27SiMn钢夹杂物特征及控制工艺优化

Inclusion characteristics and control process optimization of 27SiMn steel

27SiMn钢中高熔点夹杂物是引起探伤缺陷的主要原因。为了进一步控制27SiMn钢中夹杂物,对国内某钢铁企业“BOF→LF→CC”工艺流程生产的27SiMn钢进行研究。采用分阶段取样方式分别在LF进站、钙处理前、软吹后、中间包及铸坯中提取试样,探究27SiMn钢中各工序夹杂物的特征。结果表明,LF精炼过程中,夹杂物主要以MgO-Al_(2)O_(3)、硅酸盐及Al_(2)O_(3)-CaO-MgO夹杂物为主;在软吹及浇注阶段,主要以(CaS)-Al_(2)O_(3)-MgO-SiO_(2)-CaO系为主,同时钢液内存在大量CaS颗粒,表明钙处理后钢液内仍存在高熔点夹杂物。在此基础上,研究了27SiMn钢液内CaS及钙铝酸盐类夹杂物的热力学形成机理。发现钢液中w([Al])为0.022%时,钢液w([Ca])控制在0.0013%~0.0035%有利于12CaO·7Al_(2)O_(3)生成;同时,为防止在钢液内大量生成CaS,阻碍Al_(2)O_(3)夹杂物转变为12CaO·7Al_(2)O_(3),w([S])应控制在0.0015%~0.0039%。基于夹杂物特征研究和热力学计算,提出工艺优化方案,调整精炼渣碱度至3.2以上,增加渣系硫容量,同时将渣中w((Al_(2)O_(3)))由10%~11%提高至13%以上,促进炉渣流动性;减少铝块脱氧剂的加入,由130 kg/炉降至120 kg/炉;进行轻钙处理操作,硅钙线喂入量由400 m/炉减少至200 m/炉。并进行了工业优化试验,发现软吹后钢液内w([Ca])约为0.0024%,连铸阶段进一步降至0.0018%左右,w([S])控制在0.002%左右;在Al_(2)O_(3)-SiO_(2)-CaO-(8%)MgO体系中,夹杂物平均成分由1600~1800℃高熔点区进入到1400~1500℃液相区,钙处理效果显著改善,提高了钢材质量。

High melting point inclusions in 27SiMn steel are the main cause of flaw detection defects.In order to further control the inclusions in 27SiMn steel,a study was conducted on 27SiMn steel produced by the"BOF→LF→CC"process in a domestic steel company.Liquid steel were sampled at the initial stage,before calcium treatment,after soft blowing in LF refining process,in tundish and casting billet.The samples were analyzed to investigate the characteristics of inclusions in 27SiMn steel.The results show that the inclusions are mainly MgO-Al_(2)O_(3),MgO-SiO_(2) and Al_(2)O_(3)-CaO-MgO inclusions in LF refining process.In the soft-blowing and casting stage,there is existing(CaS)-Al_(2)O_(3)-MgO-SiO_(2)-CaO inclusion,while a large number of CaS particles exist in the molten steel,which indicates that there are still high melting point inclusions in 27SiMn steel after calcium treatment.On this basis,the thermodynamical formation mechanism of CaS and calcium aluminate inclusions within the 27SiMn steel liquid were investigated.It is found that w([Al])is 0.022% when w([Ca])is controlled between 0.0013% and 0.0035% in liquid steel,which is conducive to the generation of 12CaO·7Al_(2)O_(3).At the same time,in order to prevent the generation of CaS in molten steel and hinder the transformation of Al_(2)O_(3) inclusions into 12CaO·7Al_(2)O_(3),w([S])should be controlled in the range of 0.0015%-0.0039%.Based on the study of inclusion characteristics and thermodynamic calculations,the process optimization scheme was proposed.The basicity of refining slag was adjusted to above 3.2 to increase the sulfur capacity,and w((Al_(2)O_(3)))in slag was increased from 10%-11% to above 13% to promote the fluidity.The addition of aluminum deoxidizer was reduced from 130 kg to 120 kg.silica-calcium wire was decreased from 400 m to 200 m to carry out light calcium treatment.The industrial optimization test was conducted,and it was found that w([Ca])in molten steel was about 0.0024% after soft blowing,which was further reduced to about 0.0018% at the continuous casting stage,and w([S])was controlled at about 0.002%.In the Al_(2)O_(3)-SiO_(2)-CaO-(8%)MgO system,the average composition of inclusions changes from the high melting point region of 1600-1800℃ to the 1400-1500℃ in the liquid phase zone.The effect of calcium treatment is significantly improved and the quality of steel is improved.