KR20170035563A - Austenitic high manganese steel pipe using electric resistance welding and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a steel pipe having high strength, excellent impact toughness at ultra-low temperatures, and excellent performance of pipe expansion; and a method of manufacturing the same. The method of manufacturing the steel pipe comprises: a first step of cutting a high manganese steel coil, wound as a coil, in accordance with a desired diameter; a second step of unwinding the high manganese steel coil cut and wound; a third step of trimming both sides of the high manganese steel to obtain processability of a welding unit; a fourth step of molding the high manganese steel with both trimmed sides; and a fifth step of manufacturing a steel pipe by welding the molded high manganese steel. The high manganese steel is an austenite-based hot-rolled steel material which comprises 13-33% of manganese with respect to a total weight. In the fifth step, the steel pipe is manufactured by high frequency electric resistance welding.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to austenitic high manganese steel pipe manufactured using electric resistance welding,

The present invention relates to a steel pipe excellent in expansion performance and impact toughness at a cryogenic temperature, and a method for producing the same. More specifically, the present invention relates to a steel pipe excellent in expanding performance and high impact toughness at high temperatures, which is produced through high-frequency electric resistance welding using a high-strength hot-rolled steel sheet of an austenitic structure including high manganese steel, and a manufacturing method thereof.

Crude oil and natural gas are becoming increasingly important energy sources. Most of the world's major natural gas producers are far from major markets. As such, pipelines must cross over long distances either onshore or underwater, which can cause severe deformation on the pipeline. The arctic regions undergoing earthquake active areas and / or cycles of frost-heave and thawing settlement can cause severe deformation on the pipeline. Also, pipelines lying over the sea bed undergo severe deformation due to position variations or warping caused by water currents.

Therefore, the line pipe used in such an environment requires an excellent uniform elongation in the longitudinal direction of the pipe and an excellent deformation ability such as a low yield-to-tensile strength ratio or a yield ratio (YR) in order to secure mechanical integrity.

Further, since high-pressure gas or crude oil flows through the steel pipe, a high pressure acts directly on the steel pipe, and therefore, it is required to increase the strength of the steel pipe.

However, in general, when the strength of the material is increased, the toughness is reduced. This is because alloying elements that are normally added serve to inhibit toughness even though they have a favorable effect on the strength.

In particular, in the case of LNG carriers, the LNG piping must maintain a cryogenic temperature of -196 ° C., and a steel pipe excellent in impact toughness is required even at such a low temperature condition.

A steel pipe having a high manganese content and elongation rate is required to have excellent impact toughness, and there is a problem that the steel pipe must satisfy the strength to withstand the high pressure inside.

철을 의미하며, 강을 A₁변태점(726℃) 이상으로 가열하였을 때 이루어지는 조직이다. 이러한 오스테나이트는 탄소 함유량에 따라 물리적, 기계적 성질을 달리하고, 망간(Mn)의 함유량에 따라 물성이 크게 달라지는 성질이 있다.The satisfaction of strength can be satisfied by a method using high strength steel. The base material that can be used at this time is austenitic high strength steel. Austenite is a carbon-

Means iron, and is a structure formed when the steel is heated to an A ₁ transformation point (726 ° C) or higher. These austenites have physical and mechanical properties that vary depending on the carbon content and properties that vary greatly depending on the content of manganese (Mn).

However, in the case of high manganese steel in which the content of manganese is 13 to 33% of the total weight of the base material, general TIG welding or PAW (plasma arc welding) is used and stable quality is ensured. However, Falls.

And there conventional arc welding method for welding the securing sound weld metal of the vagina with a high efficiency is disclosed as a technique, C, Si, Mn, Cr , Ni, the N content comprises a particular welding wire with PbO and CaF _2, CaO , MgO, SiO ₂ , and Al ₂ O ₃ . However, the above technology relates to a welding wire and a flux for submerged arc welding applied to a high plate high manganese steel, and it is difficult to apply the welding wire and flux to a thin steel welded steel pipe.

In order to solve the above problems, there is a demand for a steel pipe excellent in shock resistance at extremely low temperature and excellent productivity for producing the steel pipe with high strength, high tensile strength, high expansion ratio and excellent manganese content.

Korean Patent Application Publication No. 10-2013-0073472 Korean Patent Application Publication No. 10-2008-0034903 Korean Patent Application Publication No. 10-2008-0034903

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a steel pipe excellent in expansion performance and impact toughness at a cryogenic temperature.

Further, the present invention is intended to provide a user with a steel pipe in which high manganese steel is easily welded through electric resistance welding.

In addition, it is intended to provide a user with a steel pipe for piping of LNG used at a very low temperature.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are not intended to limit the invention to the precise form disclosed. It can be understood.

One example of a method for manufacturing an austenitic high manganese steel pipe for solving the above problems is a method for manufacturing a high manganese steel pipe that includes a first step of cutting a dried high manganese steel coil to a desired diameter, a second step of unwinding the high- A fourth step of forming the high manganese steel having both sides trimmed in both sides, and a fifth step of welding the formed high manganese steel to manufacture a steel pipe, in order to ensure workability of the welded part, , The high manganese steel is an austenitic hot-rolled steel having manganese content of 13% to 33% based on the total weight, and the fifth step can produce a steel pipe by high-frequency electric resistance welding.

A sixth step of performing heat treatment to soften the welded portion of the steel pipe, a seventh step of cooling the heat treated steel pipe, and an eighth step of calibrating the shape of the steel pipe to make the cooled steel pipe into a garden shape .

The fifth step may include the step of injecting an inert gas into the closed space into which the formed high manganese steel is introduced to remove oxygen in the closed space.

Further, the inert gas may be argon gas or a gas in which argon and hydrogen are mixed.

The fifth step may include uniformly injecting the inert gas onto the inner and outer surfaces of the formed high manganese steel.

In the fifth step, the high manganese steel may be welded at a welding heat input of 170 KW to 190 KW.

Meanwhile, an example of austenitic high-manganese steel pipe for solving the above-mentioned problems may be one produced by the above-mentioned manufacturing method.

The steel pipe may have a tensile strength of 800 MPa or more and an elongation of 60% or more.

Further, the steel pipe may have an expanding performance of 30% or more.

Further, the steel pipe may have a flatness performance of 40% or more.

INDUSTRIAL APPLICABILITY The present invention can provide a user with a steel pipe having high strength, excellent expanding performance, and excellent impact toughness at a very low temperature.

Further, it is possible to provide a steel pipe to a user which is easily welded through electric resistance welding of high manganese steel.

Further, it is possible to provide a user with a steel pipe for piping an LNG ship which is used at a very low temperature.

It should be understood, however, that the effects obtained by the present invention are not limited to the above-mentioned effects, and other effects not mentioned may be clearly understood by those skilled in the art to which the present invention belongs It will be possible.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate a preferred embodiment of the invention and, together with the description, serve to provide a further understanding of the technical idea of the invention, It should not be construed as limited.
Fig. 1 is a table showing conditions of Experiment 1 relating to welding of high manganese steel used in the present invention. Fig.
2 is a table showing the results of Experiment 1 relating to welding of high manganese steel used in the present invention.
3 is a table showing conditions of Experiment 2 for welding of high manganese steel used in the present invention.
4 is a table showing the results of Experiment 2 relating to welding of high manganese steel used in the present invention.
5 is a flowchart showing a method of manufacturing a steel pipe used in the present invention.
Fig. 6A is an example of a picture in the conventional electric resistance welding.
FIG. 6B is an example of a diagram of electrical resistance welding used in the present invention.
7 is a table showing the properties of the high manganese steel used in the present invention.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. In addition, the embodiment described below does not unduly limit the contents of the present invention described in the claims, and the entire configuration described in this embodiment is not necessarily essential as the solution means of the present invention.

As the development of oilfields in cold climates with bad climatic conditions becomes active, toughness of reinforced steel pipes at low temperatures is required, and steel pipes excellent in impact toughness even at extremely low temperature like piping for handling LNG gas are required.

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a steel pipe having high strength, excellent impact toughness at a cryogenic temperature, and excellent expanding performance.

Hereinafter, a manufacturing method of the steel pipe will be examined through an experiment.

The objective of the experiment is to produce an austenitic high manganese steel pipe with excellent expanding performance and excellent impact toughness at cryogenic temperature. The ultimate goal is steel pipe with tensile strength of 800Mpa or more and elongation of 60% or more and its manufacturing method .

High manganese steel used in the experiment is hot rolled steel with manganese content of 13 ~ 33%.

The manganese (Mn) contained in the hot-rolled steel can prevent excessive ferrite formation, which can lead to a reduction in plate strength, particularly at the thickness-intermediate position of such a plate. Further, manganese has been found to be very fine, such as ras martensite, lower bainite and modified upper bainite, through its powerful effect of delaying ferrite, pearlite, granular bainite and upper bainite transformation products of austenite during cooling of the austenite. And provides processing flexibility to produce alternate strong second phases in the tissue. In addition, sulfur (S) and sulfide (MnS) that can be incorporated as impurities are formed and the hot workability is improved. However, when the amount of manganese added is less than 13 wt%, the strength is increased due to the generation of a '(alpha re-) -martensite phase which damages the formability. However, The strength increases but the ductility decreases. When the amount of manganese added is more than 33% by weight, hardness is increased and cracking of hot rolling is likely to occur, which may destabilize steel and impair workability and weldability.

The hot-rolled steel material may include aluminum (Al), is generally added for deoxidation of steel, and may be added for ductility enhancement. In other words, aluminum is a stabilizing element in the ferrite phase, but increases the stacking fault energy at the slip side of the steel to suppress the formation of the ε-Martensite phase, thereby improving ductility. In addition, aluminum suppresses the formation of ε-martensite phase even in the case of low manganese addition, which contributes to minimizing addition of manganese and improving workability.

Since the hot-rolled steel may contain carbon and carbon (C) contributes to stabilize the austenite phase, it is advantageous as the addition amount thereof increases, and a '(alpha re-) Carbon is added in an amount of 0.3% by weight or more in order to prevent inhibition and deterioration of ductility. Further, in order to prevent the workability from being lowered due to the transition of the deformation behavior due to the slip deformation by increasing the stability of the austenite phase considerably, the addition amount of carbon is added to 1.5% or less.

The hot-rolled steel may include silicon. Silicon (Si) is an element that strengthens the solute, and is an element that increases the yield strength by reducing the grain size by the effect of the solid solution. It is known that when excessively added, a silicon oxide layer is formed on the surface to lower the melting strength. However, in a steel containing a large amount of manganese added, when a proper amount of silicon is added, a thin silicon oxide layer is formed on the surface to inhibit the oxidation of manganese so that a thick manganese oxide layer formed after rolling in the cold-

And it is possible to prevent the corrosion proceeding in the cold rolled steel sheet after annealing to improve the surface quality and to maintain the excellent surface quality as the base steel sheet of the electroplating material. However, when the amount of added silicon is increased, silicon oxide is formed on the surface of the steel sheet during hot rolling, which deteriorates the pickling ability and deteriorates the surface quality of the hot-rolled steel sheet. Silicon is also concentrated on the surface of the steel sheet during high temperature annealing in the continuous annealing process and continuous hot dip galvanizing process, thereby reducing the wettability of the molten zinc on the surface of the steel sheet during the hot dip coating, thereby reducing the plating ability. In addition, the addition of a large amount of silicon greatly reduces the weldability of the steel. Therefore, it is preferable that the upper limit content of silicon is 0.5 wt%.

In addition, the hot-rolled steel may contain a small amount of titanium (Ti), vanadium (V), nitrogen (N), and niobium (Nb).

Titanium (Ti) is used in the columnar phase to increase the melting temperature of a low melting point compound in which aluminum is concentrated to prevent the formation of a liquid film at 1300 ° C or lower and to increase the affinity with nitrogen, And acts as nuclei for aluminum nitride precipitation to strengthen the columnar grain boundaries. However, when the content is less than 0.005% by weight, there is no effect. When the content exceeds 0.10% by weight, excessive titanium segregates in the crystal grain boundaries,

Vanadium (V) is preferably added in an amount of more than 0% by weight as a component added for increasing the strength. When the addition amount of vanadium is 0.5% by weight or more, a low melting point compound is produced to deteriorate hot workability. % Or less.

Nitrogen (N) acts on aluminum during coagulation in austenite grains to precipitate fine nitrides to promote twinning, thereby improving the strength and ductility of the steel sheet. However, as the content of nitrogen increases, nitride is excessively precipitated It is preferable that the content of nitrogen is 0.01% by weight or less because it lowers hot workability and elongation.

Niobium (Nb) is a strong carbide-forming element that forms a carbide by bonding with carbon in the form of titanium. The carbide formed at this time is an element effective in refining crystal grains by inhibiting crystal grain growth and forms a precipitate phase at a temperature lower than that of titanium tetrachloride, which is a great element for crystal grain size refinement and precipitation strengthening effect by precipitation phase formation. However, when the content of niobium is small, the effect intended by the present invention can not be secured, and the lower limit of niobium is preferably limited to 0.02 wt%. On the other hand, as the content of niobium increases, excessive amounts of niobium are segregated in the crystal grain boundaries to cause intergranular entanglement, or the precipitated phase is excessively coarsened to lower the crystal grain growth effect, so that the upper limit of niobium is limited to 0.10 wt% .

Calcium (Ca) is added for the purpose of improving electrical resistance weldability by inhibiting the formation of MnS inclusions by forming CaS inclusions. That is, calcium (Ca) has a higher affinity with sulfur than manganese (Mn), so CaS inclusions are formed and CaS inclusions are reduced when calcium is added. Such MnS is stretched during hot rolling to cause hook defects and the like in electrical resistance welding (ERW), so that electrical resistance weldability can be improved. The calcium (Ca) is preferably added in an amount of 0.0001 to 0.0020 wt% of the total weight of the steel sheet for a line pipe according to the present invention. When the content of calcium (Ca) is less than 0.0001 wt%, the above MnS control effect can not be exerted properly. On the contrary, when the content of calcium (Ca) exceeds 0.0020% by weight, generation of CaO inclusions is excessively generated, which deteriorates performance and electrical resistance weldability.

The hot-rolled steel may further contain iron and other impurities.

<Experiment 1>

In Experiment 1, the results of the expansion performance, strength, and flatness of the steel pipe according to presence or absence of oxygen during the electrical resistance welding are derived, and it is examined whether or not to remove oxygen during welding.

Fig. 1 is a table showing conditions of Experiment 1 relating to welding of high manganese steel used in the present invention. Fig. At this time, welding of high manganese steel is performed by high frequency electric resistance welding.

Referring to FIG. 1, the same welding heat input amount (145 KW), the same gauging speed (25 M / min) and the same up-set amount (3.0 mm)

Condition 1 is to minimize the oxygen concentration in the closed space by injecting an inert gas into the closed space when performing electrical resistance welding in a closed space. That is, the oxygen concentration is reduced to 0.1% or less.

Condition 2 is the case of applying the inert gas in the closed space and reducing the oxygen concentration to 5% when the electric resistance welding is performed in the closed space.

Condition 3 corresponds to the case where electric resistance welding is performed in the atmosphere.

2 is a table showing the results of Experiment 1 relating to welding of high manganese steel used in the present invention.

Referring to FIG. 2, the performance of the steel pipe produced through the welding of high manganese steel is checked. At this time, the performance of the steel pipe can be judged by the expansion performance, strength and flatness. At this time, the expansion performance test is evaluated by the flaring expansion test using the maximum expansion rate up to the point of occurrence of the crack.

In expanding performance, it is confirmed that the conditions 1 and 2 are 15% and the condition 3 is 8%.

Considering the intensity of the crushing of the steel pipe in terms of strength, condition 1 requires energy of 13J, condition 2 requires energy of 12J, and condition 3 requires energy of 4J

In the flatness, it is understood that Condition 1 is 15%, Condition 2 is 13%, Condition 3 is 5%.

That is, according to FIG. 2, it can be confirmed that the steel pipe having the best performance is generated in the case of Condition 1. By injecting an inert gas in a confined space to remove oxygen and welding, the steel pipe's expanding performance, strength and flat performance are both excellent. This is because, during welding, the welded portion is oxidized by the oxygen near the welded portion.

Therefore, in Experiment 1, in electrical resistance welding, it is preferable to weld while minimizing the oxygen concentration through the introduction of an inert gas in the closed space. In particular, welding is preferably performed by adjusting the oxygen concentration to 0.1% or less.

<Experiment 2>

In Experiment 2, the results of the expansion performance, strength, and flatness of the steel pipe according to the amount of welding heat during the electrical resistance welding are derived, and the proper amount of welding heat input during welding is examined.

3 is a table showing conditions of Experiment 2 for welding of high manganese steel used in the present invention.

3, the same oxygen concentration (0.1%), the same gauging speed (25M / min), and the same up-set amount (3.0mm) were applied.

Electrical resistance welding is performed in a confined space, and inert gas is injected into the confined space to minimize the oxygen concentration in the confined space and to weld at a rate of 0.1% or less.

Condition 1 was 145 KW for welding, 145 KW for welding heat input for welding, Condition 2 was 175 KW for welding, Condition 3 was 185 KW for welding, Check.

4 is a table showing the results of Experiment 2 relating to welding of high manganese steel used in the present invention.

Referring to FIG. 4, the performance of the steel pipe produced through the welding of the high manganese steel is checked. At this time, the performance of the steel pipe can be judged by the expansion performance, strength and flatness.

In the expanding performance, it is confirmed that the condition 1 is 15%, the condition 2 is 24%, and the condition 3 is 30%.

Considering the intensity of the crushing of the steel pipe in terms of strength, condition 1 requires energy of 13J, condition 2 requires energy of 19J, and condition 3 requires energy of 30J

In the flatness, it can be seen that Condition 1 is 15%, Condition 2 is 20%, Condition 3 is 40%.

That is, according to FIG. 4, it can be confirmed that the steel pipe having the best performance is generated in the condition 3. By increasing the amount of heat input by welding, electric resistance welding improves both the expansion performance, strength and flat performance of the steel pipe.

However, as the heat input of the weld is increased, the performance of the steel pipe is not improved indefinitely, and the cooling rate is slow, so there is a large amount of time to diffuse due to concentration unevenness, Cellular growth is facilitated, so that ductility is increased, but the hardness value is reduced.

Therefore, according to the results of Experiment 2, it is preferable that the heat input amount of welding is 170 KW or more in order to produce a steel pipe excellent in expanding performance desired by the present invention and excellent in impact toughness at a cryogenic temperature. Further, it is more preferable that the heat input amount of the weld be 190 KW or less in order to prevent a decrease in hardness value.

As described above, in order to produce a steel pipe excellent in expanding performance and excellent impact toughness at the cryogenic temperature in Experiments 1 and 2, the welded portion is welded in the closed space, and the oxygen concentration is lowered through the introduction of the inert gas. And most preferably, the welding heat input amount in welding is 170 KW to 190 KW.

The steel pipe produced by this manufacturing method has a tensile strength of 800 MPa or more and an elongation of 60% or more.

<Manufacturing Method>

Meanwhile, a method of manufacturing a steel pipe will be examined using specific set values obtained through the above-described experiments.

FIG. 5 is a flow chart of a method of manufacturing a steel pipe used in the present invention, FIG. 6A is an example of a conventional electric resistance welding, and FIG. 6B is an example of electrical resistance welding used in the present invention.

Referring to FIG. 5 for manufacturing a steel pipe using high manganese steel, a manufacturing method is started to prepare high manganese steel. At this time, the high manganese steel is an austenitic hot-rolled steel having manganese of 13 to 33% based on the total weight.

The method for manufacturing the steel pipe starts from the step of cutting (S110) the high manganese steel coil to the desired diameter and then the high manganese steel is supplied to the manufacturing of the steel pipe through the step of loosening the dried high manganese steel (S120).

When the supply of the high manganese steel starts, the steel pipe is manufactured through welding on both sides of the supplied high manganese steel. At this time, the step of finishing both sides of the high manganese steel is performed in step S130 in order to secure the workability of the welded part.

After both sides of the high manganese are trimmed, a step of forming a high manganese steel (S140) proceeds. At this time, high manganese steel is deformed into a steel pipe shape by molding.

A step of deforming the high manganese steel into a steel pipe shape, and then welding the formed high manganese steel to manufacture a steel pipe (S150). At this time, it is preferable to weld the high manganese steel through electric resistance welding, and as described above, welding in a sealed space is more preferable.

Referring to FIGS. 6A and 6B, as shown in FIG. 6A, in the conventional case, the base material is heated and melted in the air, and the base material is welded by a press roll. Particularly, cooling water was used for cooling around the welded part. When the welding is performed in this way, the cooling water / tubular oil permeates both sides of the high manganese steel, steam is generated by the heat, and the oxygen component of the cooling water / gaseous oil reacts with the high manganese steel welded portion, and oxidation inclusions such as MnO and MnSiO ₂ are likely to be generated. However, in the case of the present invention, as shown in FIG. 6B, the base material is heated, melted, and welded by a press roll, but the process proceeds in a closed space. Therefore, unlike the prior art, cooling water is not used.

In addition, it is preferable to insert the inert gas into the closed space and weld in an oxygen-free atmosphere in which oxygen is removed. At this time, the oxygen concentration is more preferably 0.1% or less.

The inert gas to be introduced may include nitrogen, hydrogen, helium, neon, argon and the like, and more preferably, argon gas or argon and hydrogen are mixed. In addition, it is more preferable that the inert gas is evenly injected into the inside and outside of the high manganese steel which has been molded and shaped into a steel pipe.

On the other hand, it is preferable that the welding heat input amount is 170 KW to 190 KW as confirmed in Experiment 2 above.

In addition, a step of cutting the beads generated by welding at the time of molding may be included. In this case, it is more preferable to cut the bead so that the bead is maintained at a height of 0 mm to 0.3 mm.

After the high manganese steel is welded to produce a steel pipe, a heat treatment (S160) is performed to soften the welded portion of the steel pipe. At this time, it is preferable to perform heat treatment at a temperature of 800 ° C to 850 ° C. The softened welded portion may be processed and the hardness may be increased.

After the heat treatment, the step of cooling the heat-treated steel pipe (S170) proceeds.

After the heat-treated steel pipe is cooled, the shape of the steel pipe is corrected (S180) in order to make the cooled steel pipe into a garden shape. At this time, the calibration includes reduction and expansion of the steel pipe, and it is desirable that the correction is performed in the range of 2 to 5% of the final deformation amount. This makes it possible to secure the quality of the steel pipe.

<High Manganese Steel Pipe>

7 is a table showing properties of a high manganese steel pipe used in the present invention.

The basic characteristics of the steel pipe are affected by the characteristics of the base material. However, the physical properties of the steel pipe can also be changed through the manufacturing method of the steel pipe.

Referring to FIG. 7, in the present invention, one example of the steel pipe manufactured by the above-described manufacturing method has a diameter of 89.1 mm to 114.3 mm and a thickness of 3.0 T to 5.5 T, wherein manganese is 13 to 33% And has a tensile strength of 850 MPa to 900 MPa, a yield strength of 450 to 600 MPa, an elongation of 55 to 70%, and a hardness of 230 to 250 HV.

The steel pipe having the above-mentioned physical properties has an expansion performance of 30% or more and excellent impact toughness even at a very low temperature (-196 DEG C). Therefore, it can be used as a cryogenic LNG gas handling steel pipe and can be used for LNG ship piping.

100: Steel pipe
200: rolling roll
300: electric resistance welded part
310: Wires
400: gas inlet portion
1000: Sealed space

Claims (10)

A method for manufacturing an austenitic high manganese steel pipe excellent in high strength, cryogenic impact toughness and expansion performance,
A first step of cutting the dried high manganese steel coil to a desired diameter;
A second step of loosening the high-manganese steel coil cut and dried;
A third step of polishing both sides of the high manganese steel to secure the workability of the welded part;
A fourth step of forming the high manganese steel having both sides trimmed; And
A fifth step of manufacturing a steel pipe by welding the formed high manganese steel;
&Lt; / RTI &gt;
The high manganese steel is an austenitic hot-rolled steel having manganese content of 13% to 33%
The method of manufacturing an austenitic high-manganese steel pipe according to claim 5, wherein the fifth step is a step of producing a steel pipe by high-frequency electrical resistance welding.
The method according to claim 1,
A sixth step of performing heat treatment to soften a welded portion of the steel pipe;
A seventh step of cooling the heat-treated steel pipe; And
And a step of calibrating the shape of the steel pipe to make the cooled steel pipe into a quarry shape.
The method according to claim 1,
In the fifth step,
And removing the oxygen in the closed space by injecting an inert gas into the closed space into which the formed high manganese steel is introduced.
The method of claim 3,
The inert gas may include,
Argon gas or a mixture of argon and hydrogen. &Lt; RTI ID = 0.0 &gt; 21. &lt; / RTI &gt;
The method of claim 3,
In the fifth step,
And uniformly spraying the inert gas on the inner and outer surfaces of the formed high manganese steel. &Lt; RTI ID = 0.0 &gt; 21. &lt; / RTI &gt;
The method according to claim 1,
In the fifth step,
Wherein the high manganese steel is welded at a welding heat input of 170 KW to 190 KW.
Austenitic high manganese steel pipe produced by the method of any one of claims 1 to 6.
8. The method of claim 7,
In the steel pipe,
A tensile strength of 800 MPa or more,
And an elongation percentage of 60% or more.
8. The method of claim 7,
In the steel pipe,
And the expansion performance is 30% or more.
8. The method of claim 7,
In the steel pipe,
And a flatness performance of 40% or more.

Images