JP2006346726A - Method for cold-rolling clad steel tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cold-rolling method of a clad steel tube in which the projection of an external tube or an internal tube at tube end parts and peeling on the boundary between the internal tube and the external tube caused by the projection is prevented from generating. <P>SOLUTION: After chamfering the side of a base material in the tube end parts of a clad steel tube stock consisting of the base material (internal tube 2) and a clad material (external tube 1) so as to satisfy next formulas (i), (ii), the clad steel tube stock is cold-rolled. In formulas (1), (ii), the wall thickness of a tube stock is the summed thickness (mm) of the base material of the clad steel tube stock and the clad material before cold-working. Tb is the chamfering width (mm) in the thickness direction of the clad steel tube stock and Lb is a chamfering width (mm) in the longitudinal direction of the clad steel tube stock. The relationship of the thickness of the tube stock × 50% ≤ Tb ≤ the thickness of the tube stock × 90% is satisfied (i). The relationship of the thickness of the tube stock × 50% ≤ Lb is satisfied (ii). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for cold rolling a clad steel pipe that can prevent peeling at the interface caused by a difference in deformation resistance between a base material and a clad material when the clad steel pipe is cold rolled to produce a clad steel pipe. .

  In recent years, for steel pipes used in highly corrosive environments such as boilers and heat exchangers, in order to achieve both strength and corrosion resistance, carbon steel or low alloy steel as a base material and stainless steel or Ni as a cladding material can be used. There is an increasing demand for clad steel pipes in which high Cr and high Ni materials such as base alloys are adhered. In this clad steel pipe, a clad material such as stainless steel or Ni-base alloy is used for the outer pipe, and a base material made of carbon steel or low alloy steel is used for the inner pipe, or conversely, the base material is used for the outer pipe and the inner pipe is clad. Generally, materials are used.

  Such a clad steel pipe is manufactured by the following method. First, the base material and the clad material produced by the ingot casting method or continuous casting method are rolled or forged, and then ground to a predetermined size, and then a billet for clad steel pipe is formed by welding or shrink fitting. Make it. This billet is made into a clad steel pipe by hot extrusion, and a cold steel and heat treatment are appropriately combined with this pipe to make a clad steel pipe having predetermined dimensions and strength.

  Examples of the cold working method include cold rolling and cold drawing (also referred to as cold drawing). Conventionally, a clad steel pipe is manufactured by applying cold drawing to a clad steel base pipe. It was common.

  However, in cold drawing, there is a tendency for an axial stress difference between the outer surface and the inner surface of the tube, and therefore when the drawing is performed using a clad steel base tube manufactured by hot extrusion, the inner tube and the outer tube are separated. There is a problem that it is easy to occur and a large degree of processing cannot be added.

  In addition, a chemical conversion treatment such as the formation of ferrous oxalate coating is performed during the cold drawing process, but in recent years, a case where a high corrosion resistance material such as a Ni-based alloy is used as a clad material is increasing. In such an alloy, a chemical conversion treatment film is difficult to be formed, lubrication is insufficient, and drawing may be difficult.

  Therefore, it is possible to obtain a large degree of processing at a time, and the development of a method for manufacturing a clad pipe by cold rolling that can reduce the axial stress difference between the outer surface and the inner surface of the tube and that can be processed without resorting to lubrication by chemical conversion treatment. It was desired.

  In connection with the manufacture of clad steel pipes, Patent Document 1 discloses a metal outer tube for coating on the outer peripheral surface of a cylindrical billet for hot extrusion, and a vent hole corresponding to a hollow portion on the front end face and the rear end face. By using a billet for producing clad tube material provided with a metal cover for covering, it is possible to eliminate peeling defects of the clad material (clad material) during hot extrusion, and use it for rolling, drawing, etc. A method of manufacturing a clad tube is disclosed in which peeling does not occur even when the processing rate is increased in secondary processing. However, in the said literature, the problem regarding the cold processing (cold drawing processing, cold rolling) mentioned above is not examined at all.

JP-A-5-309411

  The above-mentioned problems related to cold working (cold drawing and cold rolling) used in the production of clad steel pipes are summarized as follows.

  (A) Since a large degree of work cannot be obtained by cold drawing, it is particularly difficult to deal with small diameter materials.

  (B) Although cold drawing requires chemical conversion treatment for lubrication, high corrosion resistance materials such as Ni-based alloys do not provide sufficient formation of chemical conversion coating film, resulting in insufficient lubrication and difficult drawing. is there.

  (C) In the processing by cold rolling, the difficulty described in the above (a) and (b) can be avoided. However, when a large degree of processing is given, the more easily deformable material (usually the base material) extends. Therefore, the material jumps out at the end of the tube.

  (D) In the processing by cold rolling, the material jumps out at the end of the tube, so that separation between the inner tube and the outer tube occurs at both ends of the tube, and it is necessary to cut down the separated portion. , Yield decreases.

  (E) Further, when the high temperature heat treatment is performed in order to recrystallize stainless steel used as a cladding material, for example, while the protrusion of the base material (carbon steel or low alloy steel) is generated, A large amount of scale is generated in the low alloy steel, and when the pipe is bent by a subsequent rotary type straightening machine, the scale adheres to the roll in a large amount, and a pressing flaw occurs on the outer surface of the clad steel pipe.

  When the clad steel pipe is manufactured by cold rolling, the present invention solves the above problems (c) to (e), the outer pipe or the inner pipe jumps out at the pipe end, and the inner pipe and the outer pipe resulting therefrom. It is an object of the present invention to provide a method for cold rolling of a clad steel pipe that does not cause peeling at the interface of the steel plate and no pressing flaws on the outer surface of the clad steel pipe.

  The inventors of the present invention have made studies by deciding to manufacture a clad steel pipe having excellent strength and corrosion resistance by cold rolling which is easy to obtain a large degree of work and does not require lubrication by chemical conversion treatment. In this case, it is necessary to solve the problems (c) to (e).

  The material “jumping out” at the pipe end in (c) is that when a large degree of processing is given, the base material that is likely to be deformed at the pipe end is less than the clad material due to the difference in deformation resistance between the base material and the clad material. This is a phenomenon that occurs due to large elongation.

  FIG. 1 and FIG. 2 are explanatory views of the occurrence state of this pop-up, FIG. 1 is a view schematically showing a longitudinal longitudinal section of a clad steel tube before cold rolling, and FIG. 2 is after cold rolling It is a figure which shows typically the longitudinal direction longitudinal cross-section of this clad steel pipe. The clad steel pipe or the clad steel pipe shown in these figures represents the pipe end side in cold rolling.

  FIG. 1 shows a case in which the outer tube 1 is a clad steel tube made of a clad material such as stainless steel and the inner tube 2 is made of a base material such as carbon steel. Cold rolling is applied to the clad steel tube. When applied, the base material (inner tube 2) has a smaller deformation resistance than the clad material (outer tube 1) and is more likely to be deformed. Therefore, as shown in FIG. . Note that when the clad material is an inner tube and the base material is an outer tube, the outer tube protrudes.

  When this protrusion 3 occurs, separation 4 between the inner tube 2 and the outer tube 1 occurs in the vicinity thereof as shown in FIG. 2 (problem (d)).

  The inventors of the present invention have developed a tube (in the example shown in FIG. 2, the inner tube 2) that is generated when the above-described material having a small deformation resistance is stretched more greatly, and the interface between the inner tube and the outer tube resulting therefrom. In order to prevent delamination, chamfering (beveling) was performed on the pipe with the smaller deformation resistance of the clad steel base pipe. This is based on the idea that the material (that is, the tube) is prevented from popping out by removing in advance the portion of the material that extends more greatly.

  As a result, it has been found that by optimizing the chamfering conditions, that is, the shape of the tube after chamfering (hereinafter referred to as “chamfered shape”), the tube can be prevented from popping out and the inner tube and the outer tube from being separated. Thus, the present invention has been made.

  Therefore, the cold rolling method of the clad steel pipe of the present invention is a chamfering process so that the base metal side of the pipe end portion of the clad steel base pipe made of the base material and the clad material satisfies the following formulas (i) and (ii): Then, the clad steel tube is cold-rolled.

Tube thickness x 50% ≤ Tb ≤ Tube thickness x 90% ... (i)
Tube thickness x 50% ≤ Lb (ii)
Here, tube wall thickness: the base material and the cladding material of the cladding steel tube before cold working were combined
Thickness (mm)
Tb: Chamfer width in the thickness direction of the clad steel tube (mm)
Lb: Chamfer width in the longitudinal direction of the clad steel tube (mm)
As the “base material”, carbon steel, low alloy steel, or the like is used. Further, as the “cladding material”, a high Cr or high Ni material such as stainless steel or Ni-based alloy having excellent corrosion resistance and heat resistance can be used.

  According to the cold rolling method of a clad steel pipe of the present invention, the pipe jumps out at the pipe end portion caused by the material having a small deformation resistance extending more during cold rolling, and the inner pipe and the outer pipe resulting therefrom. It is possible to produce a clad steel pipe with a high yield by preventing peeling at the interface. Further, according to this cold rolling method, it is possible to perform cold working with a large degree of work exceeding 60% at a time, and further, it is possible to process highly corrosion-resistant materials that are difficult to lubricate by chemical conversion treatment. .

  As described above, the method for cold rolling a clad steel pipe according to the present invention satisfies the following formulas (i) and (ii) on the base metal side of the pipe end portion of the clad steel base pipe made of the base material and the clad material: After the chamfering process, the clad steel tube is cold-rolled. In the equations (i) and (ii), the tube thickness is the thickness (mm) of the clad steel tube combined with the base material and the clad material of the clad steel tube before cold working. , Tb is the chamfering width (mm) in the thickness direction of the clad steel base tube, and Lb is the chamfering width (mm) in the longitudinal direction of the clad steel base tube.

Tube thickness x 50% ≤ Tb ≤ Tube thickness x 90% ... (i)
Tube thickness x 50% ≤ Lb (ii)
In the cold rolling method of the present invention, the base metal side of the pipe end of the clad steel pipe is chamfered so as to satisfy the above formulas (i) and (ii) by deforming by cold rolling. Prevents the base material (inner tube 2 in the example shown in FIG. 2) from popping out and the separation at the interface between the base material and the clad material that occurs when the base material having a low resistance extends more than the clad material. It is to do.

  The conditions of the equations (i) and (ii) are determined by conducting the following investigation.

  That is, a chamfering width Tb (mm) in the thickness direction and a chamfering width in the longitudinal direction of a clad steel base tube obtained by using a base material (STBA23 equivalent material) as an inner tube and a clad material (SUS310 equivalent material) as an outer tube. Chamfering is performed by changing Lb (mm) over a wide range, and cold rolling is performed by a pilger rolling mill to produce a clad steel pipe, the inner pipe (base material) is popped out, and peeling at the interface between the base material and the clad material is performed. The presence or absence was investigated.

  FIG. 3 is a diagram schematically showing a part of the cross-sectional shape of the clad steel tube after chamfering. Tb represents the chamfer width in the thickness direction of the clad steel tube, and Lb represents the chamfer width in the longitudinal direction. T is the thickness of the clad steel base tube, which is the sum of the thickness of the outer tube 1 and the thickness of the inner tube 2.

  Table 1 shows the dimensions (outer diameter, thickness) and degree of processing of the clad steel pipe and the clad steel pipe obtained by cold rolling. The degree of processing is a value calculated by {(cross-sectional area before processing) − (cross-sectional area after processing)} / (cross-sectional area before processing).

  Table 2 shows the survey results. In Table 2, the numbers in the Tb column and the Lb column are percentages (%) with respect to the wall thickness “T” of the clad steel tube (hereinafter also simply referred to as “element tube”). Further, in the table, ◯ mark, Δ mark, X mark, and XX mark mean the following states, respectively.

○: Rolling completed without problems (no inner pipe popping out)
△: Slightly popping out of the inner pipe, but rolling completed without peeling ×: Large jumping out of the inner pipe XX: Thickness at the end of the pipe is too thin.
Trouble that overlaps with the tip of the steel pipe

  From the results shown in Table 2, the chamfering width Tb in the thickness direction of the pipe is about 50 to 90% of the thickness of the pipe (that is, the formula (i)), and the chamfering width Lb in the longitudinal direction of the pipe. If the condition of the tube thickness is 50% or more (that is, the formula (ii)) is satisfied, the evaluation after cold rolling is marked with ○ or Δ, and the clad steel tube is cold rolled When manufacturing a clad steel pipe, it turns out that peeling at the interface between the inner pipe and the outer pipe of the clad steel pipe can be suppressed.

  The upper limit of Lb is not particularly limited. As is apparent from the results in Table 2, there is no difference in effect as long as it is 60% or more of the tube thickness. However, if Lb is too large, the chamfering cost increases, so the desirable upper limit is 100%, and more desirably 80%.

  From the results of Table 2, if only the case of ◯ is evaluated as good and this is set as a desirable range, the desirable lower limits of Tb and Lb are both “wall thickness x 60%”.

  By the way, regarding the chamfering width Tb (chamfering thickness) in the thickness direction of the raw tube, when the thickness of the clad material of the raw tube is large or when Tb is large, not only the base material portion but also the clad material portion. It will be chamfered. Therefore, the desirable upper limit of Tb (chamfer thickness) is preferably up to the base material thickness. This is because the jumping out of the material occurs in the base material having a small deformation resistance, so that even the chamfering of the clad material part has no influence on the popping out preventing effect of the material.

  A pilger rolling mill can be used for cold rolling after chamfering so as to satisfy the expressions (i) and (ii). This rolling mill is a forging type rolling mill, and can adjust the outer diameter and thickness of the clad steel pipe while crimping the base material and the clad material.

  According to the cold rolling method for a clad steel pipe according to the present invention described above, chamfering is performed on the base metal side of the pipe end portion of the clad steel base pipe made of the base material and the clad material so as to satisfy the above-mentioned specifications, and the cold rolling is performed. By removing in advance the portion that greatly extends during cold rolling, it is possible to prevent the base material from jumping out at the end of the tube and peeling at the interface between the base material and the cladding material during cold rolling. Further, since there is no jump out of the base material at the end of the pipe, there is no risk of occurrence of pressing flaws on the outer surface of the clad steel pipe due to a large amount of scale on the surface of the base material in the high temperature heat treatment described in (e) above.

  In the above description, the clad steel base pipe using the clad material for the outer pipe and the base material for the inner pipe is taken as an example, but conversely, the clad steel using the base material for the outer pipe and the clad material for the inner pipe. The same idea can be applied to a raw tube.

Example 1
A clad steel pipe using SUS304 for the outer pipe and STBA23 for the inner pipe was chamfered, and then cold-rolled by a Pilger rolling mill to produce a clad steel pipe.

  Table 3 shows the dimensions (outer diameter and wall thickness) and degree of processing of the clad steel pipe and the clad steel pipe obtained by cold rolling, and Table 4 shows the chamfered shapes (Tb and Lb).

  In the cold rolling under this condition, the rolling was completed without any problem without the inner pipe protruding or peeling.

(Example 2)
A clad steel pipe using SUS310 for the outer pipe and STBA23 for the inner pipe was chamfered, and then cold rolled by a Pilger rolling mill to produce a clad steel pipe.

  Table 5 shows the dimensions (outer diameter, thickness) and degree of processing of the clad steel pipe and the obtained clad steel pipe, and Table 6 shows the chamfered shapes (Tb and Lb).

  Also in this case, the inner tube could be rolled out without any problem without peeling or peeling.

(Example 3)
A clad steel pipe using NCF625 for the outer pipe and STBA23 for the inner pipe was chamfered and then cold-rolled by a Pilger rolling mill to produce a clad steel pipe.

  Table 7 shows the dimensions (outer diameter, thickness) and degree of processing of the clad steel pipe and the obtained clad steel pipe, and Table 8 shows the chamfered shapes (Tb and Lb).

  Also in this case, the rolling was completed without any problem without the inner pipe jumping out or peeling off.

  According to the cold rolling method of the clad steel pipe of the present invention, the pipe jumps out at the pipe end portion caused by the elongation of the material having a small deformation resistance, and the peeling at the interface between the inner pipe and the outer pipe resulting therefrom. Therefore, clad steel pipe can be produced with high yield. The degree of processing at one time can be increased, and processing of highly corrosion resistant materials such as Ni-base alloys that are difficult to lubricate by chemical conversion treatment is also possible. Therefore, this method can be suitably used for manufacturing a clad steel pipe.

It is a figure which shows typically the longitudinal direction longitudinal cross-section of the clad steel base tube before cold rolling. It is a figure which shows typically the longitudinal direction longitudinal cross-section of the clad steel pipe after cold rolling. It is a figure which shows typically a part of cross-sectional shape of the clad steel base pipe after a chamfering process implementation.

Explanation of symbols

1: Outer pipe 2: Inner pipe 3: Jump out of inner pipe 4: Peeling

Claims (1)

After chamfering the base metal side of the pipe end portion of the clad steel base pipe made of the base material and the clad material so as to satisfy the following formulas (i) and (ii), cold-rolling the clad steel base pipe A method for cold rolling a clad steel pipe.
Tube thickness x 50% ≤ Tb ≤ Tube thickness x 90% ... (i)
Tube thickness x 50% ≤ Lb (ii)
Here, tube wall thickness: the base material and the cladding material of the cladding steel tube before cold working were combined
Thickness (mm)
Tb: Chamfer width in the thickness direction of the clad steel tube (mm)
Lb: Chamfer width in the longitudinal direction of the clad steel tube (mm)
It is.

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