ROLLS: Pearlite, Bainite and Martensite Structures

By SARJIT ROLLS

Keywords: Adamite, SG Iron, Alloy steel, DPIC Solid, Enhanced carbide ICDP, SG Acicular, hot or cold rolling

At the very first instance these words could sound very tedious and overwhelming but the actual scientific mechanism is very simple.

Pearlite structure is one which is mainly achieved in static castings as the rate of cooling of the metal is slow i.e. a temperature below 600 degC is achieved only after 3 – 4 hours or more after pouring of molten material for rolls. The main characteristic of this structure is that it imparts strength with its equiaxed matrix to the rolls and is used to manufacture rouging mill rolls as in Alloy steel, Adamite, SG Iron grade. The hardness that can be achieved is in the range of 40 – 70 sH.

Bainite Structure can be achieved by both in static casting, using thicker molds, and in centrifugal casting as the rate of cooling of metal is relatively faster i.e. a temperature below 600 degC is achieved within 15 – 20 minutes after pouring of molten material for rolls. The main characteristic of this structure is that it imparts polish on the rolled product due its fine matrix. Mainly used for finishing mill rolls as in Duplex DPIC rolls, Enhanced carbide ICDP rolls, alloyed barrels and SG acicular rolls. The hardness that can be achieved is in the range of 65 – 80 sH

Martensite Structures can only be casted using centrifugal mechanism as the rate of cooling of metal is very fast i.e. a temperature below 600 degC is achieved within 3-4 minutes after pouring of molten material for rolls. The structure of the material formed is very fine in nature but overall it does not have any useful industrial application as faster the cooling more the risk of chipping of material.

NOTE: There is no fine line between the above structures. Due to variation in cooling at any point either 2 or even three of the above could exist in the same casting. But the major portion could be one of them

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