Indian Patents. 234951:METHOD AND APPARATUS FOR REDUCING AND SIZING HOT ROLLED FERROUS PRODUCTS

Title of Invention	METHOD AND APPARATUS FOR REDUCING AND SIZING HOT ROLLED FERROUS PRODUCTS
Abstract	N/A

Full Text	FORM 2 THE PATENTS ACT 1970 [39 OF 1970] COMPLETE SPECIFICATION [See Section 10] "METHOD AND APPARATUS FOR REDUCING AND SIZING HOT ROLLED FERROUS PRODUCTS" MORGAN CONSTRUCTION COMPANY, of 15 Belmont Street, Worcester, Massachusetts 01605, United States of America, The following specification particularly describes the nature of the invention and the manner in which it is to be performed :- WO 02/20189 PCT/US01/41707 1 METHOD AND APPARATUS FOR REDUCING AND SIZING HOT ROLLED FERROUS PRODUCTS CROSS REFERENCE TO RELATED APPLICATION 5 This application claims priority from U.S. Provisional Patent Application Serial No. 60/231,108 filed September 8, 2000 and U.S. Utility Patent Application filed August 10, 2001 (serial number unknown). BACKGROUND OF THE INVENTION – 10 1. Field of the Invention This invention relates to the continuous hot rolling of ferrous long products, including, inter alia, rounds, octagons, squares and the like. 15 2. Description of the Prior Art As herein employed in the rolling of rounds, the term "sizing" means imparting a final deformation during the last stage of rolling to obtain a finished nominal product diameter within a specified standard tolerance which is typically about ±0.1mm diameter tolerance and 0.1mm ovality or better. Also, as herein employed, the term 20 "free sizing" means making adjustments to the roll partings of sizing stands to produce finished product diameters which are slightly larger or slightly smaller than the nominal diameter designated for the roll grooves, but are diameters which are within an acceptable tolerance for the obtained diameter. Various techniques have been developed for sizing and free sizing ferrous long 25 products. For example, as disclosed in U.S. Patent No. 4,907,438 issued March 13, 1990 to Sasaki et al., it is known to roll round process sections through successive two roll sizing stands, with a round-round pass sequence, and with the roll passes configured to take relatively light reductions on the order of 8-15 % per pass. By feeding the sizing stands with different diameter rounds taken from different 30 stands in the upstream intermediate or finishing sections of the mill, and by changing roll diameters and groove configurations, a range of products can be sized. Some free sizing is also possible, albeit within a relatively narrow range, due to the limitations imposed by the spread which inevitably accompanies rolling in two roll WO 02/20189 PCT/US01/41707 2 passes. A further drawback with the Sasaki et al. round-round pass sequence is the development in certain products of a duplex microstructure, where the grains throughout the cross section of the product vary in size by more than about 2 ASTM 5 grain size numbers (measured in accordance with ASTM El 12-84). It is generally recognized that a.variation of more than about 2 ASTM grain size numbers in the cross section of a product can cause rupturing and surface tearing when the product is subjected to subsequent bending and cold drawing operations. Such grain size variations also contribute to poor annealed properties, which in turn 10 adversely affect cold deformation processes. The development of duplex microstructures was subsequently recognized as stemming from the inability of the light reduction round sizing passes to achieve adequate deformation throughout the product cross section within a sufficiently short time. This problem was addressed by the technique described in U.S. Patent No. 15 5,325,697 issued July 5, 1994 to Shore et al. Here, a two roll round-round light reduction sizing sequence is immediately preceded by a heavy reduction two roll oval-round pass sequence. The heavy reductions taken in the oval-round pass sequence produce a deformation pattern penetrating to the center of the product with high, strains. Before the accompanying stresses are relieved through microstructural 20 recrystallization and recovery, rolling continues in the immediately succeeding light i reduction two roll passes. In effect, therefore, the reductions taken in the four successive passes comprise one substantially continuous process, with a resulting strain pattern across the product cross section which avoids the development of a duplex microstructure. 25 Here again, however, the available range of free sizing rolling is limited due to the spread experienced when rolling in two roll passes. It is also known to employ three and four roll passes in round-round sizing sequences. These afford a wider range of free size rolling because the products are more closely confined in the roll passes and thus do not experience the degree of 30 spread encountered in two roll passes. However, as compared to two roll passes, three and four roll passes are far less efficient in achieving sufficient penetration of deformation to the center of the product. Such penetration is required to obtain a uniform grain structure from center to surface of the product. This is particularly important for products which develop their WO 02/20189 PCT/US01/41707 3 properties from grain refinement. There exists a need, therefore, for an improved method of hot rolling long products, which is capable of achieving sizing tolerances and substantially uniform center to surface grain structures, and which also has a broadened range of free sizing. 5 It is to these ends that the present invention is directed. SUMMARY OF THE INVENTION 10 In accordance with a preferred embodiment of the present invention, a round ferrous process section is initially rolled in first and second two roll passes at an elevated temperature of between about 650 to 1000°C to effect a combined heavy reduction in cross sectional area of at least about 20-55%, with an accompanying effective strain pattern dominated by a concentration of maximum effective strain at a i. ■■■■•' 15 central region of the product's cross section. Prior to the occurrence of microstructural changes due to recrystallization and recovery and while the effective strain pattern remains dominated by a concentration of maximum effective strain at a central region of the product's cross section, the product is rolled in at least third and fourth roll passes, each being defined by at least three rolls, to effect a further combined relatively 20 light reduction in product cross sectional area of not more than about 4-25%. When rolling a round process section into a finished round product in the above manner, e.g., a rod or bar, the first roll pass produces an oval cross section and the second roll pass produces a round process cross section. The third and fourth roll passes complete the shaping of the process round cross 25 section into a finished round having no more than + 0.1 mm diameter tolerance and 0.1 mm ovality, or 14 ASTM Rod or Bar tolerance, whichever is better. After cooling to a state of thermal equilibrium, the resulting product will have a grain size variation across its cross section of not more than about 2 ASTM grain size numbers. These, and other features and advantages of the present invention will now be 30 described in greater detail with reference to the accompanying drawings, wherein: BRTEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatic illustration of two alternative pass sequences in WO 02/20189 PCT/US01/41707 4 accordance with the present invention; Figures 2A-2D are finite element based simulations of the levels of effective plastic strain resulting from deformation of the product in the successive roll passes P,, P2, P3, P4 depicted in Figure 1; and 5 Figures 3A-3B are finite element based simulations of the levels of effective plastic strain resulting from deformation of the product in roll passes P3- and P4- after the product had been rolled initially in roll passes P1 and P2. 10 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring initially to Figure 1, a pass sequence in accordance with the present invention includes four roll passes P1-P4 configured to roll a round process section 10a into a finished round l0e. Roll pass P1 is defined by two work rolls 12 having grooves 15 14 configured to roll the round process section 10a into an oval 10b. Roll pass P2 is defined by two work rolls 16 having grooves 18 configured to roll the oval 10b into a process round 10c. Depending on the rolling schedule being employed, roll passes P1, P2 will be dimensioned to effect combined reductions of between about 20-55%, with from about 11 to 28% occurring in roll pass P,, and with 20 about 10 to 23% occurring in roll pass P2. Roll pass P3 is defined by three work rolls 20 having grooves 22 configured to roll the process round 10c into another process round l0d. Roll pass P4 is also defined by three work rolls 24 having grooves 26 configured to roll the process round l0d into the finished round l0e. 25 Again, depending on the rolling schedule being employed, roll passes P3, P4 will be sized to effect combined reductions of between about 3-25 %, with from about 1.8 to 17% occurring in roll pass P3, and with about 1.2 to 10% occurring in roll pass P4. With this pass sequence, for example, if the process section 10a has a diameter 30 of 14.032 mm, and the finished round is to have a diameter of 10.0 mm, the progressive areas reductions in roll passes P,-P4 will be, respectively, 22%; 18%, 10%; 8%. Typically, rolling will occur in roll passes P1-P4, at elevated temperatures of WO 02/20189 PCT/US01/41707 5 between about 650 to 1000°C. Figure 2A-2D illustrate the effective strain patterns of the product as it emerges from the successive roll passes depicted in Figure 1. As shown in Figure 2A, the oval 10b emerging from the high reduction two roll pass Pj has an effective strain pattern 5 dominated by a concentration of maximum effective strain at a central region at. Progressing outwardly from central region alf are regions b„ c,, d[ and e, having progressively lower effective strain levels, with the lowest effective strain level being at regions fu adjacent to the outer boundaries of the product cross sectional area. Figure 2B shows that the process round 10c emerging from the second high 10 reduction two roll pass P2 retains an effective strain pattern dominated by a central region a2 of maximum effective, strain, with progressively lower effective strain levels in surrounding regions b2-f2. Figure 2C shows the effective strain pattern in the process round l0d emerging from the three roll light reduction sizing pass P3. The maximum effective strain level 15 is maintained in the central region a3, which is again surrounded by regions b3-f3 of progressively lower effective strain levels. In the final light reduction three roll pass P4, as shown in Figure 2D, the effective strain pattern in the exiting round l0e continues to be dominated by maximum effective strain in region a4, with progressively lower effective levels in surrounding 20 regions b4-f4. The smallest grain size will thus be located in region a4, with progressively larger grains being located in the surrounding regions b4-f4. As the finished round l0e is then allowed to cool, the rate of cooling across its cross section will diminish from a maximum at the outermost regions f4, where the grains are larger, to a minimum at the 25 innermost region a4, where the grains are smaller. As cooling takes place, the grains in each region will grow by an amount proportional to the time needed for each region to cool, thus reducing the difference in grain size between innermost and outermost ' regions, resulting in a variation in grain size across the cross section of the product of not more than about 2 ASTM grain size. 30 Returning to Figure 1, the process round 10c emerging from roll pass P2 may alternatively be sized in four roll passes P3' and P4-. Roll pass P3- is defined by four work rolls 20' having grooves 22' configured to roll process round 10c into another process round 10d'. Roll pass P4- is also defined by four work rolls 24' having WO 02/20189 PCT/US01/41707 6 grooves 26' configured to roll the process round 10d' into a finished round 10e'. The effective strain patterns of the product as it emerges from roll passes P1 and P2 is as described previously and illustrated in Figures 2A and 2B. The effective strain patterns of the product as it emerges from roll passes P3- and P4- are depicted, 5 respectively, in Figures 3A and 3B. It will be seen that here again, the process section 10d' has an effective strain pattern dominated by a maximum effective strain in region a3- surrounded by regions b3--f3' of progressively lower strain levels. Figure 3B shows that the same basic pattern persists in the finished product 10e' emerging from roll pass P4-. 10 We claim: WO 02/20189 PCT/US01/41707 7 1 1. A method of continuously rolling a ferrous workpiece into a finished 2 round, comprising: 3 rolling said workpiece in successive first and second roll passes at an elevated 4 temperature of between about 650 to 1000°C, said first and second roll passes each 5 being defined by two work rolls and being dimensioned to effect a combined reduction 6 in the cross sectional area of said workpiece of at least about 20-55%, with an 7 accompanying effective strain pattern dominated by a concentration of maximum 8 effective strain at a central region of said cross sectional area; and 9 while said effective strain pattern remains dominated by a concentration of 10 maximum effective strain at a central region of said cross section, continuing to roll 11 said workpiece in at least third and fourth consecutive roll passes, each of said third 12 and fourth roll passes being defined by at least three rolls and being sized to effect a 13 combined reduction in the cross sectional area of said workpiece of not more than 14 about 4-25%. 1 2. The method of claim 1 wherein rolling continues in said third and fourth 2 roll passes prior to the occurrence of microstructural changes due to recrystalization 3 and recovery. 1 3. The method of claims 1 or 2 wherein said workpiece has a round cross 2 section, said first and second roll passes are configured respectively to impart 3 progressively reduced oval and round cross sections to said workpiece, and wherein 4 said third and fourth roll passes are configured to impart further progressively reduced 5 round cross sections to said workpiece. 1 4. The method of claim 3 wherein the workpiece emerges from the last of 2 said at least third and fourth roll passes as a finished round having no more than 3 ±0.1mm diameter tolerance and 0.1mm ovality. 1 5. The method of claim 1 wherein after cooling to a state of thermal 2 equilibrium, said workpiece has a grain size variation across its cross section of not 3 more than about 2 ASTM grain size numbers. 1 6. A method of continuously rolling a round ferrous workpiece, 2 comprising: 3 rolling said workpiece in successive first and second roll passes at an elevated WO 02/20189 PCT/US01/41707 8 4 temperature of between about 650 to 1000°C, said first and second roll passes each 5 being defined by two work rolls and being configured respectively to impart 6 progressively reduced oval and round cross sections to said workpiece and to effect a 7 combined reduction in the cross sectional area of said workpiece of at least about 20- 8 55%, with an accompanying effective strain pattern dominated by a concentration of 9 maximum effective strain at a central region of said cross sectional area; and 10 prior to the occurrence of microstructural changes due to recrystalization and 11 recovery, while said effective strain pattern remains dominated by a concentration of 12 maximum effective strain at a central region of said cross section, continuing to roll 13 said workpiece in at least third and fourth consecutive roll passes into a finished round, 14 each of said third and fourth roll passes being defined by at least three rolls and being 15 sized to effect a combined reduction in the cross sectional area of said workpiece of not 16 more than about 4-25%, with said finished round having no more than ±0.1mm 17 diameter tolerance and 0.01mm ovality.

Full Text

FORM 2
THE PATENTS ACT 1970
[39 OF 1970]
COMPLETE SPECIFICATION [See Section 10]
"METHOD AND APPARATUS FOR REDUCING AND SIZING HOT ROLLED FERROUS PRODUCTS"
MORGAN CONSTRUCTION COMPANY, of 15 Belmont Street, Worcester, Massachusetts 01605, United States of America,
The following specification particularly describes the nature of the invention and the manner in which it is to be performed :-

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1
METHOD AND APPARATUS FOR REDUCING AND SIZING HOT ROLLED FERROUS PRODUCTS
CROSS REFERENCE TO RELATED APPLICATION
5 This application claims priority from U.S. Provisional Patent Application Serial
No. 60/231,108 filed September 8, 2000 and U.S. Utility Patent Application filed August 10, 2001 (serial number unknown).
BACKGROUND OF THE INVENTION –
10
1. Field of the Invention
This invention relates to the continuous hot rolling of ferrous long products, including, inter alia, rounds, octagons, squares and the like.
15 2. Description of the Prior Art
As herein employed in the rolling of rounds, the term "sizing" means imparting a final deformation during the last stage of rolling to obtain a finished nominal product diameter within a specified standard tolerance which is typically about ±0.1mm diameter tolerance and 0.1mm ovality or better. Also, as herein employed, the term
20 "free sizing" means making adjustments to the roll partings of sizing stands to produce finished product diameters which are slightly larger or slightly smaller than the nominal diameter designated for the roll grooves, but are diameters which are within an acceptable tolerance for the obtained diameter.
Various techniques have been developed for sizing and free sizing ferrous long
25 products. For example, as disclosed in U.S. Patent No. 4,907,438 issued March 13,
1990 to Sasaki et al., it is known to roll round process sections through successive two
roll sizing stands, with a round-round pass sequence, and with the roll passes
configured to take relatively light reductions on the order of 8-15 % per pass.
By feeding the sizing stands with different diameter rounds taken from different
30 stands in the upstream intermediate or finishing sections of the mill, and by changing roll diameters and groove configurations, a range of products can be sized.
Some free sizing is also possible, albeit within a relatively narrow range, due to the limitations imposed by the spread which inevitably accompanies rolling in two roll

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2
passes.
A further drawback with the Sasaki et al. round-round pass sequence is the development in certain products of a duplex microstructure, where the grains throughout the cross section of the product vary in size by more than about 2 ASTM
5 grain size numbers (measured in accordance with ASTM El 12-84).
It is generally recognized that a.variation of more than about 2 ASTM grain size
numbers in the cross section of a product can cause rupturing and surface tearing when
the product is subjected to subsequent bending and cold drawing operations. Such
grain size variations also contribute to poor annealed properties, which in turn
10 adversely affect cold deformation processes.
The development of duplex microstructures was subsequently recognized as stemming from the inability of the light reduction round sizing passes to achieve adequate deformation throughout the product cross section within a sufficiently short time. This problem was addressed by the technique described in U.S. Patent No.
15 5,325,697 issued July 5, 1994 to Shore et al. Here, a two roll round-round light reduction sizing sequence is immediately preceded by a heavy reduction two roll oval-round pass sequence. The heavy reductions taken in the oval-round pass sequence produce a deformation pattern penetrating to the center of the product with high, strains. Before the accompanying stresses are relieved through microstructural
20 recrystallization and recovery, rolling continues in the immediately succeeding light
i
reduction two roll passes.
In effect, therefore, the reductions taken in the four successive passes comprise
one substantially continuous process, with a resulting strain pattern across the product
cross section which avoids the development of a duplex microstructure.
25 Here again, however, the available range of free sizing rolling is limited due to
the spread experienced when rolling in two roll passes.
It is also known to employ three and four roll passes in round-round sizing sequences. These afford a wider range of free size rolling because the products are more closely confined in the roll passes and thus do not experience the degree of
30 spread encountered in two roll passes.
However, as compared to two roll passes, three and four roll passes are far less efficient in achieving sufficient penetration of deformation to the center of the product. Such penetration is required to obtain a uniform grain structure from center to surface of the product. This is particularly important for products which develop their

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properties from grain refinement.
There exists a need, therefore, for an improved method of hot rolling long products, which is capable of achieving sizing tolerances and substantially uniform center to surface grain structures, and which also has a broadened range of free sizing.
5 It is to these ends that the present invention is directed.
SUMMARY OF THE INVENTION
10 In accordance with a preferred embodiment of the present invention, a round
ferrous process section is initially rolled in first and second two roll passes at an elevated temperature of between about 650 to 1000°C to effect a combined heavy reduction in cross sectional area of at least about 20-55%, with an accompanying
effective strain pattern dominated by a concentration of maximum effective strain at a
i. ■■■■•'
15 central region of the product's cross section. Prior to the occurrence of microstructural changes due to recrystallization and recovery and while the effective strain pattern remains dominated by a concentration of maximum effective strain at a central region of the product's cross section, the product is rolled in at least third and fourth roll passes, each being defined by at least three rolls, to effect a further combined relatively
20 light reduction in product cross sectional area of not more than about 4-25%.
When rolling a round process section into a finished round product in the above manner, e.g., a rod or bar, the first roll pass produces an oval cross section and the second roll pass produces a round process cross section.
The third and fourth roll passes complete the shaping of the process round cross
25 section into a finished round having no more than + 0.1 mm diameter tolerance and 0.1 mm ovality, or 14 ASTM Rod or Bar tolerance, whichever is better. After cooling to a state of thermal equilibrium, the resulting product will have a grain size variation across its cross section of not more than about 2 ASTM grain size numbers.
These, and other features and advantages of the present invention will now be
30 described in greater detail with reference to the accompanying drawings, wherein:
BRTEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a diagrammatic illustration of two alternative pass sequences in

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4
accordance with the present invention;
Figures 2A-2D are finite element based simulations of the levels of effective
plastic strain resulting from deformation of the product in the successive roll passes P,,
P2, P3, P4 depicted in Figure 1; and
5 Figures 3A-3B are finite element based simulations of the levels of effective
plastic strain resulting from deformation of the product in roll passes P3- and P4- after the product had been rolled initially in roll passes P1 and P2.
10 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring initially to Figure 1, a pass sequence in accordance with the present invention includes four roll passes P1-P4 configured to roll a round process section 10a into a finished round l0e. Roll pass P1 is defined by two work rolls 12 having grooves
15 14 configured to roll the round process section 10a into an oval 10b.
Roll pass P2 is defined by two work rolls 16 having grooves 18 configured to roll the oval 10b into a process round 10c. Depending on the rolling schedule being employed, roll passes P1, P2 will be dimensioned to effect combined reductions of between about 20-55%, with from about 11 to 28% occurring in roll pass P,, and with
20 about 10 to 23% occurring in roll pass P2.
Roll pass P3 is defined by three work rolls 20 having grooves 22 configured to roll the process round 10c into another process round l0d. Roll pass P4 is also defined by three work rolls 24 having grooves 26 configured to roll the process round l0d into the finished round l0e.
25 Again, depending on the rolling schedule being employed, roll passes P3, P4
will be sized to effect combined reductions of between about 3-25 %, with from about 1.8 to 17% occurring in roll pass P3, and with about 1.2 to 10% occurring in roll pass P4.
With this pass sequence, for example, if the process section 10a has a diameter
30 of 14.032 mm, and the finished round is to have a diameter of 10.0 mm, the progressive areas reductions in roll passes P,-P4 will be, respectively, 22%; 18%, 10%; 8%.
Typically, rolling will occur in roll passes P1-P4, at elevated temperatures of

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between about 650 to 1000°C.
Figure 2A-2D illustrate the effective strain patterns of the product as it emerges from the successive roll passes depicted in Figure 1. As shown in Figure 2A, the oval 10b emerging from the high reduction two roll pass Pj has an effective strain pattern
5 dominated by a concentration of maximum effective strain at a central region at. Progressing outwardly from central region alf are regions b„ c,, d[ and e, having progressively lower effective strain levels, with the lowest effective strain level being at regions fu adjacent to the outer boundaries of the product cross sectional area.
Figure 2B shows that the process round 10c emerging from the second high
10 reduction two roll pass P2 retains an effective strain pattern dominated by a central region a2 of maximum effective, strain, with progressively lower effective strain levels in surrounding regions b2-f2.
Figure 2C shows the effective strain pattern in the process round l0d emerging from the three roll light reduction sizing pass P3. The maximum effective strain level
15 is maintained in the central region a3, which is again surrounded by regions b3-f3 of progressively lower effective strain levels.
In the final light reduction three roll pass P4, as shown in Figure 2D, the effective strain pattern in the exiting round l0e continues to be dominated by maximum effective strain in region a4, with progressively lower effective levels in surrounding
20 regions b4-f4.
The smallest grain size will thus be located in region a4, with progressively
larger grains being located in the surrounding regions b4-f4. As the finished round l0e
is then allowed to cool, the rate of cooling across its cross section will diminish from a
maximum at the outermost regions f4, where the grains are larger, to a minimum at the
25 innermost region a4, where the grains are smaller. As cooling takes place, the grains
in each region will grow by an amount proportional to the time needed for each region
to cool, thus reducing the difference in grain size between innermost and outermost
' regions, resulting in a variation in grain size across the cross section of the product of
not more than about 2 ASTM grain size.
30 Returning to Figure 1, the process round 10c emerging from roll pass P2 may
alternatively be sized in four roll passes P3' and P4-. Roll pass P3- is defined by four work rolls 20' having grooves 22' configured to roll process round 10c into another process round 10d'. Roll pass P4- is also defined by four work rolls 24' having

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grooves 26' configured to roll the process round 10d' into a finished round 10e'.
The effective strain patterns of the product as it emerges from roll passes P1 and P2 is as described previously and illustrated in Figures 2A and 2B. The effective strain
patterns of the product as it emerges from roll passes P3- and P4- are depicted,
5 respectively, in Figures 3A and 3B. It will be seen that here again, the process section 10d' has an effective strain pattern dominated by a maximum effective strain in region
a3- surrounded by regions b3--f3' of progressively lower strain levels.
Figure 3B shows that the same basic pattern persists in the finished product
10e' emerging from roll pass P4-.
10 We claim:

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1 1. A method of continuously rolling a ferrous workpiece into a finished
2 round, comprising:
3 rolling said workpiece in successive first and second roll passes at an elevated
4 temperature of between about 650 to 1000°C, said first and second roll passes each
5 being defined by two work rolls and being dimensioned to effect a combined reduction
6 in the cross sectional area of said workpiece of at least about 20-55%, with an
7 accompanying effective strain pattern dominated by a concentration of maximum
8 effective strain at a central region of said cross sectional area; and
9 while said effective strain pattern remains dominated by a concentration of
10 maximum effective strain at a central region of said cross section, continuing to roll
11 said workpiece in at least third and fourth consecutive roll passes, each of said third
12 and fourth roll passes being defined by at least three rolls and being sized to effect a
13 combined reduction in the cross sectional area of said workpiece of not more than
14 about 4-25%.
1 2. The method of claim 1 wherein rolling continues in said third and fourth
2 roll passes prior to the occurrence of microstructural changes due to recrystalization
3 and recovery.
1 3. The method of claims 1 or 2 wherein said workpiece has a round cross
2 section, said first and second roll passes are configured respectively to impart
3 progressively reduced oval and round cross sections to said workpiece, and wherein
4 said third and fourth roll passes are configured to impart further progressively reduced
5 round cross sections to said workpiece.
1 4. The method of claim 3 wherein the workpiece emerges from the last of
2 said at least third and fourth roll passes as a finished round having no more than
3 ±0.1mm diameter tolerance and 0.1mm ovality.
1 5. The method of claim 1 wherein after cooling to a state of thermal
2 equilibrium, said workpiece has a grain size variation across its cross section of not
3 more than about 2 ASTM grain size numbers.
1 6. A method of continuously rolling a round ferrous workpiece,
2 comprising:
3 rolling said workpiece in successive first and second roll passes at an elevated

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4 temperature of between about 650 to 1000°C, said first and second roll passes each
5 being defined by two work rolls and being configured respectively to impart
6 progressively reduced oval and round cross sections to said workpiece and to effect a
7 combined reduction in the cross sectional area of said workpiece of at least about 20-
8 55%, with an accompanying effective strain pattern dominated by a concentration of
9 maximum effective strain at a central region of said cross sectional area; and
10 prior to the occurrence of microstructural changes due to recrystalization and
11 recovery, while said effective strain pattern remains dominated by a concentration of
12 maximum effective strain at a central region of said cross section, continuing to roll
13 said workpiece in at least third and fourth consecutive roll passes into a finished round,
14 each of said third and fourth roll passes being defined by at least three rolls and being
15 sized to effect a combined reduction in the cross sectional area of said workpiece of not
16 more than about 4-25%, with said finished round having no more than ±0.1mm
17 diameter tolerance and 0.01mm ovality.

METHOD AND APPARATUS FOR REDUCING AND SIZING HOT ROLLED FERROUS PRODUCTS

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