HRB335小方坯脱方的原因分析及控制轧制

Analysis and Controlled Rolling of Rhomboidity of Small HRB335 Steel Continuous Casting Billet

脱方是小方坯连铸常见的质量缺陷,一般认为结晶器磨损严重,钢水在结晶器内冷却不均匀,以及二冷喷嘴状况不佳,二次冷却不均匀等是脱方的主要原因。分析了新疆八一钢铁股份有限公司(以下简称八钢)第一炼钢厂2号连铸机HRB335钢连铸坯脱方的成因:一是HRB335钢水过热度较高,相比过热度较低的HPB235,其坯壳厚度比HPB235的薄,坯壳厚度越薄,出结晶器后液芯长度较长,铸坯就容易变形,出现脱方的概率越大。二是喷淋管不能满足均匀冷却的要求,增大铸坯脱方概率。应对措施:增大二次冷却强度,将HRB335钢的比给水量由1.73 L/kg增加到1.83 L/kg;侧弧喷淋管支管长度由172 mm缩短到127 mm。采取上述措施后,脱方废品率大幅下降。同时,对脱方量在允差范围内的小方坯,采用控制轧制,结果表明:通过控制轧制可以对脱方较轻钢坯进行纠正。

Rhomboidity is an ordinary quality problem of continuous casting billet.Generally speaking,serious wearing of the mould,non-uniform cooling in the mould,abnormal functioning of the secondary cooling nozzle and non-uniform secondary cooling might be the main reasons.The reasons for rhomboidity of HRB335 steel continuous casting billet in No.2 continuous caster of No.1 Steelmaking Plant of Xinjiang Bayi Iron and Steel Corporation are analyzed.Firstly,because the supper heat of HRB335 steel is high,compared with the lower super heat HRB23 steel,the initial shell of steel is thinner,and the liquid core is longer,then the rate of rhomboidity will increase.Secondly,the spraying tube cannot meet the requirement of uniform cooling,which leads to the increase of the probability of casting rhomboidity.Based on the above research,some measures to improve billet quality were applied.Increase the secondary cooling intensity,in which the specific water flow for steel HRB335 was increased from 1.73 L/Kg to 1.83 L/Kg.In addition,the branch tube length of the side spraying tube was shortened from 172 mm to 127 mm.After taking these measures,the ratio of rhomboidity decreased dramatically.In the meantime,controlled rolling was implemented for those billets with slight off-squareness.It is proved that the rhomboidity can be corrected by the controlled rolling if the off-squareness of the rhomboidity billet is within the allowance value.