方坯直轧工艺对钢筋组织和性能差异性的影响

Effect of billet direct rolling process on difference in microstructure and mechanical properties of rebar

方坯直轧工艺是棒线材轧制生产未来发展趋势,该工艺是指通过提高连铸机钢坯温度并将高温钢坯直接送入轧机进行轧制的新工艺。为了掌握方坯直轧工艺对HRB400钢筋组织和性能差异性的影响,运用有限元方法对方坯轧制过程进行模拟。研究了方坯直轧工艺对定尺长度为9m的钢筋内各相体积分数及晶粒尺寸分布的影响,同时结合力学本构方程预测了钢筋的力学性能。结果表明,方坯直轧工艺生产的钢筋微观组织主要由铁素体、珠光体和微量贝氏体构成,其平均体积分数分别为61.4%、38.4%和0.2%,相比于传统热轧工艺,方坯直轧工艺可实现提高珠光体体积分数、降低铁素体体积分数的作用;方坯直轧工艺可使钢筋在轴向上的晶粒尺寸分布存在一定差异,钢筋头部、中部和尾部区域的晶粒尺寸平均值分别为7.4、7.9和8.5μm;另外,钢筋屈服强度的上限值和下限值分别为454和449MPa,说明9m的钢筋头尾屈服强度相差5MPa,其力学差异性不可忽略。

The billet direct rolling process is the trend of the future development of rod and wire rolling production which refers to a new process in which the high temperature billet is directly fed into the mill for rolling by increasing the casting billet temperature of the caster.The finite element method(FEM) was adopted to simulate the rolling process of billet and to determine the effect of billet direct rolling process on the difference of microstructure and mechanical properties of a HRB400 rebar.The effect of billet direct rolling process on the volume fraction of each phase and grain size distribution of the rebar with a cut-lengths of 9 m was calculated,and the mechanical properties of rebar were predicted with the constitutive equation of mechanical properties.The results showed that the microstructure of rebar produced by billet direct rolling process was mainly composed of ferrite,pearlite and trace bainite,of which the average volume fraction was 61.4%,38.4% and 0.2%,respectively.Compared with the traditional hot rolling process,the billet direct rolling process could increase the volume fraction of pearlite and reduce the ferrite volume fraction.There were some differences in the axial distribution of the grain size of the rebar produced by the billet direct rolling process,the average grain size in the head region,the middle region and the tail region of the rebar were 7.4,7.9 and 8.5 μm,respectively.In addition,the upper limit value of the yield strength of the rebar was 454 MPa,and the lower limit value was 449 MPa,which showed that the yield strength difference between the head region and the tail region of the rebar with a cut-lengths of 9 m produced by direct rolling process was about 5 MPa,and the difference of mechanical properties could not be ignored.