JP2011115851A - Method of manufacturing seamless steel pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a seamless steel pipe, by which a material temperature (working temperature) when piercing a material to be worked is not in ununiformity in the longitudinal direction and the generation of internal defective properties is suppressed sufficiently. <P>SOLUTION: In the method of manufacturing the seamless steel pipe, the seamless steel pipe is made by piercing a material 1 to be worked having the rough shape of a round billet, after heating, successively elongating it, next, performing sizing after reheating and successively cooling it, when heating the material to be worked before piercing, the top in the longitudinal direction of the material to be worked before piercing is heated so as to be 30-400 °C higher than that of the rear end. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technical field of manufacturing seamless steel pipes, and more particularly to a method for manufacturing seamless steel pipes capable of suppressing quality variations in the product longitudinal direction.

  A seamless steel pipe is generally a billet having a round cross section, which is obtained by casting a bloom slab having a large cross section with a continuous caster, hot rolling with a lump mill, blooming mill, billeting mill, etc. Without or without round billets, or round billets are cast with a continuous casting machine, and these round billets are used as workpieces, and the workpieces are pierced and rolled, followed by this It is manufactured by subjecting it to stretching rolling and constant diameter rolling.

  An example of the seamless steel pipe manufacturing process in a pipe factory is shown in FIG. A workpiece 1 having a round billet is heated (billet heating) in, for example, a rotary heating furnace 2 and then pierced and rolled by an inclined roll piercing and rolling machine (piercer) 3 having a plug 4 for piercing. (Piercer rolling) to form a hollow shell. The workpiece 1 after the piercer rolling is subsequently drawn and rolled. The stretch rolling includes mandrel mill rolling using a Mannesmann-mandrel mill 5 having a mandrel bar 6 for constraining the tube inner surface, rolling using an elongator 8 having a plug 9 for constraining the tube inner surface (elongator rolling), and tube inner surface. Rolling using plug mill 10 having plug 11 for restraint (plug mill rolling) and rolling using reeler 12 having plug 13 for restraining pipe inner surface (reeler rolling) in this order (Elongator plug mill reeler rolling) Executed by. The material 1 to be rolled after the rolling is reheated in, for example, a walking beam heating furnace 7 and then rolled with a constant diameter. The constant diameter rolling is performed by stretch reducer rolling using a stretch reducer 14 or sizing mill rolling using a sizer (sizing mill) 15. The workpiece 1 after the constant diameter rolling is cooled by the cooling floor 16 to be a product (seamless steel pipe) 100. In addition, reheating after extending | stretching rolling is not necessarily required if the raw tube has hold | maintained sufficient temperature for a process.

  In the technical field of production of seamless steel pipes, in order to reduce the occurrence of internal flaws in high-Cr seamless steel pipes, the composition of the round billet, the soaking temperature / heating time of the furnace, the piercer drilling efficiency, and the plug shape For limiting purposes (Patent Document 1), and for the same purpose, providing a center hole with a specific diameter on the end face of the round billet on the drilling start side (Patent Document 2), and preventing bending of the workpiece in mandrel mill rolling In order to cool the tip of the workpiece in the form of a hollow shell after piercing and before starting mandrel milling for the purpose (Patent Document 3), and in the manufacture of martensitic stainless steel seamless steel pipe, an inclined roll piercing and rolling mill In order to improve biting and slip resistance to (piercers), enable low drafting of the draft at the tip of the plug, prevent clogging, and extend plug life The inner layer scale form of the inner and outer two-layer scale and the heating forming method thereof are limited, and piercing and rolling is performed after removing the outer layer scale (Patent Document 4). Also, the yield is excellent without decreasing the productivity of hot rolling. For the purpose of obtaining seamless steel pipe products, in the sequential arrangement equipment of a drawing mill (mandrel mill or elongator plug mill reeler), reheating furnace, and drawing mill (stretch reducer), In order to obtain an austenitic stainless steel seamless pipe by means of on-line solution treatment, a variable cooling bed, a soaking furnace, and a steel pipe joining device are sequentially arranged between them. Round billet casting for the purpose of limiting reheating / cooling conditions of steel (Patent Document 6) and advantageously producing difficult-to-work seamless steel pipes Matter and slab piercing rolling conditions (particularly the roll inclination angle, roll distance, etc.) such as to limit the (Patent Document 7) have been proposed.

WO2005 / 115650 Publication WO2007 / 100042 Publication JP 05-115904 A JP 2005-115904 A JP 2003-225701 A JP 09-276907 A JP 09-300006 A

  However, in the prior art, since the material temperature (processing temperature) at the time of piercing and rolling of the workpiece becomes non-uniform in the longitudinal direction, it is not possible to sufficiently suppress the occurrence of internal surface property defects. It was left as an unresolved issue.

The present invention has been made to solve the above problems, and the gist of the present invention is as follows.
(1) A workpiece whose raw form is a round billet is heated, then pierced and rolled, subsequently stretch-rolled, then reheated, then constant-diameter rolled, and then cooled to form a seamless steel pipe. In the steel pipe manufacturing method, when the workpiece is heated before drilling, the workpiece is heated so that the front end in the longitudinal direction of the workpiece before piercing and rolling is 30 to 400 ° C. higher than the rear end. A method for producing a seamless steel pipe characterized by the above.
(2) When heating the work material before drilling, the work material is uniformly heated in a heating furnace, and then only the tip portion is heated by induction heating. A method for producing seamless steel pipes.
(3) Production of a seamless steel pipe according to (1) above, wherein when the workpiece is heated before drilling, the front end of the workpiece is heated to a temperature higher than the rear end in a heating furnace. Method.
(4) The joint according to (3), wherein the heating furnace is a rotary heating furnace configured to be able to heat the outer peripheral side in the radial direction in the furnace by 30 to 400 ° C. higher than the vicinity of the center. Manufacturing method of steelless pipe.
(5) The heating furnace is a walking beam type heating furnace configured such that one end in a direction perpendicular to the conveying direction in the furnace is 30 to 400 ° C. higher than the other end, and is configured to be heated. A method for producing a seamless steel pipe according to 1.

  In the above item, since the technique for obtaining the main effect is the heating temperature before piercing, the apparatus such as reheating after drawing and rolling may be omitted if there is no particular problem in manufacturing.

  According to the present invention, the variation in the longitudinal direction material of the seamless steel pipe can be reduced, and the occurrence of poor inner surface properties can be effectively prevented.

Explanatory drawing of a rotary heating furnace that can be preferably used in the present invention Explanatory drawing of a walking beam heating furnace that can be preferably used in the present invention Induction heating pattern diagram showing an example of an embodiment of the present invention Explanatory drawing of wrinkle generation mechanism in the prior art Schematic showing an example of seamless steel pipe manufacturing process

  In the prior art, in the billet heating in the seamless steel pipe manufacturing process shown in FIG. 5, the workpiece 1 is uniformly heated in a heating furnace such as a rotary heating furnace 2. However, the present inventors have found that such a conventional technique causes internal flaws in the product by the following mechanism. That is, as shown in the explanatory diagram of the wrinkle generation mechanism in FIG. 4, in the subsequent Piercer rolling, the plug temperature (the temperature of the plug 4) increases with the progress of rolling, and the heat removal received by the workpiece 1 from the plug 4 is also increased. Since it changes with the progress of rolling, the processing temperature of the workpiece 1 (the temperature of the workpiece 1) changes in the longitudinal direction, resulting in variations in the longitudinal material of the workpiece 1 due to this. Product internal flaws will occur.

  On the other hand, in this invention, a to-be-rolled material is billet-heated so that the front-end | tip of the longitudinal direction of the to-be-processed material before a piercer rolling may be 30-400 degreeC higher than a rear end. Thereby, the heat removal by the plug 4 can be compensated, the material variation in the longitudinal direction of the workpiece can be effectively reduced, and the occurrence of internal flaws on the product can be effectively suppressed. If the temperature difference between the front and rear ends (tip temperature minus rear end temperature) of the workpiece before piercer rolling is less than 30 ° C. or more than 400 ° C. (outside the scope of the present invention), the tip to the rear end of the workpiece during piercer rolling It is extremely difficult to keep the working temperature in the temperature range below the temperature at which the work material melts or the grain boundary in the high temperature region becomes brittle and above the temperature at which the work material does not decrease in ductility. Therefore, the front-rear end temperature difference needs to be 30 ° C. or higher and 400 ° C. or lower (within the scope of the present invention).

In addition, it is preferable that the temperature difference between the front and rear ends is 50 to 200 ° C., because the material of the workpiece can be made more uniform and the rate of wrinkle generation can be further reduced.
In order to heat the billet so that the temperature difference between the front and rear ends is within the range of the present invention, the workpiece is heated uniformly in a heating furnace, and then only the tip portion is heated by induction heating. A method in which the front end of the workpiece is heated to a higher temperature than the rear end can be preferably used.

  The length of the heated portion of the workpiece when heated by induction heating is preferably a length portion within a range from the tip position of the workpiece to a position in the length direction of 5 to 50% of the entire length. When the heating part length is out of this preferable range, it is difficult to set the temperature difference between the front and rear ends within the preferable range (50 to 200 ° C.). On the other hand, in the case of using a method in which the front end of the workpiece is heated to a temperature higher than the rear end in the heating furnace, as a heating furnace for billet heating, as shown in FIG. 2 (or the vicinity of the center than the outer peripheral side) can be heated 30 to 400 ° C., the rotary heating furnace 20 can be heated, or one end in the direction perpendicular to the conveying direction in the furnace as shown in FIG. If the walking beam type heating furnace 70 that can be heated to 30 to 400 ° C. is used, a small-scale modification to the existing rotary heating furnace 2 or walking beam type heating furnace 7 for billet heating is possible. It is preferable because the present invention can be implemented only by adding.

  A workpiece with a steel billet equivalent to JIS STKM13A with a diameter of 190 mm x length of 3 m round billet is billet-heated and then pierced to form a hollow tube with an outer diameter of 205 mm and a wall thickness of 20 mm. , This is mandrel mill rolled, then reheated, then stretch reducer rolled, then cooled in the cooling bed to produce a seamless steel pipe (product) with an outer diameter of 85 mm x wall thickness of 8.5 mm. As shown in Table 1, various changes were made and the inner surface properties of the products were investigated. The results are shown in Table 1. An induction heating pattern when induction heating is performed after furnace heating is shown in FIG. As shown in Table 1, inner surface flaws occurred in the comparative example and the conventional example, whereas the inner surface property was good in the example of the present invention.

  A work piece having a steel billet equivalent to 13% Cr steel (equivalent to JIS SUS410) and having a round billet with a diameter of 230 mm × length of 5 m is billet-heated and then pierce-rolled to an outer diameter of 245 mm × thickness of 30 mm. This is a hollow steel tube shape, rolled by an elongator, plug mill, and reeler, then reheated, then sizing mill rolled, then cooled in a cooling bed, and a seamless steel tube having an outer diameter of 195 mm and a wall thickness of 22 mm (product) In the mascot, the heating conditions of the round billet were variously changed as shown in Table 2, and the inner surface properties of the products were investigated. The results are shown in Table 2. An induction heating pattern when induction heating is performed after furnace heating is shown in FIG. As shown in Table 2, while the inner surface flaws occurred in the comparative example and the conventional example, the inner surface property was good in the example of the present invention.

  In this material, as shown in FIG. 4, when entering the high temperature embrittlement region on the rear end side of rolling, soot is generated, so that the front end temperature is 1350 ° C. or lower and the rear end temperature is It is desirable to set it as 1300 degrees C or less.

1 Work Material 2 Rotary Heating Furnace 3 Piercer (Inclined Roll Punching Roller)
4, 9, 11, 13 Plug 5 Mannesmann-mandrel mill 6 Mandrel bar 7 Walking beam furnace 8 Elongator
10 Plug mill
12 Reeler
14 Stretch reducer
15 Sizer (sizing mill)
16 Cooling floor
20 Rotary heating furnace configured to be able to heat the outer peripheral side in the radial direction in the furnace 30 to 400 ° C higher than near the center
70 Walking beam type heating furnace configured so that one end in the direction perpendicular to the conveying direction in the furnace can be heated 30 to 400 ° C higher than the other end.
100 products (seamless steel pipe)

Claims (5)

  Production of a seamless steel pipe in which a workpiece having a round billet is heated, pierced and rolled, subsequently stretch-rolled, subsequently reheated, then re-heated, then rolled with a constant diameter, and then cooled to become a seamless steel pipe In the method, when heating the workpiece before piercing, the workpiece is heated so that the front end in the longitudinal direction of the workpiece before piercing and rolling is at a temperature 30 to 400 ° C. higher than the rear end. To produce seamless steel pipe.   2. The seamless steel pipe according to claim 1, wherein when the workpiece is heated before drilling, the workpiece is uniformly heated in a heating furnace, and then only its tip is heated by induction heating. Production method.   The method for manufacturing a seamless steel pipe according to claim 1, wherein when the workpiece is heated before drilling, the tip of the workpiece is heated to a temperature higher than the rear end in a heating furnace.   4. The production of a seamless steel pipe according to claim 3, wherein the heating furnace is a rotary heating furnace configured to be able to heat the outer peripheral side in the radial direction in the furnace by 30 to 400 ° C. higher than the vicinity of the center. Method.   The seam according to claim 3, wherein the heating furnace is a walking beam type heating furnace configured such that one end in a direction orthogonal to the conveying direction in the furnace can be heated by 30 to 400 ° C higher than the other end. Manufacturing method of steelless pipe.

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