82B高速线材拉拔过程中显微组织的演变分析

借助扫描电子显微镜(SEM)观察分析研究了82B线材在拉拔过程中显微组织和芯部马氏体的演变规律。分析认为:由于索氏体属于细片状珠光体,拉拔变形时,承受滑移的铁素体相不易引起应力集中;渗碳体相为细薄片层形态,也能够发生塑性变形,经过多道次的拉拔,索氏体基体变形量较大,没有出现任何裂纹。而芯部由偏析形成的马氏体,其塑性变形能力明显低于索氏体,基本无变形,在基本拉应力和附加拉应力的共同作用下,在早期拉拔时就在芯部出现裂纹,在后期拉拔过程中,裂纹沿着拉拔方向不断扩展。为减少断丝,可采用加大吹风量、扩大连铸坯、控制钢水过热度、增加电磁搅拌等工艺,来提高索氏体含量和细化渗碳体片层及预防马氏体的形成,以提高拉拔性能。

ANALYSIS OF MICROSTRUCTURE EVOLUTION OF 82B HIGH- SPEED WIRE ROD IN DRAWING- PROCESS

In the paper the microstructure and martensite evolution of 82B wire rod in drawing- process were observed and analyzed by scanning electron microscopy（ SEM）. The analysis suggested that since the sorbite was fine lamellar pearlite,when wire rod were deformed by drawing,the withstand slipping ferrite phase were unlikely to cause stress concentration; cementite phase was thin lamellar form,which could occur plastic deformation. When drawing for multi- passes,the deformation of matrix sorbite was very big and without any cracks. In the center,the plastic deformation ability of martensite formed by segregation was significantly lower than the sorbite and the martensite had basically no deformation,which were found out some cracks in the early drawing under the common action of the basic tensile stress and the additional tensile stress and then the centre cracks expanded along the drawing direction in the drawing process. The drawing performance could be improved by increasing the amount of wind,enlarging continuous casting slab,controlling the superheat of liquid steel and adding electromagnetic stirring,etc in order to increase the content of sorbite,fine cementite lamina and prevent the formation of martensite.