Steel plate
A kind of steel plate and unit technology, applied in the direction of coating, furnace type, hot dipping process, etc., can solve the problem of inability to combine tensile strength, ductility and hole expandability, etc., and achieve excellent tensile strength and hole expandability. , The effect of excellent hole expansion and excellent uniform elongation
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Embodiment 1
[0152] First, in order to investigate the influence of the heating rate in the first annealing, experiments described below were performed.
[0153] A slab having the following chemical composition was produced using a vacuum melting furnace: C: 0.10%, Si: 1.0%, Mn: 4.3%, P: 0.010%, S: 0.0020%, Al: 0.03% by mass % %, N: 0.0020% and O: 0.0012%, and the remainder is iron and impurities. The obtained slab was heated to 1200°C, hot rolled at a finish rolling temperature of 921°C, and the average cooling rate in the temperature range from 800°C to the coiling start temperature was set to 50°C / sec. Cooling was performed, and coiling was performed at 450°C. The coiled hot-rolled steel sheet was cooled to room temperature, and then first annealed. In the heating before the first annealing, the average heating rate in the temperature range of 300 to 550° C. is set to various values in the range of 0.01 to 30° C. / sec. The annealing temperature (highest heating temperature) in the f...
Embodiment 2
[0158] Next, in order to investigate the influence of the annealing temperature in the first annealing, experiments described below were performed.
[0159] The slab used in Example 1 was heated to 1200°C, hot rolled at a finish rolling temperature of 921°C, and the average cooling rate in the temperature range from 800°C to the coiling start temperature was set to 50°C / seconds to cool, and coiled at 450°C. The coiled hot-rolled steel sheet was cooled to room temperature, and then first annealed. The average heating rate in the range of 300° C. to 550° C. (in the range of 300° C. to the annealing temperature when the annealing temperature is lower than 550° C.) before the first annealing was set to 3.5° C. / sec. Next, the heating of each sample was completed at 450 to 850° C., and thereafter, each sample was held at each annealing temperature for 7200 seconds, and then each sample was air-cooled to room temperature. Thereafter, each sample was subjected to cold rolling at a ...
Embodiment 3
[0162] Next, in order to investigate the influence of the heating rate in the second annealing, experiments described below were performed.
[0163] The slab used in Example 1 was heated to 1200°C, hot rolled at a finish rolling temperature of 921°C, and the average cooling rate in the section from 800°C to the coiling start temperature was set to 50°C / sec And cooling was performed, and the coiling process was performed at 450 degreeC. After that, in the first annealing, set the average heating rate of 300 to 550°C to 2.5°C / sec to heat each sample, hold each sample at 590°C for 7200 seconds, and then air each sample Cool to room temperature. After that, each sample was cold-rolled at a cold rolling rate of 52%, and then each sample was heated at an average heating rate in the range of 300 to 550° C. at 0.01 to 30° C. / sec. Each sample was further held at the second annealing temperature of 620° C. for 600 seconds, and then the average cooling rate in the temperature range fro...
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