JPS63317218A - Production of high frequency bending pipe of low hardness as it is worked - Google Patents

Abstract

PURPOSE:To manufacture a high frequency bending pipe of low hardness as it is worked by heating the outer surface of the blank pipe of carbon steel contg. C, Si, Mn, P, S, Al and N at specific ratio within specified temp. range and executing bending with cooling it with water. CONSTITUTION:The carbon steel blank pipe 1 whose weight ratio of contg. component is 0.05-0.30% C, 0.10-0.50% Si, 0.30-1.50% Mn, <=0.03% P, <=0.03% S, 0.005-0.05% Al and <=0.015% N and satisfying C+Mn/6+(Cr+Mo+ V)/5+(Ni+Cu)/15<=0.38% is supported by a supporting base 6, a high frequency heating coil 3 is passed by a guide roller 2 and held by the clamp 5 of a bending arm 4 to execute bending. In that case it is locally heated at 850-1050 deg.C by a coil 3 and cooled by a fountain 7. The elbowless with small bending radius and low hardness as it is worked can thus be manufactured.

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 and chemical plants.

(Prior art) Conventionally, 1, 0 to 2.
As a carbon steel bent pipe having a small bending radius of OX (outer diameter of the pipe), welded pipe joints (hereinafter referred to as elbows) specified in Japanese Industrial Standards JIS B 2311°2312, etc. are used. The processing of the elbow is a high-temperature pipe expansion bending process known as Hamburg processing, which is published in the 3rd edition Steel Handbook VI P, 179, compiled by the Japan Iron and Steel Institute.In terms of materials, the raw pipe and the bent pipe are almost the same. have a property. However, since the product shape is only a bent part with a 0 bend angle up to 180 degrees, the number of welding steps increases during piping construction, and the number of inspection steps for welded parts also increases. The problem is that the construction period becomes longer and the construction cost becomes higher.

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 cold bending, but when trying to obtain an elbow brace with a small bending radius, it is not suitable for practical use because it does not satisfy the dimensional tolerance of the aspect ratio among the cross-sectional shape and dimensional tolerances of the bent part. becomes.

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 3 x (outer diameter of the pipe), the heated bending area is narrowed by forced air cooling, which allows processing without buckling, so there are no problems with the material of the bent part. No, however, 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 part (up to 1 to 2 mm below the surface) becomes faster.
Hardening of the outer surface layer of the bent portion is unavoidable. Normally, in pipe welding of carbon steel pipes, it is desired that the maximum hardness for practical use is t (v248 or less) from the viewpoint of safety against fracture. I have a problem with not being satisfied.

One effective solution to this problem is softening annealing, but it requires a large furnace due to the shape of the elbow, and has low productivity and high cost. On the other hand, as shown in Japanese Patent Application No. 62-7862 previously filed by the present applicants, carbon steel that satisfies C◆Mn/6≦0.339g is used as the raw tube, and Surface is 850-9
There is a method of heating the material to 50° C. and bending it while cooling with water to obtain a low-hardness elbow brace while still undergoing high-frequency bending. However, even with this method, if the wall thickness of the raw pipe is large, the temperature of the outer surface of the pipe can be reduced to 950°C.
Even if the tube is heated to the upper limit of 950°C, the temperature on the inner surface of the tube is too low to stabilize the structure after bending, and if an attempt is made to stabilize the structure, the temperature on the outer surface of the tube will exceed 950°C, making it impossible to bend the tube. Since the hardness of the outer surface of the pipe increases after processing, it is difficult to obtain stable quality from thick-walled elbow braces.

(Problems to be solved by the invention) That is, the present invention overcomes these conventional drawbacks.
From thick-walled steel pipes with mechanical properties comparable to STM^106B 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 effects of various components and high-frequency bending conditions on improving the hardness of the outer surface layer, and found that the outer surface temperature of the raw pipe exceeded 950°C and 1050°C. Even at heating temperatures below ℃, the steel pipe of the present invention has the formula C+ as shown in FIG.
Mn/6+ (Cr+Mo+V) 15◆(Ni+Cu
)/15 (hereinafter referred to as C equivalent) and the maximum hardness after bending was found to show a good correlation.

The present invention has been made based on the above knowledge, and the gist thereof is as follows: (1) A method for manufacturing a high-frequency bent pipe whose radius of curvature is three times or less the outside diameter of the pipe, in which: in weight %, C0 .05~0.309g Si 0.10~0.50k Mn 0.30~1.50% P≦0.03! k S ≦0.03k A! 0.005 to 0.05 zero N ≦ 0.015, the remainder consists of Fe and unavoidable impurities, C + Mn/6
+ (Cr+Mo+V)15+ (Ni+Cu)15≦
Carbon steel that satisfies 0.38% is used as a raw tube, heated until the outer surface of the raw tube reaches 850 to 1050℃, and then bent while cooling with water. A method for manufacturing high-frequency bent pipes.

(2) In a method for manufacturing a high-frequency bent pipe whose radius of curvature is three times or less the outside diameter of the pipe, in weight %, G 0.05-0.30% St 0.10-0.50k Mn 0.30-1. 50! k P ≦ 0.03 S ≦ 0.03 zero^cross 0.005 to 0.05 k N ≦ 0.0154 k and Cr ≦ 0.50 k Nl ≦ 0.50 zero MO ≦ 0.50 zero V ≦ 0. 10k Ti ≦0.05k Nb ≦0.050B ≦0.003k Cu ≦0.500Zr ≦0.050Ca ≦0.005%F One or more of the following, the remainder being Fe and unavoidable Consisting of impurities, C+Mn/6
+ (Cr+Mo+V) 150 (N i+Cu) 1
Carbon steel that satisfies 5≦0.389g is used as a raw tube, heated until the outer surface of the raw tube reaches 850 to 1050℃, and then bent while cooling with water. In the manufacturing method of high frequency bent pipe.

In addition, in the present invention, the carbon am used as the raw pipe of the bent pipe
The pipe is preferably a seamless steel pipe, but electric resistance welded steel pipes, uO steel pipes, etc. can also be used.

(Function) Fig. 2 shows an example of a pipe bending device used to carry out the bending method of the present invention, in which 1 is a steel pipe to be bent, 2 is a guide roller that supports and guides the steel pipe, and 3 is an annular pipe. , a heating device consisting 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 equipped with a clamp 5 at the tip; 6 is a tube end support The arrow on the table 7 is the cooling water sprayed from the heating device 3, and the shaded area 8 is 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. The wall thickness of the tube is 12.5
mm to 50.4 m+++, the heating temperature range of the outer surface needs to be 950 to 1050° C. in order to stabilize the structure. That is, the minimum heating temperature is to set the heating temperature of the inner surface to AC3 or higher. The wall thickness of the tube is 12
．． If it is less than 5mm, the heating temperature range of the outer surface is 850~
Can operate at 950°C.

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 reason for limiting the components of the raw pipe used in the present invention will be described.

C is an element necessary to ensure the strength of the steel pipe, and the amount necessary to exhibit its function is 0.05 zero or more. However, if the C content exceeds 0.30%, the welding workability of the steel pipe will be significantly impaired and the hardness after top bending will become significantly high, so the upper limit was set at 0.30.

St is an element that is used as a deoxidizing element and is also effective in securing external high temperature strength, and in order to exhibit at least the deoxidizing function, it is necessary to have an amount of o, to % or more. However, since a large amount of content impairs high-frequency bending property, the upper limit was set to Q, 50%.

Mn is the most effective reinforcing element next to C, and the amount required to exhibit its function is 0.3ON or more.

However, excessive addition increases the maximum hardness after bending and impairs welding workability, so the upper limit was regulated to 1.50 mm.

P and S are elements that are mixed as impurities, but the upper limit of each is set at 0.03% to prevent cracking during high-temperature bending.
It is regulated as below.

^! is an effective element as a grain refining element, and by its addition, it was possible to increase the upper limit content of C, 51, and Mn. In order to perform this function, o, o
The content of os is required to be 0.050 or more, but since a large amount of content impairs the toughness of the steel pipe, it is set to 0.050.

The upper limit of N was set at Q and QISk within a range that did not cause any problem in weldability.

In addition to the above basic ingredients, the following regulations have been established for selectively used ingredients.

Nb, TL, and Zr are all elements that have a crystal grain refining effect, but the addition amount of each 0.0 does not saturate the effect.
The upper limit was set at 5%.

V has a grain refining and reinforcing effect, but 0. Since the effect is saturated above IH, o, tox was set as the upper limit.

Cr, Mo, Ni, and Cu are effective as reinforcing elements, but addition of large amounts of any of them increases the hardness after bending, so the upper limits of each are regulated to o and sox.

Ca contributes to improving toughness by controlling the form of sulfides, but excessive addition causes deterioration of weldability, so o, oos
x is the upper limit.

B has the effect of increasing the strength of steel pipes when added in a small amount, but the effect is saturated when added in a large amount exceeding Q, QQ3k, so the upper limit was set at 0.003%.

The upper limit value of the C equivalent is set to 0.0 to lower than IV248, since the maximum hardness of the outer surface side after bending shows a good correlation with the C equivalent under the conditions of the high-frequency bending process.
It was set to 38% or less.

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. The Al-A3 steel pipe is a comparison steel pipe and is an as-rolled carbon tI4tI4 pipe with a C equivalent of more than 0.38!6, and the 81 to B12 steel pipes are steel pipes of the present invention and have a C equivalent of 0.38.
Below is the as-rolled steel pipe.

Table 2 shows the mechanical properties and bending conditions of the raw steel pipes in Table 1, and the maximum hardness of the bent portion after bending.

For mechanical properties in Table 2, JIS No. 12 test pieces were used.
Tensile strength and elongation were measured.

As shown in Table 2, the maximum heating temperature for all test tubes is 8
High frequency bending is performed at 50N and 1050°C using spray water cooling. Figure 1 shows the relationship between C equivalent and maximum hardness when bending is performed under these conditions.As is clear from Figure 1, A1 to A with a C equivalent of more than 0.313%
It is clear that the comparison steel pipes of 8 steel pipes all have a maximum hardness of lv248 or more and cannot be put to practical use.

On the other hand, B1-B1, which is the steel pipe used in the present invention,
By setting the C equivalent to 0.38 or less, the 2@ tube makes it possible to manufacture a high-frequency bent tube that satisfies a maximum hardness of Hv24a or less.

(Effects of the Invention) According to the present invention, bent pipes with a small bending radius for power generation and chemical plants, which are conventionally configured with elbows, can be bent at high frequency using seamless steel pipes or steel pipes manufactured by other manufacturing methods as raw pipes. It becomes possible to manufacture elbow braces by 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 the C equivalent and the maximum hardness (lv) after bending, and the bending conditions at this time were that the maximum heating temperature of the outer surface was 850 to 1050°C, and spray water cooling. FIG. 2 is a plan view of an example of a bending machine used in an embodiment of the present invention. 1... Steel pipe 2... Guide roller 3...
・Heating device 4...Bending arm 5...Clamp 6...Pipe end support stand...Spray cooling water 8...Maximum hardness in heating processing area HV) Figure 2 1: Steel pipe 2: Guide roller 3: Heating device 4: Bending arm 5: Clamp 6: Pipe end support 7: Spray cooling water 8: Heating processing area procedural amendment document dated February 4, 1927, Kunio Ogawa, Commissioner of the Patent Office, loss 1. Display of 13 items Patent Application No. 822/- Caustic Location: 3308 Marunouchi Shigesu Building, 2-6-2 Marunouchi, Chiyoda-ku, Tokyo Contents of the Amendment The following matters in the specification of the present application have been amended as shown in the attached sheet. We will correct it. Note 1: The scope of claims is amended as shown in the attached sheet. 2. r C+Mn/ on page 8, line 3 and page 9, line 10
6+ (Cr+Mo+V) 15+ (Ni+Cu)
15≦0.38o4J and r C+Mn/6+ (Cr+Mo+V) 15+ (
Ni+Cu) /Is≦0.38! l; Correct as J. Claim (1) 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 the following is achieved by weight%: G 0.05 to 0.30 Zero St 0.10 to 0.50% Mn 0 .30-1.50% P ≦0.03'4 S ≦0.03c* A text 0.005-0.05 Hori N ≦o, ots% The remainder consists of Fe and inevitable impurities, c + Mn7'
a+ (Cr+Mo+V) 15+ (Ni+Cu)
Carbon steel that satisfies /15≦0.38* is used as a raw tube, heated until the outer surface of the raw tube reaches 850 to 1050℃, and then bent while cooling with water. Manufacturing method of hard high frequency bent pipe. (2) In a method for manufacturing a high-frequency bent pipe whose radius of curvature is three times or less the outer diameter of the pipe, in weight %, G 0.05 to 0.30k Si 0.10 to 0.50! k Mn 0.30 to 1.50% P ≦0.03% S ≦0.034k A or 0.005 to 0.054k N ≦0. O15* and Cr ≦0.50 zero Ni ≦0.50 zero Mo ≦0.50! ■ One or two of the following: ≦0.10!6 Ti ≦0.05% Nb ≦0.050B ≦0.0030Cu ≦0.50!6 Zr ≦0.05I Ca ≦0.005% The remainder consists of Fe and unavoidable impurities, C+Mn/6
+ (Cr+Mo+V)15+ (Ni+Cu)/15
Carbon steel that satisfies ≦0.38!4 is used as a raw tube, and the outer surface of the raw tube is heated until the temperature reaches 850 to 1050℃, and then bent while cooling with water. A manufacturing method for high-frequency bent pipes.

Claims (2)

[Claims] (1) In a method for manufacturing a high-frequency bent pipe whose radius of curvature is three times or less the outer diameter of the pipe, in weight %, C 0.05-0.30% Si 0.10-0.50% Mn 0.30-1 .50% P≦0.03% S≦0.03% Al 0.005-0.05% N≦0.015% The remainder consists of Fe and inevitable impurities, C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu
)/5≦0.38% is used as a raw tube, heated until the outer surface of the raw tube reaches 850 to 1050℃, and then bent while cooling with water. A method for manufacturing high-frequency bent pipes with low hardness. (2) In a method for manufacturing a high-frequency bent pipe whose radius of curvature is 3 times or less the outer diameter of the pipe, the following is determined by weight%: C 0.05 to 0.30% Si 0.10 to 0.50% Mn 0.30 to 1 .50% P≦0.03% S≦0.03% Al 0.005-0.05% N≦0.015% and Cr≦0.50% Ni≦0.50% Mo≦0.50% One or more of the following: V≦0.10% Ti≦0.05% Nb≦0.05% B≦0.003% Cu≦0.50% Zr≦0.05% Ca≦0.005% , the remainder consists of Fe and unavoidable impurities, C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu
)/5≦0.38% is used as a raw tube, heated until the outer surface of the raw tube reaches 850 to 1050℃, and then bent while cooling with water. A method for manufacturing high-frequency bent pipes with low hardness.