1. Boiling steel plate
Boiling steel plate is hot rolled from common carbon structural steel. The boiling steel is a kind of steel with incomplete deoxidization. Only a certain amount of weak deoxidizer is used to deoxidize the molten steel. The oxygen content of the molten steel is high. When molten steel is injected into the ingot mould, the carbon and oxygen reactions produce a large number of gases, forming the boiling of molten steel, which is named boiling steel. The carbon content of the boiling steel is low, and the silicon content in the steel is low (Si < 0.07%) due to the absence of ferrosilicon deoxidization.
The outer layer of boiling steel is crystallized under the condition of violent agitation of molten steel formed by boiling. Therefore, the surface layer is pure, compact, with good appearance quality, good plasticity and stamping performance, without large concentrated shrinkage, fewer cutting heads and high yield, and the consumption process of boiling steel is simple, the consumption of ferroalloys is low, and the cost of steel is low. The boiling steel plate is widely used in the manufacture of various stamping parts, construction and engineering structures, and some less important machine parts. However, there are many impurities, serious segregation, non-compact structure and uneven mechanical properties in the core of boiling steel. At the same time, due to the high gas content in steel, the toughness is low, the cold brittleness and aging sensitivity are high, and the welding performance is poor. Therefore, the boiling steel plate is not suitable for manufacturing welding structures and other important structures which accept impact load and work at low temperature.
2. Sedative plate
Killed steel plate is hot rolled from common carbon structural steel. Killed steel is a complete deoxidized steel. Before pouring, it is stopped to deoxidize adequately with ferromanganese, ferrosilicon and aluminium. The oxygen content of molten steel is low (usually 0.002-0.003%). The molten steel is quiet in ingot mould and does not boil. Killed steel is named after it.
Under normal operation conditions, there are no bubbles in killed steel, and the structure is dense on average. Oxygen content is low, oxide inclusions in steel are less, purity is higher, cold brittleness and aging tendency is small. At the same time, killed steel has smaller segregation, average performance and higher quality. The defects of killed steel are concentrated shrinkage, low yield and high price. As a result, killed steel is mainly used for components subjected to impact at low temperature, welding structures and other components requiring high strength.
Low alloy steel plates are both killed and semi-killed steel plates. Because of its high strength, superior performance, large amount of steel can be saved and structural weight can be reduced, its application has become more and more common.
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