JPH09279250A - Production of electric resistance welded tube having high toughness and high strength in welded part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electric resistance welded tube having high toughness and high strength in a welded part by restraining rising of local hardening on an A1 transformation line after heating and water-cooling the welded part. SOLUTION: The electric resistance welded part after welding is widely heated to A3 transformation pt. or higher with latter part induction heaters 3a, 3b making eccentricity by 10-15mm from the tube axial direction center of front part induction heaters after heating the A3 transformation pt. or higher with the front part induction heaters 1a, 1b arranged just above the welded line W. Further, this welded part is heated to A1 transformation pt. or lower with induction heaters 4a, 4b making eccentricity by ±15mm from the A1 transformation line AL after water-cooling and again water-cooling, and a fixed shape working having <=0.5% reduction ratio of area is applied to obtain the enlargement of high toughness zone and the stability of hardness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength electric resistance welded steel pipe having excellent weld toughness suitable for use as a line pipe for transporting oil and natural gas, an oil well pipe for mining, and a high-strength structural steel pipe. Manufacturing method.

[0002]

2. Description of the Related Art An electric resistance welded steel pipe is an open pipe formed by continuously forming a raw strip steel into a cylindrical shape by a group of forming rolls, and heating both edge portions to be welded to a welding temperature by a contact tip or an induction coil. After that, both ends are pressure-bonded by a squeeze roll to manufacture. ERW steel pipe, after cutting the weld beads on the inner and outer surfaces of ERW pipe, heat the welded portion locally to the austenitizing temperature by a post heat treatment device called a post-annealer,
Normalize or anneal. ERW steel pipe continues
In the air-cooling zone, the welded part is air-cooled to 400 to 500 ° C. or less, then water-cooled and immediately molded into a product with a predetermined outer diameter and circularity by a standard machine called a sizer.

On the other hand, in the recent transportation of oil and natural gas by electric resistance welded steel pipe line pipes, it is required to improve the efficiency of line pipe transportation by increasing the internal pressure of the pipes, and it is more and more excellent in toughness, high strength and weldability. Steel pipes have been demanded. Therefore, as a material of ERW steel pipe,
In addition to lowering C and increasing Mn, it has become unavoidable to apply materials in which fine graining and precipitation strengthening are achieved by adding Nb, V, Ti and the like. That is, APIX7 defined by the American Petroleum Institute (API) as the standard for ERW pipes.
0 or more, strength equivalent to X80 class, specifically, tensile strength of 590 N / mm ² or more, yield strength of 360 N /
Since high-strength electric resistance welded steel pipes having a size of about mm ² or more are often required, Nb, V, Ti, etc. are added to refine the crystal grains by the alloying elements and the precipitation of carbonitrides of those alloying elements. It is necessary to strengthen by

However, in the electric resistance welded steel pipe using the above materials, the post-annealing treatment and the subsequent air-cooling process soften the post-annealing heat-affected zone around the electric resistance welded portion. There is a problem that the tensile strength in the vicinity of the welded portion is more likely to be reduced than in the base metal portion, and it has been observed that the weld line is at the tensile test fracture position.

As a countermeasure, C: 0.10% or less,
Mn: 0.8-2.0%, Al: 0.01-0.10%
And Nb: 0.01 to 0.10%, V: 0.
01-0.15%, Ti: 0.01-0.10%, at least one or more of them are contained, and when the electric resistance welded steel pipe is manufactured using steel composed of the balance Fe and unavoidable impurities as a raw material, after welding, Immediately after heat treatment of the electric resistance welded portion to the austenitizing temperature, the temperature around the welded portion is 30 ° C / sec.
A method for forcibly cooling to a temperature of 200 ° C. or lower at the above cooling rate (Japanese Patent Publication No. 61-3372), or FIG.
As shown in (a) and (b), an induction heater 21 in which the electric resistance welded portion after welding is arranged in series immediately above the welding line W.
After the heat treatment to the austenitizing temperature by, the periphery of the welded portion is immediately cooled at a cooling rate of 15 ° C./sec or more, and as shown in FIG. 9C, the induction heater 22 arranged in series immediately above the welding line W. Ac again
A method of manufacturing a high strength and high toughness electric resistance welded steel pipe by heating it to _one or more points has been proposed.

[0006]

SUMMARY OF THE INVENTION The above Japanese Patent Publication No. 61-33
In the heat treatment method for the welded portion typified by Japanese Patent Publication No. 72, the high-strength material has a large residual stress after forming electric resistance welding, and the shape of the locally heated rear tubular body becomes a chestnut-shaped shape, which is used in the sizer of the subsequent process. Ti, Nb, which not only deteriorates the toughness by drawing work hardening of Ti, but also aims to strengthen the solid solution precipitation of carbonitrides,
Addition of strengthening elements such as V and Mo causes a local increase in hardening on the A ₁ transformation line after heating and water cooling of the weld,
Even by reheating with an induction heater, according to the conventional method, at a position 20 to 30 mm away from the welded portion, it is not sufficiently reheated, so that problems such as hardness deviation due to local high hardness remaining in the welded portion occur.

The object of the present invention is to solve the above-mentioned drawbacks of the prior art, to suppress the local hardening increase on the A ₁ transformation line after heating and water cooling of the welded portion, and at the same time, to localize on the A ₁ transformation line. It is an object of the present invention to provide a method for producing a welded portion high toughness and high strength electric resistance welded steel pipe capable of preventing local high hardness remaining in the welded portion by sufficiently reheating in the reheating even if an increase in hardening occurs.

[0008]

In the method for manufacturing an electric resistance welded steel pipe according to claim 1 of the present invention, the electric resistance welded portion after welding is heated to the Ac ₃ transformation point or more by a pre-stage induction heater arranged immediately above the welding line. After that, the eccentricity is 10 to 15 mm from the center of the front-stage induction heater in the axial direction, and the second-stage induction heater is widely heated above the Ac ₃ transformation point, and then water-cooled again ± 5 mm from the A ₁ transformation line after water-cooling.
The eccentric induction heater is used to heat to below the Ac ₁ transformation point and to perform standard processing with a reduction amount of 0.5% or less. Thus, after heating the electric resistance welding portion than Ac ₃ transformation point, and the wide heating above Ac ₃ transformation point by subsequent induction heater is decentered, 15 ° C. / sec
After cooling with water at the above cooling rate, Ac was again used with an induction heater decentered by ± 5 mm from the A ₁ transformation line after cooling with water.
_By heating below ₁ transformation point, heating of the weld,
It is possible to suppress the local hardening increase on the A ₁ transformation line after water cooling, and even if the local hardening increase occurs on the A ₁ transformation line, it is sufficiently reheated in the reheating to locally harden the welded portion. It can prevent the remaining. Further, by performing a fixed shape processing with a sizer of 0.5% or less, deterioration of toughness due to work hardening of the electric resistance welded portion can be prevented.

The method for manufacturing an electric resistance welded steel pipe according to a second aspect of the present invention is C: 0.04 to 0.09%, Si: 0.30.
% Or less, Mn: 1.20 to 1.50% or more, P: 0.0
30% or less, including S: 0.020% or less, and C
u: 0.5% or less, Ni: 0.5% or less, Ti: 0.0
20 to 0.060%, Mo: 0.5% or less, Nb: 0.
020-0.080%, V: 0.005-0.020%
Of the steel containing at least one of the above, with the balance being Fe and unavoidable impurities, and being electric resistance welded,
After the electric resistance welded portion after welding is heated to the Ac ₃ transformation point or higher by the pre-stage induction heater arranged immediately above the welding line, the pre-stage induction heater is heated from the axial center of the pre-stage induction heater to 10
And wide heating above Ac ₃ transformation point by subsequent induction heater is ~15mm eccentric, heated to below Ac ₁ transformation point at induction heater is ± 5 mm offset from the A ₁ transformation line after the water cooling again cooled, throttle amount 0.5%
The following standard processing is applied. Using such a material, the electric resistance welded portion is heated to the Ac ₃ transformation point or higher, and then the eccentric rear induction heater is used for Ac
Wide heating at ₃ transformation points or more, water cooling at a cooling rate of 15 ° C / sec or more, and ± 5 mm from the A ₁ transformation line after water cooling
By heating again below the Ac ₁ transformation point with an eccentric induction heater, heating of the welded portion and A after water cooling are performed.
_{1 While} suppressing local hardening increase on the transformation line,
Even if a local increase in hardening occurs on the A ₁ transformation line, it can be sufficiently reheated during reheating to prevent local high hardness from remaining in the welded portion. Further, by performing a standardized process with a sizer of 0.5% or less, it is possible to prevent deterioration of toughness due to work hardening of the electric resistance welded portion, and it is possible to manufacture a high strength and high toughness electric resistance welded steel pipe. it can.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION First, the reasons for limiting the heat treatment conditions for the electric resistance welded steel pipe of the present invention will be described. In the present invention, the induction heater position for heating after electric resistance welding is
As shown in FIGS. 1 (a) and 1 (b), the centers of the former-stage induction heaters 1a and 1b are arranged on the electric resistance welding line W of the electric resistance welding steel pipe 2,
By eccentricizing the centers of the latter-stage induction heaters 3a and 3b from the electric resistance welding line W by 10 to 15 mm,
As shown in (a), the front induction heater 1a,
By 1b, the inner surface of the electric resistance welded portion is A with the electric resistance welded line W as the center.
The heating width is not less than the c ₃ transformation point, and as shown in FIG. 5 (b), the heating width is not less than the Ac ₃ transformation point around the position eccentric from the electric resistance welding line W by 10 to 15 mm by the latter-stage induction heaters 3a and 3b. Is expanded, temperature variations are suppressed, and the toughened area by water cooling is expanded. Further, the heating by the induction heater for heating is performed by heating at the Ac3 transformation point or more on the inner surface of the pipe and at less than 1020 ° C. on the outer surface of the pipe, as shown in FIG. From the temperature required to complete the transformation to (austenite structure), Ac
₃ transformation points or higher, preferably Ac ₃ transformation point or higher 1020 ° C
Is less than.

The cooling rate after heating is water cooling as shown in FIG.
As shown in, the cooling rate of 15 ° C./sec or more is necessary to obtain fine acicular ferrite that improves the toughness of the weld zone, and this cooling rate is nothing but water cooling.

As shown in FIG. 1C, the positions of the reheating induction heaters 4a and 4b after the forced cooling are as shown in FIG.
As shown in Fig. ₁ , A ₁ transformation line A after cooling that causes hardening
When the reheating temperature is at a position eccentric by a predetermined distance L, for example, ± 5 mm from above L, and the reheating temperature is at or above the Ac ₁ transformation point, the hardness suddenly decreases due to softening, and it becomes difficult to secure strength. Therefore, the Ac ₁ transformation point is set below.

In the present invention, the reason why the drawing amount in the regular processing is 0.5% or less is that, as shown in FIG. 7 and FIG.
Normally, the amount of reduction in regular processing is about 0.6 to 1% of the peripheral length, but the roundness is improved by the improvement of the steel pipe chestnut-shaped shape, and the toughness is deteriorated due to work hardening of the electric resistance welded portion. From the viewpoint of prevention, it was set to 0.5% or less.

Next, the reasons for limiting the chemical composition of the electric resistance welded steel pipe in the present invention will be explained. C is an element that improves the strength of steel, but if it is less than 0.04%, its effect is not sufficient, and an increase in the amount of C generally tends to cause a decrease in toughness, especially when forced cooling is performed. If it exceeds 0.09%, the electric resistance welded portion may be hardened, which may rather lower the toughness, so the content was made 0.04 to 0.09%.

Si is an effective element for deoxidizing the steel, but if it exceeds 0.30%, a penetrator defect due to the SiO2 component is likely to occur during electric resistance welding, so 0.30%.
It was as follows.

Like C, Mn is an element that improves the strength of steel and is also effective in improving toughness, but if it is less than 1.20%, strength equivalent to APIX70 and X80 cannot be obtained, and 1. If it exceeds 50%, a penetrator defect mainly composed of MnO component is likely to occur, and toughness is likely to be deteriorated due to the quenching effect by forced cooling.
It was set to 1.20 to 1.50%.

P is an element that reduces the toughness of the steel material,
Also, from the viewpoint of preventing the occurrence of welding defects, it is preferable that the amount is as small as possible, so the content was made 0.030% or less.

Since S is an element that lowers the toughness of the steel material like P, and it is better to be as small as possible from the viewpoint of preventing the occurrence of welding defects, S was made 0.020% or less.

In the present invention, the API X70, X
In addition to the above-mentioned components, Cu, Ni, Ti, Mo, N in order to have a strength of about 80 or more.
One or more of b and V are contained to improve the material strength by the crystal grain refining effect and precipitation effect of these elements. The reasons for limiting the components of these elements are as follows.

Cu is an element necessary for securing the strength of steel (in particular, yield strength), but if it exceeds 0.5%, the toughness of the welded portion deteriorates, so it was made 0.5% or less.

Ni, like Cu, is an element necessary for securing the strength of steel (especially yield strength). However, if it exceeds 0.5%, the toughness of the welded portion deteriorates, so it was made 0.5% or less.

Ti forms fine carbonitrides in steel and improves the strength by precipitation hardening, and at the same time refines the crystal grains to improve the toughness of the base material and the welded portion.
If it is less than 20%, the effect is not sufficient, and 0.06
If it exceeds 0%, the toughness is rather deteriorated by excessive precipitation hardening, so the content was made 0.020 to 0.060%.

Mo is an element that enhances the strength of steel,
If it exceeds 0.5%, the toughness of the welded portion will decrease, so it is not preferable.
It was set to 5% or less.

Like Ti, Nb forms fine carbonitrides in steel and improves the strength by precipitation hardening, and at the same time refines the crystal grains to improve the toughness of the base metal and welded parts. If it is less than 020%, its effect is not sufficient, and if it exceeds 0.080%, the toughness is rather deteriorated by excessive precipitation hardening, so 0.020 to 0.080.
%.

V forms carbides in steel to improve the strength by precipitation hardening, but if it is less than 0.005%, its effect is not sufficient, and if it exceeds 0.020%, it is rather caused by excessive precipitation hardening. 0.0 because it deteriorates toughness.
It was set to 05 to 0.020%.

[0026]

【Example】

Example 1 Steel types A to E having the chemical components shown in Table 1 were melted and subjected to normal hot rolling to form a hot-rolled steel sheet having a plate thickness of 12.0 mm. 0 mm, wall thickness 12.
A 0 mm electric resistance welded steel pipe was produced at a pipe producing speed of 15 m / min. Each of the obtained electric resistance welded steel pipes was heat-treated under the heat treatment and cooling conditions shown in Table 2, and then shaped into a regular shape using a sizer with the drawing amount shown in Table 2. In the circumferential tensile strength and Charpy impact test of the ERW welded portion of each of the obtained ERW steel pipes, -5
The absorbed energy E (J) at ° C was measured. Also,
The Vickers hardness of the electric resistance welded portion was measured. Table 3 shows the results. The tensile strength is based on the metallic material tensile test method specified in JIS Z2241, and the absorbed energy at -5 ° C in the Charpy impact test is JISZ.
According to the metal material impact test method specified in 2242, the Vickers hardness of the electric resistance welded portion was measured according to the Vickers hardness test method specified in JIS Z2244.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

As shown in Table 3, the examples of the present invention show uniform strength and improved toughness as compared with the conventional example 1, the conventional example 2 and the comparative example, which are for the induction heater for heating and for reheating. It is considered that the high toughness region was expanded and the hardness was stabilized by arranging the induction heaters in a staggered manner and reducing the drawing amount with the sizer.

[0031]

EFFECT OF THE INVENTION In the method for manufacturing a welded portion with high toughness and high strength ERW steel pipe of the present invention, the ERW welded portion is heated to the Ac ₃ transformation point or higher by a pre-induction heater arranged immediately above the welding line, and then the pre-induction heater. a from the tube axis direction center and wider heated by subsequent induction heater is 10~15mm eccentric, with induction heaters is ± 5 mm offset from the a ₁ transformation line after cooled with water again cooled
By heating below the c ₁ transformation point and subjecting it to standard processing with a drawing amount of 0.5% or less, it is possible to prevent the tensile strength from decreasing around the electric resistance welded part and to stabilize the hardness by expanding the toughness range. It is possible to obtain an electric resistance welded steel pipe having high toughness.

[Brief description of drawings]

1A and 1B are explanatory views of the arrangement of an induction heater according to the present invention, FIG. 1A is a plan view showing the arrangement of a heating induction heater, FIG. 1B is an explanatory view of an eccentric arrangement of a heating rear induction heater, and FIG. ) The drawing is a plan view showing the arrangement of the reheating induction heater.

FIG. 2 is a graph showing the relationship between the outer surface heating temperature and the surface bainite depth.

FIG. 3 is a graph showing the relationship between the cooling rate after heating and the ferrite grain size.

FIG. 4 is a graph showing the relationship between reheating temperature and Vickers hardness (Hv).

5A and 5B are explanatory views of the proper eccentricity amount of the heating rear induction heater, in which FIG. 5A is an explanatory view of the position and heating temperature of the heating front induction heater, and FIG. 5B is an eccentricity of the heating rear induction heater. It is explanatory drawing of a position and heating temperature.

FIG. 6 is a graph showing the relationship between the reheating induction heater eccentricity L and the peak Vickers hardness (Hv).

FIG. 7: Sizer aperture amount and peak Vickers hardness (H
It is a graph which shows the relationship with v).

FIG. 8 is a graph showing a relationship between a sizer aperture amount and absorbed energy at −5 ° C.

FIG. 9 is an explanatory view of a conventional induction heater arrangement,
(A) is a plan view showing the arrangement of the induction heater for heating, and (b) is an Ac after heating with the induction heater.
FIG. ₃ (c) is a plan view showing the arrangement of reheating induction heaters.

[Explanation of symbols]

1a, 1b, 3a, 3b, 4a, 4b, 21, 22 Induction heater 2 ERW steel pipe W Welding line AL A ₁ Transformation line

Claims (2)

[Claims] 1. In a method for producing an electric resistance welded steel pipe, after the electric resistance welded portion after welding is heated to an Ac ₃ transformation point or higher by a pre-stage induction heater arranged directly above the welding line, the pre-stage induction heater is heated from the axial center of the pipe. 10-15m
Ac ₃ by an eccentric rear induction heater
Widely heating above the transformation point, water-cooling and water-cooling again, and heating to below the Ac ₁ transformation point with an induction heater decentered by ± 5 mm from the A ₁ transformation line, and perform standard processing with a drawing amount of 0.5% or less. A method for producing a high-strength ERW steel pipe with high toughness in a welded portion. 2. A method for manufacturing an electric resistance welded steel pipe, wherein C: 0.
04-0.09%, Si: 0.30% or less, Mn: 1.
20 to 1.50% or more, P: 0.030% or less, S:
Contains 0.020% or less and Cu: 0.5% or less, N
i: 0.5% or less, Ti: 0.020 to 0.060%,
Mo: 0.5% or less, Nb: 0.020 to 0.080
%, V: 0.005 to 0.020% of one or more, and the balance is Fe and unavoidable impurities. The steel is electro-welded and the electro-welded welded part after welding. Is heated to the Ac ₃ transformation point or higher by the pre-stage induction heater arranged immediately above the welding line, and then is broadly heated to the Ac ₃ transformation point or higher by the post-stage induction heater eccentric from the axial center of the pre-stage induction heater by 10 to 15 mm, High toughness of welded part characterized by heating to below the Ac ₁ transformation point with an induction heater decentered by ± 5 mm from the A ₁ transformation line after water cooling and water cooling again, and subjecting to standard processing with a reduction of 0.5% or less High strength electric resistance welded steel pipe.