Organization And Performance Of High-boron Ring Roller Speed Steel Centrifugal Casting

In order to reduce the production costs of high speed steel roll and the content of expensive alloy elements, the new kind of wear-resistant roller material high boron high speed steel (HBHSS) was designed in this paper. Through means of Optical microscopy (OM), Scanning electron microscopy (SEM), X-ray diffraction (XRD), etc, the microstructure and properties of HBHSS made by sand casting, centrifugal casting and under different cooling speed of centrifugal casting in as-cast and heat-treated were System researched. Nodular cast iron and Semi steel were selected as the inner material of HBHSS composite roll collar respectively, Centrifugal composite technology was determined and microstructure properties were studied in Compound interface. Which provide the industry production of HBHSS compound rolls with theory and experimental basis.The results show that as-cast microstructure of HBHSS roll ring consists of dendritic matrix and different forms of borocarbides, which include M2(BC),(W, Mo)2(BC), M3(BC), M7(BC)3, M23(BC)6, the network and fishbone of eutectic borocarbides, strip and bulk of secondary borocarbides are distributed along the grain boundaries. The matrix of HBHSS made by sand casting is made up of Pearlite, martensite and a small amount of residual austenite. Under the condition of centrifugal casting and air cooling process, the matrix consists of martensite and residual austensite, the size of borocarbides clusters and matrix grain size decreases. There is nothing to do with two kind of casting process for the type and form of borocarbides. After heat treatment, the type and form of borocarbides do not change, part of borocarbides are dissolved in the matrix, leading to the phenomenon of necking and broken network appear; the matrix translate into tempering sorbite which has excellent comprehensive performance, there are precipitation of tiny secondary precipitates, the mechanical properties increased, however, HBHSS made by centrifugal casting is rapidly progressed.Under condition of centrifugal casting process, there is not effect on the type and form of borocarbides by changing cooling rate of HBHSS. Under rapid cooling, the matrix convert to martensite, microstructure is refined, the number of borocarbides is reduced. When sand mold use air cooling, segregation of alloy elements is founded in the radial direction of roll collar. However, when metal mold use air and water cooling, there is almost no segregation of alloy elements. After HBHSS made by different casting process were heated, whose mechanical properties progress, but which made under rapid cooling rate has more broken hard phase, and acquire even bigger increase.The interval to35seconds and different revolving speed of centrifugal compound casting process is determined, and metallurgical bonding between HBHSS and Nodular cast iron and Semi steel is realized. Alloy elements spread in the compounded interface, which has an impact on microstructure. For that alloy elements has greater influence of combating nodulizing, there are a large number of the eutectic carbide in nodular cast iron near compounded interface, lead to reduce their adhesive strength; but it has no greater effect on microstructure of semi steel near compounded interface, there are few ledeburite organization, and interface between HBHSS and Semi steel is very fine, the shear strength is good。 So selecting semi steel as inner material of HBHSS compound roll collar, it can get the good quality and the small change of interface, which is useful for improving adhesive strength.