热轧带钢的冷却参数与翘曲关系

Relationship between cooling parameters and warping of hot rolled strips

针对卷取温度为500℃的12 mm厚X70管线钢热轧带钢,利用MARC有限元软件建立层流冷却过程中的热-力-相变耦合的数学模型,计算两种下上冷却水比时层流冷却过程中温度场、应力、应变、相变体积分数和翘曲度随时间的变化.结果表明:1.25水比的冷却过程中,厚度方向上各面的冷却速度不一致,导致水冷前期带钢上下表面应变不同,带钢会产生向上的翘曲,冷却过程中边部最大的翘曲量达到21.84 mm;水冷后期带钢板形会逐渐恢复平直,但由于水冷过程中发生塑性变形,终冷时厚度方向上贝氏体含量的差异,卷取时带钢边部依然有-9 mm的翘曲量.上下表面的不均匀冷却是引起翘曲的根本原因.在保证X70管线钢性能条件下,采用1.58的下上水比工艺,卷取时边部翘曲量仅为-0.58 mm,合适的下上水比能大幅度减小层流冷却过程中带钢的横向翘曲.

For 12-ram-thick hot-rolled X70 pipeline steel strips coiled at 500℃, a coupled thermomechanical- phase transition model in the laminar cooling process was established by MARC finite element software, and then the changes in temperature field, stress, strain, volume fraction of phase transformations and warping degree in the duration of laminar cooling were calculated at two kinds of cooling water ratios. The results show that the maximum warpage of the strip edge is 21.84 mm because of different strain values of the upper and lower surfaces resulting from different cooling rates in the thickness direction in the early stage of water cooling at a water ratio of 1.25. The steel plate will gradually restore straight in the later cooling process. However, the warpage of the strip edge is still - 9 mm at the beginning of coiling due to the plastic deformation in water cooling and the different bainite contents in the thickness direction at finishing cooling. Uneven cooling between the upper surface and the lower surface is the fundamental reason of warping. Under the condition of ensuring the performance of X70 pipeline steel, the residual warpage of the strip edge is only - 0. 58 mm at the beginning of coiling when the water ratio is adopted to be 1.58. The proper water ratio can greatly reduce the strip＇ s transverse warping in the laminar cooling process.