【作者】 裴培；

【导师】 艾立群；

【作者基本信息】 河北理工大学 ， 钢铁冶金， 2008， 硕士

【摘要】 为了研究宣钢SWRCH35K冷镦钢的质量问题,通过现场系统取样和试验检测等方法,观察了钢中大型夹杂物,显微夹杂物的形貌,并用扫描电镜对钢中夹杂物做进一步分析,研究了冶炼过程中各个环节的夹杂物类型、数量、分布以及T[O]、N的变化规律;分析了冷镦样和盘条样的表面质量、金相组织、夹杂物等影响冷镦性能的因素,得出冷镦盘条开裂的原因。研究表明:铸坯的T[O]平均为41×10-6;铸坯N平均值为68.67×10-6;大型夹杂物平均值为105.33mg/10kg,以硅酸盐类的复合夹杂物为主;LF处理后显微夹杂物的含量较处理前有很大减少,说明精炼去除夹杂物效果较好;中间包中的显微夹杂物的数量较LF处理后有所增加,首先,原因为中间包覆盖剂只有碳化稻壳,碳化稻壳有良好的绝热保温作用,但不能防止二次氧化和吸附夹杂物;其次,长水口没有采用氩封而吸入空气;铸坯中的夹杂物中含有Ti、Zn、Na、Ka等元素是来自结晶器保护渣,说明结晶器存在卷渣现象;各个工序显微夹杂物的变化规律与T[O]的变化规律基本一致;冷镦开裂的原因主要是由于盘条表面存在折叠;盘条的金相组织为铁素体+珠光体,铁素体呈块状,铁素体占30%~50%,未发现贝氏体和魏氏体组织;盘条的晶粒度普遍较高,达到9.0~10.0级,会导致抗拉强度提高,冷镦性能变差。虽然没有发现夹杂物直接导致冷镦开裂的现象,但是,较高含量的夹杂物将限制冷镦性能进一步提高。发现钢的夹杂物中含有氯元素,并分析了氯元素的来源和对冶炼的影响。更多还原

【Abstract】 To research the quality of SWRCH35K cold-heading steel in Xunhua Iron and Steel Co.Ltd, the macro-inclusions and micro-inclusions are observed by the means of on-site systemic sampling and testing detection. Inclusions are further analysed by SEM/EDS. The amount, dimension, distribution, and contents variation of T[O] and N are studied during the production process. To investigate the cracking reasons, the effects such as inclusions, surface quality, metallographlic structure of cold-heading samples and wire rod samples are studied.It is found that: The contents of T[O] and N in billet are 41×10-6 and 68.67×10-6 in average; The macro-inclusion is 105.33mg/10kg, It is mainly multiplicity of silicate; the amount of micro-inclusion is reduced dramatically after LF process. The results show that: The refining of LF is effective on removing inclusions and the amount of inclusions is higer in the tudish than that after LF process. The reason is that: first, the carbonized rice-hull has only adiabatic function but can not prevent reoxidation and absorbing inclusions in the tudish; secondary, the extended nozzle without argon gas seal absorbs air. The elements of Ti, Zn, Na, and Ka in billet come from the mould flux. It indicates that the entrapment is in mould; the amount variation of micro-inclusion is consistent with the content of T[O] in every site; the surface fold of wire rod is the main reason of crack and the metallographic structure is made up of ferrite and perlite. The ferrite content is about 30%~50% in the lumpish shape and no bainite no marstensite are found in the wire rod. The grain size of wire rod is about 9.0~10.0. This will make the tensile strength increase, and impair the cold-heading performance. Although the inclusion is not the cracking reason, the high level amount of inclusions will restrict the improving of cold-heading performance. Chelorine is found in the inclusion of steel. Chelorine’s source and effect on the smelt precess are analysed.更多还原