JP3491339B2 - Manufacturing method of high tension electric resistance welded steel pipe - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a high-strength electric resistance welded steel pipe, and more particularly to a method for manufacturing a high tension electric resistance welded steel pipe which imparts high tension by tempering after electric resistance welded pipe.

[0002]

2. Description of the Related Art In particular, in recent years, weight reduction has been promoted in order to improve fuel consumption of machine-structured electric resistance welded steel pipes used as high-strength structural members and driving force transmission members of automobiles and the like. In addition, electric resistance welded steel pipes for cleaning oil country tubular goods and the like are also required to reduce the suspended weight due to the strength problem of the welded joint of the steel pipes, and similarly, the weight reduction of the steel pipes is also demanded.

Thus, according to the recent technological trends,
There is an increasing demand for high-strength electric resistance welded steel pipes that can reduce the weight of steel pipes as described above. By the way, the conventional method for producing a high-strength electric resistance welded steel pipe is divided into the following two methods depending on the difference in the mechanism for achieving high tension.

A) A high-strength steel strip system in which a steel strip having a high tensile strength is prepared as a steel pipe base material, and an electric resistance welded pipe is prepared using the strip steel. However, such a method has the following problems. Since the steel strip itself has high tension, it is difficult to perform roll forming during ERW pipe. Shape defects are likely to occur during electric resistance welding. During electric resistance welding, the heat-affected zone of the weld may soften and the weld strength may decrease.

B) After electro-sewn pipe, tempering (quenching, or
Quenching + tempering) tempering method. This method also has the following problems. The refining cost, that is, the equipment cost for quenching and tempering and the fuel cost are high. Productivity declines because tempering must be performed after ERW pipes.

Up to now, the former method is generally used, and the latter method is adopted only when such a method cannot be adopted. However, as the method of manufacturing the electric resistance welded steel pipe by the latter method, some of the methods have been already proposed in the past.

[0007] For example, according to the method disclosed in Japanese Patent Laid-Open No. 4-6219, Ti is added to a steel containing a relatively large amount of C and Mn to secure strength before pipe forming. It is made of a soft material that is not allowed to undergo heat treatment at 600-700 ° C after pipe forming, and it is strengthened by utilizing the precipitation hardening of Ti.

In Japanese Patent Laid-Open No. 4-103718, Mn: 1.0 to 3.0
% To secure the strength, and 500 after pipe making.
Cu: 0.7-2.0% is added in order to utilize precipitation hardening during heat treatment at a relatively low temperature of ~ 650 ° C.

Similarly, in Japanese Patent Laid-Open No. 4-103719, M
n: 1.0-3.0% Ti-added steel is used B: 0.0003-0.0
With a content of 03%, the structure obtained by heat treatment after pipe forming is a fine-grained reticulated martensite-ferrite composite structure or bainite-martensite composite structure to ensure toughness and strength.

As described above, in the conventional method of the latter method, the strength is finally secured by utilizing age hardening, or the composition is finally heat treated at a relatively high temperature so that it can be air-cooled and quenched. By doing so, it is possible to obtain a composite structure by quenching under air cooling to achieve both strength and toughness.
However, such a conventional technique has a problem that it is not economical because a large amount of a special element is added.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for manufacturing a high-strength electric resistance welded steel pipe which does not have the above-mentioned drawbacks of the prior art. More specifically, the object of the present invention is to provide a yield strength of 500 N / mm ² or more and a tensile strength.
600N / mm ² or more, elongation of 20% or more can be used to manufacture with simple means and equipment, yield strength after pipe making 700N / mm ² or more,
An object of the present invention is to provide a highly productive manufacturing method which does not cause softening of a weld heat affected zone of an electric resistance welded pipe having a tensile strength of 800 N / mm ² or more and an elongation of 15% or more.

[0012]

The inventor of the present invention has examined the conventional methods for achieving the above-mentioned objects. As a result, as long as the heat-affected zone of the welding is present, a high tensile steel strip is used in advance. That is, there are problems such as heat treatment after welding, and a tempering method is desirable in terms of characteristics.

Therefore, when the above-mentioned problems with respect to the refining method were studied in detail, in order to secure strength and weldability, C: 0.09 to 0.18%, Si: 0.25
To 0.45%, and Mn: 0.70 to 1.00% and Mo: 0.10 to 0.40% for ensuring hardenability, and the above-mentioned objects are achieved by their synergistic effect.
Moreover, the inventors have found that the target characteristics can be realized without particularly performing tempering treatment (quenching heat treatment) after quenching, and eventually equipment cost and fuel cost can be significantly reduced, and the present invention has been completed.

Here, the gist of the present invention is C: 0.09 to 0.18%, Si: 0.25 to 0.45%, and M in weight%.
n: 0.70 to 1.00%, Cu: 0.20 to 0.40%, Ni: 0.05 to 0.2
0%, Cr: 0.50 to 0.80%, Mo: 0.10 to 0.40%, S:
Steel having a steel composition of 0.0020% or less and the balance Fe and unavoidable impurities is hot-rolled at a rolling end temperature Ar _{3 to} 950 ℃, wound at 400 to 600 ℃, and electric-welded from the obtained strip steel. A high-strength ERW steel pipe with excellent corrosion resistance and ductility, characterized in that after the pipe is heat-treated at a temperature higher than 750 ° C and lower than 950 ° C, the electric resistance welded steel pipe is wound into a coil during cooling. Is a manufacturing method.

[0015]

Next, in the present invention, the reason why the steel composition and hot rolling conditions are limited as described above will be explained together with its operation. First, the electric resistance welded steel pipe manufactured according to the present invention can be used for various purposes, and the present invention is not limited to the uses. At least, there is a significance of the present invention as long as it is an electric resistance welded steel pipe that requires heat treatment in order to prevent deterioration of the toughness of the heat affected zone when manufactured by the conventional method. For example, it is used as a steel pipe for cleaning oil country tubular goods, and is also used as a power transmission member for automobiles or a steel pipe for other purposes.

The blending ratio of each component of the alloy in the electric resistance welded steel pipe manufactured according to the present invention is determined as follows.
The electric resistance welded steel pipe for cleaning oil country tubular goods is required to have corrosion resistance, weldability, and strength.

C: 0.09 to 0.18% 0.09% or more is required to give the required strength to steel, while the upper limit is 0.18% to secure weldability. Preferably, it is 0.14 to 0.16%.

Si: 0.25 to 0.45% In the case of the present invention, as in the case of C, the lower limit is set to 0.25% to secure a predetermined strength, and the upper limit is set to 0 to secure weldability.
Limit to 45%. Preferably, it is 0.30 to 0.40%.

Mn: 0.70 to 1.00% In order to secure the strength of steel, a lower limit of 0.70% is necessary,
On the other hand, there is a concern that weldability will deteriorate, so the upper limit is set to 1.00%. It is preferably 0.70 to 0.90%.

Cu: 0.20 to 0.40% Cu forms a passive film on the surface of steel and improves corrosion resistance. There is also a precipitation effect due to heat treatment. To obtain this effect, it is necessary to add 0.20% or more. When Cu is added excessively, a Cu-rich solid solution having a low melting point is formed immediately below the surface scale of the rolled material during heating during hot rolling, and surface defects occur during hot rolling. Therefore, even in the present invention, 0.40
% Or less. A preferable upper limit is 0.30%. More preferably, it is 0.22 to 0.30%.

Ni: 0.05 to 0.20% To produce a Cu-rich solid solution having a low melting point, the melting point of the Cu-rich solid solution can be increased by adding 0.05% or more of Ni,
Although it can be reduced, the amount of Ni must be added in proportion to the amount of Cu, and since Ni is expensive, the upper limit is 0.20% in consideration of economic efficiency.
Was set. Preferably, it is 0.07 to 0.12%.

Cr: 0.50 to 0.80% Addition of Cr has the effect of improving the strength and corrosion resistance of steel. To obtain this effect, a lower limit of 0.50% is required. The upper limit is about 0.80% for economic reasons.
It is preferably 0.50 to 0.70%.

Mo: 0.10 to 0.40% Mo is a hardenability improving element, and for this purpose, 0.10% or more is added. If the upper limit of 0.40% is exceeded, the welding characteristics will be deteriorated. It is preferably 0.18 to 0.30%.

S: 0.0020% or less S is one of the unavoidable impurities of steel. Under the environment of oil well pipes, hydrogen sulfide cracking occurs, and if it exceeds 0.0020% and the S content is large, a large amount of sulfide inclusions are generated inside the steel, and the resistance to hydrogen sulfide cracking decreases. Therefore, the upper limit is 0.00
Set 20%.

Next, a steel having such a steel composition is hot-rolled to form a strip steel, and then an electric resistance welded tube is manufactured by a conventional electric welding. The reasons for limiting the hot rolling conditions and the heat treatment conditions after producing the electric resistance welded pipe will be described.

Rolling Conditions Rolling End Temperature (Finishing Temperature) Ar ₃ to 950 ° C. If the rolling end temperature exceeds 950 ° C., there will be no rolling in the unrecrystallized region, resulting in insufficient strength and toughness. If it is less than Ar _3, it is rolled in the two-phase region and the strength is increased, but the ductility and toughness are significantly reduced.

Hot rolling coiling temperature ( 400-600 ° C) When the coiling temperature after hot rolling is less than 400 ° C, martensite formation occurs, the ductility and toughness decrease, and the strength increases more than necessary. It causes problems during molding. On the other hand, if the coiling temperature is 600 ° C. or higher, the effect of precipitating Cu and Mo occurs before molding and the strength increases.

The method of manufacturing the electric resistance welded pipe itself may be a conventional one, and a person skilled in the art should understand it, so further description thereof will be omitted. However, the standard operation example is as follows. That is, the flow of the manufacturing process of the electric resistance welded pipe in the present invention is as follows.

Process example: hot rolling → [forming → welding → standard (manufacturing of electric resistance welded steel pipe)] →
[Heat treatment, coil winding during cooling if necessary] That is, the hot-rolled strip steel is continuously formed into a tubular shape through, for example, five-stage roll forming, and then the butt seam is also continuously formed into an electric resistance. Welded and finally shape-corrected to form a welded steel pipe.

The electric resistance welded steel pipe thus manufactured according to the present invention is heat-treated, and will be described in further detail with reference to FIG. 1 showing an outline of manufacturing equipment for performing the heat treatment. One advantage of the present invention is that the treatment efficiency is improved by quenching for a short time as shown in FIG. 1, and if necessary, the coiling and the tempering step can be omitted immediately after quenching. In the figure, the main equipment is a. Heating furnace for quenching, b. Cooling zone, c. Winding equipment, and d. Heat insulation equipment.

That is, the electric resistance welded steel pipe continuously manufactured as described above is first prepared in the heating furnace for quenching a
The heating method is not particularly limited, for example, open flame, induction heating, etc.
Heated by. At this time, the temperature is raised to more than 750 ° C. and less than 950 ° C. by rapid heating at a heating rate of 3 ° C./sec or more. This is because if the temperature is raised too slowly, the productivity is lowered and the length of the heating equipment needs to be increased, which causes a problem of equipment cost. The heat treatment temperature is for ensuring high strength and high ductility, and if it deviates from the above temperature range, predetermined pipe characteristics cannot be obtained and the object of the present invention cannot be achieved. Preferably, heat treatment is performed within the range of 800 to 900 ° C.

The holding time in the above temperature range is preferably as short as possible. Usually 3 to 10 seconds, preferably 3 to
5 seconds. In the present invention, the retention time is basically set to be within 10 seconds. The cooling zone b is necessary for adjusting the winding start temperature. The cooling method may be water cooling or air cooling.

According to a preferred embodiment of the present invention, the winding temperature is
600 to 750 ℃. In other words, by optimizing the quenching structure (bainite and pearlite), both high strength and high ductility are satisfied. The winding in the winding facility c is performed so as not to impair the shape of the steel pipe. That is, the winding diameter is determined so that the bending deformation amount of the steel pipe itself is within the elastic range.

The heat-retaining equipment d is equipment for adjusting the temperature of the coil (steel pipe) wound up, that is, the winding temperature. It is a detachable type and a heating device for heat retention may be attached if necessary. However, it is basically preferable not to heat. Next, the operation of the present invention will be described more specifically by showing Examples of the present invention.

[0035]

【Example】

(Example 1) A series of sample steels having the steel compositions shown in Table 1 were hot-rolled under the conditions of a finishing temperature of 830 ° C and a coiling temperature of 560 ° C, and the obtained strip steel was used. A conventional ERW steel pipe was manufactured under the following conditions. Then, the obtained electric resistance welded steel pipe was subjected to heat treatment with the heat history shown in FIG.

Steel strip thickness: 2.3 mm Steel pipe size: Diameter 31.8 mm Steel pipe heat treatment condition: Temperature rising: 3 ° C./sec Holding time: 3 sec Cooling method to coiling temperature: Water cooling (spraying) Cooling method after coiling : Air cooling Each test piece specified by JIS was sampled from the finally obtained electric resistance welded steel pipe, and its mechanical properties, corrosion resistance, surface condition, and availability of steel pipe production were determined. The results are summarized in Table 2.

The test procedure was as follows. The tensile test was performed using JIS No. 5 test pieces. The corrosion resistance test was carried out under the following conditions. Corrosion test liquid: 60% by volume H ₂ SO ₄ aqueous solution Test temperature: 80 ° C Immersion time: 16 hours Specimen size: Thickness 2.3 × width 100 × length 150 mm The steel plate surface condition was pickled and visually checked. Is.

(Example 2) In this example, an electric resistance welded pipe was manufactured by using the steel type A in Table 1 in the following manner, and the winding temperature and the heat treatment temperature were variously changed, and the characteristic change was examined. . The test procedure in this example was as follows.

JIS No. 11 test piece Steel strip thickness: 2.3 mm Steel pipe size: Diameter 31.8 mm Steel pipe heat treatment condition: Temperature rising: 3 ° C / sec Holding time: 3 sec Cooling method to coiling temperature: Water cooling (spraying) coiling Subsequent cooling method: Although air cooling results are summarized in Table 3, in the present invention, the winding temperature is not necessarily limited as long as the heat treatment temperature is higher than 750 ° C and lower than 950 ° C, but preferably, Even if the heat treatment temperature is within the above range, further improvement can be seen by limiting the coiling temperature to 600 to 700 ° C.

FIG. 3 is a graph showing a simple comparison of welded impact characteristics before and after heat treatment of a steel pipe manufactured from a steel strip of steel type A in this example. It can be seen that the electric shock resistance of the electric resistance welded steel pipe manufactured according to the present invention is greatly improved.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

According to the present invention, a high-quality high-strength electric-resistance welded steel pipe can be manufactured easily and inexpensively, and its industrial significance from a practical viewpoint is considered to be very great.

[Brief description of drawings]

FIG. 1 is a schematic diagram of heat treatment equipment for electric resistance welded steel pipe according to the present invention.

FIG. 2 is an explanatory diagram of a heat history of an electric resistance welded steel pipe in an example.

FIG. 3 is a graph comparing the impact properties of welded steel pipes obtained in Example 2 before and after heat treatment in a simple manner.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C21D 8 / 10,9 / 50,9 / 08 B21C 37/08 B23K 13/00 C22C 38/00-38 / 60

Claims (2)

(57) [Claims] 1. By weight%, C: 0.09 to 0.18%, Si: 0.25 to 0.45%, Mn: 0.70 to
1.00%, Cu: 0.20 to 0.40%, Ni: 0.05 to 0.20%, Cr: 0.50 to
Steel having a steel composition of 0.80%, Mo: 0.10 to 0.40%, S: 0.0020% or less, and the balance Fe and unavoidable impurities is hot-rolled at a rolling end temperature Ar _{3 to} 950 ° C. to 400 to 6
Winding at 00 ℃, ERW pipe from the obtained strip steel, 750 ℃
A method for producing a high-strength electric resistance welded steel pipe excellent in corrosion resistance and ductility, which comprises performing heat treatment at a temperature lower than 950 ° C. 2. The method for producing a high-strength electric resistance welded steel pipe according to claim 1, wherein the electric resistance welded steel pipe is wound into a coil during cooling after the heat treatment.