alloy forged steel, alloy cast steel and cast iron
Commonly used materials for rolling mill roll are alloy forged steel, alloy cast steel and cast iron, etc.
(1) Alloy forged steel. Alloy forged steel for rolls has been specified in China’s national standards, and steels for hot rolling and cold rolling are listed in GB/T 13314-1991. The steel for hot rolling rolls has 55Mn2, 55Cr, 60CrMnMo, 60SiMnMo, etc. The steel for cold rolling rolls is 9Cr, 9Cr2, 9CrV, 9Cr2W, 9Cr2Mo, 60CrMoV, 80CrN13W, 8CrMoV, etc.
(2) Alloy cast steel. There are not many types of alloy cast steel used for rolls, and there is no uniform standard. With the development of electro slag remelting technology, the quality of alloy cast steel is gradually increasing, and the future meeting of cast steel rolls will be widely used.
(3) Cast iron. Cast iron can be divided into ordinary cast iron, alloy cast iron and ductile iron. When casting rolls, different casts can be used to obtain cast iron rolls of different hardness. Therefore, there are semi-cold rolls, chill rolls and infinite chill rolls:
-Semi-cold roll. There is no obvious white layer on the surface of the roll, and the surface hardness of the roll is HS≥50.
-Chill rolls. The surface has a distinct white layer, the core is a gray layer, the middle is a layer of hemp, and the surface hardness of the roll is HS≥60.
-Infinite chill roll. The surface is a white mouth layer, but there is no obvious boundary between the white mouth layer and the gray mouth layer, and the roll surface hardness is HS ≥ 65.
TINVO cast iron rolls have high hardness, smooth surface and wear resistance, and the manufacturing process is simple and inexpensive. The disadvantage is that the strength is lower than that of steel rolls. Only the strength of the ductile iron roll is good.
Roller material requirements:
(1) Abrasion resistance is the most common form of damage of the roll, which affects the surface precision and dimensional accuracy of the rolled piece. Since the wear mechanism of the rolled piece and the roll in the roll gap is complicated, there is still no wear resistance. The index can characterize the roll wear resistance, so the wear resistance of the roll can only be judged indirectly based on composition and hardness.
The basis for selecting the hardness of the rolls is the rolling stock, the rolling mill and the rolling conditions, as well as the cost, and sometimes importantly, the operating habits and experience with the rolls. The higher the hardness, the worse the toughness must be considered. The hardness of the rolls is generally measured in terms of Shore hardness because the Shore hardness machine is portable and can be used on rolls without leaving a small indentation on the rolls.
(2) Toughness index The toughness index will be selected according to the main damage of the roll surface. The toughness indexes that can be selected are yield strength, impact toughness, hot and cold fatigue, fracture toughness, and contact fatigue strength. According to the specific use conditions of the rolls and the main damage mechanism, it is generally only necessary to select one of them as the roll toughness index.
Rolls may have residual stresses due to uncoordinated deformation during casting, heat treatment, surfacing, and cutting. When used, the residual stress and the working stress are superimposed to jointly induce different damage phenomena.
(3) The strength requirements of the working layer and the core of the core strength roll are different. Generally speaking, the roll strength should be the core strength to resist bending and torsion stress and avoid breaking the roller.
The working layer of the roll sometimes requires strength directly, such as compressive strength, which can represent the ability of the roll surface to resist fracturing. Due to the high cost of testing the toughness index, the strength of the roll surface against various cracks is sometimes roughly indicated by the strength.
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