关键词: 70钢, 表层网状渗碳体, 结晶器振动, 空燃比

Abstract: In order to solve the problem of high order defect rate of network cementite structure on the surface of 70 steel wire rod, it was found that network cementite originated from the overflow area of solidification hook with abnormal oscillation marks on the surface of billet by means of analyzing metallographic structure of wire rod.The main reasons that caused abnormal oscillation marks on the surface layer of high carbon steel billet were the poor lubrication and excessive frictional resistance between the billet and the mold. The practice indicated that the proportion of abnormal oscillation marks on the surface of 70 steel billet was reduced from 22.09 % to 6.54 % and the defect rate of superficial network cementite on the surface of wire rod was reduced from 3.47 % to less than 0.50 % by adjusting the stroke M value of mold from 2.7 mm·min/m to 2.9 mm·min/m, the oscillation frequency of mold from 200 times/min to 180 times/min, the air-fuel ratio of heating furnace from 0.60－0.65 to 0.68－0.70, and the temperature of heating furnace from 1 040－1 080 ℃ to 1 050－1 090 ℃. Finally, the decarburization layer 
didn’t exceeded the standard, and the quality and performance of finished product meted the requirements. 

Key words: 70 steel, superficial network cementite, mold oscillation, air-fuel ratio