Cast iron roll
The carbon content of cast iron roll is about 2.5%~3.5%. According to the main material, it can be divided into four categories: ordinary cast iron roll, high Ni-Cr infinite cold-hardened composite cast iron roll, high chromium composite cast iron roll and alloy nodular cast iron roll. Common structures in cast iron rolls can be divided into three categories: matrix, cementite and graphite. The matrix structures are mainly tensitic, ferrite, pearlite, bainite and martensite. The forms of graphite in cast iron generally include flake and spherical:
Ordinary cast iron roll
Ordinary cast iron rolls can be divided into three types: cold cast iron rolls, medium and low alloy infinite cold cast iron rolls, and medium and low alloy nodular cast iron rolls. Cold cast iron is made by supercooling hot iron and freezing the die surface. This chills the roll body surface, creating a hard, wear-resistant white layer. Cold cast iron rollers can be non-ductile iron, ductile composite, or spherical core. Infinite cold-hardened cast iron lies between cold-hardened cast iron and gray cast iron. The working layer has graphite and blends smoothly into the core. These low-end rolls are mainly used in various rolling mills: sheet, three-high Lauter medium plate, wire, bar, and section rolling mills.
high nickel chromium infinite cold cast composite iron roll
Unlimited-hardened cast iron is between cold-hardened and gray cast iron. Graphite distributes uniformly in the working layer. Its content increases with depth, reducing hardness. Also known as unbounded cold-hardened cast iron. Higher alloy elements in cold-hardened cast iron make high nickel-chromium rolls. These are produced by full washing or centrifugal casting.
High Ni Cr infinite chilled cast iron resists abrasion due to its carbide-rich matrix. Graphite provides heat resistance and strength. It is used for finishing wide, medium, and thick plate rolling mills, as well as strip rolling mills.
High chromium composite cast iron roll
The high chromium composite cast iron roll is made of high chromium white wear-resistant cast iron containing 12-22% chromium as the outer material of the roll body, and generally uses nodular cast iron as the material of the roll core and neck. The high alloy composite cast iron roll is produced by centrifugal composite casting process. Due to the presence of strip-like Cr7C3 eutectic carbides, chrysanthemum-like Mo2C eutectic carbides and granular Cr23C6 secondary carbides in the matrix, high chromium cast iron rolls have excellent wear resistance. It is widely used for roughing and finishing rolling of hot strip rolling mill, roughing and finishing rolling of wide and medium thickness plate rolling mill and finishing rolling of small section steel and plate rolling mill.
Alloy nodular cast iron roll
Alloy nodular cast iron rolls have high tensile strength, heavy load and good abrasion resistance because of the uniform distribution of graphite from the roll body to the core. The matrix structure of alloy nodular cast iron roll can be roughly divided into two categories according to the matrix structure of the roll body: Pearlite nodular cast iron roll and acicular nodular cast iron roll, alloy nodular cast iron roll is generally cast as a whole, but acicular cast iron roll due to high alloy content, casting stress, can be used centrifugal composite casting process, to obtain the ideal comprehensive performance. Alloy nodular cast iron rolls have good thermal shock resistance and wear resistance, and are widely used in large blooming mill, section mill, bar joint mill and large seamless tube mill.
Cast steel roll
ast steel rolls include steel rolls (0.4-1.4% carbon) and semi-steel rolls (1.4-2.4% carbon). Steel rolls, with low carbon, have low hardness, typically comprising ferrite and pearlite. Higher carbon increases pearlite and reduces ferrite. Adding Cr, Ni, Mo, or special heat treatments boosts hardness. Steel rolls, with high tensile strength and toughness, suit high rolling temperatures and heavy loads in billet or blooming mills. With heat treatment, achieving HS90+ hardness, they serve as cold rolling work rollers.
Semi-steel rolls have carbon content between steel and cast iron rolls. They mainly consist of pearlite and some carbide, offering strength higher than steel rolls but lower than cast iron rolls. Their hardness surpasses ordinary steel rolls. Semi-steel rolls exhibit minimal internal hardness drop, ideal for deep hole roll manufacture. They are used in roughing and finishing stands of section steel mills and the front work rolls of hot strip mills. Increasing silicon content enhances thermal cracking resistance and toughness through graphitization, making them suitable for blooming mill opening rolls, large section steel rough rolls, continuous rolling mill opening rolls, and hot strip rolling mill stands.
Alloy cast steel roll
The chemical composition and heat treatment process of the roller body create an outer matrix of pearlite or bainite. Pearlite can be flake, spherical, or sorbitite. Tempered sorbitite offers high strength, toughness, and thermal cracking resistance. Phase-tempered sorbitite provides excellent wear resistance, making it effective in blooming mills.
Alloy cast steel rolls possess high tensile strength, toughness, wear resistance, and heat cracking resistance. These rolls are primarily used for billet rolls in blooming mills and rough rolls in section mills.
Casting high chromium steel roll
High chromium steel rollers use high chromium steel (C: 0.5-1.5%, Cr: 8-15%) for the outer material and ductile iron for the core. The centrifugal composite casting process combines these materials. The chromium-rich outer layer offers excellent wear resistance. The low carbide content in the working layer substrate provides hot cracking resistance. Due to these properties, high chromium steel rolls are currently preferred for coarse rolls in hot rolling mills.
Centrifugal composite high speed steel roll
The high speed steel roll not only has high thermal cracking resistance, but also its high wear resistance and red hardness can greatly prolong the life of the roll and improve the quality of the rolling material. It can be used for the front work roll of the tropical tandem mill finishing rolling.
Semi-steel roll
Semi-steel rolls usually have a carbon content of 1.4-2.4%. Their mechanical properties fall between cast steel and cast iron. They feature small hardness drop and high wear resistance. These rolls are widely used in rough and middle rolling stands of section steel mills, and in rough and finishing rolling of hot strip mills. Eutectic and pseudo-eutectic carbides in the matrix make them suitable for billet continuous rolling stands and finishing mills. Increasing silicon content improves crack resistance, resulting in graphite cast steel rolls. These rolls combine the advantages of cast steel and cast iron, making them ideal for billet hot rolling mills and section steel mills.
Forging steel roll
Forged steel rolls undergo smelting, forging, and heat treatment, giving the working layer high hardness, wear resistance, and accident resistance. The roll neck and core have high strength and toughness. These properties make forged steel rolls indispensable in cold and non-ferrous rolling. They come in two types: hot forged and cold forged. Hot forged rolls are used for hot rolling billets and rough rolls for section steel. Cold forged rolls, used for cold rolling, require a uniform high hardness surface to ensure dimensional accuracy and surface quality.
The roll body needs a deep hardened layer for high accident resistance, demanding pure metallurgical quality and structural uniformity. Currently, China primarily uses cold rolls with 2% chromium, featuring a work layer above HS90 of about 10mm. The newly developed Cr5 series contains 5% chromium, with a work layer above HS90 exceeding 30mm. The Cr5 series exhibits superior properties, gradually replacing the traditional Cr2 series and setting the development direction for cold work rolls.
