Rolls are one of the most crucial consumables in steel rolling production, and their performance directly affects the rolling efficiency, product quality, and cost control. According to the different materials, rolls can be roughly divided into two major categories: cast iron rolls and cast steel rolls. Each material has different organizational structures, performance characteristics, and application scenarios. This article will provide a systematic introduction to common roll materials, helping users fully understand the characteristics and application scope of various types of rolls, facilitating scientific selection, and improving production efficiency.
Cast Iron Rolls: Types and Characteristics
Cast iron rolls typically contain 2.5% to 3.5% carbon. Based on the main alloying elements and structure, cast iron rolls can be categorized into four main types:
- Ordinary Cast Iron Rolls.
- High Nickel-Chromium Indefinite Chilled Composite Cast Iron Rolls.
- High Chromium Composite Cast Iron Rolls
- Alloy Ductile Cast Iron Rolls.
Structural Components of Cast Iron Rolls
The microstructure of cast iron rolls generally includes three components: matrix, cementite, and graphite.
The matrix may consist of cementite, ferrite, pearlite, bainite, or martensite.
Graphite appears in two common forms: flake and spheroidal (nodular).
1. Ordinary Cast Iron Rolls
Ordinary cast iron rolls include:
- Chilled Cast Iron Rolls.
- Low and Medium Alloy Indefinite Chilled Cast Iron Rolls.
- Low and Medium Alloy Ductile Iron Rolls.
Chilled Cast Iron Rolls are produced by using the self-super cooling of molten iron and the chilling effect of the mold. This process forms a hard white layer (white cast iron) on the roll surface with high hardness and excellent wear resistance.
Based on manufacturing process and core material, chilled cast iron rolls are classified into:
- Non-ductile iron type.
- Composite ductile iron type.
- Spheroidal graphite (SG) core type.
Indefinite Chilled Cast Iron Rolls sit between chilled cast iron and gray cast iron. They contain graphite in the working layer, and the transition between the roll body and the core is gradual, without a distinct boundary. These rolls offer a balance of hardness and toughness and are often used in low-end applications such as:
- Thin plate mills.
- Three-high plate mills.
- Wire rod mills.
- Bar mills.
- Section mills.
2. High Nickel-Chromium Indefinite Chilled Composite Cast Iron Rolls
These rolls are a specialized type of indefinite chilled cast iron roll, alloyed with high levels of nickel, chromium, and molybdenum. They are produced using full flushing (overflow method) or centrifugal composite casting.
The working layer contains evenly distributed graphite and a high density of carbides, providing excellent wear resistance and thermal fatigue resistance. The presence of graphite enhances thermal conductivity and helps resist cracking under temperature fluctuations.
Applications:
- Wide and medium plate mills.
- Strip mills.
3. High Chromium Composite Cast Iron Rolls
Manufacturers produce high chromium composite cast iron rolls using centrifugal composite casting. They make the outer working layer from high chromium white cast iron containing 12–22% chromium, while they use ductile iron for the core and neck to enhance toughness.
The microstructure includes:
- Lath-shaped Cr₇C₃ eutectic carbides.
- Rosette-shaped Mo₂C eutectic carbides.
- Granular Cr₂₃C₆ secondary carbides.
- These carbides give the roll excellent abrasion resistance and thermal fatigue performance.
Applications:
- Roughing and finishing work rolls in hot strip mills.
- Work rolls in wide and medium-thickness plate mills.
- Finishing rolls in small steel and plate mills.
4. Alloy ductile iron rolls
Alloy ductile iron rolls have high tensile strength, can withstand heavy loads, and have good wear resistance because the graphite is evenly distributed in a spherical shape from the roll body to the core. The matrix structure is carbide and pearlite or acicular. Based on the matrix structure of the roll body, these rolls are generally classified into two types: pearlitic ductile iron rolls and acicular (bainitic) ductile iron rolls. Metallurgists divide cast steel rolls into two categories: steel rolls with a carbon content of 0.4–1.4%, and adamite rolls with a carbon content of 1.4–2.4%. These alloy rolls offer excellent thermal shock resistance and wear resistance, making them ideal for use in large-scale roughing mills, steel section mills, bar mills, and seamless pipe rolling mills.
Cast steel rolls
Metallurgists divide cast steel rolls into two categories: steel rolls with a carbon content of 0.4–1.4%, and adamite rolls with a carbon content of 1.4–2.4%. Steel rolls have low carbon content, so the hardness is low. Their structure is generally composed of ferrite and pearlite. As the carbon content increases, the amount of ferrite decreases, and the amount of pearlite increases. Engineers increase the hardness of steel rolls by adding alloy elements such as Cr, Ni, and Mo or by performing special heat treatments. Due to their high tensile strength and toughness, manufacturers use these rolls in slab mills or primary mills where rolling temperatures and loads are high. They also serve as support roles. When engineers apply special heat treatment to achieve a hardness above HS90, operators can use them as cold rolling work rolls.
Adamite rolls have a carbon content between cast steel and cast iron. Their structure is mainly pearlite with some carbide, giving them higher strength than cast steel but lower than cast iron, and better hardness than general cast steel rolls. Their key feature is minimal internal hardness drop, making them ideal for deep-hole rolls.
Engineers enhance thermal crack resistance and toughness by increasing silicon content and applying graphitization. Steel mills widely use adamite rolls in roughing and finishing stands for section steel, and in front-end working rolls of hot strip mills. They also perform well as blanking rolls in primary mills, roughing rolls for large sections, and vertical rolls for hot strip mills.
1. Alloy cast steel rolls
According to its chemical composition and heat treatment process, the outer layer matrix structure of the roll body can be pearlite and bainite. Pearlite can be lamellar or spherical, or troostite type. Tempered troostite not only has high toughness, but also has excellent thermal cracking resistance, especially the tempered troostite structure with phase also has excellent wear resistance, so when used in the primary rolling mill, the rolling effect is good.
Manufacturers design alloy cast steel rolls with high tensile strength and toughness, along with certain wear and thermal cracking resistance. Steel mills mainly use them as blanking rolls for primary rolling mills and roughing rolls for section steel rolling mills.
2. Casting high chromium steel rolls
Manufacturers use high chromium steel (C: 0.5–1.5%, Cr: 8–15%) as the outer layer of the roll body and ductile iron as the core material. They produce these rolls using the centrifugal composite casting process.Because the outer layer of the roll body has a matrix structure that is richer in chromium than the high chromium composite cast iron material, it has excellent wear resistance. In addition, due to the low carbide content in the matrix structure of the working layer of the high chromium steel roll body, it has excellent thermal crack resistance. Based on this, high chromium steel rolls are the current development trend of material selection for roughing rolls of hot rolling mills.
3. Centrifugal composite high-speed steel rolls
High-speed steel rolls not only have high thermal crack resistance, but also their high wear resistance and red hardness can greatly extend the life of the rolls and improve the quality of rolled products. They can be used for the front-end working rolls of hot rolling mills.
4. Adamite Rolls
The carbon content of Adamite rolls is typically between 1.4% and 2.4%. Their mechanical properties fall between those of cast steel and cast iron. Adamite rolls offer high wear resistance and minimal hardness drop during operation, making them ideal for demanding rolling conditions.
They are widely used in:
- Roughing and intermediate stands of steel section rolling mills.
- Roughing and early finishing of hot strip continuous rolling mills.
We refer to the rolls as high-carbon Adamite rolls when the carbon content exceeds 1.9%.”
Let me know if you want it in a more technical or promotional tone. These contain eutectic and pseudo-eutectic carbides in the matrix, improving wear resistance. High-carbon Adamite rolls are commonly used in:
- Billet continuous rolling stands.
- Intermediate and finishing stands in steel section mills.
For hot rolling applications, we increase the silicon content in the alloy to improve thermal crack resistance. This creates a variant known as graphite Adamite rolls or graphitic cast steel rolls. These rolls combine the toughness of cast steel with the heat resistance of cast iron. Steel mills widely use them in:
- Billet hot continuous rolling mills.
- Steel section rolling mills.
Forged steel rolls
Forged steel rolls are made through smelting, forging, and heat treatment. They feature uniform high hardness, excellent wear and accident resistance, and strong toughness in the core and neck. These properties make forged rolls superior to cast rolls in cold and non-ferrous rolling.
Based on usage, forged rolls fall into two types: hot rolls and cold rolls. We use hot rolls for hot rolling, blanking, and rough rolling of steel sections. Cold rolls require very high surface hardness and uniformity in cold rolling to ensure dimensional accuracy and surface quality. They must also have deep, hardened layers and strong accident resistance.
High-quality cold rolls need pure metallurgical structures and uniform organization. The industry widely uses C2 series cold rolls in China, which contain 2% Cr and have approximately 10mm hardened layers. The Cr5 series, containing 5% Cr and over 30mm hardened layers above HS90, delivers better performance and is set to replace the C2 series as the future mainstream for cold rolling work rolls.
Conclusing
CYKC GROUP provides high-performance rolls to global steel companies.
High-quality products, stable delivery, professional services – CYKC GROUP is your trustworthy choice. Contact us now to make your production more efficient!
Contact us: cykc@cykcgroup.com.cn.