High-strength steel is one of the development trends of […]
High-strength steel is one of the development trends of color-coated products. Color-coated steel sheets, color steel sheets, color-coated coils, and color steel coils are currently used in foreign countries with color steel sheets with a yield strength of 350 grades. There are usually two processes for producing such strength steel plates. First, carbon-manganese steel is used. In the steelmaking process, strengthening elements such as C and Mn are used, and strong hot-rolling and cold-rolling rolling forces are used to produce relatively thin high-strength steels. Color-coated steel plates, such as Baosteel's domestic and foreign steel mills (from ore to finished products), adopt such production processes. Another method is to reduce the annealing temperature of the hot-dip galvanizing unit so that the material is not completely annealed, and also partially retain the rolling hardness to increase the strength. At present, most of the domestic galvanizing and color coating plants use this process because they have no In the steel process, there is no corresponding high-strength steel grade in the market to purchase rolled hard or hot-rolled steel.
But doing so will bring about three hazards:
1, due to lower annealing temperature, coupled with the temperature of the band steel plate is not uniform, then annealing temperature is near the recrystallization critical temperature of the steel plate, which leads to the steel plate width direction of the intensity of the strip is not uniform, after processing the plate type is difficult to get Guarantee.
2. Lowering the annealing temperature inevitably leads to poor cleaning performance, because the fine oxidation of the surface is required to be reduced in the reducing gas at a high temperature, and thus, the plating adhesion of the hot-dip aluminum-plating zinc will have an adverse effect.
3. Lowering the annealing temperature improves the yield strength, but the tensile strength does not increase correspondingly. This leads to an increase in the yield ratio of the material. The yield ratio has a considerable influence on the processability, seismic resistance, and fire resistance of the material. . For example, high-strength steels produced by lowering the exit temperature method have a significant decrease in strength in the event of a fire and seriously affect the fire resistance rating of buildings.