Hot rolling heating temperature
CGO steels with MnS as inhibitors and Hi-B steels with MnS+AlN inhibitors must be heated at high temperatures in the continuous casting slab to make the coarse MnS in the slab >1μm solid solution (mainly present in slab thickness In the direction of the equiaxed central zone, the finely dispersed MnS (10 to 1000 angstroms) of £50 nm is precipitated during the hot rolling process, so the quality of the heating directly affects the magnetic level of the post process.
The billet heating temperature is required to be in the range of 1360 to 1380°C (the MnS solution temperature is 1320°C at equilibrium).
Because the content of Mn and C in Hi-B steel is higher than that of Q steel, the heating temperature of the slab needs to be in the range of 1380-1400°C.
Slabs require that the temperature of each part be uniform, to avoid the occurrence of magnetic fluctuations and black prints caused by uneven slab temperatures.
Rough rolling
Since fine MnS precipitates during finish rolling, it is necessary to control the temperature, time, and thickness of thin slabs after rough rolling and before they enter the finishing mill (MnS starts to precipitate at about 1200°C and γ-phase at 1100 to 1150°C. The precipitation rate is the fastest at the highest temperature, and the precipitation is basically stopped at <950°C. Therefore, the high rolling rate at high reduction rate is used during rough rolling to ensure that the temperature of the thin slab is as high as possible (in the hot rolling process, it is controlled at RT4min). Mainly to ensure that the temperature into the finishing rolling is greater than 1160 ± 20 °C, Q steel is currently 31180 °C, NQ0831190 °C, Hi-B31200 °C).
Finishing
Control the finish rolling and finish rolling temperature and temperature, the Q-steel opening and rolling temperature is 1160±20°C, and the final rolling temperature is controlled above 960°C;
The open-rolling temperature of Hi-B steel> 1190 °C, the final rolling temperature> 960 °C, generally controlled above 980 °C;
In the finish rolling process, the main purpose is to generate a large number of dislocations during the rolling process, making it a precipitation core of MnS, and promoting finer and more uniform precipitation of MnS.
Dynamic recrystallization is achieved during the rolling process to completely destroy the columnar crystals in the slab and fully recrystallize.
Coiling
Immediately after finish rolling, water cooling to about 550°C. Coiling:
Dispersion of carbides in the crystal grains (acicular Fe3C) acts as an additional inhibitor.
Rapid cooling after rolling prevents precipitation of AlN.
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