不变形大尺寸氧化物夹杂是造成弹簧疲劳失效的主要原因,可通过获得具有良好变形性能的低熔点塑性夹杂物,减少轧制后氧化物夹杂的尺寸,以减轻夹杂物的不利影响。为了研究工业化生产的硅脱氧弹簧钢中氧化物夹杂在轧制过程中的演变行为,采用SEM+EDS分析连铸坯、中间坯到成品线材各阶段中氧化物夹杂的形貌、成分、尺寸和密度变化。结果表明,连铸坯中主要为SiO2-Al2O3和SiO2-Al2O3-CaO两类呈球状的夹杂物,基本处于低熔点区,中间坯中SiO2-Al2O3和SiO2-Al2O3-CaO类夹杂物呈长条状,同时发现了蝌蚪状的SiO2类夹杂物,线材中存在5类夹杂物,其中4类呈长条状的夹杂物,除了SiO2-Al2O3和SiO2-Al2O3-CaO类夹杂物外,还包括CaO、MgO含量较高的SiO2-CaO-MgO和SiO2-Al2O3-CaO-MgO类夹杂物。从铸坯到中间坯,宽度不超过3 μm的夹杂物密度由1.1个/mm2增加至3.2个/mm2,占比由50%增加至80%,成品材中宽度不超过3 μm的夹杂物几乎达到100%。各阶段中宽度不超过3 μm的小尺寸夹杂物主要由SiO2-Al2O3、SiO2-Al2O3-CaO、SiO2组成。轧制过程中,SiO2-Al2O3、SiO2-Al2O3-CaO类夹杂物的长宽比不断增加,并且其变形指数高于其他类型的夹杂物,同时,由于压缩比的原因,中间坯中所有夹杂物的变形指数明显高于线材中夹杂物的变形指数。依据夹杂物的形貌及成分演变,结合夹杂物在加热过程中结晶行为,推测连铸坯中夹杂物在高温加热时析出了结晶相,该结晶相在后续轧制过程中分离,形成了SiO2类夹杂物和高CaO、MgO含量的复合夹杂物。
Abstract
Large non-deformable oxide inclusion is the main cause of spring fatigue failure. The negative effect of inclusion can be alleviated by reducing the size of oxide inclusion after hot rolling by obtaining low melting point plastic inclusion with good deforming properties. In order to study the evolution behavior of oxide inclusion in industrially produced silicon deoxidized spring steel during rolling process, The morphology, composition, size and density of oxide inclusions in continuous casting bloom, rolled billet and wire rod were analyzed by SEM+EDS. The results show that SiO2-Al2O3 and SiO2-Al2O3-CaO were spherical inclusions in the continuous casting bloom, which were basically in the low melting point region. SiO2-Al2O3 and SiO2-Al2O3-CaO inclusions in the rolled billet were long strip shape, and the tadpole-like SiO2 inclusions were also found. There were five kinds of inclusions in the wire rod, four of which were long strip shape inclusions, in addition to SiO2-Al2O3 and SiO2-Al2O3-CaO inclusions,also include SiO2-CaO-MgO and SiO2-Al2O3-CaO-MgO inclusions with high content of CaO and MgO. From the bloom to the rolled billet, the width less than 3 μm inclusions density increased from 1.1 /mm2 to 3.2 /mm2, and the proportion increased from 50% to 80%. In the wire rod the width less than 3 μm inclusions almost reached 100%. The width less than 3 μm inclusions in each stage were mainly composed of SiO2-Al2O3、SiO2-Al2O3-CaO、SiO2. During the rolling process, the aspect ratio of SiO2-Al2O3 and SiO2-Al2O3-CaO inclusions increased continuously, and their deformation index was higher than other types of inclusions. Meanwhile, due to the compression ratio, the deformation index of all inclusions in the rolled billet was higher than those in the wire rod. According to the morphology and composition evolution of the inclusions, combined with the crystallization behavior of the inclusions during heating, it is reasonable to speculate that the crystalline phase precipitated in the continuous casting bloom inclusions during high temperature heating, and the crystalline phase was separated in the subsequent rolling process, forming SiO2 inclusions and high CaO and MgO content composite inclusions.
关键词
弹簧钢 /
硅脱氧 /
氧化物夹杂 /
轧制 /
变形 /
结晶
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Key words
spring steel /
silicon deoxidized /
oxide inclusions /
hot rolling /
deformation behavior /
crystallization
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脚注
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基金
河南省重点研发专项资助项目(221111231000)
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