Roll Material Selection for Rough Rolling of Large-scale Steel and Rail Mill
Rolls are an integral part of a rolling mill, and their performance directly affects the rolling process and product quality. Large-scale steel and rail mills generally use small-diameter work roll, large-diameter back-up roll and intermediate roll to form the rolling system. The roll materials of the rolling mill mainly include centrifugally cast rolls, forged rolls and cast iron rolls. There are various roll materials with different grades. The choice of roll material largely affects the rolling process and product quality, and is a crucial factor to determine the life cycle of the rolls. Different roll materials have different properties and cost-effectiveness. This article mainly introduces the roll material selection for rough rolling of large-scale steel and rail mills.
First, centrifugally cast rolls. Centrifugally cast rolls are made of cast iron and alloyed by adding certain metals such as chromium, molybdenum, nickel and vanadium, etc. During casting, the steel-forming alloying elements enter the core of the roll, forming a homogeneous and uniform structure, and its surface is even, homogeneous and wear-resistant. The advantages of centrifugally cast rolls are that the hardness of the surface is generally greater than HRC55, and the roughness of the surface can reach Ra0.4 um. The compressive strength is higher than 230MPa and the core strength can reach 300MPa. The defects of centrifugally cast rolls mainly include excessive casting pores, harder roll surface which not easy to form, severe wear and short life. Due to its high cost, the centrifugally cast roll is not recommended as the roll material of the rough rolling of the rail mill.
Second, forged rolls. Forged rolls are made of high-quality alloy steel through forging and rolling, which can achieve ideal work hardening effect and make the surface of the roll even and wear-resistant. The advantages of forged rolls are that the surface hardness is generally higher than HRC60, the compressive strength is higher than 390MPa and the microstructure is more uniform and fine. The disadvantage of forged roll is that the cost is higher and its durability is also not satisfactory.
Finally, cast iron roll. Cast iron roll is made of gray cast iron with low-carbon content and its surface hardness is generally not more than HRC45-50. The advantages of cast iron roll are low cost, excellent impact toughness and thermal shock resistance, and some grades also have a good wear resistance. The disadvantages of cast iron roll are low strength, high wear rate, large roughness of the surface, and soft surface easier to form.
In summary, among the three roll materials for rough rolling of large-scale steel and rail mills, the centrifugally cast roll is not recommended due to its high cost. The choice of forged roll and cast iron roll should be based on the equipment performance, process parameters and cost. The forged roll has a higher cost but longer life, and its surface hardness can reach HRC60; and the cast iron roll has a lower cost but shorter life and its surface hardness not more than HRC50.
