摘要
研究了中高碳钢中复合延性夹杂物形成的热力学条件及其热稳定性.通过Thermo-Calc热力学计算及夹杂物显微观察等方法,分析了S含量及Ca处理对复合延性夹杂物形成及数量的影响,并利用高温淬火实验研究了复合延性夹杂物的热稳定性.计算及实验结果表明:在0.001%—0.01%S含量范围内,不进行Ca处理时,随着S含量升高,复合延性夹杂物的数量增多,但氧化物被包裹的比例不超过90%;Ca处理能大幅度提高氧化物被包裹的比例,使含0.006%S的钢中氧化物接近100%被包裹;S含量提高及Ca处理促进复合延性夹杂物出现的原因是将硫化物的析出温度提高到了基体凝固点以上;基体热履历对复合夹杂物的稳定性有重要影响,即过高的钢坯加热温度使硫化物从氧化物上部分或完全脱离;在Ca处理同时,保持S含量在0.006%以上才能抑制硫化物完全脱离,以保证复合延性夹杂物的热稳定性.
Formation of a special kind of complex ductile inclusions （CDI）, which were character as oxides covered by sulphides, was investigated in a medium-high carbon steel. It was believed that fatigue and toughness properties of carbon steels were benefited from CDI formation, for oxides were separated from steel matrix. By means of thermodynamic calculation and inclusion microscopy in medium-high carbon steels with different S content and with Ca-treated, CDI in 0.55C steels has been researched. And thermal-stability of the CDI was researched by high temperature quenching. The results show that the frequency of CDI formation increase with S content changes from 0.001% to 0.01%. However, the fraction of covered oxides is no more than 90% without Ca-treated and can be promoted to about 100% in 0.006% S steel after Ca-treated. The reason of improved CDI formation by increasing S content and Ca-treated is that sulphides precipitation temperature could be promoted to higher than solid line of matrix, which is clearly showed by thermodynamic calculation. Furthermore, thermo-stability of CDI is affected heavily by heating history of matrix steel. Sulphide will dissolute from oxide when heat steel casting to an improper high temperature. Fortunately, the dissolution process could be stunted with redundant S content. It shows that thermo-stability of CDI could be received in Ca-treated steels with more than 0.006%S.
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2012年第11期1321-1328,共8页
Acta Metallurgica Sinica
基金
国家铁道部重大课题项目2009J015和2009J016资助~~
关键词
中高碳钢
复合延性夹杂物
S含量
Ca处理
热力学计算
medium-high carbon steel, complex ductile inclusion, S content, Ca-treated, thermodynamic calculation
