Abstract:
In recent years, low energy consumption and low cost CSP short-process technology has been rapidly developed in Chinese iron and steel industry. However, compared with the traditional hot rolling process, the yield strength of CSP products is higher, which is extremely unfavorable for the formability of steel used in stamping.Therefore, the dynamic recrystalization behavior and cooling phase transformation of austenite of DC04 cold-rolled deep-drawing steel were analized through thermal simulation experiments, and the dynamic recrystalization model was established, which was used to guide the production practice of CSP production line, and the cold-rolled deep-drawing steel sheet with rich 111texture was successfully trial-produced. The experimental results show that the dynamic recrystallization model of DC04 cold-rolled deep-drawing steel in CSP production line is
Z=
ε·exp295.21/(
RT). The judgment conditions of dynamic recrystallization are
Z=1.94×10
10exp(61.34
εc) and
Z=2.57×10
8exp(24.99
εs).Based on the 3D dynamic recrystallization diagram, it is determined that the thermal deformation of the strip at F
3 stand in actual production is in the austenite part recrystallization region. In the trial production using F
3 stand bypassing scheme, the microstructure of the obtained strip is mostly equiaxed grain with low strength. However, the grains of the strips produced by the conventional rolling process of F
3 stand non-bypassing scheme,the grains contact with each other at sharp or right angles, and the strength is about 30 MPa higher than former. The F
1and F
2 stands of CSP production line adopt high temperature, high reduction rate and low deformation rate rolling, which can make the strip microstructure undergo complete dynamic recrystallization, complete the transformation of columnar crystal to equiaxed crystal, and avoid the generation of mixed crystal. The performance of cold-rolled sheets produced using a 70% cold rolling cumulative reduction, bell annealing at 710 ℃, and the F
3 stand by passing and non-bypassing schemes were compared. The cold-rolled sheets produced with the F
3 stand bypassing scheme showed little difference in strength compared to those produced with the conventional non-bypassing scheme, but exhibited higher elongation
A80 and
r values reaching 45% and 2.1. Additionally, the proportion of the favorable texture component 111 was higher, resulting in excellent deep-drawing performance.