贝氏体钢生产流程中典型夹杂物变化规律

Variation law of typical inclusions in bainitic steel production process

贝氏体钢轨强度高、塑性好,具有优良的抗接触疲劳和耐磨性,被誉为“21世纪的钢轨钢”,但贝氏体钢生产工艺具有一定的特殊性,钢中的夹杂物严重影响钢轨的塑性、韧性以及抗疲劳性能。为了研究贝氏体钢中典型夹杂物的变化规律,以国内某钢厂150t转炉→双150t LF→VD脱气→280mm×380mm方坯连铸生产的贝氏体钢为研究对象,对生产全流程取样,结合氧氮分析、钢液成分分析和非金属夹杂物分析,研究典型夹杂物的来源和形成机理。研究结果表明,贝氏体钢生产过程中氧氮含量持续降低,浇铸末期钢中氧、氮质量分数分别为0.0008%和0.0040%;一次LF化渣后夹杂物为CaO-SiO_(2)-Al_(2)O_(3),主要是合金、脱氧剂和白灰带入的Ca、Al_(s)与钢中的氧或氧化物发生反应的脱氧产物;一次LF合金化后,夹杂物为CaO-SiO_(2)-Al_(2)O_(3)-MgO,夹杂物中CaO和MgO含量增加,Al_(2)O_(3)含量降低;二次LF进站夹杂物为CaO-SiO_(2)-Al_(2)O_(3)-MgO,夹杂物中SiO_(2)含量有所降低;二次LF合金化后夹杂物仍为CaO-SiO_(2)-Al_(2)O_(3)-MgO,夹杂物中Al_(2)O_(3)含量降低,MgO含量升高;VD精炼至铸坯中夹杂物主要是CaO-SiO_(2)-Al_(2)O_(3)-MgO,VD精炼后成分基本稳定;从铸坯到钢轨夹杂物发生明显转变,MgO和Al_(2)O_(3)含量升高,SiO_(2)和CaO含量降低,钢轨中出现一定比例的镁铝尖晶石夹杂物,判断为冷却过程夹杂物转变所致。

Bainitic rail has high strength,good plasticity and excellent contact fatigue and wear resistance.It is known as“rail steel in the 21 st century”.However,the production process of bainitic steel has certain particularity,and the inclusions in steel seriously affect the plasticity,toughness and fatigue resistance of rail.In order to study the variation law of typical inclusions in bainitic steel,the bainitic steel produced by a domestic steel plant with 150 t converter→double 150 t LF→VD→280 mm×380 mm bloom continuous casting was taken as the research object.The source and formation mechanism of typical inclusions were studied by sampling the whole production process,combined with oxygen and nitrogen analysis,liquid steel composition analysis and non-metallic inclusion analysis.The results show that the oxygen and nitrogen content in bainitic steel decreases continuously during the whole process,and the mass fraction of oxygen and nitrogen in steel at the end of pouring are 0.0008%and 0.0040%respectively.The inclusion after primary LF slagging is CaO-SiO_(2)-Al_(2)O_(3),which is mainly the deoxidation product of the reaction between Ca and Al_(s) brought by alloy,deoxidizer and lime and oxygen or oxide in steel.After primary LF alloying,the inclusion is CaO-SiO_(2)-Al_(2)O_(3)-MgO,the content of CaO and MgO in the inclusion increases and the content of Al_(2)O_(3) decreases.The secondary LF incoming inclusions are CaO-SiO_(2)-Al_(2)O_(3)-MgO,and the SiO_(2) content in the inclusions decreases.After secondary LF alloying,the inclusion is still CaO-SiO_(2)-Al_(2)O_(3)-MgO,the content of Al_(2)O_(3) in the inclusion decreases and the content of MgO increases.The inclusions in VD and bloom are mainly CaO-SiO_(2)-Al_(2)O_(3)-MgO,after VD refining,the composition is basically stable.There is an obvious transformation from bloom to rail inclusion,the content of MgO and Al_(2)O_(3) increases,the content of SiO_(2) and CaO decreases,and a certain proportion of magnesium aluminum spinel inclusions appear in the rail,which is judged to be caused by the transformation of inclusions during cooling.