Hot rolling treatment is a crucial process for enhancing the toughness of steel plates. It is characterized by heating the steel plate to a temperature above the upper critical point of the ferrite-austenite phase transition by approximately 30℃ to 50℃ or even higher, to achieve austenitization, and then maintaining a uniform temperature before cooling it in the open atmosphere. The conventional hot rolling treatment, where the steel plate is air-cooled after normalizing, still results in the growth of ferrite grains, leading to lower strength in the steel plate. By employing a controlled cooling rate after normalizing, the phase transformation temperature can be reduced, the type of phase transformation can be controlled, the phase transformation structure can be refined, and the growth of carbides and nitrides of micro-alloying elements can be suppressed, causing them to precipitate uniformly at low temperatures, thereby improving the strength of the steel while maintaining its toughness. From the perspective of composition design, under the condition of ensuring the same mechanical properties, the content of carbon or alloy elements in the steel can be reduced to improve the weldability of the steel. To this end, relevant researchers or manufacturers have conducted exploratory research and development on normalizing cooling equipment and processes, and have achieved certain practical effects. Normalizing Cooling System (NCC - N) after Annealing FurnaceThe NCC system is installed after the roller hearth normalizing furnace. After medium and heavy plate steel is heated and discharged, it undergoes controlled cooling through the NCC system, rapidly reducing the steel plate to the phase transition temperature, followed by cooling on the cold bed. In some cases, a straightening machine is also added after the NCC equipment.
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