Commonly used roll materials and selection requirements

The roller is an important part of the rolling mill in the steel rolling mill. It uses the pressure generated by a pair or a group of rollers to roll steel. It mainly bears the effects of dynamic and static loads, wear and temperature changes during rolling. Rolls can be divided into cast iron rolls, cast steel rolls, forged steel rolls, special rolls, etc. according to their materials. The main performance indicators of the roll are the core strength of the roll and the toughness and wear resistance of the working layer (surface layer).

Commonly used roll materials include alloy forged steel, alloy cast steel, cast iron, etc.:
(1) Alloy forged steel. The alloy forged steel used for rolls has been stipulated in our country's standards. The GB/T 13314-1991 standard lists steel for hot rolling rolls and cold rolling rolls. Hot rolling roll steels include 55Mn2, 55Cr, 60CrMnMo, 60SiMnMo, etc. Cold rolling steel includes 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 unified standard. With the development of electroslag remelting technology, the quality of alloy cast steel is gradually improving, and Hehui cast steel rolls will be widely used in the future.
(3) Cast iron. Cast iron can be divided into ordinary cast iron, alloy cast iron and ductile iron. When casting rolls, different casting molds are used to obtain cast iron rolls with different hardnesses. Therefore, there are semi-chilled rolls, chilled rolls and infinitely chilled rolls:
1) Semi-chilled roll. There is no obvious white layer on the surface of the roll, and the roll surface hardness is HS≥50:
2) Chilled roll. There is an obvious white layer on the surface, a gray layer in the center, and a pitted layer in the middle. The roller surface hardness is HS≥60.
3) Infinitely chilled rollers. The surface is a white layer, but there is no obvious boundary between the white layer and the gray layer. The roller surface hardness is HS≥65.
Cast iron rollers have high hardness, smooth surface, and are wear-resistant. The manufacturing process is simple and cheap. The disadvantage is that it is less strong than steel rolls. Ductile iron rollers have better strength.
Roll material requirements:
(1) Wear resistance Wear is a common form of damage to rolls, which affects the surface accuracy and dimensional accuracy of the rolled pieces. Since the wear mechanism between the rolled pieces and the rolls in the roll gap is relatively complex, there is no wear resistance index so far. It can characterize the wear resistance of the roll, so the wear resistance of the roll can only be judged indirectly based on the composition and hardness.
The selection of roll hardness is based on the rolling stock, rolling mill and rolling conditions, as well as cost. Sometimes more importantly, operating habits and roll use experience are more important. The higher the hardness, the worse the toughness, which must be considered comprehensively. The hardness of a roll is generally measured by Shore hardness because Shore hardness machines are portable and can be used on the roll, leaving only a small indentation on the roll.
(2) Toughness index The toughness index will be selected according to the main damage on the roller surface. The toughness indexes that can be selected include yield strength, impact toughness, cold and hot fatigue, fracture toughness, contact fatigue strength, etc. According to the specific use conditions and main damage mechanism of the roll, generally only one of them needs to be selected as the roll toughness index.
The roll may leave residual stress due to uncoordinated deformation during the casting, heat treatment, surfacing and cutting processes. During use, residual stress and working stress are superimposed, which together cause different damage phenomena.
(3) Core strength The working layer and core of the roll have different strength requirements. Generally speaking, the strength of the roll should be the core strength, which is used to resist bending and torsional stress and avoid roll breakage.
Sometimes the working layer of a roll directly requires strength. For example, the compressive strength can represent the ability of the roll surface to resist fracturing. Due to the high cost of testing toughness indicators, strength is sometimes used to roughly indicate the ability of the roll surface to resist various cracks.