| As the bearing parts of wagons, the bolster and the side bearer made of B+ steel are important. All of the weight of carriage and goods is transmitted to axles via them. With the development of high-speed and heavy-duty wagons, the better mechanical properties of the bolster and the side bearer are needed. The more thick wall thickness of parts, the higher bearing weight it can, but the increased weight of itself is restricting the development of the demand of high speed.B+ steel used to wagons is researched in this paper. Via analyzing the theory and the numerical simulation, the result of test indicated that: when the wall thickness below 50mm, the size of the sample is 200mm×200mm which can reduce the influence of different length-width ratio on course of foundry, in order to research the influence of the wall thickness on the filling and solidification. The samples are were prepared under industrial conditions, and the change of density, microstructure, tensile property, impact property and the hardness due to the change of wall thickness. The result of tests indicated that, the wall thickness of B+ steel array from 14mm to 50mm,(the degree of density, tensile-strength and ballistic work at the edge of parts are constant; the degree of density, tensile-strength and ballistic work at the center of parts reduce. When the wall thickness at the center of parts reach 50mm,the degree of density, tensile-strength and ballistic work is 30 percent of those at the edge of parts. Hardness at the edge of parts is invariant comparing at the center of parts. Microstructure is invariant at the edge of parts, but at the center of parts the number of the rarefaction and the small shrinkage cavity increase.Using mathematic method to analyse, the relationship of the wall thickness and the degree of density and mechanical properties were determined, and the regression curve equation were obtained. The result of numerical simulation indicated that: the wall thickness of B+ steel arraying from 14mm to 50mm, the change of the temperature field is small, the change of velocity field is obvious, from intensive turbulent state to stable stratosphere. Therefore, the floating velocity field make the solidification temperature field more even. Analyzing the result of numerical simulation by tempgrad, Niyama and the method of volume shrinkage mass, it was found that the wall thickness of B+ steel arraying from 14mm to 50mm, the area of defect reduce gradually. It is certified that the smaller size of sample, the more dispersal defect distribution.The research provides the theory basis for the design of truck, casting process and production. |
