Sulfur Content On Precipitation And Mechanical Properties Of High Speed Steel Wheels Of The Second Phase

High-speed wheel is one of the most important parts in the high-speed railway transportation, but China’s high-speed railway wheels basically rely on imports, at present. With the rapid development of high-speed railway, to realize localization of high-speed wheel has a great significance, but the poor toughness is the largest difficult to wheels localization. So, how to improve the toughness level of the wheel steels for the operation redundant safety allowance improvement is an important research subject in key materials localization of high-speed railway in our country. A serial of analysis and testing methods, such as Thermo-Calc thermodynamic calculation, mechanical testing, scanning electron microscopy, energy spectrum analysis and model theoretical calculations, et al, have been employed in present paper. The effect of sulfur content on second phase precipitation and mechanical properties of high speed wheel steels has been studied. The effect of re-dissolution and precipitation of sulfide on second phase in wheel steels has been researched also, for considering the high-speed wheel steels need to experience the reheating process in the industrial production. The experimental results are listed as follows:With the increasing of sulfur contents, strength and hardness of the wheel steels basically kept the same, but impact toughness and fracture toughness increased firstly and then decreased, and got the maximum value when the sulfur content was0.011%.The effect of sulfur contents on the microstructure and pearlite colony size of the wheel steels was not significant, when the amount increased from0.002%to0.014%. But with the increasing of sulfur contents, the amount of single Al2O3phases in wheel steels was decreased, while the amount of single MnS phases and MnS+Al2O3complex phases was increased. The amount of MnS+Al2O3complex phases didn’t increase any more, when the sulfur content was up to0.011%. However, when the sulfur content was as high as0.014%, the amount of MnS+Al2O3complex phases was not significantly increased, but the amount of MnS phases was increased. Increasing of sulfur contents could promote the covering ability of MnS phase to Al2O3phases effectively, by transforming hard Al2O3phases into ductile MnS+Al2O3complex phases, and reduced the mosaic stress between Al2O3phases and the matrix, which was the main reason to improve the toughness, In addition, too large content of sulfur was harm to the toughness of steels, for the excessive amount of MnS was got.The re-dissolution of MnS was affected by the high temperature hot working process, which would change the type, morphology and size of the second phases in wheel steels. During the heat treatment at1300℃, the destruction of the covered oxide phase by sulfide phase was largely in low sulfur wheel steels for the re-dissolution of MnS, but the destruction of the covered effect was not significantly in high sulfur wheel steels. However the covered effect of Al2O3by MnS was partly reduced in high sulfur wheel steels, when the temperature was up to1350℃. So, the hot working temperature should tried to low (below1300℃), in order to reduce the influence of MnS re-dissolusion on the covered effect of Al2O3by MnS in the sulfur contained wheel steels.