Stands situated from the beginning of the mill, where the stock temperature is high and the bar speed is low, the contact time and contact angle are therefore high and require a different material than later stands. The wear mechanism in roughing is predominantly thermal, resulting in fire-cracking and a poor suface. Strength in these early stand to intermediate should be considered, breakage and impact damage are most common from roughing to intermediate with less due to heavy reductions and colder bars moving forward, etc. These issues demand a roll material with good bending strength and fracture toughness. Depending on mill conditions and industry’s common practice, conventional grades offers improved wear resistance on these early stands.
But as bar progresses trough the mill, thermal wear lessens but mechanical wear increases due to mechanical abrasions. Harder roll grades with higher carbide and alloy cntenst become the preffered oftions.
CONVENTIONAL GRADES
SG PEARLITIC
SG Pearlitic is characterised by nodular graphite and carbides arranged in a pearlitic matrix. Its properties are similar to Alloy Indefinite Chill except the graphite structure is changed from flake shapes to spheroidal forms. SG Pearlitic rolls will have higher strength than Indefinite Chill. SG Pearlitic rolls are suitable both roughing and finishing, and a wide range of applications. This grade can be produced by Static casting (Monoblock) or using the Centrifugal Cast (CC) Double pour method. In addition various SG Pearlitic grades have been introduced:
SGP grades alloyed with Chromium to achieve a deep penetration of carbides. These grades have a lower hardness drop and good wear resistance properties and is recommended for rolls with deep grooves.
SGP grades alloyed with Molybdenum and Nickel subjected to high temperature heat treatment have an excellent resistance to fire cracking properties along with high strength. The impact resistance is also increased over that of flake graphite iron.
SPECIFICATIONS
Production Type Static Monobloc or Centrifugal Cast Double Pour Materials
Chemical C 3.00-3.40 | Si 1.00-2.00 | Mn 0.30-0.80 | Ni 1.00-2.60 | Cr 0.10-0.90 | Mo 0.30-0.80
Hardness 40-65 HSc | Tensile ≥ 400-600 Mpa | Bending ≥ 600-900 Mpa
SG ACICULAR
SG Acicular, alloyed with the Nickel, Manganese and Chromium with a Bainitic-Acicular-Martensitic matrix has a higher UTS, hardness and is more wear resistant than the SG Pearlitic quality. Semi- continuous carbides maintain the wear resistance while at the same time exhibiting high strength and resistance to firecracks. Extensive heat treatment procedure ensures an acicular matrix. This grade can be produced by Static casting (Monoblock) or using the Centrifugal Cast (CC) Double pour method.
SG Acicular grades alloyed with Chromium to achieve a deep penetration of carbides. These grades have a lower hardness drop, better wear resistance properties, and is recommended for rolls with deep grooves.
SPECIFICATIONS
Production Type Static Monobloc or Centrifugal Cast Double Pour Materials
Chemical C 3.00-3.50 | Si 1.00-2.20 | Mn 0.30-1.00 | Ni 2.50-5.00 | Cr 0.30-1.50 | Mo 0.30-1.00
Hardness 61-78 HSc | Tensile ≥ 400-500 Mpa | Bending ≥ 600-750 Mpa
ALLOY INDEFINITE CHILL
Alloy Indefinite Chill rolls consist of cast iron with fine interdendritic graphite evenly dispersed throughout the barrel of the roll. The size, shape and distribution of the graphite together with the carbide content is controlled by the chilling effect and the alloy content. The addition of alloys such as manganese, nickel, chromium, and molybdenum changes the matrix structure from pearlitic, through bainite, to martensitic. The carbide form is altered from semi-continuous to rigid continuity enhancing the strength, hardness in depth and wear resistance properties.
The fine graphite enhances the resistance to the thermal stresses by increasing the thermal conductivity, thus reducing fire cracks. Its increased shock resistance (damping capacity) helps to reduce spalling particularly when large reductions in section are required.
The gradual change in hardness makes it ideal for deeper grooving and can be used in both roughing and finishing stands for bar and sections, and for roughing and intermediate stands of wire and rod mills. AIC rolls with artensitic structure and high hardness are suitable for finishing stands of wire mills. This grade can be produced by Static casting (Monoblock) or using the Centrifugal Cast (CC) Double pour method.
SPECIFICATIONS
Production Type Static Monobloc or Centrifugal Cast Double Pour Materials
Chemical C 3.00-3.50 | Si 0.60-1.20 | Mn 0.50-1.20 | Ni 1.00-5.00 | Cr 0.70-2.00 | Mo 0.10-0.50
Hardness 51-85 HSc | Tensile ≥ 380-500 Mpa | Bending ≥ 580-700 Mpa
