高速铁路车轮钢中大尺寸CaO-Al_(2)O_(3)-SiO_(2)类夹杂物的形成机理

Formation mechanism of large-size CaO-Al_(2)O_(3)-SiO_(2) inclusion in high-speed railway wheel steel

为了研究高速铁路车轮钢中大尺寸CaO-Al_(2)O_(3)-SiO_(2)类夹杂物的形成机理,利用扫描电镜(SEM)和能谱分析仪(EDS)对夹杂物的特征进行分析,并通过FactSage热力学软件对夹杂物的形成过程进行计算。研究表明,车轮钢连铸坯中的夹杂物为CaO-Al_(2)O_(3)-SiO_(2)类,可分为2种类型,第1种是在钢液降温和凝固过程中形成的小尺寸固态和半固态夹杂物,第2种是来源于精炼过程中的大尺寸液态夹杂物。在液态夹杂物中,尺寸大于10μm夹杂物所占比例高达43%,可追溯到精炼过程中的钙处理阶段。钢液经过钙处理后会反应形成液态的CaO-Al_(2)O_(3)-SiO_(2)类夹杂物,这类夹杂物由于与钢液的接触角较小,只有40°左右,不易从钢液中去除,最终会遗传到连铸坯中。热力学计算结果表明,仅控制Al含量无法抑制液态CaO-Al_(2)O_(3)-SiO_(2)类夹杂物的形成,还需要控制合适的Ca含量才能避免此类夹杂物的出现。在钢液的钙处理阶段,Al质量分数为0.013%的条件下,当将Ca质量分数控制在0.0007%时,能够形成液相比例为20%的夹杂物,这种夹杂物既不会影响钢液的浇注,又易于从钢液中去除。而如此精确的Ca含量需要精准的钙处理工艺以及合理的Al含量和精炼渣成分才能得到。该研究结果为车轮钢中大尺寸夹杂物的精确控制提供一定的指导。

To investigate the formation mechanism of large-size CaO-Al_(2)O_(3)-SiO_(2)inclusions in high-speed railway wheel steel,the characteristics of inclusions were analyzed by scanning electron microscopy(SEM)and energy dis-persive spectrometer(EDS).Additionally,the formation process was calculated using FactSage thermodynamic software.The results reveal that the inclusions in the continuous casting billet of wheel steel are mainly CaO-Al_(2)O_(3)-SiO_(2),categorized into two different types.The first type is the small-size solid and semi-solid inclusion formed dur-ing the cooling and solidification process of liquid steel.The second type is the large-size liquid inclusion originating from the refining process.Notably,among these liquid inclusions,up to 43%exceed 10μm in size and can be traced back to the calcium treatment stage during the refining process.Following calcium treatment,the liquid steel under-goes a reaction leading to the formation of liquid CaO-Al_(2)O_(3)-SiO_(2)inclusions.Due to their low contact angle with the liquid steel,only about 40°,these inclusions are difficult to remove and consequently persist in continuous casting billet.The thermodynamic calculation results reveal that only controlling Al content is insufficient in inhibiting the formation of liquid CaO-Al_(2)O_(3)-SiO_(2),inclusions.It is necessary to control the appropriate Ca content to avoid the ap-pearance of such inclusions.During the calcium treatment stage of liquid steel,under the condition of Al mass frac-tion of 0.013%,when the Ca mass fraction is maintained at 0.0007%,the inclusions with a liquid phase ratio of 2o%can be formed.These inclusions do not affect the continuous casting of liquid steel and can be easily removed.Achieving such accurate Ca content necessitates precise calcium treatment,as well as appropriate Al content and re-fining slag composition.The research results provide some guidance for the precise control of large-size inclusions in wheel steel.