JPH0538517A - Manufacturing method of multi-layer type electric resistance welded oil country tubular goods with excellent crushing property - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a method for manufacturing an electric resistance welded well tube having excellent crushing properties. [Structure] Molten alloy steel having excellent hardenability is laminated on a base material slab to form a multi-layer slab, and cooling in hot rolling is performed by cooling from the laminated steel side having excellent hardenability at 10 to 100 ° C / sec. Pipe is made with the steel side as the inner surface of the steel pipe, and the sizing amount is 1 to
A multi-layer type electric resistance welded oil country tubular good having excellent crushing property is specified at 20%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a multi-layer type electric resistance welded well tube having excellent crushing properties.

[0002]

2. Description of the Related Art In recent years, the depth of excavation of oil wells has tended to become deeper and deeper, and along with this, there is an increasing demand for oil well pipes having excellent crushing characteristics. In addition, as the crush resistance is improved, it is possible to reduce the thickness of the oil country tubular goods, which has a great advantage for the customer, such as reducing the weight of the entire oil well and reducing the amount of steel materials purchased. From these points as well,
The demand for oil country tubular goods with excellent crushing properties is extremely high.

As a prior art relating to an oil country tubular good having excellent crushing characteristics, there is one described in Japanese Patent Application Laid-Open No. 59-260442 (high pressure crush type oil country tubular goods having a high yield strength on the inner and outer surface portions of the pipe). In this technology, the yield strength of the inner and outer surface portions of the pipe is increased and the crushing property is improved by effectively utilizing the strain aging strengthening by heat treatment at a low temperature after the production of the electric resistance welded steel pipe.

[0004]

Conventionally, when manufacturing an electric resistance welded oil country tubular good having excellent crushing characteristics, no manufacturing method has been known which can satisfy the effect, and the present invention provides an electric welding tube having excellent crushing characteristics. It is an object of the present invention to provide a method for manufacturing a sewing oil well pipe.

[0005]

The gist of the present invention is to form a multi-layer slab by laminating a base alloy slab made of low alloy steel with a molten alloy steel having a hardenability superior to that of the base slab. , The multilayer slab is hot-rolled, subsequently the laminated steel side is cooled at an average cooling rate of 10 to 100 ° C./sec, and the cooling stop temperature is set to 100 to 600 ° C., thus obtained multilayer hot rolled steel A method for producing a multi-layer type electric resistance welded well tube having excellent crushing characteristics, which is characterized in that the laminated steel side of the strip is formed as the inner surface side of the steel pipe and the sizing processing amount at that time is set to 1 to 20%. ..

That is, the present invention uses two types of low-alloy steels having different hardenability, and a base slab made of one low-alloy steel is hardened to the other low-alloy base slab. Hot-rolling a multi-layer slab made by stacking steel by injecting it in a molten state, and then rapidly cooling the hot-rolled steel strip obtained only from the laminated steel side with high hardenability and hardening it By forming a pipe so that the steel side is the inner surface of the steel pipe and setting the sizing amount at that time to 1% or more and 20% or less, the strength of the inner surface side of the steel pipe is increased and the crushing property is improved.

In the present invention, the material cost can be kept low by using a slab in which low alloy steels are made into a multi-layer structure. Also, the adhesion strength during multi-layering is extremely good because of the low alloy steels. Hereinafter, the present invention will be described in detail. The yield strength of the steel pipe is a controlling factor of the crushing property of the oil well pipe. It is considered that the crushing phenomenon occurs instantaneously when the wall thickness inner surface side of the steel pipe yields, and therefore, the yield strength on the wall thickness inner surface side of the steel pipe is considered to control the crush value. That is, when the other crushing controlling factors such as the roundness, the wall thickness deviation, and the residual stress are equal, the higher the yield strength on the inner surface side of the wall thickness of the steel pipe, the better the crushing property. However, excessively increasing the strength of the steel pipe is not preferable because it deteriorates the low temperature toughness and corrosion characteristics of the steel.

The present invention provides a method for improving only the strength on the inner surface side of the wall thickness position that governs the crushing property without increasing the strength of the steel pipe more than necessary, thereby improving the crushing property. .. The gist of the present invention is to utilize a multi-layer slab in which a low alloy steel, which is more hardenable than a base slab made of low alloy steel, is sprayed in a molten state and laminated.

In order to effectively bond low-alloy steels having different hardenability, one low-alloy steel is sprayed in a molten state as in the present invention and laminated with the base slab of the other low-alloy steel. The method is very effective. Thus, by injecting molten steel onto a substrate slab of another steel, the interface between the two steels is completely metallurgically bonded, which results in very good adhesion.

Next, the multi-layer slab is hot-rolled, and the cooling conditions and the cooling stop temperature after that are important. Cooling after hot rolling needs to be performed only from the side of the laminated steel having excellent hardenability that is injected and laminated. By cooling only from the laminated steel side having excellent hardenability in this way, the surface of the steel side can be strengthened. As a result, the strength of only one side can be increased without increasing the strength of the entire steel plate more than necessary. Next, specific cooling conditions and cooling stop temperatures will be described.

First, regarding the cooling rate, in order to strengthen the laminated steel side, it is necessary to quench rapidly at an average cooling rate of 10 ° C./second or more. Thus, the average cooling rate is 10
By quenching only from one side (laminated steel side) at a rate of ° C / sec or more, it is possible to strengthen only the laminated steel side having high hardenability without increasing the strength of the base material side more than necessary. Further, if the cooling rate exceeds 100 ° C./sec, the surface may be hardened more than necessary and cracks may occur. Therefore, the cooling rate is 10 ℃
/ Sec to 100 ° C / sec is highly preferred.

Next, regarding the cooling stop temperature, it is necessary to stop the cooling at 600 ° C. or lower in order to suppress the softening of the laminated steel side strengthened by the recuperation after the rapid cooling. Further, at temperatures below 100 ° C., there is no softening due to recuperation, so a cooling stop temperature of 600 ° C. to 100 ° C. is appropriate. It is possible to strengthen only one side (laminated steel side) by the above cooling conditions, and by making the laminated steel side of this steel material the inner surface side of the steel pipe, it is possible to manufacture oil well pipes with excellent crushing characteristics. ..

Next, the pipe making conditions will be described. By using the multi-layer steel material as described above, it is possible to manufacture an oil country tubular good excellent in crushing characteristics, but in order to further improve the crushing characteristics, sizing reduction in pipe making is important. That is, in the present invention, one side of the multi-layer steel material is rapidly cooled and reinforced, the reinforced side is the inner surface side of the steel pipe, and in addition to this, the cold working amount (sizing reduction) during pipe making is increased. As a result, the inner surface side is further strengthened, which makes it possible to further improve the crushing property.

The electric resistance welded steel pipe is manufactured by cold forming and electric resistance welding of a hot rolled steel plate. In this case, the work hardening due to cold working increases the strength, especially the yield strength, as compared with the steel plate stage.
In the present invention, in order to further effectively expand this work hardening,
It is intended to increase the sizing reduction.
Generally, in electric resistance welded steel pipe, sizing is performed to control the dimensional accuracy, and its reduction amount = (outer diameter before sizing−outer diameter after sizing) ÷ outer diameter before sizing × 10.
0% is at most about 0.5%. In the present invention, in order to maximize the work hardening by sizing and strengthen the inner surface of the steel pipe, the sizing reduction is 1%.
That is all. By performing such a strong cold working, the laminated steel side reinforced by the one-sided quenching of hot rolling is further strengthened, which makes it possible to manufacture an electric resistance welded well tube having excellent crushing properties.

For the purpose of improving work hardening by sizing reduction, 1% or more is required. On the other hand, if it exceeds 20%, it becomes difficult to operate due to problems such as flaws, so 1% or more and 20% or less is the optimum condition for sizing reduction. As described above, a base material slab made of a low alloy steel is laminated with a molten low alloy steel having better hardenability than the base material slab to form a multi-layer slab, and the multi-layer slab is hot-rolled to obtain The laminated steel side of the obtained multi-layer hot rolled steel strip was cooled at an average cooling rate of 10 to 100 ° C./second, and the cooling stop temperature was 100 to 600 ° C. By making the laminated steel side the inner surface side of the steel pipe and strengthening it by making the sizing amount at the time of pipe making 1% or more and 20% or less, it is possible to manufacture a multi-layer ERW oil well pipe with excellent crushing characteristics. Becomes

In such a multi-layer ERW oil well pipe,
There are no particular restrictions on the components of the steel on the base material side and the laminated steel side. However, it is desirable to make the component system as inexpensive as possible in view of cost. As a result of the investigation so far, if a material made of low alloy steel with the following composition is used,
It is possible to produce a multi-layer type electric resistance welded oil country tubular good with excellent crushing properties very effectively. The contents will be briefly described below.

First, the component system of the low alloy steel to be laminated will be described. Since it is necessary to strengthen by one-side quenching after hot rolling, it is important to use a component system having excellent hardenability. Further, at this time, it is desirable that an expensive element such as Ni is not added as much as possible. Therefore, it is preferable to add C, Si, Mn as a basic component and a relatively inexpensive element such as B, Mo, Cr, etc., if necessary. desirable.

First, regarding C, C is the most effective element for improving the hardenability. When the cooling conditions are the same, the strength is largely controlled by the C content. From that point, the C content is preferably 0.05% or more. On the other hand, C is an extremely effective strengthening element, and it is feared that by increasing the amount thereof, the hardenability of the material is improved, and as a result, the strength becomes too high. If it is hardened excessively, cracks may occur on the coil surface, so the upper limit of C content was made 0.50%.

Si is also an element necessary for increasing strength, but 0.10 to 0.30% is preferable from the viewpoint of weldability.
Similar to C, Mn is also an element essential for improving hardenability. However, if it is less than 0.50%, the toughness is lowered, so that it is not preferable, and if it exceeds 2.0%, the strength and hardness become too high, so 0.5 to 2.0% is preferable.

Further, it is very effective to add B, Mo, Cr or the like, if necessary. Especially for B, it is generally said that the hardenability of steel is dramatically improved if solid solution B of several ppm or more is present. However, addition of B in an unnecessarily large amount is not preferable because it embrittles the grain boundaries. From the above, B is 0.0003% (3ppm) to 0.0030%
About 30 ppm is the most preferable range. However, in order to secure the solid solution B, it is necessary to add Ti at the same time as B. B has a strong affinity with N, which exists inevitably after refining, and forms nitride (BN), so that solid solution B, which has an effect on hardenability, decreases or disappears. In order to prevent this and effectively utilize the hardenability improving effect of B, it is desirable to add Ti. Ti has a stronger affinity with N than B and forms Ti-based nitride (Ti-N), so that the formation of BN can be prevented.

The amount of Ti added was set to 0.010 to 0.035% in order to bond all solid solution N with Ti. From the above, it is preferable to set the upper limit of N to 100 ppm (0.0100%). It is also effective to add Cr and Mo in appropriate amounts instead of B. Cr is an element effective in improving hardenability, but when added in a large amount, Cr-based oxide is generated in the welded portion and the quality of the welded portion is deteriorated. Therefore, the upper limit is preferably 1.00%. .. 0.10
If it is less than%, the effect is small. Mo is also an element effective in improving the hardenability and is 0.10 to 1.00.
The range of% is effective. The reason is that if it is less than 0.10%, its effect cannot be expected, and if it is added in excess of 1.00%, its effect is not improved.

Fine graining by addition of Nb and V is also effective for improving strength, especially yield strength. Appropriate addition range is 0.010% or more and 0.100% or less for both Nb and V. The reason is that if it is less than 0.010%, the effect cannot be expected, and if it is added in excess of 0.100%, the effect is saturated. The components shown above may be selected according to necessity (steel material thickness, required hardness). Next, the base material components will be described. Since the strength of the steel material depends on the strength of the base material that occupies most of the wall thickness, the component system may be selected as necessary. However, a hardenability-improving element such as B, Cr, or Mo added to the laminated steel is not added, and a low alloy steel containing C, Si, and Mn and the balance Fe and elements inevitably present Is preferable in terms of cost. When considering the toughness of steel materials, Nb, V
It is effective to make the particles finer by adding one or two of the above.

Next, a method of laminating the molten alloy on the substrate will be briefly described. First, as the base material, a slab that is continuously cast or cast after being refined in a converter is used. However, the continuous casting slab is more advantageous in terms of productivity and cost. The molten alloy is laminated on the base material slab. At this time, the property of the surface of the slab is not particularly limited, and a normal continuous cast slab may be used. That is, prior preparation such as grinding the slab surface with a grinder before injecting the molten alloy is not essential.

A method of injecting the molten alloy 2 onto the base material slab 1 is shown in FIG. Base slab temperature when laminating the molten alloy is not particularly limited, even in hot conditions after casting, it may be a cold state after the slab cooling, or more A ₃ transformation point in order to enhance the binding preferable. From the viewpoint of productivity, it is most preferable to inject the molten alloy in the hot state immediately after continuous casting.

The lamination of the molten alloy is carried out by atomizing with an inert gas 3, and the inert gas at this time is preferably Ar or N ₂ in consideration of cost and safety. Further, the thickness for laminating the molten alloy may be selected by controlling the injection amount, the time, and the atomizing gas amount ratio, if necessary.

[0026]

EXAMPLES A, B, C, D, E and F in Tables 1 and 2 are examples of the present invention. The laminated steel side is strengthened by rapidly cooling one surface of the multi-layer slab of the component system (laminated steel, base material) shown in Table 1 and Table 2, and the laminated steel side is formed to be the inner surface of the steel pipe. It is possible to further strengthen the pipe by increasing the amount of sizing process at this time, thereby improving the crushing property.

On the other hand, G, H and I in Tables 1 and 2 are comparative materials of the present invention. For G, the sizing amount is small, for H and I, the cooling stop temperature is high, and the cooling rate is low, so that the crushing property is lower than that of the present invention. As described above, by combining the component system, the cooling conditions, and the sizing processing amount as in the present invention, it is possible to strengthen the inner surface side of the steel pipe and improve the crushing property.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

EFFECTS OF THE INVENTION The present invention is a base slab made of a low alloy steel, the alloy steel having a hardenability superior to that of the base slab is injected from the molten state and laminated, and the slab is hot-rolled,
Then, when rapidly cooling and hardening only from the laminated steel side and using the multi-layer coil as a raw material to manufacture an electric resistance welded oil country tubular good, the laminated steel side is the inner surface of the steel pipe, and the sizing amount is 1% or more 20% or more.
By setting the content to be not more than%, this is a technology for significantly improving the crushing property of the oil country tubular goods compared with the conventional material, and is extremely effective.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a stacking state on a base material slab.

FIG. 2 is an explanatory diagram of an example of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisaro Kamiyama 5-3 Tokai-cho, Tokai-shi, Aichi Nippon Steel Co., Ltd. Nagoya Steel Works

Claims (1)

[Claims] 1. A base slab made of a low alloy steel is laminated with a molten alloy steel having a hardenability higher than that of the base slab to form a multi-layer slab, and the multi-layer slab is hot-rolled. The laminated steel side is cooled at an average cooling rate of 10 to 100 ° C./sec, the cooling stop temperature is set to 100 to 600 ° C., and the laminated steel side of the thus obtained multi-layer hot-rolled steel strip is used as the inner surface side of the steel pipe. And a sizing amount in that case is set to 1 to 20%, and a method for producing a multi-layer type electric resistance welded oil country tubular good having excellent crushing characteristics.