What is a cast iron roll？
Cast iron rolls are divided into: general cast iron rolls, high nickel and chromium infinite chilled cast iron rolls, chromium composite cast iron rolls, and nodular cast iron rolls.
General cast iron roll：
General cast iron rolls can be divided into chilled cast iron rolls, medium and low alloy infinitely chilled cast iron rolls, and medium and low alloy nodular cast iron rolls.
Chilled cast iron is a kind of cast iron obtained by using the supercooling of molten iron itself and the quenching of the surface of the mold. The surface of the rod 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 according to the production process and core materials: non-ductile iron, nodular composite, and spherical core.
The infinite chilled cast iron roll is a material between chilled cast iron and gray cast iron. There is graphite in the matrix structure of the working layer of the roll body, and there is no obvious dividing line between the working layer of the roll body and the core. Rolls are such low-end rolls.
General cast iron roll application:
Generally, cast iron rolls are mainly used for rolls for stacked thin plate mills, roll Lauter plate mills, wire rod mills, bar mills and section steel mills.
High Ni-Cr Infinitely Chilled Cast Composite Iron Rolls
Infinitely chilled cast iron is a raw material between chilled cast iron and gray cast iron. Infinitely chilled cast iron rolls have evenly distributed graphite in the working layer matrix arrangement of the roll body, and the content of stone circles is from the surface of the roll body to the As the depth increases, the hardness decreases.
Therefore, there is no obvious dividing line between the working layer and the core of the roll body. It is also called unbounded chilled cast iron roll. When the raw material of the roll contains high chromium, nickel, and molybdenum alloy elements, it is high nickel-chromium infinite chilled cast iron. The roll is produced by full flushing (overflow method) or centrifugal composite casting process.
Chromium Composite Cast Iron Rolls
Chromium composite cast iron roll is a kind of chromium white wear cast iron containing 12% ~ 22% chromium. It is the outer material of the roll body. Generally, nodular cast iron is used as the rolling core and neck material, and it is rolled by alloy composite cast iron produced by centrifugal composite cast iron process. . There are Cr7C3 type eutectic carbides on the body, chrysanthemum-shaped Mo2C type eutectic carbides, granular Cr23C6 type secondary carbides, and high chromium cast iron rolls with good wear resistance.
Application of chrome composite cast iron roll:
Chromium composite cast iron rolls are widely used in hot strip continuous rolling mills and pre-finishing work, rough rolling and finishing work of light plates, and small steel.
Ductile cast iron roll
Since the graphite is evenly distributed into a spherical shape from the body to the core, the ductile cast iron has good tensile strength, can withstand heavy loads, and has good wear resistance. The gas structure is carbide and pearlite or acicular body. According to the basic structure of the roller body, the ductile cast iron roller can be divided into two categories: pearlitic ductile cast iron rolling and acicular zone nodular cast iron rolling
The ductile cast iron roll adopts integral casting, but the needle-shaped cast iron roll has high casting stress due to its good alloy content, and the ideal comprehensive performance can be obtained by adopting the centrifugal composite casting process.
Application of Ductile Cast Iron Rolls
Thermal shock and wear resistance, widely used in large steel rolling mills, continuous bar mills and large seamless pipe mills.
Alloying Principle of Infinitely Chilled Cast Iron Roll
C: On the one hand, high carbon content hinders the precipitation of cementite, and on the other hand, due to the increase in the number of graphite cores formed, graphite can be refined. However, if it is too high, it will form graphite floating. Under the condition of constant cooling rate, increase the carbon content within a certain range, reduce the depth of the white layer, and increase the amount of surface carburized body. Combined with the actual carbon content, take 3.1%~3.6% .
Si : Silicon can reduce the solubility of carbon in austenite, not only can increase the eutectoid transformation temperature, but also widen the temperature range of eutectoid transformation, and shorten the incubation period of pearlite and bainite.
Within a certain range, with the increase of silicon content, the diameter of graphite balls becomes smaller. Silicon is controlled at 1.4%~1.8%. The two elements of carbon and silicon directly affect the comprehensive performance of cast iron rolls.
Carbon and silicon should be considered uniformly. The upper limit of carbon equivalent is based on the principle that graphite floating should not occur as much as possible, and the lower limit should meet the performance requirements of the roll to ensure that there is a suitable content of carbide. Therefore, the carbon equivalent is controlled at 3.9%~4.4%.
Mn: manganese element lowers the eutectoid transformation temperature and plays a role in stabilizing and refining pearlite. Manganese can improve the strength and hardness of the roll, but when the content is too high, the segregation is serious, and the as-cast state will precipitate network carbide along the grain boundary. To reduce its toughness, comprehensive consideration should be controlled at 0.4%~0.8%.
Cr : Chromium is the most effective element to increase the depth of the white layer of chilled cast iron rolls. It can significantly offset the adverse effects of silicon and is beneficial to the formation of pearlite structure.
In alloy ductile iron, proper addition of chromium can make some free carbides appear in the structure, which is beneficial to the improvement of hardness and wear resistance, and the chromium content is controlled at 0.2%~0.4%.
Mo: As a stable pearlite element, molybdenum can refine the white layer structure in chilled cast iron, improve the material strength, and improve the thermal strength of the roll.
In alloy ductile iron rolls, appropriately increasing molybdenum content can promote the formation of pearlite structure and increase the dispersion of pearlite. Molybdenum inhibits the decomposition of austenite and is beneficial to the formation of bainite structure. But molybdenum is easy to segregate, so its content should not be too high. It should be controlled at 0.2%~0.6%.
P, S: Control phosphorus content w<0.2%, sulfur content w<0.02%.