摘要
The paper mainly discussed the inclusions and the purity of molten steel and continuous casting slab in tapping,argon-bubbling,LF refining,VD vacuum degassing and continuous casting tundish processes during the steel making.At the same time,the improvement measures of smelting process were indicated. Si-Al-Ba alloy and Ca-Si deoxidation eventually were adopted in 120 t converter.The amount of the tapping was about 135t.After feeding Al wire and adding premelted slag in furnace,picked up the sample after the bottom argon-bubbling which had been done for over 5 minutes.The lime,fluorite,calcium carbide and Al powders were used to produce white slag in LF.Then the alloy compositions were adjusted. Feeding Ca wire after the treatment,and took out over 5 minutes' soft converting.The VD vacuum degassing should be kept for 15 minutes bellow 1.5 torr.After that,Ca wire could be fed.Finally,casting the slab into the size of 260 mm×2 280 mm. The research showed: (1) In converter procedure,the dephosphorization effect turned out good when the ratio of dephosphorization was 88.2%.The final oxygen and nitrogen contents satisfied the demand,and the effects of the final control and bottom-blowing were good. (2) During the LF refining process,the nitrogen seldom added.It showed the excellent sealing effect and the optimization of techniques on operating which had reached the domestic leading level. (3) After the VD vacuum degassing process,the Si,Mn,P,O,N contents were almost steady.The sulphur content kept decreasing to 0.003%and the[H]content was 1.9 ppm.The effect of the vacuum degassing process was good. (4) The oxygen content was controlled at 11 ppm in the continuous casting process,and the nitrogen content had increased to 53ppm with theΔ[N]28 ppm.Therefore,in order to prevent the molten steel from reoxidization,the protection of the continuous casting should be controlled rigorously. (5) The inclusions that existed before the LF refining process were mostly MnO-Al_2O_3-SiO_3 composite inclusions,while the inclusions were mostly calcium-aluminates inclusions after feeding Ca wires to LF or VD furnace.When the Ca/Al had reached to 0.1,7 Al_2O_3 12CaO were produced.The compositions and the sizes of the inclusions in continuous casting slab had changed obviously after the Ca treatment.The sizes were all within 100μm. (6) In order to prepare for the exploitation of the high-quality clean steel,the best process for feeding Ca wire,in LF or VD,and whether it should take one-step wire-feeding way or two-step way as well as the techniques of feeding Ca wire need to be studied further.The desulphurization in LF refining process didn' t reach balance.The ratio of desulphurization could be improved if extending the LF refining time and improving the kinetic condition.
The paper mainly discussed the inclusions and the purity of molten steel and continuous casting slab in tapping,argon-bubbling,LF refining,VD vacuum degassing and continuous casting tundish processes during the steel making.At the same time,the improvement measures of smelting process were indicated. Si-Al-Ba alloy and Ca-Si deoxidation eventually were adopted in 120 t converter.The amount of the tapping was about 135t.After feeding Al wire and adding premelted slag in furnace,picked up the sample after the bottom argon-bubbling which had been done for over 5 minutes.The lime,fluorite,calcium carbide and Al powders were used to produce white slag in LF.Then the alloy compositions were adjusted. Feeding Ca wire after the treatment,and took out over 5 minutes' soft converting.The VD vacuum degassing should be kept for 15 minutes bellow 1.5 torr.After that,Ca wire could be fed.Finally,casting the slab into the size of 260 mm×2 280 mm. The research showed: (1) In converter procedure,the dephosphorization effect turned out good when the ratio of dephosphorization was 88.2%.The final oxygen and nitrogen contents satisfied the demand,and the effects of the final control and bottom-blowing were good. (2) During the LF refining process,the nitrogen seldom added.It showed the excellent sealing effect and the optimization of techniques on operating which had reached the domestic leading level. (3) After the VD vacuum degassing process,the Si,Mn,P,O,N contents were almost steady.The sulphur content kept decreasing to 0.003%and the[H]content was 1.9 ppm.The effect of the vacuum degassing process was good. (4) The oxygen content was controlled at 11 ppm in the continuous casting process,and the nitrogen content had increased to 53ppm with theΔ[N]28 ppm.Therefore,in order to prevent the molten steel from reoxidization,the protection of the continuous casting should be controlled rigorously. (5) The inclusions that existed before the LF refining process were mostly MnO-Al_2O_3-SiO_3 composite inclusions,while the inclusions were mostly calcium-aluminates inclusions after feeding Ca wires to LF or VD furnace.When the Ca/Al had reached to 0.1,7 Al_2O_3 12CaO were produced.The compositions and the sizes of the inclusions in continuous casting slab had changed obviously after the Ca treatment.The sizes were all within 100μm. (6) In order to prepare for the exploitation of the high-quality clean steel,the best process for feeding Ca wire,in LF or VD,and whether it should take one-step wire-feeding way or two-step way as well as the techniques of feeding Ca wire need to be studied further.The desulphurization in LF refining process didn' t reach balance.The ratio of desulphurization could be improved if extending the LF refining time and improving the kinetic condition.
