Fe element is 2.2; In M₂₃C₆ carbide, the mass fractions of chromium, iron, and molybdenum are 55%, 37%, and 2%, respectively. The mass ratio of Cr/Fe element is 1.5.