Abstract: The process of developed C70S6BY non-quenched and tempered hot-rolled round steel is 80 t top-bottom combined blowing converter-LF+VD refining-240 mm×240 mm bloom continuous casting-Φ60 mm round steel continuous  rolling-slow  cooling-finishing  and  non-destructive  testing process.  The  Al₂O₃-CaO-SiO₂  slag  with basicity4～8  has been  used, LF refining    time is 45~60 min; after LF, the[S]≤0.010% and [O]≤0.001%; sulphur alloying is carried out  after  VD,[S]  is  controlled  at  0.063%~0.065%.Before  VD  tapping,100～150m  of  magnesium-containing  cored  wire  is  fed, and  the  yield  of  Mg  is  11%  to17%, and  the  ratio  of magnesium  to  sulphur  content  is  approximately 1.56%.The  superheat  of  the  tundish  liquid  is   15~30  ℃,and  the  casting  speed  is 0.9  m/min. After  normalizing, the  tensile  strength  and yield  strength  of test  steel  are  957  MPa  and  563  MPa.  The material  elongation  and reduction  of area  are  12%  and  21%.After  the  magnesium  modification  treatment, the  percentage  of sulphide  inclusions  with  length-width  ratio  1~2  reaches more than 55%.

摘要： C70S6BY非调质热轧圆钢经过80 t顶底复吹转炉-LF+VD精炼-240 mm×240 mm方坯连铸-Φ60 mm圆钢连轧-缓冷-精整、探伤工艺生产。采用碱度4~8 Al₂O₃-CaO-SiO₂渣系，LF精炼45~60 min；LF离站［S］≤0.010%，［O］ ≤0.001%；VD后硫合金化，［S］控制在0.063%～0.065%。VD出钢前喂入含镁包芯线100~150 m，Mg收得率在11%~17%，镁硫含量比值约为1.56%。中间包钢水过热度15~30 ℃，铸坯拉速0.9 m/min。经正火后，试验钢抗拉强度和屈服强度达957 MPa和563 MPa；伸长率和断面收缩率达12%和21%。镁改质处理后，硫化物夹杂长宽比1~2占比达到55%以上。