厚壁无缝钢管张减过程横向壁厚不均研究

为解决热轧厚壁无缝钢管横向壁厚分布不均的问题,建立三维热力耦合有限元模型,对张力减径轧制过程进行了动态模拟,并结合工业试验验证仿真模型.根据仿真结果分析了轧制过程中温度、应变和摩擦力的分布,研究了单道次轧制时金属的径向和周向流动规律,并结合整个轧制过程对金属的横向流动及壁厚不均的形成过程进行了分析,研究了轧制过程中温度对金属流动行为的影响,从而总结出横向壁厚分布不均的原因.结果表明:(1)在经过单道次轧制时,金属的周向流动为从孔型顶部流向辊缝,对应孔型角±30°位置处金属的周向流动最活跃,靠近孔型顶部和辊缝位置的金属周向流动性较差.但从整个轧制过程来看,金属总的周向流动为从孔型顶部和辊缝向孔型角±30°位置处流动,从而导致孔型角±30°位置处的壁厚比孔型顶部和辊缝位置要厚.(2)温度分布对金属横向流动有重大影响.由于塑性功换热的原因,孔型角±30°位置处金属的温度比辊缝和孔型顶部处高,此处金属较软,阻力较小,孔型顶部和辊缝处金属向此处的流动性增强,导致钢管截面呈内边方形.

Study on transverse wall thickness variation of thick-walled seamless steel tubes during stretch-reducing hot rolling

In order to solve the transverse wall thickness variation problem of thick-walled seamless steel tubes produced by hot rolling, a coupled thermo-mechanical finite element model was established to simulate the stretch reducing hot rolling process, and industrial trials were performed to verify the model. Based on simulation results, the authors analyzed temperature, strain and friction force distributions in the rolling process, studied the radial and circumferential flow laws of metal in single pass rolling, the transverse flow law in the whole rolling process and the formation of thickness variation, discussed the influence of temperature on metal flow behavior, and finally summarized the reasons of transverse wall thickness variation. The metal circumferential flow direction is from the roller top to roller gap after rolled by a single pass. Circumferential flow of metal near the ±30℃ position of roller groove angle is the most active, and circumferential flow of metal near the roller top and gap positions is much weaker. However, after the whole rolling process, metal flows from the roller top and gap position to the ±30℃ position of roller groove angle along circumference. This causes that the thickness of the ±30℃ position is bigger than the roller top and gap position. Temperature has huge influence on metal transverse flow behavior. Because of plastic work, metal temperature at the ±30℃ position of roller groove angle increases higher than other positions, which softens and lowers the resistance of this place. So the metal fluidity of the roller top and gap positions toward the ±30℃ position is strengthened, leading to tube cross section appearing a hexagonal bore.