304 cold rolling refers to a material processing method in which the steel strip is rolled at room temperature to gradually reduce the thickness of the steel strip. The raw material of cold rolling is generally the steel coil after hot rolling and annealing. During the cold rolling process of 304 stainless steel, the metastable austenite structure will undergo strain-induced martensitic transformation, which will increase the strength and hardness of the steel and decrease its plasticity, resulting in significant work hardening.

As the number of rolling passes increases, the total rolling deformation rate increases, the work hardening effect becomes more and more obvious, and the material becomes harder and harder. The strength and hardness of the 304 hot-rolled coil in the conventional annealed state are lower, and the plasticity is better, which is conducive to rolling. If the hot-rolled coil is directly cold-rolled without annealing, the material production cost can be greatly reduced.

Feasibility analysis of direct cold rolling of hot rolled coil without annealing

1.1 Mechanical property analysis The 304 stainless steel coil samples in the hot-rolled state and hot-rolled annealed state were taken at the production site, and the mechanical properties were tested. The results are shown in Table 1. Comparing the mechanical properties of hot-rolled and hot-rolled annealed 304, it can be seen that compared with hot-rolled and annealed, the average yield strength is 80.9 MPa higher, the average tensile strength is 40.7 MPa higher, and the elongation is 5.7% lower.

From the point of view of mechanical properties, there is little difference in the strength of hot-rolled 304 sheets before and after annealing. The hardening process of hot-rolled unannealed steel sheets is a little faster than that of annealed sheets, but it is not obvious, and the load on cold-rolling equipment has not changed much.

1.2 Analysis of metallographic structure The 304 in the hot-rolled and hot-rolled annealed state was sampled, polished and etched with HCl-FeCl3 solution. The metallographic structure is shown in the figure.