【作者】 徐忠良；

【导师】 蒋建清； 方峰；

【作者基本信息】 东南大学 ， 材料学， 2006， 硕士

【摘要】 SWRS82B热轧盘条是制造大跨度桥梁缆索用镀锌钢丝的原材料。目前,国产SWRS82B盘条生产的镀锌钢丝,其抗拉强度等指标已达到相关标准和使用要求,但扭转性能仍不能满足使用要求,因此,SWRS82B盘条仍然依赖进口。利用SEM对镀锌钢丝扭转断口进行了观察与分析,并将其分成三种类型:第一类是平断断口,断口光滑平整,扭转值通常大于20圈,属于材料达到剪切应力极限而破坏的正常切断;第二类是台阶状断口,断口呈现小的台阶状,扭转值通常在10~18圈,主要是由材料内部的带状组织(马氏体)引起的异常断裂;第三类称为斜楔状断口,断面和钢丝轴线成小于45℃的夹角,扭转值一般在10圈以下,主要是钢丝表面的缺陷造成的。研究了钢丝表面裂纹的形式和尺寸对扭转性能的影响,结果表明:钢丝表面横向裂纹对扭转性能的影响最为严重,裂纹走向和变形走向垂直的次之,裂纹走向和变形走向一致的影响最小。钢丝镀锌后扭转值发生明显降低,研究结果表明,钢丝镀锌前处理对扭转性能基本没有影响,热镀锌过程是造成钢丝扭转性能降低的主要因素。盘条在冷拉拔变形过程中,片状渗碳体发生部分断裂或碎化。采用DSC研究了钢丝在加热过程中能量的变化情况,结果表明:在DSC曲线上400~500℃的温度范围内,出现了转变峰,峰值对应钢丝热镀锌的温度450℃。通过SEM观察了镀锌后渗碳体的形态,结果表明,部分渗碳体由原来的片状转变成了球状。因此钢丝在加热过程中出现了转变峰。通过盘条生产工艺和化学成分的调整:添加合金元素钒以细化晶粒,轧后采用强冷的方式,以提高珠光体转变的过冷度,从而减小珠光体的片层间距。盘条质量改进后,珠光体片层间距由原来的0.14μm减小到0.12μm;盘条的抗拉强度略有提高,面缩率由原来的37%增加到41%;钢丝对表面裂纹的敏感性也有所降低,横向裂纹的临界尺寸由原来的0.05mm提高到0.15mm;镀锌钢丝的平均扭转值由20圈提高到25圈。DSC结果表明,盘条质量改进后生产的钢丝,其加热过程中DSC曲线上出现转变峰的温度明显推迟,由原来的400~500℃推迟至450℃~550℃的范围,说明盘条组织的细化,有利于减少拉丝过程中形变能的储存,从而提高渗碳体球化转变的温度。SEM观察结果表明,镀锌后渗碳体球化的程度有所降低。通过试制SWRS82B热轧盘条生产工艺和化学成分的改进,采用小方坯连铸连轧工艺生产的SWRS82B热轧盘条,可以生产出满足性能要求的镀锌钢丝。更多还原

【Abstract】 SWRS82B wire was the raw material of hot-dip strand for long-span bridges. At present, the strength of hot-dip strand’s could reach acceptance criterion, which produced by homemade WRS82B wire. Nevertheless, it’s torsion capability couldn’t.The torsion fractures are classified as three types: even fracture, sidestep fracture and fastigiated fracture. Even fracture belongs to normal rupture. The strand ruptures when cut-stress reaches its critical value. The reason of sidestep fracture is that zonary structure decreases the cut-stress of hot-dip steel strand. The disfigurements on the steel strand surface will cause fastigiated fracture easily. The form of crack on steel strand surface, as well as the depth of the crack, affects the torsion capability critically. Transverse crack is worse than the other two types of crack.The torsion value of steel strand decreased markedly after galvanization. It was shown that the pre-processes of galvanization didn’t affect it. The differential scanning calorimeter(DSC) experiments indicated that there was a exothermic reaction at 450℃, Which was almost equal to the temperature of galvanization. SEM results show that Fe3C transforms into spherical structure after drawing and galvanization.The grain of wire refined when alloy Vanadium was appended, and interlamellar spacing of pearlite was reduced from 0.14μm to 0.12μm by cooling quickly. Performance of wire was promoted evidently. DSC experiments indicated that temperature rang, during which cementite laminate transformed into spherical structure, increased from 400~500℃to 450~550℃after SWRS82B wire was advanced in quality. the critical depth of the transverse crack increased from 0.05mm to 0.15mm. Mostly the torsion value increased from 22 to 25.When the quality of SWRS82B wire was improved, the production results showed that hot-dip steel strand could meet the use requirement, especially for torsion performance.更多还原