Classification of Rolls

The carbon content of cast iron rolls is about 2.5%-3.5%. According to the main materials, they can be divided into four categories: ordinary cast iron rolls, high nickel-chromium infinite chilled composite cast iron rolls, high chromium composite cast iron rolls and alloy ductile iron rolls. The common structures in cast iron rolls can be divided into three major categories: matrix, cementite, and graphite. The matrix structure is mainly composed of tenite, ferrite, pearlite, bainite and martensite. The shape of graphite in cast iron is generally Flaky and spherical.

 1. Ordinary cast iron roll

Ordinary cast iron rolls can be divided into chilled cast iron rolls, medium and low alloy infinite chilled cast iron rolls, and medium and low alloy ductile iron rolls.

Chilled cast iron is a kind of cast iron obtained by the method of hot metal’s own supercooling and mold surface chilling. The surface of the roll body is chilled to form a white layer, which has high hardness and good wear resistance. Chilled cast iron rolls can be divided into three categories: non-nodular iron, nodular composite, and spherical core according to the manufacturing process and core material. Infinite chilled cast iron roll is a material between chilled cast iron and gray cast iron. Graphite exists in the matrix structure of the working layer of the roll body, and there is no obvious dividing line between the working layer and the core of the roll body. Ordinary cast iron rolls are mainly used for rolls for stacked thin plate mills, three-high Lauter plate mills, wire rod mills, bar mills and section steel mills.

2. High nickel chromium infinite chilled cast composite iron roll

Infinite chilled cast iron is a material between chilled cast iron and gray cast iron. Infinite chilled cast iron roll body working layer set has evenly distributed graphite in the matrix structure, and the content of graphite goes from the surface of the roll body. As the depth increases, the hardness decreases. Therefore, there is no obvious dividing line between the working layer of the roll body and the core. It is also called unbounded chilled cast iron roll. Infinite chilled cast iron roll material contains high chromium, nickel and molybdenum. The alloy elements are high nickel-chromium infinite chilled cast iron rolls, which are produced by full flushing (overflow method) or centrifugal compound casting process.

There are a large number of carbides in the matrix structure of the working layer of the high nickel-chromium infinite chilled cast iron roll body, so it has higher wear resistance. Because of the existence of graphite in the matrix structure, it has good heat resistance and is widely used as finishing rolls for wide, medium and heavy plate mills and strip mills.

3. High chromium composite cast iron roll

The high chromium composite cast iron roll is made of high chromium white wear-resistant cast iron with 12-22% chromium as the outer layer of the roll body. Generally, nodular cast iron is used as the material of the roll core and roll neck. It is produced by centrifugal compound casting technology. High-alloy composite cast iron rolls. Due to the existence of 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 and are widely used in roughing and finishing work rolls of hot strip continuous rolling mill, roughing and finishing work rolls of wide and medium plate mills, and finishing rolling of small section and plate mills.

4. Alloy ductile iron roll

The alloy ductile cast iron roll has a uniform distribution of graphite from the roll body to the core, so it has high tensile strength, can withstand heavy loads, and has good wear resistance. The matrix structure is carbides and pearlite or needles. The alloy ductile iron rolls can be roughly divided into two categories according to the matrix structure of the roll body: pearlite ductile iron rolls and needle-shaped ductile iron rolls.

Alloy spheroidal graphite cast iron rolls generally adopt integral casting, but needle-shaped cast iron rolls have high alloy content and large casting stress. Centrifugal compound casting technology can be used to obtain ideal comprehensive performance. Alloy ductile iron rolls have good thermal shock resistance and wear resistance, and are widely used as rolls for large blooming mills, section steel rolling mills, bar continuous rolling mills and large seamless tube rolling mills.