Effect Of Trace Alloying Elements Ti、Zr And Rare Earth On Inclusions In Steel

Oxides metallurgy is defined as a new technology for refining grain by use dispersion of fine nonmetallic inclusions as intragranular ferrite nucleated sites. In the investigated oxides of Ti、Al、Zr and RE, Ti and Zr oxides could promote the formation of acicular ferrite, which can refine micro structure and improve the toughness and strength. Presently Oxides metallurgy is mainly applied in improvement of the toughness in the welding expansion zone of the low carbon steel plate and the toughness of hot forged steel. There is few research in the low alloy high-strength steel and on process conditions of intragranular ferrite formation.The thermal simulation of deoxidizing process was carried out to investigate the effects of alloy elements Ti, Zr and rare earth on the size, morphology and distribution of inclusions in steel, dispersion capacity of sulfide, and microstructure of steel. The experimental results are as following.Alloy elements Zr and Ti have effects to control of the shape and size of MnS inclusion. Complex inclusion formed from the Zr and Ti deoxidation product and MnS are spherical, and the diameter of most inclusions is less than1.5μm. TiOx-Al2O3-MnS composite inclusions are formed from titanium oxide, alumina and MnS, and some of inclusions are ones which core composited of TiO2and MnS is surrounded by MnS inclusion. Add the appropriate amount of zirconium into the molten steel, ZrO2-SiO2-Al2O3-MnS, ZrO2-SiO2-MnS composite inclusions are got, which have smaller size and larger amount. Most of inclusions are ZrO2-TiO2-SiO2-Al2O3-MnS, as alloy Ti and Zr are added into molten steel. Lower sulphur content makes inclusions smaller and more.Alloy elements Ce and La also have effects to control of the shape and size of MnS inclusion. The inclusions formed from the rare earth deoxidation product are spherical, and have bigger size. Inclusions which are smaller than5μm in diameter are not found. Lower sulphur content makes inclusions smaller and more. Most of inclusions are composited by sulfide, oxysulfide of cerium, SiO2, Al2O3and MnS, as alloy Ce is added into molten steel. Most of inclusions are composited by lanthanum oxide, SiO2, Al2O3and MnS, as alloy La is added into molten steel.