Classification of Roll Forgings by Material

Roll forgings can be categorized into three main types based on their material composition: cast iron rolls, cast steel rolls, and forged steel rolls.

1. Cast Iron Rolls
   Cast iron rolls typically have a carbon content of 2.5%–3.5% and can be further classified into four main types based on their primary material composition:

   • Chilled cast iron rolls
   • Indefinite chilled cast iron rolls
   • High chromium cast iron rolls
   • Spheroidal graphite cast iron rolls

   The microstructure of cast iron rolls can be divided into three primary components: matrix, carbide, and graphite. The matrix structures include austenite, ferrite, pearlite, bainite, and martensite. Graphite in cast iron appears in two main forms: flake and spheroidal.

2. Cast Steel Rolls
   Cast steel rolls are divided into two categories based on their carbon content:

   • Steel rolls (carbon content: 0.4%–1.4%)
   • Semi-steel rolls (carbon content: 1.4%–2.4%)

   Steel rolls have a lower carbon content, resulting in lower hardness. Their structure is typically composed of ferrite and pearlite. As carbon content increases, the amount of ferrite decreases while pearlite increases. To enhance hardness, alloying elements such as chromium, nickel, manganese, molybdenum, and vanadium can be added, or specialized heat treatments can be applied.

   Due to their high tensile strength and toughness, steel rolls are suitable for applications involving high rolling temperatures and heavy rolling loads, such as roughing mills or blooming mills. They are also used as support rolls. When subjected to specialized heat treatment, achieving a hardness of over HS90, steel rolls can also serve as work rolls for cold rolling processes.

   Semi-Steel Rolls
   Semi-steel rolls have a carbon content between that of cast steel and cast iron rolls. Their hardness is higher than that of general cast steel rolls but lower than that of cast iron rolls. The key characteristic of semi-steel rolls is their minimal drop in hardness internally, making them particularly suitable for manufacturing deep-groove rolls.

   By increasing silicon content and undergoing graphitization treatment, semi-steel rolls can achieve high resistance to thermal cracking and improved strength and toughness. This makes them effective for use in blooming mill rolls, large-section roughing rolls, continuous blooming mill rolls, and vertical rolls in hot strip mills, ensuring excellent rolling performance.

3. Forged Steel Rolls
   Forged steel rolls undergo processes of smelting, forging, and heat treatment to ensure the working layer of the roll body has high hardness, excellent wear resistance, and superior accident resistance. At the same time, the roll neck and the core of the roll body maintain sufficient strength and high toughness.

   The unique properties of forged steel rolls give them an irreplaceable advantage over cast rolls in cold rolling and non-ferrous rolling applications.