JPH05279738A - Manufacture of wear resistant steel pipe - Google Patents

Abstract

PURPOSE:To easily obtain a steel pipe excellent in wear resistance by subjecting a steel sheet using, as stock, a double-layered slab using low alloy steel contg. high carbon components as an external layer material and low alloy steel contg. low carbon components as an internal layer material to forming and executing seam welding. CONSTITUTION:Low alloy steel contg. high carbon components fundamentally consisting of, by weight, 0.25 to 0.6% S, <=0.6% Si, 0.5 to 3% Mn and <=0.1% Al is used as an external layer material. Furthermore, low alloy steel consisting of 0.01 to 0.15% C, <=0.6% Si, 1.2 to 2% Mn, 0.004 to 0.3% Ti, <=0.006% N and <=0.1% Al, and the balance Fe is used as an internal layer material. A double-layered slab consisting of the internal layer material good in weldability and the external layer material having wear resistance is heated to >=1000 deg.C, and rolling is finished at >=800 deg.C. Next, it is subjected to accelerated cooling to <=550 deg.C at 5 to 40 deg.C/sec cooling rate. Then, the steel sheet is air-cooled, is thereafter subjected to UOE forming and is subjected to seam welding by an internal and external faces one layer submerged welding method.

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 wear-resistant steel pipe on the inner surface of a steel pipe required for oil or gas excavation or line pipes.

[0002]

2. Description of the Related Art In recent years, horizontal excavation has become popular when excavating oil and gas, but wear and damage on 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, it is required to improve the wear resistance of the inner surface of the pipe.

In order to improve the wear resistance, for example, as disclosed in JP-A-62-270725,
It is effective to increase the hardness of the entire steel sheet, but when UOE forming of the steel sheet is followed by latent arc welding of the inner and outer surfaces of one layer to reduce the welding time, the base metal is diluted so much that the weld metal A large amount of C is mixed in with and cracks occur in the weld metal part.

Therefore, it is not preferable to increase the hardness of the entire steel pipe. In addition, in order to suppress the occurrence of cracks during welding, it is difficult to completely prevent cracks in the weld metal even when performing inner / outer surface multilayer welding while carefully performing preheating for each layer, etc. Will increase enormously and productivity will become extremely poor.

Further, in recent years, techniques for spraying different metals, ceramics, etc., and methods for applying surface treatment to harden only the vicinity of the surface of the steel pipe have been investigated, but both are not good measures from the viewpoint of productivity. I can't say.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a manufacturing method for manufacturing a steel pipe having excellent wear resistance at low cost.

[0007]

The gist of the present invention is as a component of the outer layer material, in% by weight, C: 0.25 to 0.6%, Si:
0.6% or less, Mn: 0.5 to 3.0%, Al: 0.1
0% or less is a low alloy steel with a high carbon content and excellent wear resistance characteristics with a basic content of 0% or less.
C: 0.01 to 0.15%, Si: 0.6% or less, M
n: 1.2 to 2.0%, Ti: 0.004 to 0.03
%, N: 0.006% or less, Al: 0.10% or less, Ni: 0.05 to 4.00%, Cu: 0.
05 to 1.50%, Cr: 0.05 to 1.00%, M
o: 0.05 to 0.35%, V: 0.005 to 0.08
0%, Nb: 0.01 to 0.10%, Ca: 0.000
A multi-layer slab containing 5 to 0.005% of one kind or two kinds or more and a balance Fe and inevitable impurities of a low alloy steel is heated to a temperature of 1000 ° C or higher, and rolling is completed at a temperature of 800 ° C or higher. And then cooling at 5-40 ° C / sec for 5
This is to accelerate-cool down to 50 ° C. or lower to an arbitrary temperature, and then allow the steel plate to cool, and perform seam welding by UOE forming and a one-layer inner and outer surface latent arc welding method.

[0008]

A multi-layer slab is disclosed, for example, in JP-A-63-108947.
Although it is manufactured by the method disclosed in the publication, the slab manufacturing means is not particularly limited here. A schematic diagram of a multi-layer slab is shown in FIG. The slab 3 including the outer layer portion 1 and the inner layer portion 2 having different components is a multi-layer slab.

According to the present invention, the outer layer portion 1 is made of a low alloy steel having a high carbon content to ensure wear resistance in the outer layer portion and the inner layer portion 2
Is a low alloy steel with a low carbon content and good weldability, which suppresses the occurrence of cracks during inner-outer surface single-layer latent arc welding after UOE forming, and makes it possible to inexpensively manufacture steel pipes with excellent wear resistance. It is possible. The outer layer thickness t at this time is
It can be set appropriately according to the thickness of the final product,
Generally, about 5 to 20% of the total thickness w is suitable.

The present invention will be described in detail below. First, the reasons for limiting the steel components in the present invention will be described. The component of the outer layer material increases hardness to ensure wear resistance, and the hardness depends on the amount of C when the hot rolling and cooling conditions after rolling are constant. The wear-resistant steel pipe of the present invention is aimed at a Vickers hardness of 400 or more, and in that respect, the amount of C must be 0.25% or more. On the other hand, if the C content exceeds 0.6%, cracking occurs during hot rolling or UOE molding, so the upper limit was made 0.6%.

Si is an element contained in deoxidized upper steel,
The excessive addition impairs weldability and weld heat affected zone (HAZ) toughness. Therefore, it is necessary to set the upper limit to 0.6% or less.

Mn is an element that contributes to an increase in hardness.
If the Mn content is less than 0.5%, the hardness cannot be increased. If the Mn content exceeds 3.0%, the moldability of UOE deteriorates. Therefore, the Mn content is set to 0.5 to 3.0%.

Al is generally an element contained in deoxidized upper steel, but since deoxidation is also performed by Si and Mn or Ti, the lower limit of Al is not limited in the present invention. However, if the amount of Al increases, the cleanliness of the steel deteriorates and the HAZ toughness deteriorates, so the upper limit is made 0.1%.

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 hardenability, so that the selective addition is not against the gist of the present invention. ..
Further, addition of Ca and Zr for the purpose of controlling the morphology of nonmetallic inclusions does not impair the gist of the present invention.

The components of the inner layer material are premised on maintaining the basic characteristics of a steel pipe for oil wells and a slurry pipe (line pipe). It is necessary to add 0.01% or more of C in order to obtain the required tensile strength. However,
Excessive addition of C causes deterioration of weldability, so the upper limit is made 0.15%.

Si is an element contained in deoxidized upper steel,
The excessive addition impairs weldability and weld heat affected zone (HAZ) toughness. Therefore, it is necessary to set the upper limit to 0.6% or less.

Mn is an element useful for ensuring strength, toughness and hardenability, and it is necessary to add 1.2% or more. However, if the Mn content is too large, the weldability and HAZ toughness are deteriorated, so the upper limit is made 2.0%.

Ti is useful for suppressing coarsening of austenite grains during welding and ensuring HAZ toughness. However, addition of less than 0.004% has no effect, and addition of 0.
If it is added more than 03%, the precipitation hardening of TiC causes conversely HA.
Since the Z toughness is deteriorated, the addition amount is 0.004 to
It is limited to 0.03%.

N is generally contained in steel as an unavoidable impurity, but excessive addition of N causes deterioration of HAZ toughness, so its upper limit is made 0.006%.

Al is generally an element contained in deoxidized upper steel, but since deoxidation is also performed by Si and Mn or Ti, the lower limit of Al is not limited in the present invention. However, if the amount of Al increases, the cleanliness of the steel deteriorates and the HAZ toughness deteriorates, so the upper limit is made 0.1%.

Note that P and S are contained in steel as inevitable impurities. In the present invention, the amount is not particularly limited,
Since these deteriorate the toughness of the base material and the weld,
The amount is preferably as small as possible, 0.03 each
%, Preferably 0.01% or less.

In the steel of the present invention, if necessary, N
i: 0.05 to 4.00%, Cu: 0.05 to 1.50
%, Cr: 0.05 to 1.00%, Mo: 0.05 to
0.35%, V: 0.005-0.080%, Nb:
0.01-0.1%, Ca: 0.0005-0.005
%, Any one kind or two or more kinds may be contained.

The main purpose of incorporating these elements is to enable the strength and toughness to be improved and the production plate thickness to be expanded without impairing the characteristics of the steel of the present invention, and the addition amount thereof is weldability and HAZ toughness. It is of a nature that should be naturally restricted from the standpoint of the above.

Ni improves the strength and toughness of the base metal without adversely affecting the weldability and HAZ toughness.
If the amount is 5% or less, the effect is small, and the addition of 4.00% or more is not preferable for weldability, so the upper limit was made 4.00%.

Cu has an effect similar to that of Ni, as well as an effect of corrosion resistance, resistance to hydrogen-induced cracking, etc., but 1.50%
If it exceeds, Cu-cracks are generated during hot rolling, which makes manufacturing difficult. Therefore, the upper limit is set to 1.50%.

Cr is an element that enhances the strength of the base material,
It is necessary to add 0.05% or more. However, if the amount of Cr exceeds 1.00%, the weldability and HAZ toughness deteriorate, so the upper limit is made 1.00%.

Mo is an element that improves the strength of the base material, and its effect is not achieved unless it is added in an amount of 0.05% or more. However, if it exceeds 0.35%, the weld zone toughness and weldability are deteriorated, which is not preferable, so the upper limit is limited to 0.35%.

V is an element to be added for making the rolling structure finer and strengthening the precipitation. It is an element that improves both strength and toughness, but if it is less than 0.005%, its effect is not sufficiently obtained, and 0 is obtained. If it exceeds 0.080%, it is harmful to the weldability and weld toughness, so the range is 0.005-0.08.
Limited to 0.

Nb contributes to grain refinement and precipitation hardening, and has the effect of strengthening the steel. In order to exert this effect, it is necessary to add 0.01% or more of Nb. However, if Nb is added in an amount of 0.1% or more, the toughness of the welded portion deteriorates, so the upper limit was made 0.1%.

Ca controls the sulfide morphology, increases Charpy absorbed energy and improves low temperature toughness.
Also effective in improving hydrogen-induced cracking resistance. But C
If the amount of a is 0.0005% or less, there is no practical effect, and if it exceeds 0.005%, large amounts of CaO and CaS are formed to form large inclusions, which impair not only the toughness of the steel but also the cleanliness. Since the weldability is also adversely affected, the range of the Ca addition amount is set to 0.0005 to 0.005%.

Next, the hot rolling conditions for the multi-layer slab will be described. First, the heating temperature of the slab needs to be 1000 ° C. or higher. If the heating temperature is less than 1000 ° C., the austenite grains of the outer layer material become extremely fine, and the hardenability deteriorates during cooling, so that the increase in hardness becomes insufficient. Also, in the inner layer material, the solid solution of Nb and V is insufficient and the strength cannot be secured.

Next, the rolling end temperature must be 800 ° C. or higher. When the rolling is completed at less than 800 ° C., the austenite is excessively fine-grained or stretched, so that the hardenability is lowered and the hardness of the outer layer material is insufficiently increased.

Next, the cooling after rolling is performed at a cooling rate of 5 to 40.
Accelerated cooling to an arbitrary temperature of 550 ° C. or less at ℃ / sec, and then cooling. The reason why the cooling rate is 5 to 40 ° C / sec is
If it is less than 5 ° C / sec, the hardness of the outer layer material is insufficiently increased, and if it exceeds 40 ° C / sec, coarse and large amounts of martensite are produced, which deteriorates ductility and causes cracking. Because it induces.

The cooling stop temperature is designated as an arbitrary temperature of 550 ° C. or lower, when the cooling stop temperature exceeds 550 ° C.
This is because the outer layer material softens during cooling after cooling is stopped and the increase in hardness becomes insufficient, and a sufficient strength increase cannot be expected in the inner layer material. The lower limit of the cooling stop temperature varies depending on the required characteristics and components, but the conditions can be appropriately selected. As the cooling medium, spray water or water is generally suitable.

When the steel produced according to the present invention is reheated for the purpose of dehydrogenation or the like, if it exceeds 600 ° C., the strength is deteriorated, which is not preferable. However, reheating to a temperature of about 600 ° C. or less does not impair the characteristics of the present invention, although the strength is slightly reduced.

The steel sheet produced under the above conditions is UO
After E-forming, seam welding is performed by the inner and outer surface single layer latent arc welding method. In order to manufacture a steel pipe at low cost, it is essential to reduce the welding time, and the seam welding by the inner and outer surface one-layer latent arc welding method is effective. At this time, if the hardness of the entire steel sheet is extremely high, cracking occurs during inner-outer surface single-layer latent arc welding.

However, this multi-layered steel sheet uses low carbon low alloy steel having good weldability as the inner layer material, and the ratio of the inner layer material to the total thickness is 80% or more. Even in such a case, welding cracks can be prevented in advance by setting the welding material and welding conditions while paying attention to the dilution rate, and a steel pipe having excellent wear resistance can be manufactured at low cost.

[0038]

EXAMPLES Table 1 shows the chemical composition, production conditions and mechanical properties of the test steel pipes. After manufacturing steel sheets of various thicknesses, U
The mechanical properties of the steel pipe produced by OE molding and the inner-outer surface single-layer latent arc welding method, and the crack generation state of the seam weld were investigated. The tensile properties were investigated using API tensile test pieces, and the Charpy properties were examined using JIS No. 4 test pieces taken from the 1/4 t part of the inner layer material. Regarding the wear resistance, the outer layer material was measured with a Vickers hardness meter, and the target was Hv 400 or higher. In Table 1, Steels 1 to 4 are steels of the present invention, and 5 to 11 are comparative steels.

[0039]

[Table 1]

[0040]

[Table 2]

Steels 1 to 4 of the present invention show good wear resistance without cracking at seam welds. On the other hand, in Comparative Steel 5, since the slab reheating temperature is too low, the hardness of the outer layer material is low and good wear resistance cannot be obtained, and at the same time, sufficient strength cannot be obtained with the inner layer material. In Comparative Steel 6, the rolling finish temperature is too low, so the hardness of the outer layer material is low, and good wear resistance cannot be obtained. Comparative Steel 7 has a low cooling rate at the time of accelerated cooling, so that the hardness of the outer layer material is low, and good wear resistance cannot be obtained.

Comparative steel 8 deteriorates in toughness because the cooling rate during accelerated cooling is too high, and cracks occur in the outer layer material. Since the comparative steel 9 has an excessively high cooling stop temperature, the hardness of the outer layer material is low, so that good wear resistance cannot be obtained, and at the same time, sufficient strength cannot be obtained with the inner layer material. Since the comparative steel 10 is a single-layer slab with a high C content, its toughness deteriorates and cracks occur during seam welding. Since the comparative steel 11 is a single-layer slab of low C component system, the hardness of the surface layer is low and the wear resistance is deteriorated.

[0043]

INDUSTRIAL APPLICABILITY The present invention provides a means for inexpensively producing a steel pipe having excellent wear resistance, and this steel pipe can be expected to have a very great industrial effect.

[Brief description of drawings]

FIG. 1 is a schematic view of a multi-layer slab.

[Explanation of symbols] 1 outer layer 2 inner layer 3 slab

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C22C 38/14 38/50

Claims (2)

[Claims] 1. As a component of the outer layer material, in% by weight, C: 0.25 to 0.6%, Si: 0.6% or less, Mn: 0.5 to 3.0%, Al: 0.10% Below is a low content of high carbon components with excellent wear resistance characteristics based on
Gold steel, in% by weight as a component of the inner layer material, C: 0.01 to 0.15%, Si: 0.6% or less, Mn: 1.2 to 2.0%, Ti: 0.004 to 0 0.03%, N: 0.006% or less, Al: 0.10% or less, balance multi-layer made of low alloy steel containing Fe and unavoidable impurities
The slab is heated to a temperature of 1000 ° C or higher, 800 ° C or higher
At the cooling rate of 5-40 ° C / sec.
Accelerated cooling to an arbitrary temperature below 550 ° C, then let it cool
Steel plate is UOE-formed and seamed by inner-outer surface 1-layer latent arc welding method
A method for manufacturing a wear-resistant steel pipe characterized by welding. 2. In% by weight as a component of the inner layer material, Ni: 0.05 to 4.00%, Cu: 0.05 to 1.50%, Cr: 0.05 to 1.00%, Mo: 0 0.05 to 0.35%, V: 0.005 to 0.080%, Nb: 0.01 to 0.10%, Ca: 0.0005 to 0.005%, or a combination of two or more thereof. The method for producing a wear-resistant steel pipe according to claim 1, wherein