Study On Continuous Casting Mold Fluxes For Alloy Steel In Shigang

Because of the special compositions and solidification characteristics of alloy steel, there are a lot of difference between carbon steel casting and alloy steel casting for the choice of mold fluxes. Selecting a suitable mold fluxes is the guarantee for good quality of continuous casting strands and the smooth running of continuous casting process.Ever the surface quality problem of the strands was serious in Shijiazhuang Iron and Steel (Group) Co.Ltd.(Shi Gang), the high grinded strands and the grinding rate seriously affected the company's normal production. Therefore, this paper will research about the surface quality problem of 20CrMnTi,42CrMo and GCr15. By practical production survey of 20CrMnTi,42CrMo and GCr15 during Jan to July in 2008, we found that the main problem of strand surface quality were surface depression,micro-cracks,surface cracks and internal cracks,surface scab. In this paper we have analysed the causes of surface quality problem of above three typical steel, we also researched on the relationship between property and the compositions of the slag system CaO-SiO2-Na2O-CaF2-Al2O3-MgO-MnO-BaO. The range of the main components about experimental flux was: CaO/SiO2=0.6-1.1,CaF2=5-15%,Na2O=2-10%,MgO=0-8%,MnO=0-8%,BaO=0-12%,Al2O3=3%. We designed the mold fluxes according to the quality analysis of strand and the relationship between property and the compositions, made industrial test with the conditions of continuous casting plants, determined the range of physical and chemical properties about continuous casting mold fluxes. With the research we could make the following main conclusions:①The relationship between melting temperature, viscosity, transition temperature and the compositions of the slag system as following:1 ) The viscosity of the slag decreases with increasing in the range of CaO/SiO2=0.6～1.1, CaF2=5%～15%,Na2O=2%～10%,MgO=0～5%,MnO=0～5% and BaO=0～7%,kept invariant in the range of MgO=5%～8%,MnO=5%～8% and BaO=7%～12%;2)The melting temperature of the slag decreases with increasing in the range of CaO/SiO2=0.6～0.85, MnO=0～8%, Na2O=2%～10%, CaF2=5%～15% and BaO=0～12%, increased with increasing in the range of CaO/SiO2=0.85～1.1, MgO=0～8%;3)The transition temperature of the slag decreases with increasing in the range of CaF2=5%～12%, MnO=0～8%, MgO=0～5%, Na2O=2%～10% and BaO=0～12%, increases with increasing in the range of CaO/SiO2=0.6～1.1, CaF2=12%～15%, MgO=5～8%.②Under the existing process conditions, the properties range of mold fluxes is suitable for ShiGang alloy steel as following:1 ) The properties range of mold fluxes for 20CrMnTi steel was : Tm=1150±30℃,η1300℃=0.60±0.15Pa·s,CaO/ SiO2=0.85±0.10,fluxes consumption at 0.52~0.56Kg / T;2)The properties range of mold fluxes for 42CrMo steel was : Tm=1060±30℃,η1300℃=0.45±0.15Pa·s,CaO/ SiO2=0.7±0.10,fluxes consumption at 0.40~0.48Kg / T;3) The properties range of mold fluxes for GCr15 steel was : Tm=1040±30℃,η1300℃=0.40±0.15Pa·s,CaO/ SiO2=0.7±0.10,fluxes consumption at 0.20~0.23Kg / T.③The quality of the above alloy steel in shigang have a substantial increase by the optimization of mold fluxes and the improvement of continuous casting process,the grinding rate of 20CrMnTi steel has decreased from 84.52% to 2.99%. the grinding rate of 42CrMo steel has decreased from 34.72% to 1.53%. the grinding rate of GCr15 steel has decreased from 1.25% to 0.326%.