X80管线钢精炼过程夹杂物形成与演变

Formation and evolution of inclusions in the refining process of X80 pipeline steel

通过工业试验取样研究了X80管线钢精炼过程夹杂物的类型、尺寸、成分等变化规律,并结合FactSage8.1软件对钙处理和钢液冷却凝固过程夹杂物的演变机理进行了热力学计算分析.试验结果表明,LF精炼结束时夹杂物主要为MgO–Al_(2)O_(3)和MgO–Al_(2)O_(3)–CaO,数量占比分别为25%、75%,其尺寸主要分布在1~5μm之间,且1~2μm和2~5μm的夹杂物比例分别为56.0%、37.3%;RH精炼中T[O]、[N]质量分数分别由LF精炼结束时的0.0022%、0.0059%降低至0.0010%、0.0035%,夹杂物数量密度由LF结束约23.07 mm^(–2)降低至7.44 mm^(–2),夹杂物去除率约67.8%;钙处理时,夹杂物主要为MgO–Al_(2)O_(3)–CaO和CaS–Al_(2)O_(3)–CaO系,夹杂物中CaS平均质量分数由RH精炼结束时的8%增加至36%,CaO平均质量分数由24%减少至12%;软吹结束时,尺寸<40μm的夹杂物中SiO_(2)占比在0~2.5%之间;尺寸>40μm的夹杂物中SiO_(2)占比在6.0%~8.0%之间,尺寸>40μm的夹杂物主要为CaO–Al_(2)O_(3)–MgO–SiO_(2),其化学成分与精炼渣化学成分基本一致,其来源为精炼渣卷入.热力学计算结果表明,当[Ca]质量分数在10.5×10^(–6)~15.8×10^(–6)时,尖晶石夹杂全部完成改性,夹杂物全部为液态钙铝酸盐;当钢液在浇铸温度下,夹杂物主要为液态的钙铝酸盐,当温度降低至1428℃时,液态夹杂物完全转化为固态,随着温度继续下降1309℃以下,夹杂物的类型基本不发生改变,整个温降过程夹杂物中CaO含量减少,CaS含量增加.

To further meet the requirements for using pipeline steel in extreme environments and to improve its safety in service,the inclusion control level in pipeline steel urgently needs improvement.In this paper,the variation laws of inclusion type,size,and composition in the refining process of X80 pipeline steel were studied through industrial trial sampling,and the evolution mechanism of inclusions during calcium treatment and steel cooling and solidification was analyzed using thermodynamic calculations with FactSage 8.1 software.The trial results showed mainly MgO-Al_(2)O_(3)and MgO-Al_(2)O_(3)-CaO inclusions after LF refining in proportions of 25%and 75%,respectively,with sizes mainly distributed between 1-5μm,and the proportion of inclusions of 1-2μm and 2-5μm were 56.0%and 37.3%,respectively.The contents of T[O]and[N]were reduced from 0.0022%and 0.0059%after LF refining to 0.0010%and 0.0035%after RH refining,respectively,and the number density of inclusions was reduced from approximately 23.07 mm^(–2)after LF to 7.44 mm^(–2),with an inclusions removal rate of approximately 67.8%.The inclusions were mainly MgO−Al_(2)O_(3)-CaO and CaS-Al_(2)O_(3)-CaO systems during calcium treatment,the average CaS content in the inclusions increased from 8%after RH refining to 36%,and the average CaO content decreased from 24%to 12%.After soft blowing,the SiO_(2)content ranged from 0 to 2.5%in the inclusions smaller than 40μm and from 6.0%to 8.0%in the inclusions larger than 40μm,and the inclusions larger than 40μm were mainly CaO-Al_(2)O_(3)-MgO-SiO_(2),whose chemical composition is essentially identical to that of the refining slag,whose source is the refining slag involved;thermodynamic calculations show that when the[Ca]content is between 10.5×10^(-6)-15.8×10^(-6),all spinel inclusions are modified,and all the inclusions are liquid calcium aluminates;when the steel is at casting temperature,the inclusions are mainly liquid calcium aluminates,and when the temperature is lowered to 1428℃,the liquid inclusions completely transform into solid.As the temperature drops below 1309℃,the type of inclusions essentially remains constant.During the entire temperature drop,the CaO content in the inclusions decreased,and the CaS content increased.