The carbon content of alloy adamite rolls is usually 1.5%~2.3%, and contains various alloy elements such as Cr, Ni, Mo, V, etc. Generally, the free carbide content is about 6%~10%, which has the advantages of small hardness drop and wear resistance. High performance, good toughness, significantly reduced consumption, and significantly improved surface quality of profiles and rail beams, etc., are widely used to replace cast steel rolls and ordinary low-alloy cast iron rolls, such as large section steel roughing rolls, section steel mills for blooming and intermediate rolling mills Stand, hot strip rolling mills for blooming and finishing work rolls.
The adamite rolls with a carbon content of less than 1.8% contains alloying elements such as chromium, nickel, molybdenum, etc. Its microstructure is tempered sorbate, and its matrix is distributed with fine-grained and rod-shaped carbides, and its hardness ranges from HS35-55. As the carbon content increases, more and more eutectic carbides appear in the structure of the semi-steel roll.
Adjust the carbon content and alloying element content of the semi-steel roll according to the use of the roll, and cooperate with the corresponding heat treatment process to control the structure of the adamite rolls with different matrix, carbide content, and shape, so as to meet the requirements of different rolling mills. Therefore, the semi-steel roll material has been developed into a series of materials, which are suitable for the use requirements of different types of rolling mills.
The carbide content and shape distribution of the working layer of the semi-steel roll body change little along the radius direction of the roll body. Its outstanding performance is that the hardness of the active layer of the roll has little drop, which is suitable for large and medium-sized steel rolling mills with deep openings. For intermediate rolling stands and continuous billet rolling mill rolls, the use of a pre-drilled heat treatment process to produce section steel semi-steel rolls is better.
Semi-steel rolls are also widely used in small steel bar and wire rod rough rolling stands; 4-high roughing, finishing work rolls, and small vertical rolls in hot strip rolling mills. Hot rolled medium and narrow strip steel finishing rolls, etc.
Most of the adamite rolls are produced by static integral casting. In 2002, a centrifugal composite semi-steel backup roll was developed and trial-produced in China. The outer layer of the roll body is made of semi-steel material, and the body and neck of the roll are made of ductile iron. Hot rolled medium-wide steel finishing mill. The semi-steel roller ring is produced by centrifugal casting. The outer layer of the roller ring is made of high-carbon semi-steel, and the inner layer of the roller ring is made of graphite steel or ductile iron. On the high-speed rotating centrifuge, the steel and water of two different materials are respectively poured into the composite casting.
Adamite rolls must be subjected to high-temperature diffusion annealing treatment: chromium and carbon are important elements to form carbides of semi-steel rolls and thus are also important elements to improve the wear resistance of rolls. However, since the solidification of the roll is a non-equilibrium process, the crystallization of the solid solution from the molten steel is a segregation crystallization process, so there is serious chromium segregation in the as-cast microstructure of the semi-steel roll. The austenite grain boundary is a chromium-rich area and a carbon-rich area, where secondary carbides will precipitate and form a network, which greatly damages the microstructure and properties of the roll. Therefore, in order to eliminate the chromium segregation caused by the solidification segregation of the roll, it is necessary to carry out a high-temperature diffusion annealing treatment on the semi-steel roll.
The influence of non-metallic inclusions on the microstructure of adamite rolls: when there are a large number of high-melting non-metallic inclusions in the molten steel, it is easy to form a pseudo-eutectic carbide core, and the eutectic or pseudo-eutectic carbides precipitated during the solidification process are preferred It grows up, and it is easy to form large carbides. The huge cementite is easy to become the occurrence point of thermal cracking and accelerates the expansion of cracks. The existence of non-metallic inclusions will make the fracture toughness value and The plasticity index decrease. Therefore, semi-steel rolls generally require the total amount of non-metallic inclusions to be controlled below 0.05%.
Use caution of adamite rolls
a. The adamite rolls have poor thermal crack resistance and have high requirements for cooling water. The amount of cooling water at the bottom of the hole and groove is small, which is easy to form hot cracks. The position and direction of the cooling water supply should be adjusted to ensure sufficient cooling water.
b. Strictly follow the process regulations during production, correctly control the reduction, avoid rolling black-headed steel and cold steel, reduce rolling accidents, and increase the roughness of the roll surface; after rolling high-alloy steel, the roll should be kept without cooling water. Under the condition of idling, slow cooling is carried out, and rolling is carried out when the temperature of the rolls drops to a certain extent. Install the guide plate correctly and check it frequently to prevent misalignment.
c. When machining the car, the circumferential cracks visible to the naked eye should be turned clean, and the crack detection should be carried out on the machine again to ensure that there are no residual cracks.
d. The roll structure design should be improved, and the roll ring width should be reasonably determined. The roll ring width of the steel roll is generally more excellent than half of the depth of the pass; reduces the stress concentration at the connection between the roll neck and the roll body, such as increasing the transition arc radius.