JPS63177925A - Manufacture of high frequency bent tube having low hardness as worked - Google Patents

Abstract

PURPOSE:To manufacture an inexpensive elbowless which has a small bend radius by high frequency bending,and also, whose hardness is <=HV 248 is worked, by heating the outside surface of a tube stock consisting of carbon steel of a specific component, to a range of 850-950 deg.C, and bringing it to bending, while executing water-cooling. CONSTITUTION:The titled method is used for manufacturing a high frequency bent tube whose radius of curvature is <=three times of the outside diameter of the tube, and carbon steel components as a tube stock are 0.05-0.25% C, 0.10-0.35% Si, and 0.30-1.00% Mn by wt.%, and as for the remainder, Fe and impurities are contained, and the component is limited to that which satisfies C+Mn/6<=0.33%. The tip part of such a steel tube 1 is clamped tightly by a clamp 5, heated until the outside surface becomes 850-950 deg.C, by a heating device 3 consisting of a high frequency inductor, and also, propelled in the direction as indicated with an arrow by a suitable means, by which the steel tube 1 is brought to bending. In such a way, an elbowless having a small bend radius, and also, having low hardness as worked can be manufactured at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing high-frequency bent pipes used in piping systems for power generation, chemical plants, etc.

(Conventional technology) Conventionally, weight percent used for power generation, chemical plants, etc.
C0.25X or less, Mn 1.0096 or less A S
TMA106B class 1.0-2. Welded pipe fittings (hereinafter referred to as elbows) specified in Japanese Industrial Standards JISB2304.2305, etc. are used for bent pipes made of carbon or raw steel that have a small bending radius of OX (outer diameter of the pipe). . For elbow processing, refer to the 3rd edition of the Steel Handbook compiled by the Japan Iron and Steel Association.
VP, 179, is a tube expansion bending process at a high temperature commonly known as the Hamburg process, and in terms of materials, the raw tube and the bent tube have almost the same properties. however,
Since the product shape is a product with only a bent part with a 0 bend angle up to 180 degrees, there is an increase in welding man-hours during piping construction. There is a problem that the construction cost will also increase.

Therefore, there is a demand for a bent pipe (hereinafter referred to as "elbowless") with fewer welded parts, that is, a bent pipe having straight pipe parts at both ends of the bent part.

One method for manufacturing elbow braces is by bending, but if you try to obtain an elbow brace with a small bending radius, it cannot be put into practical use because it does not satisfy the dimensional tolerance of the aspect ratio among the cross-sectional shape dimensional tolerances of the bent part. Become something.

Another method is high-frequency bending known from, for example, Japanese Patent Laid-Open No. 53-135870 and Japanese Patent Laid-Open No. 53-135871. With this processing method, if the bending radius exceeds 3x (outer diameter of the pipe), the heated bending area is made narrower by forced air cooling, and the processing can be performed without buckling, so there are no problems with the material of the bent part. . However, as desired 1.0-3. In the case of a small bending radius of OX (outer diameter of the pipe), forced cooling is required to further narrow the heated bending area to prevent buckling. Therefore, the cooling rate of the outer surface layer of the bent portion (1 to 2++v below the surface) increases, and hardening of the outer surface layer of the bent portion is unavoidable. Normally, in pipe welding of carbon steel pipes, Hv248 is the highest hardness that can be used practically from the viewpoint of safety against destruction.
Although the following is desired, there is a problem in that within the above-mentioned component range, this hardness regulation cannot be satisfied by high-frequency bending as it is. Soft annealing is an effective solution to this problem, but
Due to the shape of the elbow brace, a large furnace is required, and the productivity is poor and the cost is high. Therefore, the elbow brace that has been processed by high-frequency bending has not been put into practical use.

(Problems to be Solved by the Invention) That is, the present invention overcomes such conventional drawbacks, and A.
From steel pipes with mechanical properties comparable to STM A106B class, high-frequency bending allows for small bending radius and
The object of the present invention is to provide an inexpensive method for manufacturing an elbow brace that has a Hv of 248 or less in the as-processed state.

(Means for Solving the Problems) The present inventors investigated the influence of each element, C and Mn, and the influence of high-frequency bending conditions on improving the hardness of the outer surface layer, and as a result, as shown in Fig. 1. It was found that there is a good correlation between the C equivalent given by the formula c-+-Mn/s (hereinafter referred to as C equivalent) and the maximum hardness after bending. These relationships are expressed by the formula (maximum hardness) = 607 X (C equivalent) +
43.

The present invention has been made based on the above-mentioned knowledge, and the gist thereof is to provide a method for manufacturing a high-frequency bent pipe having a radius of curvature of 3 times or less of the outside diameter of the pipe, in which C0.05 to 0 in weight % is provided. .25%, Si0.1'O~0.35%, Mn 0.30~1.00%, the balance consists of Fe and impurities, and carbon steel that satisfies C+Mn/6≦0.33% is used as the raw tube. , heat the outer surface of the raw tube until it reaches 850 to 950°C,
A method for manufacturing a high-frequency bent pipe with low hardness as it is processed, characterized by bending the pipe while cooling with water.

In addition, in the present invention, seamless steel pipes are suitable for the carbon steel pipes used as the base pipes of bent pipes, but electric resistance welded steel pipes, UO#4
Applications such as pipes are also possible.

(Function) Fig. 2 shows an example of a pipe bending device used to carry out the wood invention bending method, in which 1 is a steel pipe to be bent, 2 is a guide roller that supports and guides the copper pipe, and 3 is a pipe bending device. A heating device which is annular and consists of a high frequency inductor that locally heats the steel pipe 1 from its outer periphery in a narrow width and has a cooling tank; 4 is a rotatable bending arm with a clamp 5 at the tip; 6 is a tube end; The support stand, the arrow 7 indicates the cooling water sprayed from the heating device 3, and the shaded area 8 indicates the heating processing area. The apparatus is capable of bending the steel pipe 1 by tightening the distal end of the steel pipe 1 with a clamp 5, heating the steel pipe 1 locally at a high temperature with a heating device 3, and propelling the pipe in the direction of the arrow with an appropriate means.

The reasons for the limitations of the present invention will be explained below.

First, regarding bending conditions, under normal bending conditions, when heating with a high-frequency heating coil, a coil as narrow as possible is used in order to narrow the heating bending area. Therefore, it is difficult to uniformly heat the entire wall thickness, and the temperature of the inner surface is lower than that of the outer surface. In order to stabilize the structure, it is necessary to operate at an outer surface heating temperature range of 850 to 950°C. That is, the minimum heating temperature is to increase the heating temperature of the inner surface to c3 or higher, and the maximum heating temperature is to prevent the structure of the outer surface from becoming coarse.

When manufacturing a high-frequency bent pipe with a small bending radius, it is necessary to forcibly apply a sufficient axial compressive force to reduce the wall thickness of the bent portion subjected to tensile processing. At this time, if the width of the heating process becomes wide, wrinkles will occur on the inside after the bending process starts, and furthermore, buckling will occur, making it impossible to process.

Therefore, in order to narrow the heating processing width as much as possible, spray water cooling, which has a cooling effect rather than forced air cooling, is performed immediately after heating processing, and this water cooling makes the deformation resistance in the water cooling area much larger than the deformation resistance in the heating processing area. This is an attempt to solve the above problems. This spray water cooling has a slower cooling rate than the conventional forced water cooling for the purpose of hardening.

Next, the reasons for limiting the components of the raw pipe used in the present invention will be described. C is an element necessary to ensure mechanical properties, and the amount necessary to exhibit its function is 0.05% or more. However, increasing the C content impairs the welding workability of steel pipes, so the upper limit was set at 0.25%.

Mn is also an element necessary to ensure mechanical properties,
The amount necessary to exhibit its function is 0.30% or more. However, excessive content impairs welding workability and excessively increases hardenability, so the upper limit was set at 1.00%.

St is a necessary element as a deoxidizing element, and must be contained in an amount of 0.10% or more in order to exhibit at least a deoxidizing function. It is also an element that affects mechanical properties and hardenability, albeit to a small extent.

However, since a large amount of content impairs high-frequency bending workability, the upper limit was set at 0.35%.

C and Mn are elements that contribute to improving mechanical properties and hardness upon cooling, and their synergistic effects can be summarized by C equivalent. The lower limit of C equivalent is preferably 0.20% or more in order to satisfy the tensile strength of 42.2 kgf/mm2 or more of the raw pipe as hot rolled, and it is preferable to set the lower limit of C equivalent to 0.20% or more in order to satisfy the tensile strength of 42.2 kgf/mm2 or more of the raw pipe as hot rolled. When used as a raw pipe, the content is preferably 0.18% or more. The upper limit of the C equivalent was set to 0.33% or less in order to keep the maximum hardness on the outer surface side to Hv24B or less under the conditions of the high-frequency bending process. From the relational expression between C equivalent and maximum hardness, the C equivalent corresponding to Hv248 is 0.34%,
It was set at 0.33% or less to allow for a margin in consideration of variations in manufacturing conditions.

Next, the characteristics of the steel pipe of the present invention will be shown in Examples in comparison with comparative materials.

(Example) Table 1 shows the chemical composition of the steel pipes subjected to bending. A1 to A2m plates are comparison steel pipes, which are as-rolled steel pipes with a C equivalent of more than 0.33%. 81～B1
The 2M pipe is a steel pipe of the present invention, which is an as-rolled steel pipe with a carbon equivalent of 0.33% or less. B13 is also a steel pipe of the present invention, but
It is a tempered steel pipe with a C equivalent of 0.33% or less.

Table 1 (wtt) Table 2 shows the mechanical properties of the raw steel pipes of Table 1 and the maximum hardness of the bent portion after bending.

Regarding mechanical properties in Table 2, yield strength, tensile strength, and elongation were measured using JIS No. 12 test pieces.

As shown in Table 2, the maximum heating temperature for all test tubes is 8
High-frequency bending is performed by spray water cooling at 50 to 950°C. When bending is performed under these conditions,
It is clear that all comparison steel pipes, A1 to A2fII pipes having a C equivalent of more than 0.33%, have a maximum hardness of Hv24B or more and cannot be put to practical use.

In contrast, steel pipes 81 to 8 used in the present invention
The 13 fjA tube has a C equivalent of 0.33% or less, making it possible to manufacture a high-frequency bent tube that satisfies a maximum hardness of Hv248 or less.

(Effects of the Invention) Therefore, according to the present invention, bent pipes with a small bending radius for use in power generation and chemical plants, which are conventionally constructed with elbows, can be replaced with seamless steel pipes or steel pipes manufactured by other manufacturing methods. It becomes possible to manufacture elbowless pipes by high-frequency bending, which has the advantages of significant cost reduction and low hardness, which contributes to safety.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between C equivalent and maximum hardness Hv after bending. The bending conditions at this time are that the maximum heating temperature of the outer surface is 850 to 950°C and spray water cooling. FIG. 2 is a plan view of an example of a bending machine used in carrying out the present invention. 1... Steel pipe 2... Guide roller 3
...Heating device 4...Bending arm 5...
・Clamp 6...Pipe end support stand 7...
Spray cooling water 8... Heating processing area Figure 1 Figure 2 Figure 2, Guide roller 3 Heating device 4 Bending arm 5 - Clamp procedure amendment March 9, Showa Otsu 2nd year Showa/:, 1st year patent application no. q2bτ Name (Name, (ni5);, 1tl;, = 1-comL';; Shikinasha 4, Agent
(4 apologies),
− Amendment The following matters in the specification of the application will be amended. Note 1, page 7, line 5 K: "Heating temperature Ac3 or higher" is corrected to "Heating temperature Ac3 or higher." 2. On page 7, line 8, line 9, it says "when manufacturing". Correct it to "when manufacturing." 3. In the second line of page 8, the phrase "for the present invention" is corrected to "for the present invention." Procedural amendment written on April 72, 1989, Patent Application No. 262 of 1988 Relationship to Case Applicant 4, Agent
(Ball 2λ±) Address: 33G, Marunouchi Building, 2-6-2 Marunouchi, Chiyoda-ku, Tokyo Name (3667)
Teruo Taniyama T1 1 1.・5. Date of amendment order White 4ε Amendment We will amend the following circles in the specification of the application. 1, page 2, line 7, it says "r J Engineering 5B2304.2305, etc." r JI
SB2311, 2312, etc. corrections. 2. On page 2, line 10, ``Iron and Steel Handbook IV P, 179 J'' is corrected to ``Steel Handbook M P, 179 j.

Claims (1)

[Claims] A method for manufacturing a high-frequency bent pipe whose radius of curvature is three times or less the outer diameter of the pipe, which contains, in weight %, C 0.05-0.25%, Si 0.10-0.35%, Mn 0.30~1.00%, the balance is Fe and impurities, and carbon steel that satisfies C+Mn/6≦0.33% is used as a raw tube and heated until the outer surface of the raw tube reaches 850~950℃. ,
A method for manufacturing a high-frequency bent pipe with low hardness as it is processed, characterized by bending it while cooling with water.