Papers by Author: Bin Han

Abstract: Based on the particularity of loose and broken of the surrounding rock of roadway, there will be rib spalling after excavating of roadway without support problem. Through analyzing for the specific reasons of the rib spalling, the theory of forepoling pre-stressed system and forepoling support project were put forward. The broken rock zone test in normal roadway support indicating that this technology can effectively prevent the rib spalling before and after digging, having good supporting effect and economic benefits.

Abstract: Laser surface melting has been performed on high chrome steels by a 5kW CW CO2 laser using different overlapping ratios. The microstructures of laser melted steels were analysed by SEM and the hardness profiles were determined by a Vickers hardness tester. The corrosion characteristics of laser melted steels in 3.5% NaCl solution were studied by electrochemical corrosion equipment. The melted zone of a single laser track exhibits a mixed structure of dendritic, cellular and equiaxed austenite while the overlapped melted zone is only composed of austenitic dendrites. Using a large overlapping ratio (OR) gives a more uniform hardened-depth. The microhardness with an OR of 33.3% is higher compared to 16.7% and 50%. The corrosion resistance of laser melted steel is improved arising from the dissolution of carbides, the increasing of alloying elements in the solid solution and the large amount of austenite. Among all the studied specimens the one, which is laser treated with 33.3% OR presents the better corrosion resistance.

Abstract: In order to improve surface properties, high chromium austenitic base heat-resistant cast steel was scanned with a 5kW continuous wave CO2 laser, the specimen was aged at the temperature of 600°C~900°C. The microstructure and phase composition of the specimen were analysed with optical microscopy, electronic microscope and X-ray diffractionse. The hardness was measured. The results show that as-cast structure of high chromium cast steel is coarse and non-homogeneous, and mainly consist of austenite, ledeburite and carbides. After laser surface melting, the section is divided into the melted zone consisted of fine austenite and carbides, the heat affected zone composed of austenite and eutectic carbides, and the base meta1. The melted zone is very fine structures with dendritic crystals, only at the bottom a cellular structure is observed. A continuous carbide network is located in the austenitic grain boundaries at the heat affected zone. Carbides particles distribute dispersed out, the hardness of melted zone increases 35% than the base metal after aging. The area and the hardness of various zones are related to the laser processing parameters. The hardening depth of melted zone and heat affected zone may be up to 200μm~300μm.