Effect Of Magnesium Alloying On Microstructure And Mechanical Properties Of Low Carbon Steel

In this paper,it used low carbon steel as the carrier to study different magnesium content(0%,0.0016%,0.0021%,0.0033% and 0.0064%)of low carbon steel inclusion characteristics(morphology,classification,composition,size and distribution),the effect of microstructure,mechanical properties,mechanism of inclusions in IAF induced nucleation in low carbon steel.The results show that:(1)Modification of inclusions in low carbon steel treated by magnesium alloy.After the treatment of magnesium alloy composite inclusions of low carbon steel in separate Al2O3 inclusions and Mn S inclusions were modified as circular or nearly circular spinel(mainly for Mg O-Al2O3-Si O2-Mn S compound inclusions);magnesium content was 0.0064%,the inclusion realizable for Mg O-Si O2-Mn O compound inclusion.(2)The treatment of low carbon steel with magnesium alloy could effectively refine the inclusions,and made the inclusions in steel more dispersive.The content of magnesium in steel increased,the size of inclusions decreased,the number of inclusions increased and the distribution was more uniform;when magnesium content was 0.0064%,the average particle size of inclusions was 1.12 ?m or so,the number of inclusions per unit volume reached 16.18×105 ?·mm-3,and it was more dispersed in the molten steel.(3)Magnesium alloy solidification could refine the low carbon steel,and the microstructure was finer with the increase of Mg content.The Mg-Al composite inclusions produced by the treatment of low carbon steel by magnesium alloy could induce IAF nucleation.and with the increase of Mg content,the volume of IAF structure increased.When the content of Mg in the steel reached 0.0064%,the influence of the solid solution of magnesium on the microstructure was more than that of the inclusion.Therefore,the microstructure was characterized by a large number of GB,and no IAF was found.(4)The mechanism of IAF formation induced by Al-O-Mg complex inclusions was in accordance with the minimum mismatch.In the(100)Mg O·Al2O3|(100)?Fe direction,there was a low mismatch between the Mg-Al spinel complex inclusions and the alpha phase,which could be used as the core of IAF to induce nucleation.(5)The treatment of low carbon steel with magnesium alloy could improve its strength and ductility.The yield strength and tensile strength of the low carbon steel with the Mg content of 0.0033% were higher than that of the low carbon steel with Mg content of 0%,0.0016%,0.0021% and0.0064%,and the tensile strength was about 576.26 Mpa and the yield strength was about 437.17 Mpa.(6)In five groups of magnesium content,the plastic of low carbon steel with magnesium content of 0.0064% was the best.By qualitative and quantitative analysis of tensile fracture surface,it was found that the tensile fracture of low carbon steel under different magnesium content is ductile fracture.With magnesium content decreased,tensile fracture dimple diameter decreased,dimple average density increased,magnesium content was low carbon steel 0.0064%,the fracture dimple diameter of about 3.38 ?m,the average dimple density 0.315 ?/ ?m2.