In the tandem cold rolling (TCR) process, the work hardening effect has a direct influence on the rolling force, which affects the strip shape, including the strip crown and flatness, significantly. However, previous studies focus on the single finite element (FE) model, ignoring the work hardening effect. To investigate the effect of the rolling force on strip shape, herein, a novel elastic–plastic multistand FE model for the TCR process with consideration of the work hardening effect is proposed for the first time using a segmentation modeling strategy, data transfer technologies, and element remesh technology. The proposed FE model is verified by comparing with industrial experimental results. The effects of rolling force on the strip crown and flatness at each stand are investigated quantitatively using the developed FE model. The results illustrate that the strip crown at 40 mm from the edge (C 40) is in a decreasing trend when the rolling force decreases from stand 1 (S1) to stand 4 (S4). By contrast, interestingly, two opposite trends of C 40 are found at stand 5 (S5). This work provides a fresh perspective on the TCR simulation and contributes to further understanding the effect of the rolling force on the strip shape.

The evolution of microstructure and residual stress during the tempering of 700 L low-carbon micro-alloyed steel was studied using a crack compliance method for measuring residual stress. Additionally, a non-isothermal tempering dilatation test, Vickers micro-hardness test, and transmission electron microscopy were used. The evolution of residual stress during tempering consists of two stages. The first stage coincided with cementite precipitation. Under the initial residual stress, the transformation plasticity due to cementite precipitation leads to partial relaxation of the micro-stress evoked by the austenite-to-ferrite transformation during quenching. It also caused the material surface and the core to exhibit different residual stress evolution trends. After tempering at 300 ∘ C for 30 min, the residual stress was reduced from 487 MPa to 200 MPa; however, the elastic strain energy remained unchanged. The second stage coincided with alloy carbide precipitation and Mn partitioning, but the precipitation of the alloy carbide only reduced the elastic strain energy by 8.7%. Thus, the change in activation energy was the main reason for the relaxation of residual stress at this stage. After tempering at 600 ∘ C for 30 min, the residual stress was reduced to 174 MPa, the elastic strain energy was reduced by 72.72%, and the residual stress was controlled.

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The strip shape inheritance model is widely applied to improve the strip shape quality in tandem cold rolling (TCR). However, the inheritance mechanism is still currently unclear. To bridge this gap, this paper presents a new numerical method for calculating the strip crown inheritance factor. In addition, the effects of the entry strip crown on exit strip crown and flatness were quantitatively analysed at each stand in the TCR using a novel three-dimensional (3D) multi-stand elastic–plastic finite element (FE) model. The results show that the strip crown inheritance factor increases slowly from S1 (stand 1) to S3 (stand 3), while rising sharply from S3 to S5 (stand 5), reaching a peak value of 0.495 μm/μm at S5. This trend coincides with that of strip plastic rigidity, which verifies that the strip crown inheritance factor is dependent on the strip plastic rigidity. Furthermore, the variation of strip crown and flatness under different entry strip crowns from S1 to S5 is jointly influenced by the pass reduction and strip plastic rigidity. Moreover, the strip crown inheritance factor increases with the deformation resistance of the strip at both S1 and S5. These findings not only offer a fresh perspective to understand the mechanism of strip crown inheritance, but also provide an important basis for optimising the strip shape control in the TCR process.