The Oxide Metallurgy Behaviour In Medium Carbon Steel And The Effect Of Pulsed Magnetic Field

In the twenty-first century, the giant and high-parameter development of the mechanical engineering structure put forward higher requirements on the strength and toughness of steel materials. Studies have shown that refining grain structure is the most effective way to make steel materials meet this requirement. Currently the most promising two grain refinement technology is the pulse magnetic field treatment technology and oxide metallurgy technology. Pulsed magnetic field treatment technology and oxide metallurgy technology have made great progress in refinement of grain structure, during liquid phase transformation and solid phase transformation respectively. Based on deep understanding the theoretical basis of grain refinement by oxide metallurgy, it is of great theoretical significance and great engineering application value to double refinement by combining the pulsed magnetic field treatment technology and the oxide metallurgy technology.In this paper, the metallurgical behavior in 45 steel and the effect of pulsed magnetic field were studied by means of thermodynamics calculation, high-temperature laser con-focal microscopy, transmission and scanning electron microscopy, electron diffraction technique. At the same time, the effect of pulsed magnetic field on the microstructure evolution during solidification was studied by computer simulation. The main results are as follows:(1) H2O3 becomes more difficult to precipitate with the decrease of oxygen content; Al can inhibit the precipitation of Ti2O3, but little effect of Mn; in 45 steel, inclusions inducing intra-granular ferrite are most complex oxide, with the refractory oxide as the core and with the MnS and Ti/VN/C ambient precipitation, because of the lower mismath with oxide and lower precipitation temperature; there are large number of dislocations in complex inclusions, and these dislocations are expand into ferrites under mismatch stress.(2) PMF is propitious to the ascending of inclusions, which leads to the collision growth and the decrease of shape factor of inclusions; the exerting of PMF can restrains the effect of temperature field and flow field on inclusions resulting in the decrease of migration rate of inclusions in liquid region, which lead to the uniform distribution of inclusion in solid phase region; When the PMF is applied to the molten metal, a bigger force pointing to the advancing solidification front was exerted on inclusions, which forces inclusions to drift more easily to the advancing solidification front, resulting in a more uniform distribution of particles throughout the final solidification structure and the dual refining of grains.(3) In the range of pulse magnetic field parameters, the increases of pulse magnetic field intensity or prolonging of the working time can make the grain size decrease; when the cooling rate is 100℃/min, the voltage is 100v, and the period is 1.5s, the grain size of 45 steel can be most effectively refined, reduced by increasing the pulsed magnetic field intensity or prolonging the working time(4) In the CA-FE simulation, the pulsed magnetic field after equivalent treatment can change the crystal area distribution during solidification process, which is beneficial to the increase of the proportion of equiaxed grains and the decrease of grain size.