The Process Research Of Laser Alloying With Chromium Molybdenum And Boron On 45 Steel

Chromium, molybdenum, boron and chromium-molybdenum-boron alloying layer were prepared on the surface of 45 steel using a CO2 laser equipment. The influence of laser process parameters and ingredients on the microstructure and properties of the alloyed layer was investigated. The process parameters for chromium, molybdenum and boron alloying were optimized. The results are shown as follows:(1)The optimal process parameters of laser alloying of Chromium on 45 steel are obtained when laser power, scanning speed, coating thickness, focal length of laser and overlapping rate is 5.2kw, 8mm.s-1, 0.15 mm, 330 mm and 30%, respectively. The average hardness and the thickness of the chromium alloying layer obtained by the optimum process parameters are 473 HV and 1350?m. The thickness of the heat affected zone is 120?m, and its hardness is gradient distribution from 473 HV to 201 HV. The Cr laser alloyed layer with column structure are composed of Fe-Cr, CrxFey phases.(2)The optimal process parameters of laser alloying of Molybdenum on 45 steel are obtained when laser power, scanning speed, coating thickness, focal length of laser and overlapping rate is 4.3kw, 8mm.s-1, 0.20 mm, 330 mm and 30%, respectively. The average hardness and the thickness of the molybdenum alloying layer obtained by the optimum process parameters are 723 HV and 890?m. The thickness of the heat affected zone is 120?m, and its hardness is gradient distribution from 723 HV to 203 HV. The Mo laser alloyed layer is composed of Fe2 Mo, FeMo and Mo2 C phases. The microstructure of the layer displays a transition from equiaxed at outside to columnar crystal in the inside.(3)The optimal process parameters of laser alloying of Boron on 45 steel are obtained when laser power, scanning speed, the content of KBF4, focal length of laser, overlapping rate and coating thickness is 4kw, 8mm.s-1, 3%, 320 mm, 30% and 0.15 mm, respectively. The average hardness and the thickness of the Boron alloying layer obtained by the optimum parameters are 1350 HV and 860?m. The thickness of the heat affected zone is 100?m, and its hardness is gradient distribution from 1350 HV to 230 HV. The microstructure of the Boron alloy layer is composed of Fe2 B and a small amount of ?-Fe and exists with a form of cellular crystal outside transitioning to a dendrite inside.(4)The optimal process parameters of the laser alloying of Chromium Molybdenum and Boron on 45 steel are obtained when laser power, scanning speed, the content of Cr, Mo, B, focal length of laser, overlapping rate and coating thickness is 3.7kw, 8mm.s-1, 2:1:1, 330 mm, 30% and 0.15 mm, respectively. The average hardness of the alloying layer obtained by the optimum technological parameters is 970 HV. The hardness of the heat affected zone is gradient distribution from 970 HV to 230 HV. The tenary alloyed layer with a form of irregular reticular cellular crystal and column crystal is composed of Fe2 B, FeMo, Fe-Cr, Cr2 B and Cr7BC4 phases.