Study On Isothermal Pearlite Transformation Of Si-Mn Cast Steel Under High Magnetic Field

A lot of studies have shown that with exerted magnetic field in the process of Fe-based alloy's phase transformation will enable alloy microstructure change, through controlling magnetic field strength and processing temperature and holding time, you can achieve the purpose of speeding up the transformation or improve alloy mechanical properties. This paper let 50Si2Mn3 steel in the condition of isothermal pearlitic transformation under strong magnetic field, mainly has studied on the influence of magnetic field on both the volume fraction and the morphology of transformed pearlite; and carried out spheroidal annealing of 50Si2Mn3 steel under strong magnetic field and studied the influence of high magnetic field on the cementite spheroidizing process and granular pearlite morphology.(1) Strong magnetic field has accelerated the nucleation and growth process of pearlite, promoted the pearlitic transformation obviously, and with the increase of magnetic field and holding time, pearlite volume fraction increases. Strong magnetic field increases the size of pearlite colonies while decreases the interlamellar spacing. Effect of high magnetic field on pearlite transformation in high temperature even more significant, at lower temperatures,â–³T of austenite has greater impact on pearlite transformation.In this experimental condition, the preceding phase of eutectoid transformatio-n is ferrite.Cementite formed at both formed ferrite's sides and its internal posi-tion. Primary cementite in pearlitic grains has the shape of short rod or granul-ar, with the grain growing up, cementite becomes continuous and two-phase parallel arrangement.(2) High magnetic field improve Fe atom transition probability in the proc-ess of pearlitic transformation, magnetization difference between new and old p -hase in provide additional magnetic driving forceâ–³G_M~H in the process of pearli-te transformation,â–³G_~HM is proportional to magnetic field.â–³G_M~H reduced the pea-rlitic transformation nucleation barrier and the critical nucleus radius, increased pearlite nucleation rate and grain growth rate, so the incubation period of the isothermal transformation decreased, and the temperature when transformation ta-ke place elevated, C curve of transformation came to left compared to that with non-magnetic field.(3) When the spheroidal annealing under high magnetic field, interface energy between ferritie and cementite rised, volume changes caused by magnetostrictive resulted in the deformation energy increase during the process of pearlite grain growth, which makes the granular pearlite, with smaller interfacial area, has the lowest interface and deformation energy, easily formed.At relatively high temperatures, the effect of isothermal annealing of cementite spheroidization is obvious, and with the appearance of greater granular pearlite particles and larger particle spacing. High magnetic fields reduced the rate of both carbide particle migration and salvation, and increased the nucleation rate of pearlite, lowered the critical nucleus radius, thus more small size nucleus stability became stable and preserved when pearlite growing up, causing cementite particle size and particle space reduced.