汽车用Qst32-3冷镦钢丝表面粗糙原因分析

Qst32-3热轧盘条制作的汽车用冷镦钢丝冷成型后产品表面粗糙,严重影响产品质量。对冷镦钢丝进行化学成分和力学性能分析,均满足EN 10263-2标准要求;对Ф14 mm Qst32-3热轧盘条和Ф13.5 mm冷镦钢丝进行金相组织检验,盘条显微组织为铁素体和珠光体,铁素体晶粒度8.5级,经酸洗拉拔及球化退火后,冷镦钢丝显微组织为铁素体和球化体,中心部位铁素体晶粒度8级,表层局部区域铁素体晶粒度1级。试验及分析表明:热轧盘条球化后晶粒度级别不发生变化;压缩率小于7%时,球化后部分晶粒开始长大,压缩率在7%～26.5%时,球化后晶粒产生粗大现象。晶粒粗大导致表面粗糙,热轧盘条球化退火前的拉拔压缩率较小是造成表面粗晶的原因。

Surface roughness cause analysis of Qst32-3 cold heading steel wire for automobile

The product of cold heading steel wire made by Qst32-3 hot-rolled wire rod after cold forming has a rough surface,which affects product quality seriously.The cold heading steel wire is chemical composition and mechanical properties analyzed,it meets the requirement of EN 10263-2 standard.The microstructure of diameter 14 mm Qst32-3 hot-rolled wire rod and diameter 13.5 mm cold heading steel wire are examined,the microstructure of wire rod is ferrite and pearlite,ferrite grain size is 8.5,after pickling,drawing and spheroidizing annealing,the microstructure of cold heading steel wire is ferrite and spheroidization,the ferrite grain size in the center is 8 and surface local area is 1.The experiment and analysis show that the grain size of hot rolled wire rod will not change after spheroidizing annealing,part grain will grow after spheroidizing annealing while compression ratio is lower than 7%,grain size grows coarsely after spheroidizing annealing while compression ratio is 7%~26.5%,as the compression ratio increase,grain coarse causes surface rough,the small compression ratio before hot-rolled wire rod spheroidizing annealing is the reason of surface rough grain.