Secondary cooling control method for reinforcing surface solidification structure of microalloyed steel continuous casting bloom

A secondary cooling control method for reinforcing a surface solidification structure of a microalloyed steel continuous casting bloom, wherein the secondary cooling control method comprises the following steps:

• Step S1:
• obtaining a microalloyed steel specimen, heating the microalloyed steel specimen to a predetermined temperature, sufficiently redissolving secondary phase particles in a microalloyed steel, then cooling the microalloyed steel specimen at a predetermined cooling rate to a room temperature, during a cooling process, in situ observing the precipitation behavior of secondary phase particles in the microalloyed steel with a high-temperature confocal microscope, and determining a temperature range T of a concentrated precipitation of the secondary phase particles, wherein a lower limit of the temperature range T is T1;
• Step S2:
• cooling the microalloyed steel at different cooling rates, obtaining a particle size and a volume fraction of the secondary phase particles in the microalloyed steel at the different cooling rates, establishing a quantitative relationship between a cooling rate and an average particle size and an average volume fraction of the secondary phase particles, and determining an optimal average cooling rate ν1 based on the quantitative relationship;
• Step S3:
• establishing a solidification and heat transfer mathematical model of the microalloyed steel based on an initial water flowrate of secondary cooling zones, calculating a surface temperature of a continuous casting bloom and an average cooling rate of the secondary cooling zones by using the solidification and heat transfer mathematical model, and determining and controlling a precipitation process of the secondary phase particles on the continuous casting bloom surface with the temperature range T of the concentrated precipitation of the secondary phase particles;
• Step S4:
• establishing a quantitative relationship between a cooling rate νc of a last segment during the precipitation process and a temperature at an end of the last segment, and determining an optimal average cooling rate ν2 based on the quantitative relationship and a lower limit T1 of the temperature range T of the concentrated precipitation of the secondary phase particles;
• Step S5:
• establishing a quantitative relationship between the cooling rate νc of the last segment of the precipitation segment and a straightening point temperature, and determining an optimal average cooling rate ν3 based on the quantitative relationship and an upper limit of a third brittle temperature zone;
• Step S6:
• determining an optimal average cooling rate range ν0 based on the optimal average cooling rate ν1, the optimal average cooling rate ν2, and the optimal average cooling rate ν3, the optimal average cooling rate range ν0 controlling a precipitation of the secondary phase particles, and ν0=ν1∩ν2∩ν3;
• and
• Step S7:
• calculating an average cooling rate νc of the precipitation process, and controlling the secondary cooling of the continuous casting bloom based on the average cooling rate νc of the precipitation process and the optimal average cooling rate range ν0.