JP2011230182A - Method for manufacturing high manganese-steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for highly productively manufacturing high manganese-steel with high quality, wherein generation of surface defects such as a surface crack is suppressed.SOLUTION: The method is for manufacturing high manganese-steel by continuous casting method. In the method, molten steel temperature T (unit: °C) in a molten steel container shortly before supplying hot water to a mold is controlled to satisfy the following formula (1) while casting speed Vc (unit: m/min) is selected within a range of the following formula (2): a≤T≤a+50 (1), Vc≥0.02×(T-a) (2). Here, a is a value determined by the following formula (3) based on the composition of the steel. (C%), etc., in the formula are respectively contents of C, etc., (unit: mass%) in the chemical composition: a=1562-{62×(C%)+6×(Si%)+4.1×(Mn%)+1.5×(Cr%)} (3).

Description

  The present invention is a continuous casting method capable of providing a high-quality steel material containing Mn at a content of 10% by mass or more, particularly with suppressed surface defects (referred to as “high manganese-containing steel” in the present invention). About.

  High manganese-containing steel has higher strength than that of austenitic stainless steel, low magnetic permeability, and low raw material cost, so it can be used for high-strength members, wear-resistant materials, non-magnetic materials, etc. Used for. In particular, steel having an Mn content of 10 to 31% by mass utilizes its stable non-magnetic performance, and is used as a member that does not disturb a magnetic field due to a permanent magnet or current, for example, a power generation turbine member or a magnetic levitation railway member. The

  High manganese-containing steel completes solidification in an austenite single phase during casting, and thus a columnar grain structure is likely to develop. The formed austenite columnar grains are coarse, and the grain boundaries serve as crack initiation points and propagation paths. Furthermore, being an austenite single phase often significantly reduces hot workability. Therefore, high manganese content steel is recognized as a material with high cracking susceptibility during continuous casting or hot rolling.

  As a means for suppressing the occurrence of cracks during continuous casting, Patent Document 1 discloses a steel manufacturing method containing C: 0.9 to 1.20% and Mn: 11.0 to 14.0% by weight. The P content is 0.030% or less, the secondary cooling water ratio during continuous casting is adjusted to a range of 0.7 to 1.1 L / kg, and the heating rate of the slab during the heating process is adjusted to 30 to 35. The manufacturing method adjusted to the range of ° C./h is disclosed.

JP 59-13556 A

"Steel Solidification" Appendix Data Collection on Solidification Phenomena of Steel (issued in 1977)

  In the method disclosed in Patent Document 1, it is premised on a soaking-pre-rolling step in which the surface of a continuously cast slab is cleaned after continuous casting, and the main object is to prevent the surface cracks from being promoted. It is said. However, in such a conventional manufacturing method, surface cracks in the as-cast slab stage are allowed to some extent, and an increase in cost due to slab care is inevitable. Furthermore, casting may become unstable due to the slab and the casting must be stopped urgently.

  An object of the present invention is to provide a method for producing a high-quality, high-manganese-containing steel in which generation of surface defects such as surface cracks is suppressed with high productivity.

  As a result of examining the cause of surface defects in the slab, the present inventor appropriately grasped the relationship between the liquidus temperature and the composition and the relationship between the solidus temperature and the composition, and based on the relationship, the continuous casting It came to the knowledge that generation | occurrence | production of a surface defect can be suppressed effectively by setting operation conditions. And in high manganese content steel, the knowledge that these relations differed from general carbon steel was also acquired.

The present invention completed based on the above knowledge is as follows.
(1) As basic components, in mass%, C: 0.09% to 1.5%, Si: 0.05% to 1.0%, Mn: 10% to 31%, Cr: 10% P: 0.05% or less, S: 0.02% or less, Al: 0.003% or more and 0.1% or less, N: 0.005% or more and 0.50% or less, with the balance being Fe And a high manganese-containing steel having a chemical composition comprising impurities by a continuous casting method, wherein the molten steel temperature T (unit: ° C.) in the molten steel container immediately before supplying hot water to the mold satisfies the following formula (i) And a method for producing a high manganese content steel, wherein the casting speed Vc (unit: m / min) is selected within the range of the following formula (ii):
a ≦ T ≦ a + 50 (i)
Vc ≧ 0.02 × (T−a) (ii)
Here, a is a value determined by the following formula (iii) from the composition of steel, and (C%), (Si%), (Mn%) and (Cr%) in the formula are respectively It is content (unit: mass%) of C, Si, Mn, and Cr in the composition.
a = 1562− {62 × (C%) + 6 × (Si%) + 4.1 × (Mn%) + 1.5 × (Cr%)} (iii)

(2) The molten steel temperature T in the molten steel container just before the hot water supply to the mold is controlled to satisfy the following formula (i ′), and the casting speed Vc (unit: m / min) is set to the following formula (ii ′) The method for producing a high manganese content steel according to the above (1), characterized in that it is selected within the range of:
a ≦ T ≦ a + 30 (i ′)
Vc ≧ 0.025 × (T−a) (ii ′)

(3) The method for producing a high manganese-containing steel according to (1) or (2), wherein the chemical composition further satisfies the following formula (iv):
(Mn%) + 40.2 × (C%) + 122 × (P%) <62.2 (iv)
Here, (Mn%), (C%) and (P%) in the above formula (iv) are the contents (unit: mass%) of Mn, C and P in the chemical composition, respectively.

(4) The method for producing a high manganese-containing steel according to any one of (1) to (3), wherein the chemical composition further satisfies the following formula (v):
(% C) +4.3 (% P) <1.21 (v)
Here, (C%) and (P%) in the above formula (v) are the contents of C and P (unit: mass%) in the chemical composition, respectively.

  According to the present invention, when a high manganese content steel material is produced by a continuous casting method, occurrence of a slab surface defect is prevented. Furthermore, in the suitable aspect, the continuous cast slab with a low crack sensitivity is provided also at the time of the hot rolling of a post process. Therefore, according to the present invention, it is possible to stably manufacture a steel material with good quality. The obtained steel material has sufficient hot workability even during hot rolling, and can be used for applications requiring non-magnetic performance unique to the material.

It is a graph which shows the comparison of a liquidus temperature actual value and a liquidus temperature estimated value. It is a graph which shows the relationship between casting speed and casting temperature.

Hereinafter, the production method according to the present invention will be described in detail. In the following description, “%” indicating the content of component elements in the chemical composition of the high manganese-containing steel means mass%.
1. Study on surface defects When manufacturing high manganese content steel with Mn content of 10-31 mass% by continuous casting, various castings are derived from the high Mn content in the chemical composition of the steel. Single-surface defects are likely to occur. Main slab surface defects include 1) vertical cracks, 2) rashes, and 3) microcracks.

  Among these slab surface defects, vertical cracks and rashes are caused by uneven cooling in the mold and casting temperature, that is, the flow of molten metal supplied from the tundish through the immersion nozzle to the mold and improper temperature. To do.

  Especially when the molten steel temperature in the molten steel container immediately before the hot water supply to the mold (hereinafter abbreviated as “casting temperature”) is excessively high, the initial solidified shell formed in the mold has an excessively high casting temperature. In some cases, the molten metal is remelted and broken by the pouring flow, and at this time, the broken solidified shell becomes a starting point of the surface defect.

  In order to prevent the occurrence of surface defects due to such remelting of the solidified shell, it is only necessary to avoid excessively high casting temperature. However, when the casting temperature is low, a part of the molten metal surface is solidified. There is a risk that casting will become unstable due to hot-water skinning. For this reason, in order to realize stable continuous casting while suppressing the occurrence of surface defects, it is necessary to appropriately grasp the solidification / remelting behavior of the molten steel in the mold. The physical properties most relevant to the solidification / remelting behavior of the molten steel are the liquidus temperature and the solidus temperature of the molten steel. Therefore, in order to suppress the occurrence of vertical cracks and rashes, it is necessary to accurately grasp the liquidus temperature and the solidus temperature of the molten steel in the mold.

  On the other hand, micro cracks on the surface of the slab surface are caused by thermal stress in the surface layer of the slab during cooling or reheating, and this thermal stress is concentrated at the grain boundaries of coarse austenite columnar crystals in high manganese steel. This is a crack defect on the surface of the slab generated by propagating the slab. In particular, high manganese-containing steel has a high content of additive elements and a low solidus temperature at which solidification is completed, so that eutectic carbide is easily formed in the micro-segregation part, which becomes the starting point of grain boundary cracking.

  In order to suppress microcracks, it is effective to weaken the secondary cooling during continuous casting. However, in alloy steel with a low solidus temperature, the grain boundary is fragile to a low temperature, so weak cooling is performed. However, it is not easy to prevent microcracking.

Moreover, it is preferable also from a viewpoint of ensuring the hot ductility of slab surface layer part to raise the solidus temperature of steel and to restrict | limit said solid-liquid coexistence temperature range.
Thus, it is important to accurately grasp the solidus temperature of steel from the viewpoint of suppressing microcracking and ensuring workability in the hot rolling process.

2. High Manganese Content Steel The chemical composition of the high manganese content steel according to the present invention is, as a basic component, mass%, C: 0.09% or more and 1.5% or less, Si: 0.05% or more and 1.0% or less. Mn: 10% to 31%, Cr: 10% or less, P: 0.05% or less, S: 0.02% or less, Al: 0.003% to 0.1%, N: 0.005 % And 0.50% or less, with the balance being Fe and impurities.

Hereinafter, the content range of each element will be described.
C: 0.09% or more and 1.5% or less C is an element necessary for stabilizing the austenite phase and ensuring material strength. However, when the C content exceeds 1.5%, ductility and workability deteriorate. Therefore, by setting the C content in the range of 0.09% to 1.5%, a composition suitable for the structural material can be realized.

Si: 0.05% or more and 1.0% or less Si is an element necessary for deoxidation, has an effect of solid solution strengthening, and is indispensable for an alloy component. In order to ensure these effects, the Si content is set to 0.05% or more. However, when the Si content exceeds 1.0%, the effect is saturated and workability (ductility) deteriorates. Therefore, the Si content is 1.0% or less.

Mn: 10% or more and 31% or less Mn is an element necessary for stabilizing the austenite phase and ensuring the material strength. In particular, by containing 10% or more of high-concentration Mn, non-magnetic or high-strength performance at a low temperature, which is a characteristic property of the austenite phase, can be obtained. However, if the content exceeds 31%, workability is greatly impaired. Therefore, the Mn content is 10% or more and 31% or less.

Cr: 10% or less Cr is an element useful for stabilizing the austenite phase and improving the strength by solid solution strengthening. Although it may be added as necessary, when the content exceeds 10%, workability is greatly impaired.

P: 0.05% or less P is an impurity element contained in steel and causes toughness reduction or hot embrittlement. Therefore, the smaller the P content, the better. Further, if it exceeds 0.05%, the weldability is remarkably lowered. Therefore, the P content is 0.05% or less.

S: 0.02% or less Since S is an impurity element contained in steel and causes a decrease in toughness, the smaller the S content, the better. Furthermore, if it exceeds 0.02%, the amount of MnS inclusions that become the starting point of corrosion increases and the corrosion resistance is lowered. Therefore, the P content is 0.05% or less.

Al: 0.003% or more and 0.1% or less Al is an element necessary for deoxidation, and inevitably exists in steel. From the viewpoint of obtaining the effect of deoxidation, the lower limit of the Al content is 0.003%. On the other hand, if the content exceeds 0.1%, excess AlN is generated and hot workability is lowered. Therefore, the Al content is set to 0.003% to 0.1%.

N: 0.005% or more and 0.50% or less N has an effect of stabilizing the austenite phase and increasing the strength by solid solution or precipitation. Since the affinity between Mn and Cr is large, it can be easily solid-solved with high manganese-containing steel. However, when the content exceeds 0.5%, hot workability decreases. Therefore, the N content is set to be 0.005% or more and 0.50% or less.

High manganese content steel concerning the present invention can contain the following ingredients in addition to the above-mentioned basic ingredient.
V: 0.3% or less V is an element useful for improving the strength by precipitation hardening. A small amount may be added if necessary, but if the content exceeds 0.3%, the effect is saturated and workability is greatly impaired.

3. Liquidus temperature and solidus temperature It is important for producing high quality slabs with high productivity to accurately grasp the liquidus temperature and solidus temperature of continuously cast steel as described above. At some point, the liquidus temperature and the solidus temperature vary depending on the content of the alloy components. Therefore, the relationship between the liquidus temperature and the composition, and the relationship between the solidus temperature and the composition are accurately grasped. Is needed.

However, as will be described below, these relationships in high manganese steels are significantly different from those in general carbon steel.
According to Non-Patent Document 1, the following estimation formula (A) is given as an example of an estimation formula for the liquidus temperature TL (unit: ° C.) for carbon steel.

TL = 1536- {78 × (C%) + 7.6 × (Si%) + 4.9 × (Mn%) + 1.3 × (Cr%) + 34.4 × (P%) + 38 × (S%)} (A)
Here, (C%), (Si%), (Mn%), (Cr%), (P%) and (S%) in the above formula (A) are respectively C, It is content (unit: mass%) of Si, Mn, Cr, S and P.

  For a plurality of steels having a relatively high Mn content shown in Table 1, the liquidus temperature is measured by the following method, and the liquidus temperature is estimated based on the above estimation formula (A). The value was determined. In addition, the unit of content of each alloy element in Table 1 is mass%, and the balance in the chemical composition of each steel is Fe and inevitable impurities.

The method for measuring the liquidus temperature and the solidus temperature carried out in the present invention is as follows.
In an argon gas atmosphere, 70 to 80 g of a steel sample was melted in an alumina crucible having an inner diameter of 20 mm, the furnace temperature was maintained at 1480 ° C. for 15 to 20 minutes, and then the cooling rate was 10 ° C./min using temperature control of the electric furnace. Cool the furnace at At this time, the sample temperature is measured with a thermocouple in a protective tube immersed in the molten steel sample. Since characteristic points accompanying solidification appear in the cooling curve of the sample, the liquidus temperature and the solidus temperature are evaluated based on them. As the first characteristic point, the liquidus temperature is defined as the maximum temperature or plateau temperature after recuperation when solidification starts (latent heat release starts). Next, the temperature at which internal heat generation obtained by thermal analysis becomes zero is defined as the solidus temperature at which the release of latent heat of solidification ends. Here, the internal heat generation is a value analytically obtained from the cooling curve of the sample, and is the sum of the temperature differential value (cooling rate) of the sample and the external heat removal rate caused by the temperature difference between the sample and the furnace. In the temperature zone in which solidification proceeds, the sample generates latent heat of solidification, so internal heat generation is positive. However, when solidification is completed, the internal heat generation becomes zero under single-phase cooling conditions where the specific heat is constant and the cooling rate is constant.

  FIG. 1 and Table 2 show the measured values of the liquidus temperature and estimated values based on the above estimation formula (A) for each steel shown in Table 1 so that they can be compared. From these results, according to the conventional estimation formula (A), the liquidus temperature is estimated to be approximately 20 ° C. or higher (average value of deviation is 22.3 ° C.) on the low temperature side compared to the actual measurement value. Recognize. Such a large deviation is considered to be because a large numerical value is set as a contribution coefficient for a relatively low concentration of Mn in carbon steel. For example, referring to two formulas frequently used in carbon steel, Hirai's formula and Kawawa's formula (Non-Patent Document 1), the temperature drop per 1% by mass increase in Mn content is 4.8-4. It becomes about 9 ℃.

Thus, when 20 ° C. is different from the actually measured value, the above formula (A) no longer functions as an estimation formula.
Thus, when a new estimation formula is obtained from the steel composition shown in Table 1 and the measured value of the liquidus temperature shown in Table 2, the following formula (B) is obtained.

TL = 1532− {62 × (C%) + 6 × (Si%) + 4.1 × (Mn%) + 1.5 × (Cr%) + 40 × (P%) + 40 × (S%)} (B)
Here, (C%), (Si%), (Mn%), (Cr%), (P%), and (S%) in the above formula (B) are respectively C and C in the chemical composition of steel. It is content (unit: mass%) of Si, Mn, Cr, S and P.

FIG. 1 and Table 2 also show estimated values based on the estimation formula (B).
As is clear from these results, the deviation between the estimated value based on the above equation (B) and the actually measured value is much smaller than the deviation between the estimated value based on the above equation (B) and the actually measured value. The value is about 3 ° C.

Similarly to the liquidus temperature TL, the following estimation formula (C) of the solidus temperature TS was obtained from the comparison between the measurement results of the solidus temperature described above and the composition.
TS = 1467− {165 × (C%) + 6 × (Si%) + 4.1 × (Mn%) + 1.5 × (Cr%) + 500 × (P%) + 40 × (S%)} (C)

4). Continuous casting conditions for steel containing high manganese content Continuous casting of steel containing high manganese content set based on the newly calculated formula (B) for the liquidus temperature TL and formula (C) for the solidus temperature TS The conditions will be described below.

(1) Casting temperature Generally, the casting temperature controls the degree of superheated molten steel within an appropriate range with reference to the liquidus temperature. An appropriate range for casting alloy steel including high manganese-containing steel is empirically 30 to 80 ° C. as the degree of superheat based on the liquidus temperature. If the molten steel superheat degree is lower than the lower limit of 30 ° C, the so-called molten surface skinning occurs in which the molten steel temperature near the molten metal surface, which is particularly easy to cool in the mold, becomes below the liquidus and the molten metal surface partially solidifies. Casting may become unstable. On the other hand, if the degree of superheated molten steel is higher than the upper limit of 80 ° C., the solidified shell formed in the mold is easily remelted and easily broken, and there is a risk of causing rashes and breakout in the mold.

Therefore, based on the above formula (B) of the liquidus temperature of the high manganese content steel according to the present invention, the appropriate range of the casting temperature T is set as the following formula (1).
a ≦ T ≦ a + 50 (1)
Here, a is a lower limit value (unit: ° C.) of an appropriate casting temperature determined by the following formula (3) from the steel composition, and (C%), (Si%), (Mn%) in the formula ) And (Cr%) are the contents (unit: mass%) of C, Si, Mn and Cr in the chemical composition of steel, respectively.
a = 1562− {62 × (C%) + 6 × (Si%) + 4.1 × (Mn%) + 1.5 × (Cr%)} (3)

  In addition, the part in the square bracket in the said Formula (3) corresponds to what deleted the term of P content and the term of S content in the said Formula (B). Since the content of P and S in the high manganese content steel according to the present invention is 0.07% in total, according to the above formula (B), the influence of these terms on the estimated value of the liquidus temperature TL. Is less than 3 ° C. at the maximum. In addition, since the dephosphorization treatment and the desulfurization treatment are performed so that the content is about 0.02% or less in the normal steelmaking process, the terms of P content and S content are liquid. The total effect on the phase line temperature is limited to about 1 ° C. Therefore, even if the P content term and the S content term are deleted from the formula (B), the influence on the estimated value of the liquidus temperature TL is negligible. Rather, it is more advantageous from the viewpoint of workability that the liquidus temperature can be predicted with a relatively small error using only the above-mentioned four elements which are main alloy components without considering the contribution of these component elements. . For the above reason, in the above formula (1) for determining the appropriate range of the casting temperature according to the present invention, there is no term for the P content and no term for the S content.

  If the casting temperature T is lower than a, it may cause low temperature casting, which may cause troubles such as the surface of the molten metal in the continuous casting mold. become.

  On the other hand, when the casting temperature T exceeds a + 50, the initial solidified shell formed in the mold by high-temperature casting breaks due to the high-temperature pouring flow, and becomes the starting point of the defect. The traces of double skin caused by redissolving of the solidified shell in the mold appear as slab burrs and become a problem.

(2) Casting speed The casting speed Vc should be appropriately set according to the steel type in order to realize stable continuous casting.

  In the process of growth of the solidified shell formed in the mold, a stress is generated to cause the solidified shell to lift away from the mold due to a thermal contraction difference that occurs with a temperature gradient in the thickness direction of the shell. At this time, if the casting speed is appropriate, the solidified shell is pressed against the mold surface by the molten steel static pressure, so that the solidified shell does not deform. However, when the casting speed is excessively low, the solidified shell is deformed and there is a high risk of causing rashes. Therefore, in order to perform a stable casting speed, a lower limit is set to the casting speed from the viewpoint of suppressing shell deformation.

  As a result of the examination of the lower limit by the present inventors, it has been clarified that the casting temperature has a great influence as a factor for determining whether or not the solidified shell is deformed when the casting speed is lowered. In particular, as shown in FIG. 2, the difference between the casting temperature T and the lower limit value a of the appropriate casting temperature obtained by the above formula (3), that is, Ta is simply proportional to the lower limit value of the casting speed. It became clear that this was considered. And as a result of performing the casting test about several steel, this proportionality coefficient was calculated | required with 0.02 m / (min * degreeC).

From the above examination, it has been clarified that the following formula (2) is established with respect to the casting speed Vc.
Vc ≧ 0.02 × (T−a) (2)
That is, by setting the casting temperature T and the casting speed Vc so as to satisfy the above formulas (1) and (2) and performing continuous casting, surface defects in the obtained slab can be stably suppressed. Realized.

  Even if the above formulas (1) and (2) are satisfied, surface defects, specifically rashes may occur in the unsteady phase at the beginning of casting. A more preferable relationship between the casting speed T and the casting speed Vc that can stably suppress such initial rash is expressed by the following equations (1 ') and (2').

a ≦ T ≦ a + 30 (1 ′)
Vc ≧ 0.025 × (T−a) (2 ′)
On the other hand, if the casting speed is excessively high, the cooling in the mold is insufficient, and the solidified shell is not sufficiently formed in the mold, so that it is secondarily cooled out of the slab or mold in the mold. There is an increased risk that the solidified shell in the cast slab is broken and breakout occurs.

5). Preferred compositional features from the standpoint of good hot workability Next, the preferred compositional features of the high manganese-containing steel according to the present invention from the standpoint of achieving good hot workability will be described.

From the viewpoint of realizing good hot workability, the steel composition preferably satisfies the following formula (4). In order to prevent high temperature ductility from being impaired by liquid film embrittlement at the grain boundaries, this equation is used for solidus lines on the higher temperature side than 1200 ° C. which is the upper limit of normal hot working temperature such as bending correction, forging or rolling during continuous casting. In order to maintain the temperature, 1210 ° C. is selected as the lower limit of the hot embrittlement temperature, and this is a formula representing a composition condition obtained by assuming that the solidus temperature obtained by the above formula (C) satisfies 1210 ° C. or higher.
1467- {165 × (C%) + 6 × (Si%) + 4.1 × (Mn%) + 1.5 × (Cr%) + 500 × (P%) + 40 × (S%)}> 1210 (4)

  In the above formula (4), the Si content is 1% by mass or less, the coefficient in the Cr content term is relatively small, the Cr content is 10% by mass or less, and the S content is 0.02%. Since MnS is easily formed because it is less than mass% and contains high Mn, it is considered that the contribution of each element content of Si, Cr, S is small. Therefore, if the temperature influence based on the terms of each element content of Si, Cr, S is fixed at 2 ° C. and these terms are omitted, the following formula (4 ′) is obtained, and the following formula (5) is derived. .

1467- {165 × (C%) + 4.1 × (Mn%) + 500 × (P%) + 2}> 1210 (4) ′
(Mn%) + 40.2 × (C%) + 122 × (P%) <62.2 (5)
Here, (C%), (Si%), (Mn%), (Cr%), (P%), and (S%) in the above formulas (4) to (5) are respectively the chemistry of steel. It is content (unit: mass%) of C, Si, Mn, Cr, P and S in the composition.

When the left side of the above formula (5) is 62.2 or more, the solidus temperature is lowered to 1200 ° C. or less, and eutectic carbide having a melting point of 1200 ° C. or less is generated, which may cause hot embrittlement.
Moreover, in order not to impair high temperature ductility, in order to narrow the solid-liquid coexistence temperature range, it is preferable that C content and P content satisfy | fill following formula (6).

(% C) +4.3 (% P) <1.21 (6)
Here, (C%) and (P%) in the above formula (6) are the contents (unit: mass%) of C and P in the chemical composition of steel, respectively.

  The above formula (6) is based on the finding that the coexistence temperature range (liquidus temperature−solidus temperature) is preferably less than 190 ° C. from the viewpoint of ensuring hot workability. When the left side of the above formula (6) is 1.21 or more, the solid-liquid coexistence temperature range exceeds 190 ° C., so that the possibility of causing hot embrittlement increases.

  A test using a vertical continuous casting machine using 2.5 ton molten steel was performed. Molten steel having the composition shown in Table 3 was melted in a melting furnace and poured into a tundish through a ladle. The molten steel temperature of the tundish is adjusted to 1430-1490 ° C., hot water is supplied to the internal water-cooled copper plate mold that vibrates from the immersion nozzle, continuous casting is performed under the conditions shown in Table 3, and secondary water spraying is performed below the mold. Cooling was performed to obtain a slab slab having a thickness of 100 mm, a width of 800 mm, and a length of 3500 mm. Secondary cooling was performed with a specific water amount of 0.5 to 1.0 L per kg of slab weight. After cooling the slab to room temperature, the slab was examined for the presence or absence of surface defects on the slab, and a part was used as a base material sample for a hot rolling test. Hot rolling was performed under the conditions of a heating temperature of 1100 ° C., a total rolling reduction of 80%, and a finish rolling temperature of 800 ° C., and a steel plate having a surface thickness of 20 mm with no defects such as surface cracks and ear cracks was obtained.

  Table 3 shows the results of the slab surface defects.

  No. of the example of the present invention. In No. 1, very slight wrinkles occurred within 60 seconds of casting, but it was almost sound. No. When the casting speed was increased in the steel having the composition of 1, it was confirmed that the occurrence of initial rashes was suppressed (No. 1 '). No. of the example of the present invention. In Nos. 2 and 3, there was no crater defect on the surface of the slab, and there were no cracks during the hot rolling test.

  On the other hand, no. In all of 4-6, rash defects on the surface of the slab occurred. Comparative Example No. In No. 7, the molten metal surface in the mold caused by the low temperature molten steel was peeled off. Moreover, No. of the comparative example. In No. 8, crack-like microcracks estimated to have occurred during slab bending correction occurred on the slab surface.

  FIG. 2 shows the relationship between the casting speed V and Ta (the difference between the casting temperature T and the value a calculated by the above formula (3)) in the inventive example and the comparative example. It is understood that a rash occurs when the casting speed V is too low or when Ta is too high.

Claims (4)

As basic components, in mass%, C: 0.09% to 1.5%, Si: 0.05% to 1.0%, Mn: 10% to 31%, Cr: 10% or less, P : 0.05% or less, S: 0.02% or less, Al: 0.003% or more and 0.1% or less, N: 0.005% or more and 0.50% or less, with the balance being Fe and impurities A method for producing a high manganese content steel having a chemical composition by a continuous casting method,
While controlling so that the molten steel temperature T (unit: ° C) in the molten steel container immediately before supplying hot water to the mold satisfies the following formula (1),
A method for producing a high manganese content steel, wherein the casting speed Vc (unit: m / min) is selected within the range of the following formula (2):
a ≦ T ≦ a + 50 (1)
Vc ≧ 0.02 × (T−a) (2)
Here, a is a value determined by the following formula (3) from the composition of steel, and (C%), (Si%), (Mn%) and (Cr%) in the formula are respectively It is content (unit: mass%) of C, Si, Mn and Cr in the chemical composition.
a = 1562− {62 × (C%) + 6 × (Si%) + 4.1 × (Mn%) + 1.5 × (Cr%)} (3) The molten steel temperature T in the molten steel container immediately before the hot water supply to the mold is further controlled to satisfy the following formula (1 ′), and the casting speed Vc (unit: m / min) is within the range of the following formula (2 ′). The method for producing a high manganese content steel according to claim 1, wherein:
a ≦ T ≦ a + 30 (1 ′)
Vc ≧ 0.025 × (T−a) (2 ′) The manufacturing method of the high manganese content steel of Claim 1 or 2 with which the said chemical composition further satisfy | fills following formula (5):
(Mn%) + 40.2 × (C%) + 122 × (P%) <62.2 (5)
Here, (Mn%), (C%) and (P%) in the above formula (5) are the contents (unit: mass%) of Mn, C and P in the chemical composition, respectively. The manufacturing method of the high manganese content steel in any one of Claim 1 to 3 with which the said chemical composition further satisfy | fills following formula (6):
(% C) +4.3 (% P) <1.21 (6)
Here, (C%) and (P%) in the above formula (6) are the contents (unit: mass%) of C and P in the chemical composition, respectively.

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