微合金化C70S6胀断连杆断裂面掉屑缺陷分析与工艺改进

Analysis and Process Improvement on Defects of Broken Bits Dropping Out from Fracture Surface for Microalloying C70S6 Expansion-Broken Connecting Rods

采用金相显微镜、电子显微镜等分析得出,C70S6钢表面严重脱碳以及内部质量缺陷均会造成连杆胀断掉屑,通过优化Al、V、P含量,钢中铁素体含量由原5.5%-8.6%降至2.7%-4.8%;连铸过热度由≤35℃降至≤30℃,拉速由0.80-0.90m/min降至0.65-0.75m/min,末端电磁搅拌电流由200A提高至300A;轧制前铸坯涂涂料,加热炉加热时高温段空燃比由0.7-0.8降至0.5-0.6,加热温度提高至1200-1250℃;并采用提高轧后冷速等措施后,C70S6钢中心C偏析降为0.99-1.04,表面脱碳层深度≤0.50%d,晶粒度5.5-6.0级,铁素体含量≤5.0%,成功解决了连杆批量掉屑质量问题。

By metallographic microscope,electron microscope etc.analyzing,it is obtained that surface serious de-carburization of the C70S6 steel surface seriously causes the connecting rod expansion-broken bits dropping out,and inter-nal quality defects.By optimizing the content of Al,V,and P,the ferrite constituent in steel decreases from orignial 5.5%-8.6%to 2.7%-4.8%,and by using measures including continuous casting superheat reduced from≤35℃to≤30℃,casting speed reduced from 0.80-0.90 m/min to 0.65-0.75 m/min,electromagnetic stirring current at the end increased from 200 A to 300 A;coating the cast billet before rolling,air-fuel ratio in the high temperature section of the heating furnace reduced from 0.7-0.8 to 0.5-0.6,heating temperature increased to 1200-1250℃;and increas-ing cooling rate after rolling,the segregation of C in the center of the C70S6 steel is reduced to 0.99-1.04,the depth of the surface decarburization layer is≤0.50%d,the grain size rating is 5.5-6.0,and the ferrite content is≤5.0%,suc-cessfully solved the problem of bits dropping in batches of connecting rods.