Method for producing seamless metal pipe

Abstract

A solid billet is piercing-rolled using a 4 roll-type inclined rolling mill including larger-diameter cone-type main rolls arranged horizontally or vertically to face each other across a pass line and smaller-diameter auxiliary rolls arranged vertically or horizontally to face each other similarly across the pass line between the facing main rolls, while maintaining a feed angle ? and cross angle ? of the main rolls and a feed angle ? and cross angle ? of the auxiliary rolls to be within the ranges: 5???, ??25?; 3???, ??35?; and 10???+?, ?+??55?.

Claims

1. A method for producing a seamless metal pipe, the method comprising: piercing-rolling a solid billet using a 4 roll inclined rolling mill that includes a pair of cone-shaped main rolls having roll shafts supported at opposing ends thereof and arranged horizontally or vertically to face each other across a pass line and a pair of cone-shaped auxiliary rolls having roll shafts supported at opposing ends thereof and arranged vertically or horizontally to face each other similarly across the pass line between the facing main rolls, wherein the diameter of the main rolls is larger than the diameter of the auxiliary rolls; and maintaining a feed angle ? of the cone-shaped main rolls, a cross angle ? of the main rolls, a feed angle ? of the auxiliary rolls, and a cross angle ? of the auxiliary rolls to be within following ranges:
5???, ??25?;
3???, ??35?;
and
10???+?, ?+??55?.

2. The method for producing a seamless metal pipe according to claim 1, wherein the step of piercing-rolling the solid billet is expanding-piercing-rolling the solid billet so that a diameter d.sub.0 of the solid billet, a diameter d of a hollow piece after the expanding-piercing-rolling, and a wall thickness t of the hollow piece together satisfy a following relationship:
1.5???.sub.r/?.sub.??4.5 where ?.sub.r=ln(2t/d.sub.0)?.sub.?=ln {2(d?t)/d.sub.0}.

3. The method for producing a seamless metal pipe according to claim 2, wherein the piercing-rolling is performed so that an inlet diameter D.sub.1, an outlet diameter D.sub.2, and a roll cross angle ? of the cone-shaped main rolls and also an inlet diameter D.sub.1, an outlet diameter D.sub.2, and a roll cross angle ? of the cone-shaped auxiliary rolls satisfy relationships with the diameter d.sub.0 of the solid billet and the diameter d of the hollow piece after the piercing as follows:
(d/d.sub.0)/(D.sub.2/D.sub.1)<0.75+0.025?;
and
(d/d.sub.0)/(D.sub.2/D.sub.1)<0.75+0.025?.

4. The method for producing a seamless metal pipe according to claim 2, wherein the solid billet is piercing-rolled as the main rolls are being driven while the auxiliary rolls are left undriven.

5. The method for producing a seamless metal pipe according to claim 1, wherein the solid billet is piercing-rolled as the main rolls are being driven while the auxiliary rolls are left undriven.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is an illustration of the 2 roll-type piercing-rolling technique in connection with the prior inventions, with the plan view schematically showing a state of piercing-rolling.

(2) FIG. 2 is a side view schematically showing the state of piercing-rolling.

(3) FIG. 3 is a front view schematically showing the state of piercing-rolling, as seen from the entry side.

(4) FIG. 4 is an illustration of a state of stresses acting on the central portion of a billet during 2 roll-type piercing-rolling in connection with the prior inventions.

(5) FIG. 5 is an illustration of a state of stresses acting on the central portion of a billet during 4 roll-type piercing-rolling in connection with the present invention.

(6) FIG. 6 is an illustration of the 4 roll-type piercing-rolling technique in connection with the present invention, with the plan view schematically showing a state of piercing-rolling.

(7) FIG. 7 is a side view schematically showing the state of piercing-rolling.

(8) FIG. 8 is a front view schematically showing the state of piercing-rolling, as seen from the entry side.

DESCRIPTION OF EMBODIMENTS

(9) Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Throughout the specification and drawings, constituent elements having substantially the same function and arrangement are denoted by the same reference numerals, and redundant description is therefore omitted.

(10) Hereinafter, the method of the present invention will be described in comparison with the prior inventions.

(11) FIGS. 1 to 3 are illustrations of the 2 roll-type piercing-rolling technique in connection with the prior inventions, among which FIG. 1 is a plan view schematically showing a state of piercing-rolling, FIG. 2 is a side view thereof, and FIG. 3 is a front view thereof as seen from the entry side. As shown in FIGS. 1 and 2, the main rolls 1, 1 have a cone type of shape with the tips thereof directed toward the solid billet 2 entry side, and the positions at which the roll surfaces 1a, 1a at the entry side and the roll surfaces 1b, 1b at the exit side intersect each other, respectively, are the gorge portions 1g, 1g. Both ends of each roll shaft 1c, 1c are held by support frames (not shown).

(12) The roll shafts 1c, 1c are mounted in an inclined manner so that their extensions have feed angles ? with respect to a plane (horizontal plane in the illustrated example) containing the pass line with the feed angles being equal to each other but having opposite orientations (see FIG. 2) and also cross angles ? with respect to a vertical plane containing the pass line with the cross angles being equal to each other but having opposite orientations (see FIG. 1), and they rotate in the same direction at the same angular velocity as shown by the arrows.

(13) As shown in FIG. 3, disc rolls 6, 6 are provided between the main rolls 1, 1 with a solid billet 2 disposed therebetween.

(14) The solid billet 2 is pierced by a plug 4 supported on a mandrel 3 to be formed into a hollow piece 5.

(15) In contrast, the method of the present invention employs, in place of disc rolls, cone-type auxiliary rolls having functions and advantages comparable to those of the cone-type main rolls.

(16) FIGS. 6 to 8 are illustrations of the 4 roll-type piercing-rolling technique in connection with the present invention, among which FIG. 6 is a plan view schematically showing a state of piercing-rolling, FIG. 7 is a side view thereof, and FIG. 8 is a front view thereof as seen from the entry side. As shown in FIGS. 6 and 7, the cone-type main rolls 1, 1 are arranged horizontally to face each other across the pass line (X-X line), and cone-type auxiliary rolls 7, 7 are vertically arranged to face each other similarly across the pass line between the main rolls 1, 1 that face each other.

(17) The roll shafts 1c, 1c of the main rolls are mounted in an inclined manner so that their extensions have feed angles ? with respect to a plane (horizontal plane in the illustrated example) containing the pass line with the feed angles being equal to each other but having opposite orientations (see FIG. 7) and also cross angles ? with respect to a vertical plane containing the pass line with the cross angles being equal to each other but having opposite orientations (see FIG. 6). The main rolls 1, 1 rotate in the same direction at the same angular velocity as shown by the arrows. The roll shafts 7c, 7c of the auxiliary rolls 7, 7 are similarly mounted in an inclined manner with feed angles ? and cross angles ?, and they rotate in the same direction at the same angular velocity. By employing the 4 roll-type piercing-rolling technique, it is possible to achieve functions and advantages described below.

(18) FIG. 4 is an illustration of a state of stresses acting on the central portion of a billet during 2 roll-type piercing-rolling in connection with the prior inventions. When a solid billet is subjected to rotary-forging in a 2 roll-type inclined rolling mill, compressive stresses act on the central axis portion of the solid billet in the direction of reduction and tensile stresses occur in the direction perpendicular to the direction of reduction, with the result that the so-called Mannesmann phenomenon occurs at the centerline segregation, inclusions, or centerline porosity serving as the initiation point, and if the phenomenon is excessive, it will cause a failure.

(19) FIG. 5 is an illustration of a state of stresses acting on the central portion of a billet during 4 roll-type piercing-rolling in connection with the present invention. When a 4 roll-type inclined rolling mill is employed instead of the 2 roll-type inclined rolling mill, no tensile stress will occur during reduction while plastic deformation is accomplished only with compressive stresses acting in the direction of reduction, and therefore the occurrence of the Mannesmann effect can be inhibited even under rotary forging.

(20) When cone-type auxiliary rolls having functions and advantages comparable to those of the cone-type main rolls are employed in place of disc rolls, for the main rolls and the auxiliary rolls, the relationships between the pipe expansion ratio d/d.sub.0 of the pipe material and the respective diameter expansion ratios D.sub.2/D.sub.1 and D.sub.2/D.sub.1, of the main rolls and auxiliary rolls, correspond to those of the prior inventions, where the roll inlet diameters are denoted as D1, D1 and the roll outlet diameters are denoted as D2, D2, and thus the following relationships still hold.
(d/d.sub.0)/(D.sub.2/D.sub.1)<0.75+0.025?
(d/d.sub.0)/(D.sub.2/D.sub.1)<0.75+0.025?

(21) In the present invention, the roll diameter of the auxiliary rolls is smaller than the roll diameter of the main rolls, and this is intended to enlarge the dimensional range that can be obtained by piercing as much as possible by giving a large roll gap adjustment margin to the main rolls. In this connection, if the outlet diameters of the main rolls and the auxiliary rolls are equal, it is impossible to obtain a hollow piece in which the diameter d is not more than (2.sup.1/2?1)D.sub.2 due to the geometric limitations.

(22) Furthermore, with the 4 roll-type, the rolling mill has a more complicated overall configuration, in which the smaller-diameter auxiliary rolls can be =driven while the piercing-rolling loads of the auxiliary rolls are borne by the driving power for the main rolls.

(23) The gorge positions of the main rolls and auxiliary rolls need to be aligned with each other although their roll diameters may be varied, and preferably, the entry-side barrel lengths (L.sub.1, L.sub.1) forward of the gorge positions are equal to each other and the exit-side barrel lengths (L.sub.2, L.sub.2) rearward of the gorge positions are equal to each other (L.sub.1=L.sub.1, L.sub.2=L.sub.2).

(24) The present invention is not limited to a solid billet, to which the description above is directed, but it is also applicable to production methods using a hollow billet formed by bore machining.

EXAMPLES

(25) Detailed descriptions of examples are given below.

Example 1

(26) Hot workability of high alloy steels is poorer than that of stainless steels, and if their temperatures for piercing-rolling are more than 1275? C., laminations often occur. In this example, using specimens of a billet made of a 25% Cr-35% Ni-3Mo high alloy steel and having a diameter of 70 mm, with their temperature for piercing-rolling being 1200? C., high reduction rate thin-wall piercing-rolling at a pipe expansion ratio of 2 was performed as the main rolls and auxiliary rolls were being driven. Conditions for the main rolls and auxiliary rolls and conditions for piercing-rolling were as follows.

(27) 1. Conditions for Main Rolls

(28) Cross angle . . . ?=30?

(29) Feed angle . . . ?=12?

(30) Gorge diameter . . . D.sub.g=500 mm

(31) Inlet diameter . . . D.sub.1=300 mm

(32) Outlet diameter . . . D.sub.2=670 mm

(33) Roll diameter expansion ratio . . . D.sub.2/D.sub.1=2.23

(34) Entry-side barrel width . . . L.sub.1=300 mm

(35) Exit-side barrel width . . . L.sub.2=460 mm

(36) Barrel width . . . L.sub.1+L.sub.2=760 mm

(37) Barrel width ratio . . . L.sub.2/L.sub.1=1.53

(38) Roll rotational speed n=60 rpm

(39) 2. Conditions for Auxiliary Rolls

(40) Cross angle . . . ?=30?

(41) Feed angle . . . ?=12?

(42) Gorge diameter . . . D.sub.g=400 mm

(43) Inlet diameter . . . D.sub.1=240 mm

(44) Outlet diameter . . . D.sub.2=536 mm

(45) Roll diameter expansion ratio . . . D.sub.2/D.sub.1=2.23

(46) Entry-side barrel width . . . L.sub.1=300 mm

(47) Exit-side barrel width . . . L.sub.2=460 mm

(48) Barrel width . . . L.sub.1+L.sub.2=760 mm

(49) Barrel width ratio . . . L.sub.2/L.sub.1=1.53

(50) Roll rotational speed . . . n=75 rpm

(51) 3. Piercing-Rolling Conditions

(52) $\mathrm{Plug}\mathrm{diameter}\mathrm{.Math.}{d}_p=130\mathrm{mm}$$\mathrm{Billet}\mathrm{diameter}\mathrm{.Math.}{d}_0=70\mathrm{mm}$$\mathrm{Hollow}\mathrm{piece}\mathrm{diameter}\mathrm{.Math.}d=140\mathrm{mm}$$\mathrm{Hollow}\mathrm{piece}\mathrm{wall}\mathrm{thickness}\mathrm{.Math.}t=3.5\mathrm{mm}$$\mathrm{Pipe}\mathrm{expansion}\mathrm{ratio}\mathrm{.Math.}d/d_0=2.00$$\mathrm{Piercing}\text{-}\mathrm{rolling}\mathrm{ratio}\mathrm{.Math.}{d}_0^2/4t\left(d-t\right)=2.56$$\mathrm{Wall}\mathrm{thickness}\text{/}\mathrm{Outside}\mathrm{diameter}\mathrm{ratio}\mathrm{.Math.}\left(t/d\right)?100=2.5\%$$\mathrm{Roll}\mathrm{shape}\mathrm{factor}\mathrm{.Math.}\left(d/d_0\right)/\left(D_2/D_1\right)=\left(d_2/d_0\right)/\left(D_2^{}/D_1^{}\right)=0.897\mathrm{Thicknesswise}\mathrm{logarithmic}\mathrm{strain}\mathrm{.Math.}{?}_r=\ln \left(2t/d_0\right)=\ln 0.10=-2.303\mathrm{Circumferential}\mathrm{logarithmic}\mathrm{strain}\mathrm{.Math.}{?}_{?}=\ln \left\{2\left(d-t\right)/d_0\right\}=\ln 3.90=1.361$$\mathrm{Reduction}\mathrm{distribution}\mathrm{ratio}\mathrm{.Math.}-{?}_r/{?}_{?}=1.692$

(53) As described above, the reduction distribution ratio between the circumferential reduction and the thicknesswise reduction was appropriate and the roll shapes were optimized, and as a result, the piercing-rolling was accomplished without any problems although it was high reduction rate thin-wall piercing-rolling of a high alloy steel, which has poor hot workability.

Example 2

(54) Using specimens of a billet made of an 18% Cr-8% Ni austenitic stainless steel and having a diameter of 60 mm, high reduction rate thin-wall piercing-rolling at a pipe expansion ratio of 1.5 was performed as the main rolls only were being driven while the auxiliary rolls were left undriven. The billet was heated to 1250? C. Hot workability of stainless steels is much poorer than that of carbon steels. Conditions for the main rolls and auxiliary rolls and conditions for piercing-rolling were as follows.

(55) 1. Conditions for Main Rolls

(56) Cross angle ?=25?

(57) Gorge diameter . . . D.sub.g=400 mm

(58) Feed angle . . . ?=12?

(59) Inlet diameter . . . D.sub.1=240 mm

(60) Outlet diameter . . . D.sub.2=550 mm

(61) Roll diameter expansion ratio . . . D.sub.2/D.sub.1=2.29

(62) Entry-side barrel width . . . L.sub.1=300 mm

(63) Exit-side barrel width . . . L.sub.2=460 mm

(64) Barrel width . . . L.sub.1+L.sub.2=760 mm

(65) Barrel width ratio . . . L.sub.2/L.sub.1=1.53

(66) Roll rotational speed . . . n=60 rpm

(67) 2. Conditions for Auxiliary Rolls

(68) Cross angle . . . ?=25?

(69) Gorge diameter . . . D.sub.g=320 mm

(70) Feed angle . . . ?=12?

(71) Inlet diameter . . . D.sub.1=192 mm

(72) Outlet diameter . . . D.sub.2=440 mm

(73) Roll diameter expansion ratio . . . D.sub.2/D.sub.1=2.29

(74) Entry-side barrel width . . . L.sub.1=300 mm

(75) Exit-side barrel width . . . L.sub.2=460 mm

(76) Barrel width . . . L.sub.1+L.sub.2=760 mm

(77) Barrel width ratio . . . L.sub.2/L.sub.1=1.53

(78) Roll rotational speed . . . n=(undriven)

(79) 3. Piercing-Rolling Conditions

(80) $\mathrm{Plug}\mathrm{diameter}\mathrm{.Math.}{d}_p=80\mathrm{mm}$$\mathrm{Billet}\mathrm{diameter}\mathrm{.Math.}{d}_0=60\mathrm{mm}$$\mathrm{Hollow}\mathrm{piece}\mathrm{diameter}\mathrm{.Math.}d=90\mathrm{mm}$$\mathrm{Hollow}\mathrm{piece}\mathrm{wall}\mathrm{thickness}\mathrm{.Math.}t=2.7\mathrm{mm}$$\mathrm{Pipe}\mathrm{expansion}\mathrm{ratio}\mathrm{.Math.}d/d_0=1.50$$\mathrm{Piercing}\text{-}\mathrm{rolling}\mathrm{ratio}\mathrm{.Math.}{d}_0^2/4t\left(d-t\right)=3.82$$\mathrm{Wall}\mathrm{thickness}\text{/}\mathrm{Outside}\mathrm{diameter}\mathrm{ratio}\mathrm{.Math.}\left(t/d\right)?100=3.0\%$$\mathrm{Roll}\mathrm{shape}\mathrm{factor}\mathrm{.Math.}\left(d/d_0\right)/\left(D_2/D_1\right)=\left(d/d_0\right)/\left(D_2^{}/D_1^{}\right)=0.655$$\mathrm{Thicknesswise}\mathrm{logarithmic}\mathrm{strain}\mathrm{.Math.}{?}_r=\ln \left(2t/d_0\right)=\ln 0.09=-2.408$$\mathrm{Circumferential}\mathrm{logarithmic}\mathrm{strain}\mathrm{.Math.}{?}_{?}=\ln \left\{2\left(d-t\right)/d_0\right\}=\ln 2.91=1.068$$\mathrm{Reduction}\mathrm{distribution}\mathrm{ratio}\mathrm{.Math.}-{?}_r/{?}_{?}=2.255$

(81) As described above, the reduction distribution ratio between the circumferential reduction and the thicknesswise reduction, i.e., the reduction distribution ratio between the longitudinal reduction and the circumferential reduction was appropriate, and as a result, the piercing-rolling was accomplished without causing flaring or peeling. Since the roll shapes were also optimized, the occurrence of inner surface flaws or laminations were not observed although it was high reduction rate ultrathin-wall piercing-rolling of a less formable material.

(82) In the foregoing description, preferred embodiments of the present invention have been set forth in detail with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent that those having general knowledge in the field to which the present invention belongs may find various alternations and modifications within the scope of the technical ideas described in the appended claims, and it should be understood that they will naturally come under the technical scope of the present invention.

INDUSTRIAL APPLICABILITY

(83) The method of the present invention is a method using a 4 roll-type inclined rolling mill employing cone-type auxiliary rolls having functions and advantages comparable to those of the cone-type main rolls in place of disc rolls, and the method is capable of being effectively utilized particularly in piercing-rolling a less formable material such as a stainless steel or a high alloy steel.

REFERENCE SIGNS LIST

(84) 1, 1: main roll

(85) 2: solid billet

(86) 3: mandrel

(87) 4: plug

(88) 5: hollow piece

(89) 6, 6: disc roll

(90) 7, 7: auxiliary roll