8620RH非调质钢全流程洁净度研究

Study on cleanliness of 8620RH microalloyed forging steel in production process

通过Aspex全自动扫描电镜观察"电炉→LF→VD→连铸"工艺生产8620RH非调质钢的全流程夹杂物变化情况,结合钢水中T.O、氮含量的检测结果,分析了冶炼过程中钢液洁净度的变化趋势。研究表明:8620RH非调质钢样品中氧化物夹杂的主要成分是Al_2O_3-Mg O-Ca O,以Al_2O_3为主。增硫操作之后,夹杂物中CaO含量降低,硫化物和氧硫化物含量明显升高。冶炼过程夹杂物中MgO含量逐渐升高,每个工序冶炼后期的样品中含MgO夹杂物数量均明显高于该工序初期,未检测到大尺寸的镁铝尖晶石类夹杂物。采用铝脱氧方式生产的8620RH非调质钢铸坯中平均w(T.O)=10.1×10-6,达到了很高的洁净度,氧化物夹杂数量较少,尺寸较小。铸坯和轧材中氧化物类夹杂物数量均在10个/mm^2以下。轧材中硫化物多以包裹在氧化物外部的形式存在,有利于提高产品的综合性能,但轧材中存在较大尺寸的硫化物,可以适当提高钢中的氧含量,形成更多细小弥散的氧化物核心,利于硫化物的析出,改善硫化物的形态,使产品具备更好的切削性能。

In the current study, evolution characteristics of inclusions were evaluated u- sing SEM with automatic scanning feature in 8620RH non-quenched and tempered steel samples during the ＂EAF→LF→VD→CC＂production process. Cleanliness of the steel in producion process were evaluated, combined with the detection of total oxygen and nitrogen of the steel. The results show that type of oxide was Al2O3-CaO-MgO, mainly consisted of Al2O3. After adding sulfur operation, content of CaO in inclusions de- creased, and the amount of sulfides and oxysulfides increased obviously. Content of MgO increased gradually during the production process, and number density of inclu- sions with high MgO content in the end of each production steps was all higher than that in the beginning. Few large spinel inclusions were tested in steel samples. High cleanli- ness was achieved in 8620RH microalloyed forging steel dioxidized by aluminium, and w（T. O） was 10 × 10^-6in slab. Number densities of oxides in billets and rolled products are lower than 10 per mm2. Most sulfides adhere to small oxides and grow around them. Most sulfides were adhered to oxides so that it contributed to improvement of machin- ability, but there are still some large-size sulfides in rolling samples. Proper increase on T. O content could be adopted so that sulfides could percipitate on the tiny oxides and improvement on machinability can be achieved.