304系不锈钢冶金过程硬质夹杂物形成机理分析

Analysis of formation mechanism of hard inclusions during metallurgical process of 304 stainless steel

304不锈钢由于具有优异的耐蚀性、加工性能被广泛应用,而钢中硬质夹杂物对冷板表面质量影响较大。为了明晰304不锈钢中硬质夹杂物的形成机理,通过工业生产取样,利用自动扫描电镜ASPEX及统计方法,研究了304不锈钢冶炼过程中全氧含量、各类夹杂物的变化规律。研究结果表明,从AOD出钢到铸坯过程中,随着底吹搅拌的进行,钢中T[O]含量不断降低,T[O]质量分数由0.0088%降低至0.0025%。AOD出钢和LF出站夹杂物主要类型为硅酸盐,并含由少量复合型硅酸盐和镁铝尖晶石夹杂物,LF出站至铸坯,夹杂物的成分发生了部分转变,夹杂物中SiO_(2)含量减少,Al_(2)O_(3)含量升高。从AOD出钢至中间包,钢液中硬质夹杂物镁铝尖晶石和Al_(2)O_(3)很少,但从中间包到铸坯其比例显著增加,镁铝尖晶石夹杂物的比例增加了28%,钢-渣反应脱氧产物中的复合型硅酸盐夹杂物的比例也明显增加,而脱氧剂脱氧产物SiO_(2)和钢-渣反应脱氧产物中SiO_(2)-Al_(2)O_(3)的比例显著降低。铸坯中尺寸不大于10μm的夹杂物所占比例较大的分别为复合型硅酸盐、镁铝尖晶石和SiO_(2)夹杂物。利用热力学软件计算了不同组分的CaO-SiO_(2)-Al_(2)O_(3)-MgO熔体随温度降低的相变行为,熔体在温度降低过程中会析出镁铝尖晶石高熔点相,且随着熔体中MgO和Al_(2)O_(3)含量的增加,镁铝尖晶石析出的温度显著升高,更易析出镁铝尖晶石。硬质夹杂物主要是由钢-渣脱氧产物硅铝酸盐和复合型硅酸盐等在连铸凝固过程中随着温度降低凝固析出形成。

304 stainless steel is widely used due to the excellent corrosion resistance and processing performance,while the hard inclusions in the steel have a great influence on the surface quality of the cold plate.The variation law of the size and quantity of various inclusions in the smelting process of 304 stainless steel was investigated in order to clarify the formation mechanism of hard inclusions in 304 stainless steel,through sampling in industrial production and using automatic scanning electron microscope ASPEX and statistical methods.The results show that the total oxygen content of steel casting decreases continuously with the bottom blowing and stirring,and the mass percent of T[O]decreases from 0.0088%to 0.0025%in the process from AOD steel production to casting.The main types inclusions at the end of AOD and LF are silicate,and contain a small amount of compound silicate and a small amount of magnesium aluminum spinel inclusions.From the end of LF to slab,The composition of the inclusions has undergone a partial transformation,the content of SiO_(2)in the inclusions decreases,and the content of Al_(2)O_(3)increases.From AOD to tundish,the hard inclusions of magnesium-aluminum spinel and Al_(2)O_(3)in molten steel are very few,while the proportion increases significantly from tundish to slab,the ratio of magnesium-aluminum spinel increases by 28%,and the percentage of compound silicate inclusions in the deoxidation products of steel-slag reaction also increases significantly.However,the proportion of SiO_(2)-Al_(2)O_(3)in the deoxidized product of deoxidizer and the deoxidized product of steel-slag reaction decreased significantly.The largest proportions are composite silicate,magnesium-aluminum spinel and SiO_(2)inclusions among the types of inclusions with a size of≥10μm in the slab.The phase transition behavior of CaO-SiO_(2)-Al_(2)O_(3)-MgO melts with different compositions was calculated by thermodynamic software.The melt will precipitate a high melting point phase of MgO-Al_(2)O_(3)when the temperature decreases,and the precipitation temperature of magnesia-aluminum spinel increased significantly and the magnesia-aluminum spinel phase was more easily precipitated with increase of the content of MgO and Al_(2)O_(3)in the melt.The hard inclusions are mainly formed by the deoxidation products silicaluminate and composite silicate during the solidification process of continuous casting with the decreasing of temperature.