Graphite steel roll is based on the material of semi-steel roll, by controlling the content and corresponding proportion of graphitization elements and carbide forming elements, adding an appropriate amount of inoculant alloy and nodulizer to the molten steel for inoculation and spheroidization, so that the roll Spherical or agglomerated graphite is formed during solidification, specifically referring to tissues containing a small amount of free graphite.
1. Performance characteristics
The carbon content of graphite steel rolls is equivalent to that of semi-steel rolls, and the matrix microstructure is similar to that of semi-steel rolls. There are still wear-resistant particles with granular and rod-shaped carbides in the matrix structure, and there are also a certain amount of spherical graphite in the matrix structure.
Due to the excellent thermal conductivity of graphite, it can effectively reduce the thermal stress generated by the roll during work. At the same time, the existence of free point-like graphite can play a damping role in preventing crack expansion, so that the thermal cracking resistance can be significantly improved. Due to the role of natural lubricants, graphite steel rolls have unique properties, excellent thermal crack resistance, accident impact resistance, wear resistance of semi-steel rolls, and extremely small hardness drop. The hardness is generally HS35~60.
For large-scale steel rolling mills with deep holes, graphite steel rolls are subjected to finished heat treatment after rough opening, so that the bottom of the pass and the side wall – the surface of the roll can obtain a uniform microstructure, so the wear resistance of the bottom of the pass and the side wall Almost the same as the roll surface.
In addition, according to the purpose of the roll, the carbon content, alloy element content and hardness requirements of the graphite steel roll can be adjusted, and the content and shape of carbides and graphite in the structure can be controlled. Therefore, the graphite steel roll has gradually developed into a series, suitable for different types of rolling mills usage requirements.
2. Manufacturing process
Graphite steel rolls are similar to semi-steel, and most of them are produced by integral casting. According to the needs, the overflow composite process or centrifugal casting can also be used to produce composite graphite rolls whose outer layer is made of graphite steel, and whose core and roll diameter are made of alloy cast steel, such as two-roll rough rolls of hot strip rolling mills.
The casting method of the graphite steel roll ring is the same as that of the semi-steel roll ring. It is produced by centrifugal casting. The outer layer of the roll ring is graphite steel, and the inner layer is nodular cast iron. A reasonable heat treatment system should be proposed for graphite steel rolls for different purposes. The main requirements for rough rolls are high thermal stability, strength, and plasticity. The requirements for intermediate rolling and finishing mill rolls are high hardness and wear resistance.
3. Main purpose
Graphite steel rolls are mainly used in large blooming mills, billet continuous rolling mills, large and medium-sized section steel mills for rough rolling, intermediate rolling and finish rolling, small section steel and bar rough rolling, composite graphite steel rolls are used for hot strip two-roll reversible rough rolling and The roller rings used in the vertical rolls of the stove coil mill, the universal rolling mill and the cantilever rolling mill can be made of centrifugal composite graphite steel roller rings.