Classification of Cast Steel Rolls

Cast steel rolls can be divided into two categories: steel rolls (carbon content 0.4-1.4%) and semi-steel rolls (carbon content 1.4-2.4). Steel rolls have low carbon content, so their hardness is low, and their structure is generally composed of iron. The composition of ferrite and pearlite. As the carbon content increases, the number of ferrite decreases and the number of pearlite increases. In order to increase the hardness, alloy elements such as Cr, Ni, Mo can be added, or special heat treatment can be carried out. Because the steel roll has high tensile strength and toughness, it is suitable for the blooming mill or blooming mill with high rolling temperature and large rolling load, also can be used as a support roller. Such as special heat treatment to obtain high hardness above HS90, it can also be used as a cold rolling work roll.

The carbon content of the semi-steel roll is between the cast steel roll and the cast iron roll. Its structure is mainly composed of pearlite and contains certain carbides. Therefore, its strength is slightly higher than that of cast steel roll, lower than that of cast iron roll, and its hardness is higher than that of general cast steel roll. The main feature of semi-steel roll is that the internal hardness drop is very small, so it is especially suitable for manufacturing deep hole roll, and widely used in roughing and finishing stands of section mill, roughing and finishing roll of hot strip continuous rolling mill. If the silicon content in semi-steel roll material is increased and graphitized, it has high hot cracking resistance and strong toughness. As the blooming roll of blooming mill, the rough roll of large section steel, the roll of continuous rolling mill and vertical roll of hot strip continuous rolling mill, good rolling effect can be obtained.　　　　　

1. According to the chemical composition and heat treatment process of alloy cast steel roll, the outer matrix structure of roll body can be pearlite and bainite. Pearlite can be sheet or spherical, or sorbite type. Tempered sorbite not only has high strength and toughness, but also has excellent hot cracking resistance, especially the tempered sorbite with phase has excellent wear resistance. Therefore, when used in blooming mill, the rolling effect is good.　　

Alloy cast steel rolls have high tensile strength and toughness, certain wear resistance and thermal crack resistance, and are mainly used for blooming rolls of blooming mills and roughing rolls of section steel mills.

2. Cast high chromium steel roll

High chromium steel roll is produced by centrifugal compound casting process with high chromium steel (C: 0.5-1.5%, Cr: 8-15%) as outer layer material and nodular cast iron as core material. Because the outer layer of high chromium steel roller has more chromium-rich matrix structure than high chromium composite cast iron material, its wear resistance is very good. In addition, due to the low content of carbide in the working layer of high chromium steel roll body, the wear resistance is very good, Based on this, high chromium steel roll is the development trend of rough roll material selection for hot strip mill at present.

3. Centrifugal composite high-speed steel roll

High-speed steel roll not only has high resistance to hot cracking, but also has high wear resistance and red hardness, which can greatly prolong the service life of rolls and improve the quality of rolled products. It can be used in the front work roll of finishing rolling of hot strip mill.

4. Semi-steel roll

The carbon content of semi-steel roll is usually 1.4-2.4%, and its mechanical properties are between cast steel and cast iron. It has the characteristics of small hardness drop and high wear resistance. It is widely used in roughing and intermediate rolling stands of section steel rolling mill, as well as the front work roll of rough rolling and finishing rolling of hot strip continuous rolling mill. When the carbon content of semi-steel is more than 1.9%, it is called high carbon semi-steel There are eutectic carbide and pseudo eutectic carbide in it, which are used for continuous rolling mill stand, the intermediate stand of section mill and finishing mill stand.

When semi-steel rolls are used as hot rolling rolls, in order to improve the crack resistance, the silicon content is added in the composition, which becomes graphite cast steel rolls. It concentrates the advantages of cast steel and cast iron, and is widely used in hot strip rolling mill rolls and section mill rolls.

Through smelting, forging and heat treatment, the working layer of forged steel roll body has uniform high hardness, high wear resistance and excellent accident resistance, and at the same time, the strength and toughness of roll neck and core of roll body are ensured. The unique performance of forged steel roll makes it have irreplaceable advantages in cold rolling and non-ferrous rolling.

According to the service conditions, forged steel roll can be divided into forged steel hot roll and forged steel cold roll. Forged steel hot roll is mainly used for hot rolling and profile steel rough roll, and forged steel cold roll is widely used for cold roll. The cold roll of forged steel requires high and uniform hardness on the surface to ensure the dimensional accuracy and good surface quality of cold-rolled strip or steel plate. The roll body has a certain depth of hardened layer and has high accident resistance. Therefore, the original structure of the roll is required strictly, one is pure metallurgical quality, the other is uniformity of structure. At present, the cold roll material containing about 2% chromium is mainly used in our country. The working layer above hs90 is about 10 mm, while the newly developed Cr5 series cold roll with 5% chromium content and the working layer above hs90 is more than 30mm. The excellent performance of Cr5 series cold rolling roll in various aspects will replace the traditional CR2 series cold roll step by step and become the development direction of cold rolling work roll.