超低氧特殊钢中非金属夹杂物研究

摘要/Abstract

摘要： 针对超低氧含量特殊钢中大型非金属夹杂物问题开展了相关工业试验和实验室研究，研究结果表明：1）当钢液w(T.O)低于(13～15)×10-6后，通过LF精炼进一步降低钢液总氧和夹杂物含量变得困难。而RH真空精炼在钢液超低氧含量条件下则具有非常强的进一步降氧和去除夹杂物的能力，将RH精炼时间延长至33 min左右，钢液w(T.O)降至4.7×10-6，尺寸1.5 m以上夹杂物数量减少至1.77 个/mm2。2）超低氧特殊钢中夹杂物在钢二次精炼过程会经历“Al2O3→MgO-Al2O3→CaO-MgO-Al2O3→CaO-Al2O3”转变，其中Al2O3向MgO-Al2O3系夹杂物转变是由于钢液[Mg]与Al2O3夹杂物的反应，而[Mg]主要来源于[Al]还原钢包包衬MgO的反应。3）在w(T.O)=5.9×10-6的特殊钢连铸圆坯试样中检测到尺寸100～330 m的大型簇群状CaO-MgO-Al2O3系夹杂物，构成簇群的微小颗粒与钢液中微小夹杂物类似，表明是在连铸过程由钢液中微小夹杂物聚合而成。4）经过RH精炼，钢中夹杂物绝大多数已转变为液态CaO-Al2O3系夹杂物，而连铸过程发生的二次氧化，会将钢中夹杂物转变为高熔点的CaO-Al2O3系、MgO-Al2O3系或CaO-MgO-Al2O3系固态夹杂物，固态夹杂物更易聚合为大型夹杂物，因此在超低氧特殊钢生产中必须非常严格地控制二次氧化。

关键词: 特殊钢, 氧含量, 非金属夹杂物, 炉外精炼, 二次氧化, 连铸

Abstract: Systematic investigations were made on characteristics of the non-metallic inclusions in secondary refining and continuous casting of ultra-low oxygen special steel and following results were obtained: 1) It was hard to further lower the T.O content and eliminate the inclusions in LF refining when the steel T.O mass fraction was lowered to (13－15)×10-6. RH degassing had much stronger ability to eliminate the inclusions and lower the T.O to ultra-low content level. By elongating the RH degassing time to 33 minutes in the experiments, the T.O mass fraction and amount of inclusions larger than 1.5 m were decreased to 4.7×10-6 and 1.77 N/mm2 respectively. 2) In the secondary refining, the inclusions evolved from Al2O3 to MgO-Al2O3, CaO-MgO-Al2O3 and CaO-Al2O3 system inclusions progressively, in which the evolution of Al2O3 to MgO-Al2O3 inclusions was mainly due to the reaction [Mg]+ n/3Al2O3=MgO(n－1)/3Al2O3+2/3[Al] and the dissolved [Mg] in liquid steel was proved in the experiment mainly from the ladle refractories owing to the reaction 2[Al]+3(MgO)lining= 3[Mg]+Al2O3. 3) Large-sized inclusions of 100－330 m were found in specimens of cast bloom of the steel which contained 5.9×10-6 T.O. Most of the larger-sized inclusions above 100 m were CaO-MgO-Al2O3 clusters constituted by smaller particles which had very similar chemical compositions to the small inclusions found in liquid steel samples, indicating that the large-sized CaO-MgO-Al2O3 cluster inclusions in the bloom were formed due to the aggregation of the small inclusions in continuous casting. 4) Most of the inclusions had been transferred to liquid inclusions of CaO-Al2O3 system after RH degassing in the experiment. However, owing to reoxidation in continuous casting, the inclusions were changed to solid inclusions of CaO-Al2O3, MgO-Al2O3 or CaO-MgO-Al2O3 system, which were easier to aggregate to larger inclusions. Hence, reoxidation must be very strictly controlled in production of ultra-low oxygen special steels.

Key words: special steel, oxygen content, non-metallic inclusion, secondary refining, reoxidation, continuous casting

王新华1，姜敏1，于会香1，孙维2，龚志祥2. 超低氧特殊钢中非金属夹杂物研究[J]. 炼钢, 2015, 31(6): 1-.

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超低氧特殊钢中非金属夹杂物研究

Investigation on non-metallic inclusions in ultra-low oxygen special steels

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