JPH06128631A - Production of high manganese ultrahigh tensile strength steel excellent in low temperature toughness - Google Patents

Abstract

PURPOSE:To obtain high manganese ultrahigh tensile strength steel having low temp. toughness in the base metal and furthermore excellent in toughness in the weld zone by subjecting steel contg. specified C, Si, Mn, P, S, Al, B and N to hot rolling, heating and cooling under prescribed conditions. CONSTITUTION:Steel having a compsn. constituted of, by weight, 0.01 to 0.06% C, 0.01 to 1% Si, 6 to 15% Mn, <=0.005% P, <=0.01% S, 0.005 to 0.1% Al, 0.0003 to 0.01% B and <=0.01% N, and the balance Fe is refined. This steel is heated to >=1000 deg.C, is thereafter subjected to hot rolling and is successively reheated to the transformation point to 1000 deg.C. Next, it is cooled at >=0.1 deg.C/S average cooling rate in the temp. range of 700 to 300 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a tensile strength of 100 kg.
It relates to a method for producing a high-manganese ultra-high-strength steel having f / mm ² or more, which has good low temperature toughness of the base material and excellent toughness of the welded portion.

[0002]

2. Description of the Related Art At present, welded structural steel is used in various fields and has a strength level of 40 to 100 kgf / m in tensile strength.
Used in a wide range of about m ² . In recent years, the use of high-strength high-strength steel has been increasing in order to increase the size of structures and save energy. Tensile strength is 70 even among high strength steel
High-strength steels exceeding -80 kgf / mm ² are generally manufactured by quenching and tempering. Although there is a manufacturing method such as direct quenching in which quenching is performed subsequent to rolling, this is also in the category of quenching. So-called tempered high-strength steel, which is manufactured by quenching and tempering, usually requires sufficient quenching to the center of the plate thickness to secure strength and toughness.
It contains alloy elements such as Ni, Cu, Cr and Mo. In particular, in the case of a thick material or when severe low temperature toughness of -60 ° C or less is required, in order to secure hardenability and toughen the matrix, a large amount of alloying elements mainly containing Ni should be added. Will be needed. Steel containing a large amount of Ni, Cr, Mo, etc. is inevitably very expensive as compared with ordinary steel materials, and therefore cannot be widely used for structures in general.
Therefore, it is desired to establish a manufacturing technique of a high-strength steel that can be manufactured inexpensively even under the requirements of thick materials, severe strength, and low temperature toughness, and that has excellent welded joint toughness under various welding conditions.

The present inventors have previously proposed Japanese Patent Application No. 3-144089.
No. 6 in the steel containing 6 to 15% of Mn, B is added in a trace amount to prevent intergranular fracture and to obtain an excellent weld heat affected zone (H
AZ) Proposed steel with toughness (hereinafter referred to as Japanese Patent Application No. 3-
A steel having a composition of claim 144089 is referred to as a B-added high Mn steel. As a result of detailed examination of the relationship between the strength and toughness of the B-added high Mn steel and the manufacturing conditions, it was found that the strength and toughness of the present steel significantly changed depending on the specific manufacturing conditions. Therefore, even in a B-added high Mn steel, an appropriate manufacturing technique is required to obtain more excellent base material characteristics.

[0004]

HA of B-added high Mn steel
Since Z toughness is determined by the chemical composition, Japanese Patent Application No. 3-144
It is possible to secure excellent HAZ toughness in a wide heat input range by setting the component range shown in No. 089,
It has been found that the strength and toughness of the base material change depending on the manufacturing history, and in some cases, the characteristics may be significantly deteriorated as compared with the HAZ toughness. Therefore, in order to use the B-added high Mn steel as a heat-treated high-strength steel that can be manufactured at a low price as a member with severe low-temperature toughness requirements, it is necessary to establish appropriate base material manufacturing conditions for ensuring low-temperature toughness. Becomes

[0005]

[Means for Solving the Problems]
In the production of n steel, this steel causes large embrittlement due to intergranular fracture in a specific tempering temperature range. Therefore, in order to prevent deterioration of toughness, the tempering temperature should be optimized and impurity elements, particularly P content The present inventors came to the conclusion that reduction is particularly important. The gist is the percentage by weight,
C: 0.01 to 0.06%, Si: 0.01 to 1.0
%, Mn: 6 to 15%, P: 0.005% or less, S:
0.01% or less, Al: 0.005-0.1%, B:
0.0003 to 0.010%, N: 0.010% or less,
When a steel containing Cr, Mo, Ni, Cu in an appropriate amount as necessary and the balance being Fe and unavoidable impurities is manufactured by quenching and tempering, it is heated to 1000 ° C or higher and then hot rolled. Then, after reheating to a temperature range of Ac ₃ transformation point to 1000 ° C. and then cooling from that temperature, 70
The average cooling rate in the temperature range of 0 ° C to 300 ° C is 0.1 ° C / s.
Cool to the above temperature and, if necessary, 450 ℃
~ Ac ₁ transformation point +50 ° C, characterized by tempering, when manufacturing without reheating treatment, 950 ° C ~ 1
It is heated to 150 ° C and the rolling reduction at 900 ° C or less is 10-5.
At 0%, hot rolling with a finishing temperature of 750 ° C to 850 ° C is performed, and cooling is performed after cooling so that the average cooling rate in the temperature range of 700 ° C to 300 ° C is 0.1 ° C / s or more. And, if necessary, 450 ° C to Ac ₁ transformation point +
It is a method for producing a high-manganese ultra-high-strength steel excellent in low-temperature toughness, which is characterized by tempering to a temperature of 50 ° C.

[0006]

First, the reasons for limiting the chemical components will be described below. In order to achieve the target characteristics of the present invention, it is necessary to limit the amount of each constituent element to an appropriate range. C is an effective component for improving the strength, but according to the results of a detailed study by the present inventors, in the high Mn steel according to the present invention, as the amount of C increases, the base metal toughness and HAZ toughness are increased. Deteriorates. The adverse effect of C is more remarkable in the toughness of the base material, and the energy transition temperature of the Charpy test increases by about 10 to 15 ° C. per addition of 0.01%. In the present invention, C is set to 0.01% to 0.06% as a range in which the strength of the base material can be secured and the toughness of the base material is not extremely deteriorated.

Next, Si is an element effective in deoxidizing molten steel, and it is also effective in increasing strength, but if added in a large amount, coarse oxides are likely to be formed, and as in the present invention. In high strength steel, ductility and toughness are greatly impaired, so 0.0
The range was 1 to 1.0%. Mn is one of the most important constituent elements of the present invention. In the present invention, the lower limit is set to 6% as the amount necessary to ensure a stable martensite strength and HAZ toughness with a substantially single-phase martensite structure in a wide cooling rate range. If the Mn content is further increased, the HAZ toughness is improved, but if it exceeds 15%, on the contrary, the toughness starts to deteriorate. Similarly, the toughness of the base metal tends to deteriorate with the Mn amount exceeding 15%, and the deterioration amount is more remarkable than with the HAZ toughness. Therefore, in the present invention, the upper limit of the Mn amount is set to 15%.

Since P promotes grain boundary embrittlement and deteriorates the toughness of both the base material and HAZ, it is preferable to reduce P as much as possible.
In particular, when the quenching and tempering treatment is performed, the susceptibility to intergranular embrittlement becomes high, and therefore it is necessary to further reduce the value as compared with the case of using as-rolled. S also forms MnS and segregates at grain boundaries to deteriorate ductility and toughness, so it is preferable to reduce S as much as possible, but the allowable amount is 0.01% or less. Al, like Si, is effective as a deoxidizing element,
If added excessively, a coarse oxide is formed, which becomes a factor of deterioration of ductility and toughness, so it was made 0.005 to 0.1% in range.

B is a particularly important element for suppressing grain boundary embrittlement in high Mn steel, and 0.0003% or more must be added to bring about the effect. However, if the addition exceeds 0.010%, precipitates are easily generated, the grain boundary embrittlement suppressing effect is lost, and the toughness is deteriorated by the precipitates, so 0.0003 to 0.0
The range was 10%. Since N forms BN and reduces the grain boundary embrittlement suppression effect of B, it is preferable that the content is small, but the upper limit was made 0.010% as an allowable range.

The above are the reasons for limiting each of the basic components of the steel of the present invention. For the purpose of improving the properties of the base material and HAZ, one or more of Cr and Mo, or Ni, may be added, if necessary.
One or more of Cu, and one or more of Cr and Mo,
Also, one or more of Ni and Cu can be contained. Cr is effective in increasing the strength of the base material, particularly the yield point, but if it is added in an amount exceeding 2.0%, the toughness is lowered, so the upper limit was made 2.0%. Mo is a useful element because it raises the yield point and has the effect of suppressing grain boundary embrittlement, similar to Cr, but it is a useful element, but when added in excess of 2.0%, the effect of suppressing grain boundary embrittlement is saturated. On the other hand, it deteriorates the toughness, which is not preferable. Therefore, the upper limit of Mo is set to 2.0%.

The higher the Ni content, the toughness of the base metal and the HAZ.
Both the toughness and the transition temperature are improved, but on the other hand, the shelf energy tends to decrease, and the toughness improving effect is saturated even if the addition amount exceeds 3.0%. The upper limit was 0.0%. The effect of Cu is qualitatively similar to that of Ni, but the addition of a large amount exceeding 1.5% causes problems such as cracking of the slab and precipitation embrittlement, so the upper limit is set to 1.5%. did.

The above are the reasons for limiting the chemical composition of the present invention. In order to obtain preferable strength and toughness in the B-added high Mn steel, it is melted in a melting furnace such as a converter or an electric furnace within the above composition range. When manufacturing a steel slab manufactured by the ingot-casting method, continuous casting method, or the like into a steel sheet, it is necessary to use the following appropriate manufacturing method. That is, in the case of manufacturing as-quenched or by quenching and tempering treatment, after heating to 1000 ° C. or higher, hot rolling is performed, followed by reheating to a temperature range of Ac ₃ transformation point to 1000 ° C. and then cooling from that temperature. 700 ° C-3
Cooling is performed so that the average cooling rate in the temperature range of 00 ° C is 0.1 ° C / s or more, or after cooling, 450 ° C to A
it is necessary to temper at a temperature of c ₁ transformation point + 50 ° C.. In the case of manufacturing without reheating treatment, 950 ° C to 1
It is heated to 150 ° C and the rolling reduction at 900 ° C or less is 10-5.
At 0%, hot rolling with a finishing temperature of 750 ° C to 850 ° C is performed, and cooling is performed after cooling so that the average cooling rate in the temperature range of 700 ° C to 300 ° C is 0.1 ° C / s or more. Alternatively, after cooling, it is necessary to further temper to a temperature of 450 ° C. to Ac ₁ transformation point + 50 ° C. The reason is shown below.

First, in the case of manufacturing as-quenched or by quenching and tempering treatment, hot rolling prior to heat treatment is performed to obtain a desired sheet thickness. Since the main purpose of this hot rolling is to adjust the shape, it is not necessary to use particularly complicated rolling conditions, and the heating temperature is 1000 ° C. in order to achieve sufficient solution treatment.
It should be above ℃. Therefore, 1000 cold steel pieces
After reheating above ℃, or after solidifying molten steel,
Even if the temperature distribution of the steel slabs is kept uniform at 1000 ° C. or more during cooling and then hot rolling is performed, the effect is not different. The cooling after hot rolling may be air cooling, water cooling or slow cooling. After hot rolling, it is reheated to a temperature range of Ac ₃ transformation point to 1000 ° C.

[0014] This is because if it is less than Ac ₃ point, it is not completely austenitized, so that the structure becomes non-uniform and the strength and toughness are deteriorated, and when it exceeds 1000 ° C, the austenite grains are mixed and coarsened and the toughness is deteriorated. Therefore, it is necessary to set this temperature range. In general tempered high-strength steel, in order to suppress the formation of coarse bainite that is harmful to toughness, cooling after heating is an essential condition to cool with water cooling or the like at the highest possible cooling rate. However, since the amount of Mn is increased and the hardenability is sufficiently ensured, it is not necessary to perform rapid cooling.

However, in order to ensure the martensite single-phase structure for ensuring the strength and to avoid grain boundary segregation of impurities due to slow cooling, 700 ° C. to 30 ° C. at the time of cooling
Cooling is preferably performed so that the average cooling rate in the temperature range of 0 ° C. is 0.1 ° C./s or more. As long as this condition is satisfied, quenching treatment such as water cooling is not necessarily required. The heating temperature to 700 ° C. or less than 300 ° C. is not particularly limited, but it is preferable to avoid slow cooling such as furnace cooling in the sense that it does not promote grain boundary embrittlement as much as possible.

By the above manufacturing method, it is possible to obtain sufficiently excellent strength and toughness, and it is an essential condition to carry out tempering treatment at a relatively high temperature for improving toughness like ordinary tempered high strength steel. is not. However, Ac ₃ transformation point to 100
The yield strength becomes lower if it is reheated to 0 ° C or left to cool. If it is necessary to further increase the yield strength, 45
If tempered in the temperature range of 0 ° C. to Ac ₁ transformation point + 50 ° C., the yield point can be increased without significantly lowering the tensile strength and the toughness. That is, FIG. 1 contains about 0.02% C, about 0.1% Si, about 0.001% B, and about 8% to 1% Mn.
Steel containing 0% is reheated to 850 ° C, water-quenched, and then tempered at various temperatures, strength and toughness (absorption energy of 7.0 kgf in Charpy test).
It is a diagram in which the relationship between the temperature at which m is reached: vTr _7.0 ) was investigated. However, the B-added high Mn steel shows remarkable toughness deterioration in the tempering temperature range of 400 ° C. or less, so tempering is avoided in this temperature range. Need to give. This deterioration of toughness is due to grain boundary fracture.

In the as-quenched state (as Q), the addition of B suppresses the intergranular fracture, so that the toughness is good and the as-quenched state can be used. However, since the yield strength (0.2% proof stress) tends to be slightly lower if it is quenched, it is necessary to temper it if high yield strength is required. As is clear from FIG. 1, the tempering temperature is 450.
In the range of 0 ° C to 550 ° C, 0.2% proof stress can be increased without causing a significant decrease in tensile strength, and within this temperature range, deterioration of toughness does not occur. A large decrease in 0.2% proof stress occurs at 600 ° C. or higher, but this is due to the precipitation of austenite due to tempering beyond the Ac ₁ transformation point. In the case of aiming at a low yield point steel or a low yield ratio steel, it is possible to lower the yield point without hindering the toughness and tensile strength by tempering beyond the Ac ₁ transformation point.

However, for example, when the 10 to 12% Mn steel in FIG. 1 is tempered to 650 ° C. and tempered largely beyond the Ac ₁ transformation point, the toughness deteriorates. From the examination based on the experimental results, it is preferable to set the Ac ₁ transformation point + 50 ° C. as the upper limit of the tempering temperature. Therefore, the tempering temperature in the case of tempering is set to a range of 450 ° C. to Ac ₁ transformation point + 50 ° C. as an allowable range for deterioration of toughness depending on the application. Cooling conditions after heating to the tempering temperature are not critical, but slow cooling such as furnace cooling should be avoided because it promotes grain boundary embrittlement.

Further, the steel of the present invention can be manufactured without the above-mentioned reheating treatment. in this case,
The heating temperature is 950 in order to improve the strength and toughness by achieving both fine graining of the austenite grain size during heating and solution treatment.
The range from ℃ to 1150 ℃ is preferable. In addition, if rolling is performed without restricting the rolling conditions, grain refinement may be insufficient and there is a concern that toughness may be reduced. Further, 0.2% proof stress may be extremely reduced. In order to improve the toughness and increase the 0.2% proof stress, the reduction ratio at 900 ° C or lower is 10 to 50%
Therefore, it is necessary to perform hot rolling within the condition that the finishing temperature is 750 ° C to 850 ° C. If the rolling reduction at 900 ° C. or less is less than 10%, the effect is not clear, and if it exceeds 50%, the anisotropy of the material becomes remarkable. Further, when the finishing temperature is less than 750 ° C., the separation becomes remarkable, the shelf energy of the Charpy test decreases, and the anisotropy of the material also increases, which is not preferable, and conversely, when the rolling is finished at a high temperature exceeding 850 ° C., We cannot expect an increase in 2% proof stress. The reason for limiting the cooling rate after rolling is the same as the reason for limiting the cooling rate during quenching in the quenching and tempering process.

Under the above-mentioned manufacturing conditions, it is possible to obtain sufficiently excellent strength and toughness even as it is rolled, but if it is necessary to adjust the strength or further increase the yield stress, tempering is further performed. In this case as well, for the same reason as the reason for limiting the tempering conditions in the quenching and tempering treatment, it is necessary to set the tempering temperature range to 450 ° C to the Ac ₁ transformation point + 50 ° C.

[0021]

EXAMPLES Tables 1, 2 and 3 show the chemical composition, base material manufacturing history, base material strength and toughness, HAZ toughness, etc. of the steel plates and comparative steel plates manufactured according to the present invention. The steels of the present invention shown in Table 1 are manufactured according to the methods of claims 1 and 2. Here, No. 1-No. No. 14 is the steel of the present invention. 15-No. 25 is a comparative steel. Further, Table 3 shows the steel No. of the present invention of Table 1. No. 7 was used, the results of studying the relationship between the base material manufacturing history, the base material strength toughness and the rolling conditions, and the tempering conditions without hot-rolling or after hot rolling or tempering after rolling. is there. All the test pieces were taken in the direction parallel to the rolling direction from the center part of the plate thickness. The strength of the base material was evaluated by the 0.2% proof stress and tensile strength of the round bar tensile test. On the other hand, the base metal toughness is −
The absorption energy at 60 ° C was used for evaluation. Further, the HAZ toughness was evaluated by the absorbed energy at -60 ° C of the Charpy impact test when the welding reproduction heat cycle in which the maximum heating temperature was 1400 ° C and the cooling time from 800 ° C to 500 ° C was 160 seconds was applied. By the way, this heat cycle condition corresponds to the heat history in FL when submerged arc welding is performed on a steel sheet having a thickness of about 20 mm with a heat input of about 100 kJ / cm.

[0022]

[Table 1]

[0023]

[Table 2]

As is clear from Table 2, No. 1 to N
o. 14 of the steels manufactured according to the present invention have superior base metal strength, toughness and HAZ toughness as compared with the comparative steels, and exhibit sufficient absorbed energy in the Charpy test for ensuring the safety of the structure even at a low temperature of -60 ° C. I understand. Further, the tensile strength of the base material is 100 kgf / mm ² or more. That is, according to the present invention, it is apparent that a steel having extremely high strength, excellent base material and HAZ toughness can be obtained.

On the other hand, No. 15-No. 25 comparative steels did not meet the requirements of the invention, and therefore the base metal strength,
It is also clear from Table 2 that the toughness or HAZ toughness is inferior to the steel of the present invention. That is, comparative steel No. 15,
Since No. 16 does not contain B, the HAZ toughness is extremely poor. No. Since No. 17 has an excessive amount of P, the base material toughness and HAZ toughness are poor. No. 18-No. No. 21, the component range is within the range of the present invention, but since the tempering temperature is out of the proper range, sufficient base material toughness cannot be obtained. In addition, No.
22 and 23 have a high reheating temperature of 1200 ° C. and coarse austenite, so that the base material toughness is poor. No. 24, 2
In No. 5, since the cooling after reheating was done by furnace cooling, the cooling rate was outside the range of the present invention, and the strength was slightly lower than that of the present invention, and the toughness of the base material was deteriorated.

[0026]

[Table 3]

Table 3 shows the relationship between the hot rolling conditions and the strength and toughness of the base material when the reheating treatment is not performed. The steels manufactured under the conditions A to H satisfying the requirements of the present invention show excellent base metal toughness as compared with the comparative steel and have a 0.2% content.
The yield strength is also high. On the other hand, the steels manufactured under the conditions I to N that deviate from the scope of the present invention have poor toughness and low 0.2% proof stress, although the chemical composition is within the scope of the present invention. That is, since the heating temperatures of Comparative Steels I and J are too high,
Inferior toughness. In addition, Comparative Steel I has a reduction rate of 900 ° C. or less,
Since the finishing temperature is out of the range of the present invention, 0.2% proof stress is also low. Although the heating temperatures of the comparative steels K to M are within the range of the present invention,
Since the rolling reduction of 900 ° C. or less or the finishing temperature is out of the range of the present invention, sufficient characteristics cannot be obtained. Comparative steel N shows that even if the hot rolling conditions satisfy the requirements of the present invention, the toughness deteriorates significantly if the subsequent tempering conditions deviate from the proper range. From the above examples, according to the present invention, the tensile strength is 100 kgf / mm ² or more,
It is also clear that an ultra-high tensile steel having an excellent base material and HAZ toughness that can withstand safe use even at a low temperature of about -60 ° C can be obtained.

[0028]

INDUSTRIAL APPLICABILITY The present invention does not contain a large amount of expensive alloying elements such as Ni, but has extremely high tensile strength, excellent base metal toughness, and super high tensile strength having excellent HAZ toughness in a wide heat input range. It is possible to manufacture steel, and by using the steel according to the present invention, it becomes possible to manufacture a welded structure having high strength and high safety even under severe use conditions, and the effect is extremely remarkable. is there.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between base material toughness and tempering temperature for steels with different Mn contents,

FIG. 2 is a diagram showing a relationship between base material strength and tempering temperature for steels having different Mn amounts.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication C22C 38/58

Claims (7)

[Claims] 1. By weight%, C: 0.01 to 0.06% Si: 0.01 to 1.0% Mn: 6 to 15% P: 0.005% or less S: 0.01% or less Al: Steel containing 0.005 to 0.1% B: 0.0003 to 0.010% N: 0.010% or less, and the balance being Fe and inevitable impurities,
After heating to 1000 ° C or higher, hot rolling is performed, followed by Ac ₃
After being reheated to a temperature range of transformation point to 1000 ° C., when cooling from the temperature, cooling is performed so that the average cooling rate in the temperature range of 700 ° C. to 300 ° C. is 0.1 ° C./s or more. Of high-manganese ultra-high-strength steel with excellent low-temperature toughness. 2. By weight%, C: 0.01 to 0.06% Si: 0.01 to 1.0% Mn: 6 to 15% P: 0.005% or less S: 0.01% or less Al: Steel containing 0.005 to 0.1% B: 0.0003 to 0.010% N: 0.010% or less, and the balance being Fe and inevitable impurities,
After heating to 1000 ° C or higher, hot rolling is performed, followed by Ac ₃
After reheating to the temperature range of the transformation point to 1000 ° C. and then cooling from the temperature range, cooling is performed so that the average cooling rate in the temperature range of 700 ° C. to 300 ° C. is 0.1 ° C./s or more, and then 450 ° C. A method for producing a high-manganese ultra-high-strength steel excellent in low-temperature toughness, which comprises tempering at a temperature of Ac ₁ transformation point + 50 ° C. 3. C: 0.01 to 0.06% Si: 0.01 to 1.0% Mn: 6 to 15% P: 0.005% or less S: 0.01% or less Al: Steel containing 0.005 to 0.1% B: 0.0003 to 0.010% N: 0.010% or less, and the balance being Fe and inevitable impurities,
It is heated to 950 ° C to 1150 ° C, the rolling reduction at 900 ° C or lower is 10 to 50%, and the finishing temperature is 750 to 850 ° C.
Hot rolling, which is 700 ℃ at the time of cooling after rolling
A method for producing a high-manganese ultra-high-strength steel having excellent low-temperature toughness, which comprises cooling so that an average cooling rate in a temperature range of to 300 ° C is 0.1 ° C / s or more. 4. C: 0.01 to 0.06% Si: 0.01 to 1.0% Mn: 6 to 15% P: 0.005% or less S: 0.01% or less Al: Steel containing 0.005 to 0.1% B: 0.0003 to 0.010% N: 0.010% or less, and the balance being Fe and inevitable impurities,
It is heated to 950 ° C to 1150 ° C, the rolling reduction at 900 ° C or lower is 10 to 50%, and the finishing temperature is 750 to 850 ° C.
Hot rolling, which is 700 ℃ at the time of cooling after rolling
Cooling is performed so that the average cooling rate in the temperature range of ˜300 ° C. is 0.1 ° C./s or more, and then 450 ° C. to Ac ₁ transformation point +
A method for producing high-manganese ultra-high-strength steel excellent in low-temperature toughness, characterized by tempering to a temperature of 50 ° C. 5. The low temperature according to claim 1, further comprising one or two of Cr: 2.0% or less and Mo: 2.0% or less by weight. A method for producing a high-manganese ultra-high-strength steel having excellent toughness. 6. The low temperature according to any one of claims 1 to 4, further containing one or two of Ni: 3.0% or less and Cu: 1.5% or less by weight. A method for producing a high-manganese ultra-high-strength steel having excellent toughness. 7. Further, by weight, one or two of Cr: 2.0% or less, Mo: 2.0% or less, and one of Ni: 3.0% or less and Cu: 1.5% or less, or Two types are contained, The manufacturing method of the high manganese super high strength steel excellent in the low temperature toughness of Claim 1 characterized by the above-mentioned.