Heat treatment at high temperatures is a crucial process for enhancing the toughness of steel plates. It involves heating the steel plate to above the upper critical point of the ferrite-austenite phase transformation, approximately 30℃ to 50℃ or higher, to achieve austenitization. After uniform heat preservation, the steel plate is cooled in a free atmosphere. The conventional heat treatment process, 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. However, by employing controlled cooling rates 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 microalloying elements can be suppressed, causing them to precipitate as fine particles at low temperatures. This improves 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 carbon or alloy element content in the steel can be reduced to improve its weldability. For this purpose, researchers or manufacturers have conducted exploratory research and development on normalizing cooling equipment and processes, achieving certain application effects. Normalizing Cooling System (NCC - N)The NCC system is installed after the roller hearth normalizing furnace. After medium and thick steel plates are heated and discharged, they undergo controlled cooling through the NCC system, rapidly reducing the plate temperature to the phase transformation point, followed by cooling on the cold bed. Some installations also include a straightening machine after the NCC equipment.
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