27SiMn钢非金属夹杂物生成及演变规律

Formation and evolution of nonmetallic inclusions in 27SiMn steel

为研究27SiMn钢中非金属夹杂物的生成及演变规律,对某钢厂生产现状进行系统分析。通过工业试验探究“LF进站→钙处理前→软吹后→中间包→铸坯”各阶段夹杂物演变行为,并针对27SiMn钢钙处理现状,应用热力学计算了钙处理钢液中的Al-Ca平衡反应。结果表明,钙处理前夹杂物以CaO-MgO-Al_(2)O_(3)三元系夹杂物为主,Al_(2)O_(3)质量分数约为67%;软吹后,在CaO-MgO-Al_(2)O_(3)系三元相图中,Al_(2)O_(3)质量分数减少了约35%,夹杂物成分平均向CaO质量分数高的一侧移动。在CaS-CaO-Al_(2)O_(3)系三元相图中,由于夹杂物成分内含有较高的CaS质量分数,约为21%,夹杂物成分也未进入液相区域;铸坯工序,夹杂物多数转变为球状CaO-MgO-Al_(2)O_(3)-SiO_(2)复合夹杂,且观察到大量CaS夹杂物。经热力学分析,在1873 K下,钢中w([Al])=0.022%时,w([Ca])控制在0.0013%~0.0035%之间,处在利于生成12CaO·7Al_(2)O_(3)区域,可提高对夹杂物液态改性效果;同时,为防止钢液内纯CaS夹杂物析出,w([S])应控制在0.0048%以下。

In order to study the formation and evolution of non-metallic inclusions in 27SiMn steel,the production status of a steel plant was systematically analyzed.The evolution behavior of inclusions in each stage of“LF inlet→before calcium treatment→after soft blowing→tundish→slab”was explored through industrial experiments.According to the current situation of calcium treatment of 27SiMn steel,the Al-Ca equilibrium reaction in the molten steel treated with calcium was calculated by thermodynamics.The results show that the inclusions before calcium treatment are mainly CaO-MgO-Al_(2)O_(3)ternary inclusions,and the mass fraction of Al_(2)O_(3)is about 67%.After soft blowing,in the ternary phase diagram of CaO-MgO-Al_(2)O_(3)system,the mass fraction of Al_(2)O_(3)was reduced by about 35%,and the inclusions moved to the side with high CaO mass fraction on average.In the ternary phase diagram of CaS-CaO-Al_(2)O_(3)system,the inclusion composition does not enter the liquid phase region because of the high CaS mass fraction in the inclusion composition,which is about 21%.In the casting process,most of the inclusions were transformed into spherical CaO-MgO-Al_(2)O_(3)-SiO_(2)composite inclusions,and a large number of CaS inclusions were observed.Through thermodynamic analysis,at 1873 K,when w([Al])=0.022%in steel,w([Ca])is controlled between 0.0013%and 0.0035%,which is in the region conducive to the formation of 12CaO·7Al_(2)O_(3),which can improve the liquid modification effect of inclusions.At the same time,in order to prevent the precipitation of pure CaS inclusions in molten steel,w([S])should be controlled below 0.0048%.