Investigation On Behavior Of Inclusions In Heavy Rail Steel (u71mn)

The inclusions can reduce the plasticity,toughness and fatigue life of the steel,make cold-forming and. hot-forming characteristics and even some physical performance of the steel bad. It influence to the intensity, extension, toughness, cutability corrosion-resisting, surface finish, weld performance of various fields of steel. The concrete influence intensity that the performance of the inclusion to steel are decided by a series of factors, such as quantity, particle magnitude, shape and distribution and so on.The EAF-LF-CC process system in Jinan steel factory is a rail steel production line that has the special characteristics. It places strict requirement on the molten steel quality.This process affects the formation of the micro-inclusions in the molten and the size, mechanical behavior, and the dispersion of the inclusions closely affects the product quality.In this thesis, a systematic study is conducted on the process inclusions course source, formation mechanism of inclusion, develop law and so on in order to guide the production, some control measure of optimizing the course inclusion are put forward to obtain high-quality tube bloom.The conclusion:1) It is obvious for deoxidation and removing inclusions in the LF furnacce refining process, but the number of inclusions increases from LF furnace to tundish, which showed that there are second oxide and mold powder of tundish in the hot steel. So it must protect hot steel.2) From the level of inclusion, it is not too high, but the distribution of inclusions, the large number, from components, mainly for sulfide-manganese, and aluminum silicate and degeneration of (Mg, Al Spinel), manganese sulfide is more than others,MgAl2O4 relatively less, which show inclusion is the main deoxy-based product, internal inclusions is more than the inclusion of external inclusion,so it should optimize the industrial deoxy for reducing the inclusion.3) From LF furnace to billet process, the inclusion size below 10μm is main, but the ratio below 5μm is not high, that show inclusions floated more obvious, but still need to further reduce the size of the particle size.The floating of inclusions is more obvious in LF, while the floating of tundish less, therefore, it should be improved industrial technology of tundish.4) During LF Refining desulfurization process, the fluctuations of the desulfurization rate is very big, from 27.5% to 51.28%, a difference of 23.78%, respectively individual furnace beyond the [S] in the upper and lower limits, the high [S] content of the steel become useful for too many MnS inclusions, therefore, it must standardize operation in smelting works, and strictly control [S] content of steel. in LF.