Fig. 1 Macrostructure characterization of columnar grains of the as-cast high Cr steel and schematic diagrams of hot deformation with different size grains under different deformation directions

Fig. 2 True stress-true strain curves of the deformed samples with different size columnar grains under various directions: a and e 1 s−1, b and f 0.1 s−1, c and g 0.01 s−1, d and h 0.001 s−1. The dash line represents the sample with large grains (d = 2.5 mm) under PRCD, the solid lines in a-d indicate the sample with small grains (d = 1 mm) under PRCD, and the solid lines in e-h reflect the sample with large grains under PPCD

Fig. 3 Microstructural evolution of the deformed samples with different size grains under various directions: a-d with small grains (d = 1 mm) under PRCD, e-h with coarse grains (d = 2.5 mm) under PRCD, i-l with coarse grains under PPCD

Fig. 4 Relationship between stress and deformation parameters of the deformed samples with different size grains under various deformation directions: a and e ln $\dot{\varepsilon }$-σ, b and f ln $\dot{\varepsilon }$-lnσ, c and g ln $\dot{\varepsilon }$-ln[sinh(ασ)], d and h ln[sinh(ασ)]-1000/T. The dash line in Figure represents the sample with large grains (d = 2.5 mm) under PRCD, the solid line in a–d indicates the sample with small grains (d = 1 mm) PRCD, and the solid line in e–h reflects the sample with large size grains (d = 2.5 mm) under PPCD

Fig. 5 Calculated values of α a, n b and Q c. The linear relationship between lnZ-ln[sinh(ασ)] for the deformed samples with different size grains d and under various deformation directions e

Fig. 6 Relationship between strain hardening rate (θ) and flow stress (σ) for DRX of the X12Cr steels with different sizes of columnar grains: a-c θ-σ curve, d-f −∂θ/∂σ-σ curve. The red line represents the small grain (d = 1 mm), while the blue line indicates the large grain (d = 2.5 mm)

Fig. 7 Relationship between strain hardening rate (θ) and flow stress (σ) for DRX of the high Cr steels with columnar grains under different deformation directions: a-c θ-σ curve, d-f −∂θ/∂σ-σ curve. The red line represents the direction under PRCD, while the green line indicates the direction under PPCD