JPH0598351A - Production of welded steel tube excellent in wear resistance - Google Patents

Abstract

PURPOSE:To efficiently obtain a welded steel tube excellent in wear resistance on the internal surface side by applying hot rolling to a double layer slab consisting of an outer layer material and an inner layer material, where steel compositions are respectively specified, subjecting the resulting stock to forming and to welding to form it into a steel tube, and performing heating and cooling under respectively specified conditions. CONSTITUTION:A slab composed of a high carbon low alloy steel containing, by weight, 0.2-0.6% C and 0.1-3.0% Mn is used as an outer layer material. Further, a slab composed of a low alloy steel containing 0.01-0.3% C, 0.1-3.0% Mn, and one or more kinds among 0.01-0.10% Nb, 0.01-0.10% V, 0.05-0.50% Mo, and 0.005-0.10% Ti is used as an inner layer material. A duble layer slab 3 consisting of the above slabs is hot-rolled, and the resulting stock for welded steel tube is formed into circular shape and then formed into a welded steel tube by means of welding. Subsequently, the whole tube is heated up to 800-1000 deg.C and cooled rapidly. By this method, hardening can be done and the high carbon steel layer, as the outer layer, alone can be hardened. Moreover, it is also effective to performing reheating up to 200-600 deg.C after rapid cooling, if necessary.

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 welded steel pipe having excellent wear resistance on the inner surface of the steel pipe, which is required in the fields of oil and gas excavation and transportation.

[0002]

2. Description of the Related Art With the recent demand for steel pipes, the demand for abrasion resistance on the inner surface of the steel pipes tends to increase. In the field of oil and gas excavation, development by horizontal digging has become popular, and at this time, damage due to abrasion of the inner surface of the casing pipe due to contact between the drill pipe and the casing pipe has become a problem. Further, in the case of a slurry pipe and the like, it is required to improve the abrasion resistance of the inner surface of the pipe.

In order to improve the abrasion resistance, it is effective to increase the hardness as disclosed in, for example, Japanese Patent Laid-Open No. 62-270725, but in order to achieve both the corrosion resistance and the low temperature toughness, It is not preferable to increase the hardness of the entire steel pipe. Further, in recent years, in order to cure only the vicinity of the surface of the steel pipe, techniques for spraying different metals, ceramics, etc., and methods for applying surface treatment have been studied, but none of them is a good measure from the viewpoint of productivity.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks and provides an efficient method for producing a welded steel pipe excellent in abrasion resistance on the inner surface side without impairing productivity.

[0005]

The essential point of the present invention is that the outer layer component material is C: 0.2 to 0.6 wt% and Mn: 0.
A low-alloy steel with a high carbon content and a basic component of 1 to 3.0 wt% and excellent wear resistance, with a C: 0.01-
0.3 wt%, Mn: 0.1 to 3.0 wt% as a basic component, Nb: 0.01 to 0.10 wt%, V: 0.01 to
0.10 wt%, Mo: 0.05 to 0.50 wt%, Ti:
A slab made of a low alloy steel containing one or more of 0.005 to 0.10 wt%, the multi-layer slab is hot rolled to produce a material for welded steel pipe, and the material for welded steel pipe is used. Forming into a circular shape, then welding to form a welded steel pipe, and then heating the entire pipe to 800 ° C. to 1000 ° C., and then cooling, a method for producing a welded steel pipe having excellent wear resistance characteristics,
Also, the outer layer component material is C: 0.2 to 0.6 wt%, Mn:
Low alloy steel with high carbon content and excellent wear resistance with 0.1 to 3.0 wt% as the basic component, and C: 0.0
1 to 0.3 wt%, Mn: 0.1 to 3.0 wt% as a basic component, Nb: 0.01 to 0.10 wt%, V: 0.01 to
0.10 wt%, Mo: 0.05 to 0.50 wt%, Ti:
A slab made of a low alloy steel containing one or more of 0.005 to 0.10 wt%, the multi-layer slab is hot rolled to produce a material for welded steel pipe, and the material for welded steel pipe is used. After forming into a circular shape, it is welded into a welded steel pipe, and then the whole pipe is heated to 800 ° C to 1000 ° C, then cooled, and the entire pipe is reheated at 200 ° C to 600 ° C. It is a method of manufacturing a welded steel pipe having excellent wear characteristics.

As a method for producing a multi-layer slab, a known casting method such as a continuous casting method or an ingot casting method may be used. For example, a multi-layer steel material may be produced by the continuous casting method described in JP-A-63-108947. However, the means is not particularly particular.

As shown in FIG. 1, the multi-layer slab is a slab 3 in which the components of the outer layer portion 1 and the inner layer portion 2 are different. In the present invention, the outer layer portion 1 is made to have a C content higher than that of the inner layer portion 2, and the wear resistance characteristic is enhanced, whereby the wear resistance characteristic can be effectively enhanced without hardening the entire steel. ..
The thickness of the outer layer portion t at this time can be appropriately set depending on the thickness of the final product, but generally the total thickness w
5% to 20% is suitable.

The present invention will be described in detail below. The present invention relates to a welded steel pipe made of a multi-layer steel material in which the outer layer material is a low-alloy steel with a high carbon content and excellent abrasion resistance.
It is characterized in that only the high carbon component layer of the outer layer is hardened by quenching by heating to a temperature of 0 ° C. or more and 900 ° C. or less and then rapidly cooling. It is also effective to reheat at a temperature of 200 ° C. or higher and 600 ° C. or lower after rapid cooling if necessary.

Further, in the present invention, by making the inner layer component material a relatively low carbon component material, it is possible to prevent the strength of the entire pipe from increasing more than necessary, which results in corrosion resistance and low temperature. High toughness can be secured.

Next, the reasons for limiting the components of the steel in the present invention will be explained. The components of the outer layer component material are intended for wear resistance due to high hardness. It is said that the obtained hardness is governed by the amount of C when the cooling conditions after hot rolling and rolling or the tube heat treatment conditions after pipe making are the same. In the wear-resistant steel pipe of the present invention, the hardness is aimed at Vickers hardness of 400 points or more, and from this point, the C content needs to be 0.2% or more. On the other hand, when the amount of C exceeds 0.6%, cracking occurs during hot rolling and cracking during steel pipe forming.

Mn also contributes to the increase in hardness. If the lower limit of 0.1% by weight of Mn is lower than this, the curing ability is small,
And because the steelmaking cost becomes high, on the other hand, the Mn content is 3%.
If it exceeds, the steel pipe formability deteriorates and the cost increases.

Nb, V, Mo, Ti, Cu, Ni, C
Although the addition of r and B is not an essential condition of the present invention, the addition of these elements contributes to the refinement of the structure and the improvement of the hardenability, so that the selective addition is not against the gist of the present invention. .. Further, addition of Al and Si for the purpose of deoxidation and addition of Ca and Zr for the purpose of controlling the morphology of non-metallic inclusions are also within the scope of the present invention.

The components of the inner layer component material are premised on maintaining the basic performance as a steel pipe for oil wells or a slurry pipe (line pipe). C is an element necessary for obtaining strength, and if the amount of C is less than 0.01 wt%, sufficient strength cannot be obtained. On the other hand, if the amount of C exceeds 0.3 wt%, it becomes difficult to secure corrosion resistance and low temperature toughness.

Mn is also an element necessary for obtaining strength, and Mn
If the lower limit of the amount is 0.1 wt%, if the amount is lower than this, the strengthening ability is small and the steelmaking cost becomes high. On the other hand, Mn content is 3%
If it exceeds 1.0, the formability of the steel pipe deteriorates, the cost increases, and the center segregation part hardens, deteriorating the corrosion resistance and low temperature toughness.

Further, it is effective to add one kind or two or more kinds of Nb, V, Mo and Ti for the purpose of refining the structure and increasing the strength. Nb is effective for refining the austenite grains during hot rolling, brings about the refining of ferrite grains generated by the subsequent transformation, and is effective for improving the corrosion resistance and the low temperature toughness. To obtain such Nb addition effect, it is necessary to add 0.01 wt% or more. Further, the effect does not change even if added in excess of 0.10 wt%, so the upper limit was made 0.10 wt%.

V is precipitated as carbonitride after ferrite transformation, and has the effect of suppressing coarsening of ferrite grains and the effect of strengthening by the precipitate. The lower limit of 0.01% by weight of V amount is not effective at lower amount, while the V amount is 0.10 wt%.
%, The effect does not change, so the upper limit is 0.10 wt.
%.

Mo is a solid solution strengthening element that is effective in securing strength and is an element that is effective in increasing strength without deterioration of corrosion resistance and low temperature toughness. The lower limit of Mo amount is 0.05
This is because wt% has a lower strengthening ability at a lower amount. On the other hand, when the amount of Mo exceeds 0.50 wt%, the strength is increased more than necessary and the cost is increased.

Ti precipitates as carbonitrides and has an effect of suppressing coarsening of austenite grains during reheating of the slab before hot rolling and an effect of suppressing coarsening of ferrite grains after ferrite transformation. The lower limit of the Ti amount of 0.005 wt% has no effect when the amount is lower than this, while the Ti amount is less than 0.005%.
The effect does not change even if it exceeds 10 wt%, so the upper limit is
It was set to 0.10 wt%.

Although addition of Cu, Ni and B is not an essential condition of the present invention, addition of these elements contributes to an increase in strength and an improvement in hardenability, so that selective addition of the elements of the present invention is required. It does not violate the spirit.

The addition of Al and Si for the purpose of deoxidation and the addition of Ca and Zr for the purpose of controlling the morphology of non-metallic inclusions are not contrary to the gist of the present invention.

Further, it is desirable to reduce harmful elements of P and S as much as possible for the purpose of improving corrosion resistance and improving low temperature toughness.

Next, the hot rolling conditions for the multi-layer slab will be described. The heating conditions need to be set in consideration of solid solution of appropriately added alloy elements, but are not particularly limited. The finish rolling temperature and the cooling rate after finish rolling need to be set in consideration of the components of the outer layer and the inner layer and the intended overall strength, corrosion resistance, and low temperature toughness, but are not particularly limited.

The steel strip after hot rolling is used as a raw material, formed and welded to produce a steel pipe, and then the whole pipe is heat treated. The conditions at this time will be described below. Regarding the heating conditions, it is necessary to heat to the austenite region, and from that point, the lower limit temperature was set to 800 ° C. If it exceeds 1000 ° C, cracks may occur during cooling, so the upper limit was made 1000 ° C.

Next, regarding cooling conditions, although there are no particular restrictions on the cooling rate and the cooling stop temperature, a cooling rate of 10 ° C./sec or more is desirable to effectively cure the outer layer portion. The cooling stop temperature is preferably about 400 ° C. or lower in order to prevent softening due to reheat.
The cooling rate and the cooling stop temperature as described above differ depending on the required characteristics (wear resistance) and components, and the conditions may be appropriately selected.

After cooling, it is effective to reheat it if necessary. The hardness may be too high if it is rapidly cooled, and reheating, that is, tempering is effective for adjusting the hardness. Regarding the temperature in this case, if it is less than 200 ° C., there is no tempering effect, and if it exceeds 600 ° C., the outer layer portion may be softened. Therefore, the temperature range of 200 ° C. or more and 600 ° C. or less is suitable.

[0026]

EXAMPLES 1 to 8 in Table 1 are examples of the present invention. 1 to
By rolling the multi-layer slab of No. 8 into a welded steel pipe after rolling, and further subjecting the entire pipe to heat treatment, only the outer layer portion of the high carbon component is effectively hardened, and the hardness (strength) of the entire steel pipe becomes unnecessarily high. Welded steel pipes with excellent wear resistance properties have been obtained without increasing.

On the other hand, 9 and 10 in Table 1 are examples of single-layer steel pipes as comparative materials for the present invention. Since 9 has a low carbon content, the hardness is insufficient. Further, since 10 has a high carbon content, the whole is hardened by heat treatment and is not suitable for practical use.

[0028]

[Table 1]

[0029]

INDUSTRIAL APPLICABILITY The present invention makes it possible to manufacture a welded steel pipe having excellent wear resistance characteristics without increasing the hardness (strength) of the entire steel pipe more than necessary. Further, since the productivity of the present invention is high and the manufacturing cost is low, an extremely great effect in industry is expected.

[Brief description of drawings]

FIG. 1 is a perspective view showing an overview of a multi-layer slab.

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Claims (2)

[Claims] 1. A low-alloy steel having a high carbon content and excellent wear resistance characteristics, which comprises C: 0.2 to 0.6 wt% and Mn: 0.1 to 3.0 wt% as a basic component as an outer layer component material. In the inner layer component material, C: 0.01 to 0.3 wt%, Mn: 0.1 to 3.0 wt% are basic components, Nb: 0.01 to 0.10 wt%, V: 0.01 to A slab made of a low alloy steel containing one or more of 0.10 wt%, Mo: 0.05 to 0.50 wt% and Ti: 0.005 to 0.10 wt%, and the multi-layer slab is heat-treated. Hot-rolled to produce a material for welded steel pipe, formed into a circular shape using the material for welded steel pipe, and welded to form a welded steel pipe, and then the entire pipe is 800 to 1000 ° C.
A method for producing a welded steel pipe having excellent wear resistance, which comprises heating the steel sheet to a desired temperature and then cooling it. 2. The excellent wear resistance property according to claim 1, wherein the entire tube is heated to 800 ° C. to 1000 ° C. and then cooled, and then the entire tube is reheated at 200 ° C. to 600 ° C. Manufacturing method of welded steel pipe.