Microstructural Formation And Evolution Mechanisms Of Nanostructural Steels Preparation By Aluminothermic Reaction

This paper mainly reviews the structural models, microstructure, excellentproperties, preparation method of nanocrystalline materials and the significance ofmicrostructure nanocrystallization in the steels. Nanostructued steels were prepared byaluminothermic reaction in the experimental part. The prepared materials consist ofpure Fe,20#,45#, T8, hypoeutectic cast iron, eutectic cast iron and hypereutectic castiron. Then the microstructure of every material is investigated and the formationmechanism of it is discussed. The results can be summarized as follows:1The pure Fe prepared by aluminothermic reaction is mainly composed ofnanocrystalline ferrite of bcc structure, a little amorphous also exist. Thenucleation way of the nanacrystalline is mainly homogeneous nucleation. Theaverage grain size of nanocrystalline prepared on copper and glass substrate isabout40.9nm and36.2nm respectively.220#and45#alloys prepared by aluminothermic reaction are both composed ofnanocrystructural ferriete and micro-region perrite of which the lamellae width isabout150nm, finer than traditional materials. With the content of C elementincreasing, the grain size of nanocrystalline ferrite decrease gradually. All materialsprepared on glass substrate are better crystalliend than that on the copper, and theirgrain size of nanocrystalline phase are all smaller than that of the copper.3T8steels prepared by aluminothermic reaction are composed of pearlite and a littlecementite.The lamellate distance is about220nm, finer than traditional materialsbut larger than45#prepared by the aluminothermic reaction. With the content of Celement increasing, lamellate width of pearlite of20#,45#and T8decreases at fitstand then increases significantly. Lamellae width of pearlite of the steel prepared onglass substrat are all a little smaller than that on the copper.4Some granular pearlites appear in the cast iron prepared by aluminothermicreaction. With the content of C element increasing, the content of granular pearlitein the hypoeutectic cast iron, eutectic cast iron and hypereutectic cast iron increasegradually, at the same time, the lamellate width of lamellate pearlite is about230nm, diameter size of granular pearlite is about200nm, they also show agradually increasing treand with the content of C element increasing.