【Corrosion Technology Edition】Daily Question 20170818: What is calm steel? What is boiling steel?

Boiling steel is steel that has not been fully deoxidized. During casting, the molten steel boils (gas escapes) inside the ingot mold; after the ingot solidifies, honeycomb-like bubbles are present within it. During rolling, these bubble cavities fuse together. This type of steel is characterized by a very low silicon content, and it is usually cast in the form of an ingot that is smaller at the top and larger at the bottom, without a insulation cover. The advantages of this steel include high yield, low production costs, as well as good surface quality and deep-drawing properties. The disadvantages are that it contains many impurities and there is significant compositional segregation, resulting in uneven properties. Killed steel, on the other hand, is steel that has been fully deoxidized. It is typically cast in the form of an ingot that is larger at the top and smaller at the bottom, with an insulation cover. During casting, the molten steel remains calm and does not boil. Since there is an insulation cover at the top of the ingot mold (which provides additional molten steel during solidification), this cover section must be removed after rolling, resulting in a lower yield. However, the structure of such steel is dense, with minimal segregation and uniform quality. High-quality steels and alloys are generally killed steel.

Calmed steel is a fully deoxidized steel, with the mass fraction of oxygen not exceeding 0.01%. Boiling steel is steel with incomplete deoxidation.

　　Boiling steel is a type of material; it is steel that has not been fully deoxidized. 　　It is generally low-carbon steel. It is steel with incomplete deoxidation; during casting, the molten steel releases large amounts of carbon monoxide gas in the ingot mold, causing boiling. Compared with normalized steel, this steel offers a higher yield, lower cost, and better surface quality; however, its internal quality is uneven. It is denoted by “Boil” or “F”, such as ordinary carbon steel plate 3Boil or A3F. 　　Calmed steel is a fully deoxidized steel, with the mass fraction of oxygen not exceeding 0.01% (usually ranging from 0.002% to 0.003%). 　　It is usually cast in an ingot shape that is larger at the top and smaller at the bottom, with a insulation cap, ensuring that the molten steel remains calm and does not boil during casting. Due to the insulation cap on the upper part of the ingot mold (which is used to supply additional molten steel during solidification), this cap section must be removed after rolling and blanking; as a result, the steel has a low shrinkage rate, a dense microstructure, minimal segregation, and uniform quality. High-quality steels and alloy steels are generally killed steels.

Calmed steel is steel that has been completely deoxygenated. It is usually cast in the form of ingots that are larger at the top and smaller at the bottom, with a insulation cover; during pouring, the molten steel remains calm and does not boil； Boiling steel is steel with incomplete deoxidation; during casting, the molten steel boils (gas escapes) inside the ingot mold

Calmed steel is steel that is completely deoxygenated, while boiling steel is steel that is incompletely deoxygenated

Steel that is completely deoxygenated is called killed steel； Steel that is not fully deoxygenated is called boiling steel.

Before casting, the molten steel is thoroughly deoxidized using ferromanganese, ferrosilicon, and aluminum; no carbon monoxide is released during solidification, resulting in a dense steel ingot. This type of steel is known as killed steel. Due to incomplete deoxidation of the molten steel, a considerable amount of oxygen remains in it. After the molten steel is poured into the ingot mold, oxygen in the steel reacts chemically with carbon, resulting in the formation of large amounts of carbon monoxide gas, which causes the molten steel to boil during pouring. Hence it is called boiling steel

Depending on the degree of deoxidation during smelting, steel can be classified into boiling steel, semi-killed steel, and killed steel. Calmed steel is a fully deoxidized steel, with the mass fraction of oxygen not exceeding 0.01% (usually ranging from 0.002% to 0.003%). It is usually cast in an ingot shape that is larger at the top and smaller at the bottom, with a insulation cap, ensuring that the molten steel remains calm and does not boil during casting. Due to the insulation cap on the upper part of the ingot mold (which is used to supply additional molten steel during solidification), this cap section must be removed after rolling and blanking; as a result, the steel has a low shrinkage rate, a dense microstructure, minimal segregation, and uniform quality. High-quality steels and alloy steels are generally killed steels. Boiling steel is steel with incomplete deoxidation; during casting, large amounts of carbon monoxide gas are released from the molten steel in the ingot mold, causing a boiling phenomenon. Compared with normalized steel, this steel offers a higher yield, lower cost, and better surface quality; however, its internal quality is uneven. It is denoted by “Boil” or “F”, such as ordinary carbon steel plate 3Boil or A3F.

Depending on the degree of deoxidation during steelmaking, steel can be classified into three categories: boiling steel, killed steel, and semi-killed steel. Boiling steel is steel that has not been fully deoxidized; during pouring, the molten steel boils inside the ingot mold as gases escape. After the ingot solidifies, honeycomb-like bubbles remain within it, and these bubbles fuse together during the rolling process. This type of steel is characterized by a low silicon content, and it is usually cast in the form of an ingot that is smaller at the top and larger at the bottom, without a insulation cover. The advantages of this type of steel are high yield, low production costs, as well as good surface quality and deep drawing properties. However, its disadvantages include a high level of impurities and significant compositional segregation, resulting in uneven properties. Killed steel, on the other hand, is steel that has been fully deoxidized. It is typically cast in the form of an ingot that is larger at the top and smaller at the bottom, with an insulation cover in place. During pouring, the molten steel does not boil. Since there is an insulation cover at the top of the ingot mold to supply additional molten steel during solidification, this cover must be removed after rolling, which results in a lower yield. Nevertheless, the structure of such steel is dense, with minimal segregation and uniform quality. High-quality steel and alloys are generally of the killed steel type.

Calmed steel is steel that is completely deoxygenated. It is usually cast in an ingot shape that is larger at the top and smaller at the bottom, with a insulation cover, ensuring that the molten steel remains calm and does not boil during pouring. Due to the insulation cap on the upper part of the ingot mold (which is used to supply additional molten steel during solidification), this cap section must be removed after rolling and blanking; as a result, the yield of steel is low, but its microstructure is dense, with minimal segregation and uniform quality. High-quality steels and alloys are generally killed steels. Boiling steel is steel with incomplete deoxidation. During pouring, the molten steel boils inside the ingot mold (as gas escapes); after the ingot solidifies, honeycomb-shaped bubbles are formed within it, and these bubble cavities fuse together during the rolling process. These types of steel are characterized by a very low silicon content, and they are usually cast as ingots that are smaller at the top and larger at the bottom, without a insulation cover. The advantages are high steel yield, low production costs, and good surface quality and deep drawing properties. The disadvantage is that steel contains many impurities and has significant compositional segregation, resulting in uneven properties.