Spring-back of sheet metal affects the dimensional accuracy of the components after stamping and has to be eliminated or corrected. Advanced high strength steels (AHSS) are prone to spring-back while forming at ambient temperatures. Hot stamping process is an effective technique to reduce the spring-back upon forming. The forming temperatures and the phase transformations associated with quenching are known to influence the spring-back. However, the detailed experimental analysis on spring-back behaviour is limited due to the difficulty in physically simulating the thermal-mechanical conditions prevailing in a typical hot forming process. In the present work, a novel V-bending technique is presented for effectively measuring the spring-back using a thermal-mechanical simulator, Gleeble™. V-bending is carried out by applying a compressive force along the longitudinal plane of AHSS steel strips at forming temperatures. Upon V-bending, samples were cooled at different cooling rates while maintaining the forming loads to simulate die quenching. Results indicate that the spring-back decreases and becomes close to zero (at a cooling rate of 20 K s⁻¹) with an increase in cooling rate for a hot stamping steel. Further, an increase in cooling rate results in spring-forward owing to the formation of an increased volume fraction of martensite.

钣金的回弹会影响冲压后组件的尺寸精度，因此必须消除或纠正。先进的高强度钢（AHSS）在环境温度下成型时容易回弹。热冲压工艺是减少成型时回弹的有效技术。已知与淬火有关的成型温度和相变会影响回弹。但是，由于难以对典型热成型过程中普遍存在的热机械条件进行物理模拟，因此对回弹行为的详细实验分析受到限制。在当前的工作中，提出了一种新颖的V型弯曲技术，可以使用热机械模拟器Gleeble™有效地测量回弹。通过在成形温度下沿AHSS钢带的纵向平面施加压力来进行V型弯曲。V型弯曲时，样品以不同的冷却速率冷却，同时保持成型载荷以模拟模具淬火。结果表明，回弹力减小并接近于零（在20 K s的冷却速率下）^-1），以提高热冲压钢的冷却速度。此外，由于马氏体体积分数的增加，冷却速率的增加导致弹簧向前运动。