Rolls for hot-rolling non-ferrous metals and method of making

Claim 2

An improved method of making a work roll for a hot-rolling mill of the type used for rolling non-ferrous metal and generally comprising the steps of: providing a steel alloy bar having a chromium content of about 4.0 to 6.0 percent; and machining said bar into a work roll having a predetermined shape; and heat-treating said work roll, to harden said steel alloy, by heating the roll to an elevated temperature then cooling the roll in a controlled atmosphere; wherein the improvement comprises: heat treating the roll by heating the roll to an elevated temperature in a controlled atmosphere then cooling the roll in an oxidizing atmosphere to harden said steel alloy and to form a dense, tightly-adherent oxide surface scale on at least the working surfaces of said work roll, which scale serves, during subsequent use for hot-rolling, to improve the average life of the roll; and maintaining said surface scale on at least said working surfaces of said roll during any subsequent finish machining operations.

Claim 3

A steel work roll produced by the method of claim 1 for a hot-rolling mill comprising a forged steel roll fabricated from a steel alloy having a chromium content of about 4.0 to 6.0 percent, the working surfaces of said roll having a dense, tightly-adherent oxide layer for improving the wear resistance of the roll.

Claim 4

A steel work roll according to claim 1, wherein the chromium content of said steel alloy is between about 5.0 and 5.5 percent.

Claim 5

A steel work roll according to claim 1, wherein said steel alloy is a chromium-molybdenum alloy.

Claim 6

A steel work roll produced by the method of claim 1 for a hot-rolling mill consisting essentially of: ______________________________________ Percent ______________________________________ Carbon 0.35-0.45 Chromium 5.00-5.50 Manganese 0.20-0.50 Silicon 0.90-1.10 Molybdenun 1.20-1.50 Vanadium 0.85-1.15 Sulfur Up to 0.03 Phosphorus Up to 0.03 ______________________________________ and the remainder iron, said work roll having an oxide surface scale forming a dense, tightly-adherent protective layer on the working surfaces of said roll.

Claim 9

A method according to claim 6, wherein said rolls are made from a chromium-molybdnum hot-work tool steel alloy and said breakdown rolls are heat treated to a hardness of between about 49 to 43 HRC, said intermediate rolls are heat treated to a hardness of between about 49 to 52 HRC, and said finishing rolls are heat treated to a hardness of about 52 HRC minimum.

Claim 10

An improved method of heat-treating the work rolls of a rolling mill of the type having a plurality of successive roll stages used for the hot-working of non-ferrous metals, said successive roll stages being characterized as containing breakdown rolls, intermediate rolls and finishing rolls, wherein the improvement comprises the steps of; heat-treating said breakdown rolls to provide greater toughness and resistance to thermal cracking as compared to either of said intermediate rolls and said finishing rolls, and heat-treating said finishing rolls to provide an increased resistance to abrasive wear as compared to either of said intermediate rolls and said breakdown rolls.

Claim 11

An improved method of heat-treating the work rolls of a rolling mill of the type having a plurality of successive roll stages used for the hot-working of non-ferrous metals, said successive roll stages being characterized as containing breakdown rolls, intermediate rolls and finishing rolls, wherein the improvement comprises the steps of; heat-treating said breakdown rolls to provide greater toughness and resistance to thermal cracking as compared to either of said intermediate rolls and said finishing rolls, and heat-treating said finishing rolls to provide an increased resistance to abrasive wear as compared to either of said intermediate rolls and said breakdown rolls.

Claim 12

The method according to claim 8 wherein said heat-treating comprises; heating the work rolls to an elevated temperature in a controlled atmosphere furnace, soaking the rolls at an elevated temperature, cooling the rolls in a controlled atmosphere, then tempering said finishing rolls to a greater hardness than either of said intermediate rolls and breakdown rolls and tempering said intermediate rolls to a greater hardness than said breakdown rolls.

Claim 13

A method according to claim 9, wherein the heat treating step includes heating said work roll to an elevated temperature of between about 1875° F. and 1975° F. for abut one-half hour after said roll reaches temperature uniformity, and cooling said roll in an oxidizing atmosphere to form thereon a protective oxide surface scale when said roll is a hot-work tool steel alloy containing from about 4.0 to 6.0 percent chromium.

Claim 14

A method according to claim 10, wherein said work roll is heated in a controlled atmosphere furnace, the atmosphere of said furnace comprising a gas consisting essentially of hydrogen, nitrogen and carbon monoxide maintained at a dew point of between about 38° F. to 46° F.

Claim 15

A method according to claim 10, including the steps of, after cooling said work roll, tempering said work roll at a temperature of about 1025° F. for about two hours after said roll reaches temperature uniformity and cooling said roll.

Claim 16

A method according to claim 12, wherein a plurality of work rolls are provided, said work rolls comprising heat treated and tempered breakdown rolls, intermediate rolls and finishing rolls and including, after the steps of tempering and cooling said work rolls, retempering said breakdown rolls at a temperature of between about 1125° F. and 1150° F. for about two hours after reaching temperature uniformity to a hardness of between about 49 to 43 HRC, retempering said intermediate rolls at a temperature of about 1050° F. for about two hours after reaching temperature uniformity to a hardness of between about 49 to 52 HRC and retempering said finishing rolls at a temperature of about 1025° F. for about two hours after reaching temperature uniformity to a hardness of 52 HRC minimum and recooling said breakdown, intermediate and finishing rolls.

Claim 17

A method according to claim 10, wherein said oxidizing atmosphere is air.

Claim 18

A method according to claim 10, wherein said oxidizing atmosphere includes steam.