JPH09194996A - Welded steel tube with high strength and high toughness and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a welded steel tube with high strength and high toughness, reduced in the amount of oxygen in a weld zone and having mechanical properties, in the weld zone, comparable to those in a base material part, while maintaining the advantage of a resistance welding method enabling high efficiency production. SOLUTION: A steel plate, having a composition containing, by weight, 0.01-0.13% C, <=0.5% Si, 0.5-2% Mn, <=0.1% Al, <=0.01% N, <=0.02% P, and <=0.01% S, is formed into tubular body. Then, the edges, abutting each other, of the tubular body is melted by laser beam irradiation and subjected to upset welding, by which the welded steel tube with high strength and high toughness, where the amount of oxygen in the weld zone is regulated to <=200ppm, is obtained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention has a high strength for use in pipelines, mechanical structural members, various plants, etc.
The present invention relates to a high toughness welded steel pipe and a method for manufacturing the same.

[0002]

2. Description of the Related Art Steel pipes are used in a wide variety of applications such as pipelines, machine structural members, heat exchangers, automobile parts, mechanical structural members, and various plants. The seamless steel pipes and welded steel pipes manufactured by the method are used. Among them, electric resistance welding, in which a steel strip is continuously formed into a tubular shape to form a tubular body (open pipe), and its opposite edges are heated by high frequency heating or resistance heating and welded. Welded steel pipes have been produced and used in large quantities from the past because of their high dimensional accuracy, high efficiency in production compared to other pipe production methods, and relatively low cost.

However, when the electric resistance welded steel pipe is used in a field in which high material characteristics and high reliability are required, the material sometimes becomes a problem. The reason why the material of the electric resistance welded steel pipe is inferior to other welded steel pipes is as follows. 1) Since the heat input to the electric resistance welded portion is smaller than that to the arc welding, the cooling speed of the electric resistance welded portion and its vicinity is high during the electric resistance welding. Therefore, the electric resistance welded portion and the vicinity thereof are easily hardened, and the quality is easily deteriorated. 2) The welded portion welded by the electric resistance welding method is in a state that it can be said to be intermediate between ordinary fusion welding such as arc welding and pressure welding, and no clear molten pool is formed at the jointed portion.
On the other hand, a considerable amount of oxides are formed by oxidation during welding, but these oxides are hard to be discharged from the inside of the steel,
As a result of the weld having a high oxygen content, the mechanical properties deteriorate.

Of the above reasons, 1) can be dealt with by performing a heat treatment. For example, the material of the hardened welded portion can be improved by subjecting the electric resistance welded pipe to normalizing on-line or performing heat treatment such as quenching and tempering, for example, as disclosed in JP-A-62-1.
Japanese Patent No. 51509 discloses a technique of performing heat treatment for quenching and tempering on a hardened weld portion.

[0005]

However, among the above reasons, in order to solve the problem 2) caused by oxidation, an additional measure is required. For example, a steel strip is upset to a tubular body during welding. Therefore, it has been attempted to discharge oxides to the outside as much as possible. However, as a result, a metal flow in the vicinity of the weld rises, so to speak, a cross section of steel during rolling appears on the inner and outer surfaces of the pipe. A steel pipe having such a metal flow may be inferior in fatigue strength and may have a problem in durability when internal pressure is applied. Of course, it is known that even if upsetting is performed, the oxide is not completely discharged, and a considerable amount of the oxide remains, which results in a large amount of oxygen in the steel.

Measures for solving the above problems have been studied, and heat input is controlled, or JP-A-63-24 is used.
As disclosed in Japanese Patent No. 1116, there is known a method of shielding the electric resistance welded portion with a non-oxidizing gas and performing electric resistance welding to reduce the amount of oxides and oxygen in the electric resistance welded portion. However, in reality, there is a limit to the improvement by controlling the heat input, and a shield device that has excellent shielding properties and can withstand continuous operation has not been developed.

From the above, it has been considered that the electric resistance welded steel pipe in which the strength and toughness of the welded portion are comparable to those of the base material cannot be manufactured conventionally. As described above, the strength and toughness of the welded portion of the electric resistance welded steel pipe manufactured by the conventional technique are inferior to those of the base metal portion, which is a major cause of limiting the applications of the electric resistance welded steel pipe. Was there.

Therefore, the object of the present invention is to solve the above-mentioned problems and to maintain the advantages of the electric resistance welding method capable of producing with high efficiency, while the oxygen content of the welded portion is small and the mechanical characteristics thereof are the base metal. It is intended to provide a high-strength / high-toughness welded steel pipe and a method for producing the same, which are comparable to those of the welded parts.

[0009]

The inventors of the present invention have the following reasons that the mechanical characteristics of the electric resistance welded part are inferior to those of the base metal part: 1) the amount of oxygen and the amount of inclusions in the welded part; The present invention has been completed as a result of repeated studies by finding out that the heat history and 3) the metal flow in the vicinity of the welded portion are particularly affected by 1).

The basis of the present invention is that a steel strip having an appropriate chemical composition is formed into a tubular body by a multi-stage roll, and the butted edges of the tubular body are preheated at an appropriate temperature and then preheated. A high-strength and high-toughness welded steel pipe is obtained by irradiating the edge part with a laser beam, melting it, and upsetting and welding.

Therefore, unlike the case of the conventional method for producing electric resistance welded steel pipe, the welded portion has a melt-solidified structure and melting of the steel occurs, so that most of the oxides produced by oxidation are melted. Emitted from steel As a result, the oxygen content of the weld is significantly reduced compared to the weld of conventional electric resistance welded steel pipe, and the extent to which the strength and toughness of the weld are reduced compared to the base metal is minimized. You can Of course, if the composition of the steel is not appropriate, the mechanical properties of the weld will not be sufficient even if a laser beam is irradiated under optimum conditions to produce a welded steel pipe.

In the high strength / high toughness welded steel pipe of the present invention, high strength means a tensile strength of 50 kgf / mm ² or more, and high toughness means a fracture surface transition temperature in a Charpy impact test ( _V T _rs ) is -50 ° C or lower.

The invention according to claim 1 is characterized by the following. % By weight, C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, and the content of P and S of unavoidable impurities is: P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
The following steel strength and high toughness welded steel pipe.

The invention described in claim 2 is characterized by the following. C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, and at least one element selected from the group consisting of the following is contained in the following range: Ti: 0.005 to 0.2%, Zr: 0.00
5 to 0.2%, Nb: 0.005 to 0.2%, V: 0.005
.About.0.2% And the content of unavoidable impurities P and S is P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
The following high strength and high toughness welded steel pipes.

The invention described in claim 3 is characterized by the following. C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, and at least one element selected from the group consisting of the following is contained in the following range: Ni: 0.03 to 1% Cu: 0.03
~ 1% Cr: 0.03 ~ 3% Mo: 0.03
-1.5% W: 0.03-1.5% B: 0.000
3 to 0.003% The content of inevitable impurities P and S is P:
Made of steel limited to 0.02% or less and S: 0.01% or less, and the oxygen content of the weld is 200 p
High strength and high toughness welded steel pipe with pm or less.

The invention described in claim 4 is characterized by the following. C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, and at least one element selected from the group consisting of the following is contained in the following range: Ca: 0.0005 to 0.01%, Mg: 0.00
05-0.01%, REM: 0.0005-0.1% And content of P and S of an unavoidable impurity is P: 0.02% or less, S: 0.01%
Made of steel limited to the following, with an oxygen content in the weld of 200 ppm
The following high strength and high toughness welded steel pipes.

The invention according to claim 5 is characterized by the following. C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, at least one element selected from the group consisting of the following is contained in the following range, Ti: 0.005 to 0.2%, Zr: 0.00
5 to 0.2%, Nb: 0.005 to 0.2%, V: 0.005
-0.2% Furthermore, at least one element selected from the group consisting of the following is contained in the following range, Ni: 0.03 to 1%, Cu: 0.03
~ 1%, Cr: 0.03 to 3%, Mo: 0.03
~ 1.5%, W: 0.03 to 1.5%, B: 0.000
3 to 0.003% And content of P and S of unavoidable impurities is P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
The following high strength and high toughness welded steel pipes.

The invention described in claim 6 is characterized by the following. C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, at least one element selected from the group consisting of the following is contained in the following range, Ti: 0.005 to 0.2%, Zr: 0.00
5 to 0.2%, Nb: 0.005 to 0.2%, V: 0.005
.About.0.2% Further, at least one element selected from the group consisting of the following is contained in the following range: Ca: 0.0005 to 0.01%, Mg: 0.00
05-0.01%, REM: 0.0005-0.1%, and the content of inevitable impurities P and S, P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
The following high strength and high toughness welded steel pipes.

The invention described in claim 7 is characterized by the following. C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, at least one element selected from the group consisting of the following is contained in the following range, Ni: 0.03 to 1%, Cu: 0.03
~ 1%, Cr: 0.03 to 3%, Mo: 0.03
~ 1.5%, W: 0.03 to 1.5%, B: 0.000
3 to 0.003%, at least one element selected from the group consisting of the following is contained in the following range: Ca: 0.0005 to 0.01%, Mg: 0.00
05-0.01%, REM: 0.0005-0.1%, and the content of inevitable impurities P and S, P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
The following are high strength and high toughness ERW welded steel pipes.

The invention according to claim 8 is characterized by the following. C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, at least one element selected from the group consisting of the following is contained in the following range, Ti: 0.005 to 0.2%, Zr: 0.00
5 to 0.2%, Nb: 0.005 to 0.2%, V: 0.005
-0.2%, at least one element selected from the group consisting of the following is contained in the following range, Ni: 0.03-1%, Cu: 0.03
~ 1%, Cr: 0.03 to 3%, Mo: 0.03
~ 1.5%, W: 0.03 to 1.5%, B: 0.000
3 to 0.003%, at least one element selected from the group consisting of the following is contained in the following range: Ca: 0.0005 to 0.01%, Mg: 0.00
05-0.01%, REM: 0.0005-0.1%, and the content of inevitable impurities P and S, P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
The following high strength and high toughness welded steel pipes.

The invention described in claim 9 is characterized by the following. (A) a step of preparing a steel sheet having the chemical composition according to any one of claims 1 to 8, (b) a step of forming the steel sheet into a tubular body, and (c) the tubular body A method for producing a high-strength / high-toughness welded steel pipe, which comprises the steps of melting and upsetting the welded edge portions of a laser beam and irradiating with a laser beam.

The invention described in claim 10 is characterized by the following. (A) a step of preparing a steel sheet having the chemical composition according to any one of claims 1 to 8, (b) a step of forming the steel sheet into a tubular body, (c) a protrusion of the tubular body Manufacture of a high-strength, high-toughness welded steel pipe, which comprises a step of preheating the combined edge portions, and a step of (d) melting the preheated edge portions of the tubular body by irradiation of a laser beam and upsetting and welding. Method.

The invention described in claim 11 is characterized by the following. (A) a step of preparing a steel sheet having the chemical composition according to any one of claims 1 to 8, (b) a step of forming the steel sheet into a tubular body, (c) a protrusion of the tubular body Preheating the combined edge portion to a temperature in the range of 600 to 1300 ° C., (d) melting the preheated edge portion of the tubular body by laser beam irradiation, and upsetting and welding. e) The weld is Ac ₃ +20
A method for producing a high-strength, high-toughness welded steel pipe, which comprises the steps of heating to a temperature range of ℃ to 1000 ℃ and then cooling.

The invention described in claim 12 is characterized by the following. (A) a step of preparing a steel sheet having the chemical composition according to any one of claims 1 to 8, (b) a step of forming the steel sheet into a tubular body, (c) a protrusion of the tubular body Preheating the combined edge portion to a temperature in the range of 600 to 1300 ° C., (d) melting the preheated edge portion of the tubular body by laser beam irradiation, and upsetting and welding. e) The weld is Ac ₃ +20
A step of heating to a temperature range of ℃ to 1000 ℃, and
(F) Next, a method for producing a high-strength / high-toughness welded steel pipe, which comprises a tempering step in a temperature range of 500 ° C. to AC ₁ .

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic explanatory view showing an example of pipe manufacturing equipment for carrying out the present invention, and FIG.
FIG. As shown in the drawings, the contact tip 2 and the top roll 4 are arranged along the moving direction of the tubular body 1.
The side roll 5, the first high-frequency heating device 6, the water cooling zone 7, and the second high-frequency heating device 8 are arranged in this order.

The steel strip is formed into a tubular body 1 by a multi-stage roll (not shown), and then the butted edges of the tubular body 1 are preheated by the contact tip 2 or high frequency induction heating. Then, the laser beam 3 is applied to the preheated edge portion of the tubular body 1 to melt it and upset and weld it. Next, in the first high-frequency heating device 6, the water-cooling zone 7 and the second high-frequency heating device 8, normal heat treatment or post-heat treatment such as quenching and tempering is performed in accordance with the purpose of use of the steel pipe.

The basis of the present invention is that, by irradiating the laser beam 3, the abutted edges of the tubular body 1 are melted and welded, and the oxide produced during the welding is discharged to the outside of the steel, and the welded portion is welded. The oxygen content is set to 200 ppm or less. As a result, oxides, which make up the majority of the oxygen content of the steel, are discharged to the outside of the steel pipe.

The oxygen content of fully deoxidized steel is usually 10
It does not exceed 0 ppm. On the other hand, the oxygen content of the welded portion of the electric resistance welded steel pipe manufactured by the conventional method is 2
It is more than 00 ppm to 300 ppm.

Steel strips having the composition Nos. 1 to 5 in Table 1 described later are used, and the inner diameter is 76.3 mmφ and the thickness is 7.5.
mm welded steel pipe, according to the method of the present invention, the preheating temperature 700 ℃,
FIG. 3 shows a comparison between the oxygen content of the welded portion when manufactured under the conditions of laser output of 5 kw and welding speed of 3 m / min and the oxygen content of the electric resistance welded portion when manufactured by the conventional electric resistance welding method. . As is apparent from FIG. 3, the weld steel oxygen content of the present invention was about 150 ppm, whereas the conventional weld seam welded steel pipe had an oxygen content of about 250 ppm.

The oxygen content of the weld is influenced by the preheating condition. That is, when the preheating temperature is increased, the load of laser irradiation on welding is reduced and the manufacturing efficiency is improved. On the other hand, since the amount of oxides generated during preheating increases,
As a result, the amount of oxide increases and the amount of oxygen also increases, deteriorating the mechanical properties. Note that the amount of inclusions, the amount of oxides, and the amount of oxygen have a substantially proportional relationship.

On the other hand, when the preheating temperature is lowered, the load of laser irradiation on welding becomes large and the manufacturing efficiency decreases,
Alternatively, a large-capacity laser irradiation equipment is required, resulting in high cost. On the other hand, as a result of reducing the amount of oxides generated during preheating, the amount of inclusions decreases, the amount of oxygen decreases, and the mechanical properties improve.

In the present invention, the welded portion is a general term including a portion having a different microstructure (metal flow, different etching sensitivity, etc.) from the base material portion, including the welded portion by laser beam irradiation. is there.

FIG. 4 is a diagram showing the influence of the preheating temperature on the toughness. Using the same welded steel pipe as described with reference to Fig. 3 above, the steel pipe subjected to quenching and tempering treatment (quenching temperature 950 ° C, tempering temperature 650 ° C, cooling rate 50 ° C / sec) had its preheating temperature and fracture surface in Charpy test. The relationship with the transition temperature ( _v Trs) was investigated. As is clear from FIG. 4, the oxygen amount increases and _v Trs rises when the preheating temperature rises.

_V Tr of -50 ° C or less, with high toughness as a guide
In order to secure s, the preheating temperature needs to be 1000 ° C. or lower, and in order to secure _v Trs of −70 ° C. or lower, the preheating temperature needs to be 750 ° C. or lower. In addition, the amount of oxygen when the preheating temperature is 1000 ° C. is 150 to 1
The amount of oxygen is 90 ppm, and the amount of oxygen is 120 to 150 ppm when the preheating temperature is 750 ° C.

Next, the reason why the chemical composition of the welded steel pipe of the present invention is limited as described above will be explained. C has the effect of increasing the strength of the steel. However, if the C content is less than 0.01 wt.%, It is difficult to secure the strength. On the other hand, if the C content exceeds 0.13 wt.%, The weldability and toughness deteriorate. Therefore, the C content should be limited to the range of 0.01 to 0.13 wt.%.

Si is a deoxidizing element. However, S
If the i content exceeds 0.5 wt.%, adverse effects such as deterioration of toughness occur. Therefore, the Si content should be limited to 0.5 wt.% Or less.

Mn also has a function of increasing the strength of steel. However, if the Mn content is less than 0.5 wt.%, Sufficient strength cannot be obtained. On the other hand, when the Mn content exceeds 2 wt.%, The weldability and toughness deteriorate. Therefore, the Mn content should be limited to the range of 0.5 to 2 wt.%.

Al is also a deoxidizing element. However, A
If the 1 content exceeds 0.1 wt.%, adverse effects such as deterioration of toughness occur. Therefore, the Al content should be limited to 0.1 wt.% Or less.

N is an element mixed into the steel as an impurity from the atmosphere during melting, but it also has the function of increasing the strength of the steel, like C. However, the N content is 0.0
If it exceeds 1 wt.%, Weldability and toughness are adversely affected. Therefore, the N content should be limited to 0.01 wt.% Or less.

Ti, Zr, Nb and V have the function of increasing the strength of the steel, and also have the function of forming carbides and nitrides to refine the austenite grains and improve the strength and toughness. Therefore, at least one element selected from the above group is contained if necessary. However, if the content is less than 0.005 wt.%, The desired effect cannot be obtained. On the other hand, its content is 0.2 wt.%
If it exceeds, the toughness deteriorates. Therefore, Ti, Zr, Nb
The content of at least one element selected from the group consisting of and V should be limited to the range of 0.005-0.2 wt.%.

Cr, Cu, Ni, Mo, W and B are
It has the effect of increasing the strength of steel. Therefore, at least one element selected from the above group is contained if necessary.

However, the content of Cr is 0.03w.
If it is less than t.%, the desired effect cannot be obtained. On the other hand, if the content exceeds 3 wt.%, The weldability and toughness deteriorate. Therefore, the Cr content should be limited to the range of 0.03 to 3 wt.%.

If the Cu content is less than 0.03 wt.%, The desired effect cannot be obtained. On the other hand, if the content exceeds 1 wt.%, The hot workability deteriorates. Therefore, the Cu content should be limited to the range of 03 to 1 wt.%.

In addition to increasing the strength of steel, Ni also has the effect of reducing the adverse effects of Cu on the hot workability. However, if the Ni content is less than 0.03 wt.%, The desired effect cannot be obtained. On the other hand, its content is 1w
If it exceeds t.%, the effect of addition is saturated. Therefore, N
The content of i should be limited to the range of 0.03 to 1 wt.%.

If the Mo content is less than 0.03 wt.%, The desired effect cannot be obtained. On the other hand, its content is 1.5 wt.%
If it exceeds, the effect of addition is saturated. Therefore, the Mo content should be limited to the range of 0.03 to 1.5 wt.%.

If the W content is less than 0.03 wt.%, The desired effect cannot be obtained. On the other hand, if its content exceeds 1.5%, the effect of addition is saturated. Therefore, the W content should be limited to the range of 0.03 to 1.5 wt.%.

When the content of B is less than 0.0003 wt.%,
The desired effect cannot be obtained. On the other hand, its content is 0.00
If it exceeds 3 wt.%, The toughness of the welded portion deteriorates. Therefore, the content of B should be limited to the range of 0.0003 to 0.003 wt.%.

[0048] Ca, Mg and REM have an effect of improving the corrosion resistance in various corrosive environments and increasing the toughness value by controlling the morphology by interlocking with S to granulate inclusions. Therefore, at least one element selected from the above group is contained if necessary. However, if the content of at least one element of Ca, Mg and REM is less than 0.0005 wt.%, The desired effect cannot be obtained. On the other hand, the contents of Ca and Mg are each 0.01
If the content of REM exceeds 0.1 wt.% and the content of REM exceeds 0.1 wt.%, the toughness of steel deteriorates. Therefore, the content of Ca and Mg is limited to the range of 0.005-0.01 wt.%,
And, the content of REM should be limited to the range of 0.0005 to 0.1 wt.%.

The unavoidable impurities P and S are detrimental to the toughness. Therefore, the P content should be limited to 0.02 wt.% Or less, and the S content should be limited to 0.01 wt.% Or less. In particular, if the S content is limited to 0.005 wt.% Or less, much more excellent toughness can be obtained.

Next, a method for manufacturing the welded steel pipe of the present invention will be described. Using the equipment shown in FIGS. 1 and 2,
The butted edges of the tubular body 1 are preheated by the contact tip 2 or high frequency induction heating. The preferable preheating temperature of the edge portion is in the range of 600 to 1300 ° C. If the preheating temperature is less than 600 ° C., the preheating is insufficient and the burden on the laser beam irradiation becomes excessive. On the other hand, when the preheating temperature is higher than 1300 ° C., the load on the laser beam irradiation is light, but the oxidation amount of the steel increases and the oxide amount increases, resulting in an increase in the oxygen amount.

In order to keep the amount of oxygen in the welded portion at 200 ppm or less and to secure _v Trs of -50 ° C or less with high toughness as a guide, as described above, the preheating temperature is 1000 ° C.
It is necessary to below, further, -70 ° C. or less of the _v
To secure the Trs, it is necessary to keep the preheating temperature below 750 ° C.

The butted edges of the tubular body 1, which have been preheated as described above, are irradiated with the laser beam 3 to melt and weld them. At the time of welding, the shape of the abutted edge portion is formed into an I shape by the top roll 4, and the side roll 5 upsets. As shown in FIG. 2, the plurality of top rolls 4 are
It is arranged so that the tubular body 1 is held obliquely from above and the laser beam 3 passes between the top rolls 4, and the welded portion is heated and melted by the laser beam 3 passing between the top rolls 4. Note that preheating is not an essential condition, and electric resistance welding can be performed only by irradiation with a laser beam.

In this way, since the fusion welding is performed by the laser beam 3, most of the oxide formed at the edge portion during preheating is discharged to the outside of the fusion pool, and a welding portion having a small amount of oxygen is formed. It It goes without saying that the amount of oxides formed during preheating is significantly smaller than that in the conventional method for producing electric resistance welded steel pipes, which is heated to a temperature just below the melting point.

When manufacturing a conventional electric resistance welded steel pipe,
Although it was necessary to apply a strong upset in order to discharge a large amount of oxides generated from the welded portion, the method of the present invention requires an extremely low upset amount as compared with the conventional method. This means that not only the deterioration of mechanical properties due to the rising of the metal flow can be reduced, but also burrs generated during upset can be removed easily.

If necessary, the welded portion of the steel pipe after welding is subjected to post heat treatment such as normalizing, quenching and tempering. Of course, such post heat treatment may not be necessary depending on the composition of the steel and the purpose of use.

In the case of performing normalizing, for example, in the first high-frequency heating device 6, after heating to a temperature range of Ac ₃ + 20 ° C. to 1000 ° C., it is cooled. In the case of local heating in the vicinity of the welded portion, heat is absorbed by the non-heated portion of the steel pipe, so special cooling may not be necessary, but air cooling is performed as necessary. Of course, the heat treatment may be applied to the entire pipe without being limited to the vicinity of the welded portion. In this case, since there is no boundary with the normalizing part, a steel pipe of a more uniform material can be obtained. The lower limit of heating temperature is Ac ₃
The temperature is + 20 ° C., and the upper limit thereof is 1000 ° C. at which austenite crystal grains do not become coarse.

Also in the case of performing quenching and tempering treatment, first, by the first high-frequency heating device 6, Ac ₃ + 20 ° C. to 1000 ° C.
In the cooling zone 7, quenching is performed by water cooling, mist cooling, or the like. The cooling rate at this time was 30 ° C./sec. With the above, the structure should be fully baked. The cooling stop temperature must be 400 ° C. or lower, and the amount of water and the length of the cooling zone should be sufficient.

After quenching, tempering performed in the second high-frequency heating device 8 is performed in the temperature range of 500 ° C. to AC ₁ .
If the tempering temperature is lower than 500 ° C, the tempering effect cannot be sufficiently obtained. The upper limit temperature for tempering is Ac ₁ , but a rough guideline is 760 ° C.

[0059]

EXAMPLES Next, the present invention will be described based on examples together with comparative examples. Steels having chemical composition within the scope of the present invention shown in Tables 1 and 2 (hereinafter referred to as steel of the present invention) and steels having chemical composition outside the scope of the present invention shown in Table 3 (hereinafter referred to as comparative steels) ) Was melted.

[0060]

[Table 1]

[0061]

[Table 2]

[0062]

[Table 3]

Inventive steel No. 1 shown in Table 1 1 to No. 5,
No. 12, No. 17, steel No. 17 of the present invention shown in Table 2. 2
1 to No. 26 and comparative steel Nos. Shown in Table 3. 6-N
o. No. 8 was used, welding was performed under the conditions shown in Table 4 by the method of the present invention, and then quenching and tempering were performed under the conditions shown in Table 5, thus welding with an inner diameter of 76.3 mmφ and a thickness of 7.5 mm. Steel pipe was manufactured. The production efficiency was equal to or higher than that of the conventional electric resistance welding method.

[0064]

[Table 4]

[0065]

[Table 5]

Inventive Steel No. 1 to No. Use 5 and book
Invention method and conventional electric sewing without laser beam irradiation
Welded steel pipe is manufactured by the welding method and
_VT _rsAnd compare it graphically in Figure 5.
You. In addition, in both the method of the present invention and the conventional method, QT (quenching)
Re-tempering treatment (tempering temperature 650 ℃, cooling rate 50 ℃ / s
ec).

As is apparent from FIG. 5, the manufacturing method of the present invention.
When the quenching temperature is 1000 ° C or less
_VT_rsIs low enough,_V
T_rsIndicates that the steel composition is within the composition range of the present invention.
Even when it was high. Invention Steel No. 1 to No. 5
The welded steel pipe produced by the method of the present invention is
T treatment (quenching temperature 950 ℃, tempering temperature 650 ℃)
Of the welded part_VT_rsOf cooling rate on
Is shown in FIG. Similarly, the invention steel No. 1 to No. From 5
QT treatment is performed on the welded steel pipe manufactured by the method of the present invention.
When subjected to heat treatment (quenching temperature 950 ° C, cooling rate 50 ° C / sec)
Of the weld_VT_rsThe effect of tempering temperature on
It shows in FIG. As is clear from FIGS. 6 and 7, cooling
Speed is over 30 ℃ / sec, tempering temperature is 500 ℃
In the above cases, it is low enough _VT_rswas gotten.

Steel No. of the present invention 1 to No. 5 and ratio
Of welded steel pipes using comparative steel No. 6 to No. 8_VT_rsFigure 8
Shown in Note that the welded steel pipes are both quenched and
Tempering treatment (Quenching temperature 900 ~ 1050 ℃, tempering temperature 650 ℃,
A cooling rate of 50 ° C / sec) was applied. As is clear from FIG.
In the invention steel No. 1 to No. 5 of steel pipe_VT
_rsIs sufficiently low when the quenching temperature is 1000 ° C or lower.
won. On the other hand, comparative steels No. 6 to No. 8 were used.
Of steel pipe_VT_rsWas quite expensive.

Inventive Steel No. 21-No. No. 26 is used, a welded steel pipe is produced by the method of the present invention, and a normalizing treatment is performed by the first high-frequency heating device, and an electric resistance welded steel pipe is produced by the conventional electric resistance welding method. FIG. 9 shows _V T _rs in the case of applying. From FIG. 9, in the case of the method of the present invention, the normalizing temperature is 1000.
It can be seen that _V T _rs decreases when the temperature is below ℃. In addition,
Although the _V T _rs rises when the normalizing temperature exceeds 1000 ° C., the difference between the method of the present invention and the conventional method is the same as when the normalizing temperature is 1000 ° C. or lower.

Table 6 shows the invention steels No. 1 to No. 5 and No. 21.
~ No. 26 and Comparative Steel Nos. 6-8, quenching and tempering treatment (quenching temperature 950 ° C, tempering temperature 6
The _{V Trs} at 50 ° C. and the cooling rate of 50 ° C./sec are shown. In addition, in Table 6, _{V Trs} of the experimentally melted material described later is also shown.

[0071]

[Table 6]

Next, according to the invention steel No. 9-No. 11, N
o. 13-No. 16, No. 18-No. 20 and comparative steel No. 27-No. 28 was melted in a laboratory by vacuum melting and cast into a 50 kg ingot.

Next, these ingots were heated at 1200 ° C.
After heating to 50 mm and rolling to a plate thickness of 50 mm to form a steel plate, it was air-cooled. A plate of 50 × 150 × 400 mm is cut out from the steel plate after air cooling, the heating temperature is 1200 ° C., the rolling end temperature is 820.
It was rolled at 12 ° C to a thickness of 12 mm. Immediately after the end of rolling, the cooling rate was about 10 ° C./sec. After being cooled to 550 ° C. in the above, it was charged in an electric furnace which was previously heated to 550 ° C. and cooled in the furnace. These steps simulate the conditions for manufacturing a steel strip by hot rolling.

From a steel sheet cooled to room temperature, 6 × 35 ×
A 1000 mm test piece was cut out and welded using an electric resistance welding simulator. As shown in the schematic perspective view of FIG. 10, the electric resistance welding simulator apparatus feeds two test steel strips 9 by a guide roll 10 and supplies the high-frequency current supplied from the contact tip 2 to the edge portions of the opposing steel strips 9. After preheating with, the squeeze roll 11 is pressure-welded, so that the carbon dioxide gas laser beam 3 is irradiated to the edge joint portion while focusing on the edge portion of the steel strip 9 which is abutted from vertically above. There is.

The welding conditions are as follows, and the heat treatments for quenching and tempering were carried out under the conditions shown in Table 5. The amount of oxygen in the weld was 140 to 150 ppm. Preheating temperature: 700 ° C., welding speed: 10 m / min. , Input power from contact tip: 200kw, laser output: 5kw, beam diameter at focus position: 0.5mm 5mm from the welded part of the welded steel pipe manufactured by the above method
A Charpy impact test piece of t was sampled and its _V T _rs was determined. The results are also shown in Table 6.

As is clear from Table 6, pipes were manufactured at the factory.
If, and, using the ERW simulator to experiment melt material
In any case of welding, the steel of the present invention is used.
When manufactured by the method of the invention_VT_rsIs -70 ° C or higher
Below, it showed extremely good toughness. The amount of S is low
And the toughness of steels with relatively few strengthening elements is even better
Was. On the other hand, when a comparative steel is used, the method of the present invention
Manufactured by_VT _rsIs -40 ° C or higher,
Success_VT_rsYou can see that it has a great influence on. What
Comparative steel No. No. 27 has a low C content and a tensile strength of 50.
kgf / mm^TwoThe tensile strength of other steels was 50kgf
/ mm^TwoThat was all.

Steel No. of the present invention. 1 to No. 5, no. 1
2, No. 17, No. 21-No. 26 and comparative steel No. 6-No. 8 and No. No. 27 was used to manufacture an electric resistance welded steel pipe by a conventional electric resistance welding method, and after quenching and tempering treatment under the same conditions as above after the electric resistance welding, the _{V Trs} thereof were both -50 ° C. It was over.

Steels of the present invention No. 1 to No. 5, No. 12, No.
17, No. 21 to No. 26 and comparative steel No. 6 to No. 8
Table 7 shows _V T _rs when ERW welded steel pipe was manufactured by preheating at 900 ° C. using No. 27 and No. 27, and was subjected to quenching and tempering treatment under the same conditions as above after ERW welding. .

[0079]

[Table 7]

As is clear from Table 7, _V T _rs is higher than that when preheated at the above-mentioned temperature of 700 ° C., but is sufficiently lower than that of the electric resistance welded steel pipe manufactured by the conventional manufacturing method.

Welding to steel Nos. 21 to 26 of the present invention
When the normalizing process is applied later _VT_rsIn Table 8 and
It is shown in Table 9. Table 8 shows the case where the preheating temperature is 700 ° C,
Table 9 shows the case where the preheating temperature is 900 ° C.

[0082]

[Table 8]

[0083]

[Table 9]

Generally, in the case of normalizing material_VT_rsIs
Although it is higher than that of the quenched and tempered materials, Tables 8 and 9
As is clear from the above, welding using the steel of the present invention
Part of _VT_rsAt -55 ° C when the preheating temperature is 700 ° C
Yes, it was -50 ° C when the preheating temperature was 900 ° C.
In contrast, the welding of electric resistance welded pipes manufactured by the conventional method
Part of_VT_rsWas about −30 ° C.

The steel No. of the present invention shown in Table 1 was used. 11-N
o. 12, No. 14-No. 15, No. 17 and No. 17 19 contains a certain amount of Ca and / or Mg, and has high strength and high toughness, and at the same time, has a high HIC resistance.
It also has both (hydrogen-induced cracking) and SSCC resistance (sulfide stress corrosion cracking).

[0086]

As described above, according to the present invention,
While maintaining the advantages of the electric resistance welding method that can be manufactured with high efficiency, the amount of oxygen in the weld is small, its mechanical properties are comparable to those of the base metal, and both the base metal and weld are high in quality. Welded steel pipes with high strength and toughness that are optimal for machine structures, various plants, line pipes, etc. can be obtained. In addition,
When used in various corrosive environments, it is needless to say that a high-strength / high-toughness steel pipe having corrosion resistance can be obtained by selecting the component composition as necessary.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an example of pipe manufacturing equipment for carrying out the present invention.

FIG. 2 is a view taken along the line AA of FIG. 1;

FIG. 3 is a diagram showing a comparison of oxygen concentrations in welded portions of electric resistance welded steel pipes manufactured by the method of the present invention and the conventional method.

FIG. 4 is a diagram showing a relationship between a preheating temperature of a welded steel pipe manufactured by the method of the present invention and _V T _rs .

FIG. 5 is a diagram showing a comparison between the quenching temperature and the _V T _rs of the welded portion when the quenching and tempering treatment is applied to the welded steel pipes manufactured by the method of the present invention and the conventional method.

FIG. 6 is a diagram showing the relationship between the cooling rate during QT processing and _V T _{rs of the} welded portion in the method of the present invention.

FIG. 7 is a diagram showing the relationship between the tempering temperature during QT processing and the _V T _{rs of the} welded portion in the method of the present invention.

FIG. 8 is a diagram showing a relationship between quenching temperature and _V T _rs during QT treatment of a welded steel pipe produced by the method of the present invention using the present invention steel and a comparative steel.

FIG. 9 is a diagram showing the relationship between the normalizing temperature and the _V T _{rs of the} welded part when the normalizing treatment is performed on the welded steel pipe manufactured by the method of the present invention and the conventional method.

FIG. 10 is a schematic perspective view showing an electric resistance welding simulator device.

[Explanation of symbols]

 1 Tubular Body 2 Contact Tip 3 Laser Beam 4 Top Roll 5 Side Roll 6 First High Frequency Heating Device 7 Water Cooling Zone 8 Second High Frequency Heating Device 9 Steel Strip 10 Guide Roll 11 Squeeze Roll

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C21D 9/50 101 C21D 9/50 101A C22C 38/04 C22C 38/04 38/58 38/58 ( 72) Inventor Masaki Omura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (12)

[Claims] 1. By weight%, C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, and the content of P and S of unavoidable impurities is: P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
High strength and high toughness welded steel pipe characterized by the following. 2. By weight%, C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, and at least one element selected from the group consisting of the following is contained in the following range: Ti: 0.005 to 0.2%, Zr: 0.00
5 to 0.2%, Nb: 0.005 to 0.2%, V: 0.005
.About.0.2% And the content of unavoidable impurities P and S is P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
High strength and high toughness welded steel pipe characterized by the following. 3. By weight%, C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, and at least one element selected from the group consisting of the following is contained in the following range: Ni: 0.03 to 1%, Cu: 0.03
~ 1%, Cr: 0.03 to 3%, Mo: 0.03
~ 1.5%, W: 0.03 to 1.5%, B: 0.000
3 to 0.003% And content of P and S of unavoidable impurities is P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
High strength and high toughness welded steel pipe characterized by the following. 4. By weight%, C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, and at least one element selected from the group consisting of the following is contained in the following range: Ca: 0.0005 to 0.01%, Mg: 0.00
05-0.01%, REM: 0.0005-0.1% And content of P and S of an unavoidable impurity is P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
High strength and high toughness welded steel pipe characterized by the following. 5. By weight%, C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, at least one element selected from the group consisting of the following is contained in the following range, Ti: 0.005 to 0.2%, Zr: 0.00
5 to 0.2%, Nb: 0.005 to 0.2%, V: 0.005
-0.2%, at least one element selected from the group consisting of the following is contained in the following range, Ni: 0.03 to 1%, Cu: 0.03
~ 1%, Cr: 0.03 to 3%, Mo: 0.03
~ 1.5%, W: 0.03 to 1.5%, B: 0.000
3 to 0.003% And content of P and S of unavoidable impurities is P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
High strength and high toughness welded steel pipe characterized by the following. 6. By weight%, C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, at least one element selected from the group consisting of the following is contained in the following range, Ti: 0.005 to 0.2%, Zr: 0.00
5 to 0.2%, Nb: 0.005 to 0.2%, V: 0.005
.About.0.2% Further, at least one element selected from the group consisting of the following is contained in the following range: Ca: 0.0005 to 0.01%, Mg: 0.00
05-0.01%, REM: 0.0005-0.1% And content of P and S of an unavoidable impurity is P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
High strength and high toughness welded steel pipe characterized by the following. 7. By weight%, C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, at least one element selected from the group consisting of the following is contained in the following range, Ni: 0.03 to 1%, Cu: 0.03
~ 1%, Cr: 0.03 to 3%, Mo: 0.03
~ 1.5%, W: 0.03 to 1.5%, B: 0.000
3 to 0.003%, at least one element selected from the group consisting of the following is contained in the following range: Ca: 0.0005 to 0.01%, Mg: 0.00
05-0.01%, REM: 0.0005-0.1% And content of P and S of an unavoidable impurity is P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
A high-strength, high-toughness electric resistance welded steel pipe characterized by the following. 8. By weight%, C: 0.01 to 0.13%, Si: 0.5%
Hereinafter, Mn: 0.5 to 2%, Al: 0.1%
Hereinafter, N: 0.01% or less is contained, at least one element selected from the group consisting of the following is contained in the following range, Ti: 0.005 to 0.2%, Zr: 0.00
5 to 0.2%, Nb: 0.005 to 0.2%, V: 0.005
.About.0.2% and at least one element selected from the group consisting of the following is contained in the following range: Ni: 0.03 to 1%, Cu: 0.03
~ 1%, Cr: 0.03 to 3%, Mo: 0.03
~ 1.5%, W: 0.03 to 1.5%, B: 0.000
3 to 0.003% Further, at least one element selected from the group consisting of the following is contained in the following range: Ca: 0.0005 to 0.01%, Mg: 0.00
05-0.01%, REM: 0.0005-0.1% And content of P and S of an unavoidable impurity is P: 0.02% or less, S: 0.01%
Made of steel limited to the following, the oxygen content of the weld is 200 ppm
A high-strength, high-toughness electric resistance welded steel pipe characterized by the following. 9. A method for producing a high-strength and high-toughness welded steel pipe, which comprises the following steps. (A) a step of preparing a steel sheet having the chemical composition according to any one of claims 1 to 8; (b) a step of forming the steel sheet into a tubular body; and (c) the above A step of melting and upsetting the welded edges of the tubular body by irradiation of a laser beam and welding. 10. The method comprises the following steps:
Manufacturing method of high strength and high toughness welded steel pipe. (A) a step of preparing a steel sheet having the chemical composition according to any one of claims 1 to 8; (b) a step of forming the steel sheet into a tubular body; (c) the tubular body And (d) melting the preheated edge of the tubular body by laser beam irradiation and upsetting and welding. 11. The method comprises the following steps:
Manufacturing method of high strength and high toughness welded steel pipe. (A) a step of preparing a steel sheet having the chemical composition according to any one of claims 1 to 8; (b) a step of forming the steel sheet into a tubular body; (c) the tubular body The butted edges of the
Preheating to a temperature in the range of ˜1300 ° C., (d) melting and upsetting and welding the preheated edge portion of the tubular body by irradiation with a laser beam, and (e) the welding Parts are heated to a temperature range of Ac ₃ + 20 ° C. to 1000 ° C. and then cooled. 12. The method comprises the following steps:
Manufacturing method of high strength and high toughness welded steel pipe. (A) a step of preparing a steel sheet having the chemical composition according to any one of claims 1 to 8; (b) a step of forming the steel sheet into a tubular body; (c) the tubular body The butted edges of the
Preheating to a temperature in the range of ˜1300 ° C., (d) melting and upsetting and welding the preheated edge of the tubular body by laser beam irradiation, and (e) welding the weld. , Ac ₃ + 20 ° C. to 1000 ° C., and (f) then tempering at a temperature in the range of 500 ° C. to AC ₁ .