The heavy cylinders between which hot or cold steel is squeezed and shaped in a rolling mill. Rolls are the main consumable of a mill after energy — they wear, are reground between campaigns and eventually scrapped — and their material is chosen stand by stand for wear resistance, strength, and resistance to the thermal cracking that hot rolling causes.
A roll must carry the rolling force without breaking, resist wear so that it holds its profile and surface for a full campaign, and — in hot mills — survive being heated by the stock and cooled by water on every revolution without crazing. No single material does all of that, so mills use different rolls stand by stand: tough materials in the roughing stands where reductions and loads are highest, and hard, wear-resistant ones in the finishing stands where surface and dimensions are made.
Most hot-mill rolls are cast. Centrifugal casting makes a composite roll: a hard, wear-resistant outer shell — indefinite chill double-poured (ICDP) iron, high-chromium iron or high-speed steel (HSS) — fused to a tough grey or ductile iron core. Static-cast rolls in adamite, graphitic steel or spheroidal-graphite (SG) iron serve the roughing and intermediate stands of bar and section mills. Cold-mill work rolls and the large back-up rolls are forged from chromium-molybdenum steels and hardened. Wire-rod finishing blocks use tungsten-carbide roll rings.
Roll hardness is stated in Shore C (HSC) or Leeb (HL) units, measured with portable testers on the barrel, and the hardness range, the depth of the hard working layer and the soundness of the bond between shell and core are what a roll order specifies. Rolls are reground in the mill's roll shop after each campaign, so the usable layer decides how many tonnes a roll will roll in its life.
The GCC's bar, wire rod and section mills and its hot strip and cold rolling mills buy rolls continuously, all imported, mainly from China, India and Europe; roll performance — tonnes rolled per millimetre of diameter used — is tracked closely by every mill.
Roll grades are largely producers' own; the Chinese national standards define cast roll grades, and the methods below are cited for hardness and soundness.
| Region | Standard | What it covers |
|---|---|---|
| China | GB/T 1503 SAC |
Cast steel rolls — grades, technical requirements and test methods |
| China | GB/T 1504 SAC |
Cast iron rolls — grades, technical requirements and test methods |
| USA | ASTM A956/A956M ASTM |
Leeb hardness testing of steel products |
| USA | ASTM A388/A388M ASTM |
Ultrasonic examination of steel forgings |
| Europe | EN 10228-3 CEN-CENELEC |
Non-destructive testing of steel forgings — ultrasonic testing of ferritic or martensitic steel forgings |
Grade equivalents and the standards bodies: Steel grades & standards
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