The back up roll is a roll that supports the work roll and is the largest and heaviest roll used in rolling mills. The roll can support intermediate roll for the purpose of avoiding deflection of the work roll and affect on the yield and quality of the plate and strip rolling mill. The quality characteristics of the backup roll are high surface hardness, good hardness uniformity and the deep hardened layer of roll body, good strength and toughness of roll neck and roll body. the backup roll has high wear resistance and peeling resistance, strong anti-accidents. The forged steel rolls of 1000mm or less are made of 86CrMoV7 and 9Cr2Mo. Its carbon content is 0.80% to 0.95% and Cr content is 2%.It can be used for some small mills. Cr4 and Cr5 back up rolls have a carbon content of 0.4% to 0.6% and a Cr content of 4% to 5%,  suitable for high-speed steel and semi-high-speed steel work rolls.

For some small mills, the forged steel backup rolls of 1000mm or less are made of 86CrMoV7 and 9Cr2Mo, its carbon content is 0.80% to 0.95% and Cr content is 2%.
The steel for Cr4 and Cr5 backup rolls has a carbon content of 0.4% to 0.6% and a Cr content of 4% to 5%. The hardened, wear resistance, peeling resistance, fatigue-resistant and anti-accident properties of the backup rolls basically eliminate the peeling phenomenon of the roll body surface and the roll cutoff accident. Cr4, Cr5 steel backup rolls are suitable for high-speed steel and semi-high-speed steel work rolls.

Characteristics of High-speed steel roll (HSS roll)

1. High-speed steel roll materials contain high alloy elements such as vanadium, tungsten, chromium, molybdenum, and niobium. The types of carbides in the roll structure are mainly MC and M2C. Comparing with ductile iron rolls with high-nickel-chromium rolls, the steel passing volume is high each time, which saves time of roll changing, improves mill operating efficiency and reduces production costs.

2. High-speed steel rolls have good thermal stability. At the rolling temperature, the roll surface has higher hardness and good wear resistance.
High-speed steel rolls have good hardenability, and the hardness from the surface of the roll body to the inside of the working layer rarely decreases, thereby ensuring that the rolls have equally good wear resistance from the outside to the inside.

3. During the use of high-speed steel rolls, under good cooling conditions, a thin and dense oxide film is formed on the surface of the roll body. This uniform, thin and dense oxide film can exist for a long time without falling off, making the high-speed steel rolls wear-resistant significantly improved.

4. High-speed steel rolls have a large material expansion coefficient and good thermal conductivity. The HSS rolls continue to shrink due to the expansion of the high-speed steel materials themselves. During the rolling process, the change of the rolling groove is small, and the consistency of the hole size is maintained for a long time, especially when rolling the bar or rebar, which is more conducive to controlling the negative tolerance of the rolling material.
5. The core of the centrifugally cast high-speed steel roll is made of alloy ductile iron, thus, the roll neck strength is strong.

Application
Bar rolling mill, splitter mill rack, high-speed wire rod finishing mill, hot-rolled narrow strip finishing mill, section and groove steel rolling mill.