Research The Optimied Composition Of Bogie With High Strength And Toughness And The Reseach For Dynamic CCT Diagram

With rapid increasing of national economy, higher requirements have beenput forward for the transportation industry in China, especially for the railwaytransportation system. To achieve high speed and heavy load, the new materialneeds to be developed for the productions of bogies with good quality.On the basis of Grade B+casting steel, the present research is focused onimproving the yield strength and the tensile strength and keeping the content ofcarbon and the toughness of casting steel. By means of theoretical analyses, inorder to reduce the heavy burden of experiments, the content of the majorenforcement element Mn is fixed at1.00wt.%, of Si fixed at0.50wt.%, of Crfixed at0.30wt.%. At the same time, to guarantee the better plastic toughness,the content of Ni, Al and the No.1rare earth is0.50wt.%,0.04wt.%and0.03wt.%, respectively. The element C is considered as the major enforcementelement because of the well-known strengthening effect and the low price. Due tothe requirements of equivalent content, the element Mo is regarded as thesecondary important enforcement element. The influences of C chemical elementand the Mo chemical element on the variations of microstructure and mechanicalproperties of steel are systematically investigated. Experimental results show thatwhen C chemical element content increases from0.21wt.%to0.27wt.%, theamount of pearlite increases. The tensile strength is increased from580.0MPa to685.9MPa and the yield strength is increased from340.6MPa to445.8MPa. Thetoughness and the plasticity are, however, decreased significantly. The tensilefracture changes from ductile fracture to brittle fracture. When Mo chemicalelement content increases from0.00wt.%to0.30wt.%, the grain size ofmicrostructure becomes finer, and the tensile strength is increased from616.4 MPa to809.8MPa and the yield strength is increased from390.8MPa to503.7MPa. The tensile fracture changes from ductile fracture to brittle fracture.In addition, by means of measuring CCT curves, the heat treatmenttemperature is determined ranging from895℃to925℃, and the coolingspeed ranging from1℃/s to2℃/s.Above all, the experimental investigations determine that with the content ofC, Si, Mn, Cr, Ni, Mo, Al and the No.1rare earth being0.25wt.%,0.50wt.%,1.00wt.%,0.30wt.%,0.50wt.%,0.10wt.%,0.04wt.%and0.03wt.%,respectively, the heat treatment temperature of the new casting steel bynormalizing temperature ranging from895℃to925℃and the cooling speedof the newly steel ranging from1℃/s to2℃/s. Under such conditions, thetensile strength is663.9MPa and yield strength418.7MPa. The elongation is22.2%. With the working temperature of-18℃, Charpy Notch of V typepresents the impact absorbing energy of31.9J. With the equivalent content ofcarbon0.58, the properties of the newly developed alloy are close to that of gradeC steel.