WO2017141740A1 - Method for producing high-strength, high-ductility steel sheet - Google Patents
Method for producing high-strength, high-ductility steel sheet Download PDFInfo
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- WO2017141740A1 WO2017141740A1 PCT/JP2017/004070 JP2017004070W WO2017141740A1 WO 2017141740 A1 WO2017141740 A1 WO 2017141740A1 JP 2017004070 W JP2017004070 W JP 2017004070W WO 2017141740 A1 WO2017141740 A1 WO 2017141740A1
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
Definitions
- the present disclosure relates to a method for manufacturing a high-strength, high-ductility steel plate useful as a thin steel plate for automobiles, and more specifically, to a method for manufacturing a steel plate made of medium Mn steel containing about 4 to 10% by mass of Mn.
- a high-strength, high-ductility steel sheet that ensures a tensile strength (TS) of 780 MPa or more and a TS ⁇ elongation (EL) of 25000 MPa% or more. Is used.
- Patent Document 1 discloses that a hot-rolled steel sheet is subjected to a heat treatment for holding at a temperature of Ac1 to Ac1 + 100 ° C. for 3 minutes or more, and then cold-rolled as it is or at a reduction rate of 20% or more.
- a method is disclosed in which medium Mn steel is produced by annealing for at least 1 minute at an ultimate temperature of Ac1-30 ° C to Ac1 + 100 ° C.
- Patent Document 2 discloses that a steel sheet after hot rolling is wound with Ar1 to Ar1 + (Ar1 ⁇ Ar3) / 2, cooled to 200 ° C. or lower, held at Ac1-200 ° C. to Ac1 for 30 minutes or more, A method of manufacturing medium Mn steel by performing cold rolling and then holding at Ac1 to Ac1 + (Ar1-Ar3) / 2 for 30 s to 360 min is disclosed.
- the medium Mn steel is intended to improve the strength-ductility balance by dissolving carbide such as cementite and causing Mn concentration from ferrite to austenite in the annealing process.
- the purpose of the present disclosure is to provide a high strength and high productivity that is superior to the conventional technology while ensuring a strength-ductility balance with a tensile strength (TS) of 780 MPa or more and a TS ⁇ elongation (EL) of 25000 MPa% or more. It is providing the manufacturing method of a ductile steel plate.
- TS tensile strength
- EL TS ⁇ elongation
- the manufacturing method of the high strength and high ductility steel sheet according to the first invention of the present disclosure is as follows: Ingredient composition is mass%, C: 0.05 to 0.30% Si: 0 to 2.5%, Mn: 4.0 to 10.0%, Al: 0 to 2.0%, P: more than 0% and 0.03% or less, S: more than 0% and 0.01% or less,
- the balance consists of iron and inevitable impurities, Hot rolled or cold rolled In a high temperature range of (Ae1 + Ae3) / 2 or more and [Ae3 + 50 ° C.] or less, the residence time at a temperature of [maximum reached temperature ⁇ 10 ° C.] or more is 3 to 200 s, An annealing step was further provided for staying for 30 to 300 s with a temperature change within ⁇ 1 ° C./s in a low temperature range of Ae 1 or more (Ae1 + 2 ⁇ Ae3) / 3 or less and 20 ° C. or more lower than the highest temperature in the
- the manufacturing method of the high strength and high ductility steel sheet according to the second invention of the present disclosure is as follows:
- the component composition of the hot-rolled sheet or cold-rolled sheet is further mass%, It contains one or more of Cr, Mo, Ni and Cu in a total amount of more than 0% and 1.0% or less.
- the manufacturing method of the high strength and high ductility steel sheet according to the third invention of the present disclosure is as follows:
- the component composition of the hot-rolled sheet or cold-rolled sheet is further mass%,
- One or more of V, Nb, and Ti are included in a total amount of more than 0% and 0.2% or less.
- the present disclosure in steel containing 4 to 10% by mass of Mn, as an annealing process, after heating for a short time in the high temperature side of the two-phase region or in the high-temperature region that slightly enters the austenite single-phase region,
- the total heating time in the annealing process is significantly shortened compared to the prior art, and in the austenite while promoting dissolution of carbides
- the productivity is higher than before. High strength and high ductility steel sheets can be manufactured.
- the inventors have promoted the dissolution of carbides in the medium Mn steel while accelerating the concentration of Mn in austenite and further suppressing the recovery of the parent phase.
- the following thought flow was used for examination.
- the manufacturing method of the high-strength and high-ductility steel plate according to the present disclosure completed as described above is as follows.
- Ingredient composition is mass%, C: 0.05 to 0.30% Si: 0 to 2.5%, Mn: 4.0 to 10.0%, Al: 0 to 2.0%, P: more than 0% and 0.03% or less, S: more than 0% and 0.01% or less,
- the balance consists of iron and inevitable impurities, Hot rolled or cold rolled In a high temperature range of (Ae1 + Ae3) / 2 or more and [Ae3 + 50 ° C.] or less, the residence time at a temperature of [maximum reached temperature ⁇ 10 ° C.] or more is 3 to 200 s,
- An annealing step was further provided for staying for 30 to 300 s with a temperature change within ⁇ 1 ° C./s in a low temperature range of Ae 1 or more (Ae1 + 2 ⁇ Ae3) / 3 or less and 20 ° C. or
- Component composition of hot-rolled or cold-rolled sheet First, the component composition of a hot-rolled sheet or cold-rolled sheet used in the embodiment of the present invention, that is, the component composition of a steel plate (hereinafter also simply referred to as “steel plate”) as a final product will be described. Hereinafter, all the units of chemical components are mass%. In addition, “content” of each component may be simply referred to as “amount”.
- C 0.05 to 0.30% C contributes to the amount of retained austenite in the steel sheet, and is an essential element for ensuring the strength and ductility of the steel sheet. In order to effectively exhibit such an action, it is necessary to contain C in the steel sheet at 0.05% or more, preferably 0.06% or more, and more preferably 0.07% or more. However, since the weldability is deteriorated when the C content in the steel sheet becomes excessive, the C content in the steel sheet is 0.30% or less, preferably 0.28% or less, and more preferably 0.26% or less.
- Si 0 to 2.5% Si is an element that contributes to an increase in the strength of the steel sheet by solid solution strengthening and contributes to an improvement in ductility by ensuring the amount of retained austenite by suppressing the decomposition of the retained austenite. May be.
- the Si amount in the steel sheet is 2.5% or less, preferably 2.3% or less, Preferably, it should be limited to 2.1% or less.
- Mn 4.0 to 10.0% Mn is very effective for securing a large amount of retained austenite in the steel sheet, and it can be concentrated in the retained austenite to increase the stability of the retained austenite, thereby contributing to the improvement of the ductility of the steel sheet. Elements. In order to exhibit these functions effectively, it is necessary to contain Mn in the steel sheet at 4.0% or more, preferably 4.5% or more, more preferably 5.0% or more. However, when the amount of Mn in the steel sheet becomes excessive, the Ae1 point is lowered, so that the temperature of Ae1 is not less than (Ae1 + 2 ⁇ Ae3) / 3 and the temperature is kept in a low temperature range that is 20 ° C.
- the Mn content in the steel sheet is 10.0% or less, preferably because the Mn diffusion does not occur sufficiently and the desired effect cannot be obtained in the targeted short time (30 to 300 s residence time). Is 9.0% or less, more preferably 8.0% or less.
- Al 0 to 2.0% Al, like Si, contributes to increasing the strength of the steel sheet by solid solution strengthening, and is an element that contributes to improving ductility by ensuring the amount of retained austenite by suppressing the decomposition of retained austenite. You may make it contain in a steel plate. In order to effectively exhibit these functions, it is preferable to contain Al in the steel sheet in an amount of 0.02% or more, further 0.1% or more, and particularly 0.3% or more. However, if the amount of Al in the steel sheet becomes excessive, the ductility of the matrix phase deteriorates and the ductility of the steel sheet deteriorates, so the Al content in the steel sheet is 2.0% or less, preferably 1.8% or less, Preferably, it should be limited to 1.6% or less.
- P more than 0% and 0.03% or less P is unavoidably present in the steel sheet as an impurity element and contributes to an increase in strength by solid solution strengthening, but segregates at the prior austenite grain boundaries and embrittles the grain boundaries. Therefore, the amount of P in the steel sheet is 0.03% or less, preferably 0.02% or less, and more preferably 0.015% or less.
- S more than 0% and 0.01% or less S is also unavoidably present in the steel sheet as an impurity element, forms MnS inclusions, and becomes a starting point of cracks when expanding holes, thereby reducing stretch flangeability.
- the S content is 0.01% or less, preferably 0.007% or less, and more preferably 0.005% or less.
- the steel plate obtained by the manufacturing method according to the embodiment of the present invention has the above-mentioned elements as basic components, and the balance is iron and inevitable impurities (N, O, etc.), but within the scope not impairing the effects of the present disclosure.
- the following permissible components can be contained.
- One or more of Cr, Mo, Ni and Cu Total amount of more than 0% and 1.0% or less
- These elements enhance the hardenability of the steel sheet and suppress the diffusion transformation such as ferrite and pearlite, and the strength It is an element useful for improving the strength-ductility balance of a steel sheet by contributing to the securing of retained austenite.
- the total amount is preferably 1.0% or less, more preferably 0.8% or less, and particularly preferably 0.6% or less. .
- V, Nb and Ti Total amount of more than 0% and 0.2% or less
- These elements are useful elements for increasing the strength of the steel sheet by precipitation strengthening. In order to effectively exhibit such an action, it is preferable to contain these elements in the steel sheet in a total amount of 0.01% or more, further 0.02% or more, particularly 0.05% or more. However, if these elements are excessively contained in the steel sheet, the cost becomes too high, so the total amount is preferably 0.2% or less, more preferably 0.18% or less, and particularly preferably 0.15% or less. .
- Hot rolled plate or cold rolled plate used in the embodiment of the present invention Next, a hot-rolled plate or a cold-rolled plate, which is an intermediate material used in the embodiment of the present invention, will be described.
- an intermediate material having the above composition is used.
- a hot-rolled plate or a cold-rolled plate may be used.
- the hot-rolled sheet is not particularly limited in the production conditions, and for example, a steel sheet obtained by hot rolling a steel material having the above component composition by a conventional method can be used.
- the cold-rolled sheet is not particularly limited in its production conditions.
- a steel sheet having the above component composition can be hot-rolled by a conventional method and further cold-rolled by a conventional method. .
- the strength after hot-rolling increases the strength of the hot-rolled sheet and makes it difficult to cold-roll. It is also recommended to use one that has been annealed and then cold rolled.
- the conventional low temperature region of the two-phase region As described above, in the embodiment of the present invention, as the annealing process, after the heat treatment for a very short time in the high temperature side of the two-phase region or the austenite single-phase region for a short time, the conventional low temperature region of the two-phase region. It differs from the above-mentioned conventional technique in that a two-stage heat treatment method in which heat treatment is performed for a shorter time than the technique is adopted.
- the heating temperature is set too high or the staying time is set too long, the austenite fraction will increase while the ferrite fraction will decrease, making it impossible to secure the strength-ductility balance of the steel sheet as the final product.
- the upper limit of the heating temperature is limited to Ae3 + 50 ° C.
- the steel plate In the high temperature range, the steel plate is allowed to stay at a temperature of [the highest temperature reached in the high temperature range ⁇ 10 ° C.] or higher for a stay time of 3 to 200 s.
- the maximum attained temperature refers to the temperature at which the highest temperature is obtained when the heat treatment is actually performed in a high temperature range. While the steel sheet is heated and held, the heating temperature is kept substantially constant. Therefore, the steel sheet is essentially held at the highest temperature reached. However, a slight temperature change during holding, specifically, a fluctuation of 10 ° C. or less is allowed. In other words, in the first stage of heating and holding, the steel sheet is heated and held at a temperature equal to or higher than the [maximum reached temperature in the high temperature range ⁇ 10 ° C.].
- the holding temperature during the heat treatment is controlled between [maximum attained temperature] to [maximum attained temperature ⁇ 10 ° C.].
- the maximum temperature reached is [Ae3 + 50 ° C.] or less, which is the upper limit of the high temperature region, and [Maximum temperature reached in the high temperature region ⁇ 10 ° C.] is equal to or higher than the lower limit (Ae1 + Ae3) / 2 of the high temperature region.
- the reverse transformation does not proceed sufficiently if the residence time at the holding temperature in the first stage of heating and holding (that is, the temperature of [the highest temperature in the high temperature range ⁇ 10 ° C.] or higher) is less than 3 s. For this reason, the amount of retained austenite in the steel plate of the final product is insufficient and the strength is lowered, so that there is a possibility that a strength-elongation balance cannot be ensured.
- the residence time at a temperature equal to or higher than the [maximum reached temperature in the high temperature range ⁇ 10 ° C.] is set to 3 to 200 s.
- ⁇ Second-stage heating and holding In a low temperature range of Ae1 or more (Ae1 + 2 ⁇ Ae3) / 3 or less and 20 ° C or more lower than the highest temperature in the high temperature range, the temperature change within ⁇ 1 ° C / s is 30 to 300 seconds.
- the first stage After sufficiently dissolving the carbide by heating and holding in the first stage, in order to appropriately control the austenite / ferrite fraction and promote the concentration of Mn in the austenite, the first stage is continued. Heat and hold in a two-phase region (low temperature region) on the lower temperature side than the temperature region (high temperature region).
- the low temperature range is Ae1 or more (Ae1 + 2 ⁇ Ae3) / 3 or less and a temperature range that is 20 ° C. or more lower than the highest temperature reached in the high temperature range, and ⁇ 1 in that temperature range. It is necessary to stay for 30 s or more at a temperature change within ° C./s, that is, in a state of slow cooling, moderate temperature rise, or constant temperature. The temperature change is indicated by plus (+) on the temperature drop side and minus (-) on the temperature rise side. However, if the staying time is made too long, the above-described effects are saturated and productivity is lowered, so the upper limit is limited to 300 s or less.
- Ae1 (° C.) and Ae3 (° C.) are obtained from thermodynamic calculation software (Thermo-Calc Software, Thermo-Calc manufactured by AB) using TCFE7 as a thermodynamic database, and the contents of C, Mn, Si and Al (Mass%), the phase fraction of each phase of FCC, BCC and cementite at each temperature is obtained, and the temperature at which transition from the two-phase state of BCC-cementite to the three-phase state of FCC-BCC-cementite is made Ae1 (° C.), FCC -The temperature at which the transition from the two-phase state of BCC to the single phase of FCC was defined as Ae3 (° C).
- cooling is performed at a cooling rate within a common sense range in order to freeze the structure, that is, not to change the appropriate austenite / ferrite fraction obtained by the heating and holding any further. Just do it. For example, it is recommended to cool from the end temperature of the second stage heat treatment to [Ae1-50 ° C.] or lower at a cooling rate of 1 ° C./s or higher. Moreover, in order to improve the toughness of a steel plate, you may perform a tempering process further as needed after the said cooling.
- a cold-rolled sheet having the components shown in Table 1 below was annealed under the heat treatment conditions shown in Table 2 below to produce a steel sheet. All the heat treatment Nos. The heating rate up to the first stage of heating and holding was constant at 10 ° C./s. In addition, heat treatment No. In 1-T, tempering was further carried out after the second stage of heating and holding. The tempering conditions were that the cooling stop temperature was held at 20 ° C. for 50 s, and then reheated to 400 ° C. at a heating rate of 30 ° C./s. After maintaining at that temperature for 20 s, cooling was performed at a cooling rate of 10 ° C./s.
- the steel plate was subjected to nital corrosion, observed with an optical microscope (400 magnifications) to identify each phase other than retained austenite, and the area ratio of each phase was measured by image analysis.
- the area ratio of retained austenite was measured by X-ray diffraction after grinding to a thickness of 1 ⁇ 4 of the steel plate (ISIJISInt. Vol. 33, (1933), No. 7, p. . 776).
- a thin film sample was prepared using FIB (FEI Nova200), and this was observed with a transmission electron microscope with a spherical aberration correction function (JEOL JEM-ARM200F).
- JEOL JEM-ARM200F a transmission electron microscope with a spherical aberration correction function
- the Mn concentration was measured using the attached EDS analyzer (JED-2300T manufactured by JEOL Ltd.).
- the tensile strength TS and the elongation (total elongation) EL were measured by a tensile test.
- the ratio of the area ratio of retained austenite is higher than that of the corresponding standard condition steel sheet and the ratio of Mn concentration Mn ⁇ R in the retained austenite to the Mn content [Mn] of the entire steel sheet.
- Mn ⁇ R / [Mn] is 1.20 or more.
- TS is 780 MPa or more
- TS ⁇ EL is 25000 MPa% or more
- test no. 1, 2, 24, 26, 28, 30 and 32 are standard conditions (standard conditions 1 to 7, respectively) in which annealing is performed by heating and holding in only one stage, as shown in Table 2, and correspond to the prior art. Is. In contrast, test no. Nos. 2 to 21, 23, 25, 27, 29, 31 and 33 are tests performed by changing various conditions for the two-stage heating and holding corresponding to the respective standard conditions.
- test no. 2 to 4, 8, 11, 12, 14 to 16, 19, 21, 23, 25, 27, and 33 are examples of the invention that satisfy all the requirements of the present disclosure.
- Table 3 in each of the inventive examples, the amount of retained austenite is increased as compared with the corresponding standard conditions, and the concentration of Mn in the retained austenite is promoted, while ensuring strength, -It can be seen that the ductility balance is improved.
- test no Reference numerals 5 to 7, 9, 10, 13, 17, 18, 20, 29, and 31 are comparative examples that do not satisfy any of the requirements of the present disclosure.
- test No. 5-7, 9, 10, 13, 17, 18, and 20 are steel types that satisfy the requirements of the component provisions of the present disclosure, but are annealed under conditions that partially deviate from the requirements of the annealing conditions. Organizational requirements are not met and mechanical properties are inferior.
- test no. 5 heat treatment No. 1-D
- the heating temperature in the first stage heating and holding maximum temperature reached
- the reverse transformation does not proceed sufficiently
- the final product The amount of retained austenite in the steel sheet is insufficient, and TS and TS ⁇ EL are inferior.
- test no. 6 heat treatment No. 1-E
- the heating temperature in the first stage heating and holding is too high outside the specified range of the present disclosure.
- the martensite fraction in the steel sheet increases, the ferrite fraction decreases and TS ⁇ EL is inferior.
- test no. No. 7 heat treatment No. 1-F
- the residence time in the first stage heating and holding is too short outside the specified range of the present disclosure, so the reverse transformation does not proceed sufficiently, and the retained austenite in the steel sheet as the final product Insufficient quantity and TS ⁇ EL is inferior.
- test no. 9 heat treatment No. 1-H
- the residence time in the first stage heating and holding is too long outside the specified range of the present disclosure, so that the austenite fraction is increased and the martensite in the steel sheet as the final product is increased.
- the amount is excessive, the amount of ferrite is insufficient, and TS ⁇ EL is inferior.
- test no. 10 heat treatment No. 1-I
- test no. 13 heat treatment No. 1-L
- the heating temperature (starting temperature and ending temperature) in the second stage heating and holding is too high outside the specified range of the present disclosure, so TS ⁇ EL of the steel sheet as the final product Is inferior.
- test no. In No. 17 heat treatment No. 1-P
- the temperature change in the second stage heating and holding is too large outside the specified range of the present disclosure, so that ⁇ TS ⁇ EL of the steel sheet as the final product is insufficient.
- test no. No. 18 (heat treatment No. 1-Q) is inferior in TS ⁇ EL of the steel sheet as the final product because the residence time in the second stage heating and holding is too short outside the specified range of the present disclosure.
- test no. 20 heat treatment No. 1-S
- the stay time in the second stage heating and holding is out of the specified range of the present disclosure and is too long, so the steel structure and mechanical properties of the steel sheet as the final product are within the acceptance criteria. Although satisfied, productivity is inferior.
- test no Although 29 and 31 are annealed under the annealing conditions specified in the present disclosure, they use steel types that partially deviate from the requirements of the component specifications of the present disclosure. Inferior.
- test no On the other hand, 31 (steel type f) has an excessively small amount of Mn, so that the amount of retained austenite is insufficient and the concentration of Mn in the retained austenite becomes insufficient, and TS ⁇ EL is inferior.
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Abstract
A method for producing a high-strength, high-ductility steel sheet, which comprises an annealing step for causing a hot-rolled sheet or cold-rolled sheet having a compositional makeup comprising, in mass%, 0.05-0.30% of C, 0-2.0% of Si, 4.0-10.0% of Mn, 0-2.5% of Al, more than 0% but not more than 0.03% of P, and more than 0% but not more than 0.01% of S, the balance being iron and incidental impurities, to reside in a high-temperature region of (Ae1 + Ae3)/2 to [Ae3 + 50°C] such that the residing time at a temperature of not lower than [the maximum temperature in the high-temperature region - 10°C] is 3-200 s, and thereafter, causing the sheet to reside in a low-temperature region which is at Ae1 to (Ae1 + 2 × Ae3)/3 and lower, and in which the temperature is equal to or lower by 20°C than the maximum temperature of the high-temperature region, for 30-300 s, with the temperature change rate within ±1°C/s.
Description
本開示は、自動車用薄鋼板などとして有用な高強度高延性鋼板の製造方法に関し、詳しくは、Ｍｎを４～１０質量％程度含有する中Ｍｎ鋼からなる鋼板の製造方法に関するものである。
The present disclosure relates to a method for manufacturing a high-strength, high-ductility steel plate useful as a thin steel plate for automobiles, and more specifically, to a method for manufacturing a steel plate made of medium Mn steel containing about 4 to 10% by mass of Mn.
例えば自動車の骨格部品などに使用される鋼板には、衝突安全性や車体軽量化による燃費軽減などを目的として高強度が求められるとともに、形状の複雑な骨格部品に加工するために優れた成形加工性も要求される。このため、具体的な機械的特性（以下、単に「特性」ともいう。）として、引張強度（ＴＳ）が７８０ＭＰａ以上で、ＴＳ×伸び（ＥＬ）が２５０００ＭＰａ％以上を確保する高強度高延性鋼板が使用されている。
For example, steel sheets used for automobile frame parts and the like are required to have high strength for the purpose of collision safety and fuel efficiency reduction by reducing the weight of the car body, and excellent forming process for processing into complex frame parts Sex is also required. For this reason, as specific mechanical properties (hereinafter, also simply referred to as “characteristics”), a high-strength, high-ductility steel sheet that ensures a tensile strength (TS) of 780 MPa or more and a TS × elongation (EL) of 25000 MPa% or more. Is used.
上記特性を備えた鋼板として、強度－延性バランスに優れる、Ｍｎ含有量が４～１０質量％程度の中Ｍｎ鋼が注目されている。
As a steel plate having the above characteristics, a medium Mn steel having an excellent balance between strength and ductility and having a Mn content of about 4 to 10% by mass is attracting attention.
たとえば、特許文献１には、熱間圧延後の鋼板をＡｃ１～Ａｃ１＋１００℃の到達温度で３分以上保持する熱処理を施した後、そのまま、または２０％以上の圧下率で冷間圧延した後、Ａｃ１－３０℃～Ａｃ１＋１００℃の到達温度で１分以上保持する焼鈍を施すことで中Ｍｎ鋼を製造する方法が開示されている。
For example, Patent Document 1 discloses that a hot-rolled steel sheet is subjected to a heat treatment for holding at a temperature of Ac1 to Ac1 + 100 ° C. for 3 minutes or more, and then cold-rolled as it is or at a reduction rate of 20% or more. A method is disclosed in which medium Mn steel is produced by annealing for at least 1 minute at an ultimate temperature of Ac1-30 ° C to Ac1 + 100 ° C.
また、特許文献２には、熱間圧延後の鋼板をＡｒ１～Ａｒ１＋（Ａｒ１ーＡｒ３）／２で巻取り、２００℃以下まで冷却した後、Ａｃ１－２００℃～Ａｃ１で３０ｍｉｎ以上保持した後、冷間圧延を施し、その後、Ａｃ１～Ａｃ１＋（Ａｒ１－Ａｒ３）／２で３０ｓ以上３６０ｍｉｎ以下の保持を行うことで中Ｍｎ鋼を製造する方法が開示されている。
Patent Document 2 discloses that a steel sheet after hot rolling is wound with Ar1 to Ar1 + (Ar1−Ar3) / 2, cooled to 200 ° C. or lower, held at Ac1-200 ° C. to Ac1 for 30 minutes or more, A method of manufacturing medium Mn steel by performing cold rolling and then holding at Ac1 to Ac1 + (Ar1-Ar3) / 2 for 30 s to 360 min is disclosed.
中Ｍｎ鋼は、焼鈍工程において、セメンタイト等の炭化物を溶解させ、フェライト中からオーステナイト中へのＭｎの濃化を起こさせることによって、強度－延性バランスを向上させようとするものである。
The medium Mn steel is intended to improve the strength-ductility balance by dissolving carbide such as cementite and causing Mn concentration from ferrite to austenite in the annealing process.
しかしながら、従来技術のように焼鈍温度を一定温度として炭化物の溶解とオーステナイトへのＭｎの濃化を進めようとしても、焼鈍温度を高くすると炭化物の溶解は促進されるものの平衡でのオーステナイト中のＭｎ濃度が低くなるためオーステナイト中へのＭｎの濃化の度合が小さくなる一方、焼鈍温度を低くすると炭化物の溶解に時間が掛かるため生産性が低くなるという問題があった。
However, even if it is attempted to proceed with the dissolution of carbides and the concentration of Mn in austenite at a constant annealing temperature as in the prior art, if the annealing temperature is increased, the dissolution of carbides is promoted, but the Mn in austenite at equilibrium is increased. Since the concentration decreases, the degree of concentration of Mn in the austenite decreases. On the other hand, if the annealing temperature is decreased, it takes time to dissolve the carbide, resulting in lower productivity.
さらに、強度を確保しようとして長時間の焼鈍を行うと、マルテンサイトや加工フェライトなど母相中の歪が緩和され回復（転移密度の低下）が進行し却って強度が低下してしまうため、鋼板全体の強度確保が困難になる問題もあった。
Furthermore, if annealing is performed for a long time in order to ensure strength, strain in the matrix phase such as martensite and processed ferrite is relaxed and recovery (decrease in the transition density) proceeds and the strength decreases, so the entire steel sheet There was also a problem that it was difficult to ensure the strength of the steel.
そこで本開示の目的は、引張強度（ＴＳ）が７８０ＭＰａ以上で、ＴＳ×伸び（ＥＬ）が２５０００ＭＰａ％以上の、強度－延性バランスを確保しつつ、従来技術よりも生産性に優れた高強度高延性鋼板の製造方法を提供することにある。
Accordingly, the purpose of the present disclosure is to provide a high strength and high productivity that is superior to the conventional technology while ensuring a strength-ductility balance with a tensile strength (TS) of 780 MPa or more and a TS × elongation (EL) of 25000 MPa% or more. It is providing the manufacturing method of a ductile steel plate.
本開示の第１発明に係る高強度高延性鋼板の製造方法は、
成分組成が、質量％で、
Ｃ：０．０５～０．３０％、
Ｓｉ：０～２．５％、
Ｍｎ：４．０～１０．０％、
Ａｌ：０～２．０％、
Ｐ：０％超０．０３％以下、
Ｓ：０％超０．０１％以下であり、
残部が鉄および不可避的不純物からなる、
熱延板または冷延板を、
（Ａｅ１＋Ａｅ３）／２以上［Ａｅ３＋５０℃］以下の高温域において、［最高到達温度－１０℃］以上の温度での滞在時間が３～２００ｓとなるように滞在させたのち、
引き続きＡｅ１以上（Ａｅ１＋２×Ａｅ３）／３以下で且つ前記高温域における最高到達温度から２０℃以上低い低温域において、±１℃／ｓ以内の温度変化で３０～３００ｓ滞在させる焼鈍工程
を備えたことを特徴とするものである。 The manufacturing method of the high strength and high ductility steel sheet according to the first invention of the present disclosure is as follows:
Ingredient composition is mass%,
C: 0.05 to 0.30%
Si: 0 to 2.5%,
Mn: 4.0 to 10.0%,
Al: 0 to 2.0%,
P: more than 0% and 0.03% or less,
S: more than 0% and 0.01% or less,
The balance consists of iron and inevitable impurities,
Hot rolled or cold rolled
In a high temperature range of (Ae1 + Ae3) / 2 or more and [Ae3 + 50 ° C.] or less, the residence time at a temperature of [maximum reached temperature −10 ° C.] or more is 3 to 200 s,
An annealing step was further provided for staying for 30 to 300 s with a temperature change within ± 1 ° C./s in a low temperature range of Ae 1 or more (Ae1 + 2 × Ae3) / 3 or less and 20 ° C. or more lower than the highest temperature in the high temperature range. It is characterized by.
成分組成が、質量％で、
Ｃ：０．０５～０．３０％、
Ｓｉ：０～２．５％、
Ｍｎ：４．０～１０．０％、
Ａｌ：０～２．０％、
Ｐ：０％超０．０３％以下、
Ｓ：０％超０．０１％以下であり、
残部が鉄および不可避的不純物からなる、
熱延板または冷延板を、
（Ａｅ１＋Ａｅ３）／２以上［Ａｅ３＋５０℃］以下の高温域において、［最高到達温度－１０℃］以上の温度での滞在時間が３～２００ｓとなるように滞在させたのち、
引き続きＡｅ１以上（Ａｅ１＋２×Ａｅ３）／３以下で且つ前記高温域における最高到達温度から２０℃以上低い低温域において、±１℃／ｓ以内の温度変化で３０～３００ｓ滞在させる焼鈍工程
を備えたことを特徴とするものである。 The manufacturing method of the high strength and high ductility steel sheet according to the first invention of the present disclosure is as follows:
Ingredient composition is mass%,
C: 0.05 to 0.30%
Si: 0 to 2.5%,
Mn: 4.0 to 10.0%,
Al: 0 to 2.0%,
P: more than 0% and 0.03% or less,
S: more than 0% and 0.01% or less,
The balance consists of iron and inevitable impurities,
Hot rolled or cold rolled
In a high temperature range of (Ae1 + Ae3) / 2 or more and [Ae3 + 50 ° C.] or less, the residence time at a temperature of [maximum reached temperature −10 ° C.] or more is 3 to 200 s,
An annealing step was further provided for staying for 30 to 300 s with a temperature change within ± 1 ° C./s in a low temperature range of Ae 1 or more (Ae1 + 2 × Ae3) / 3 or less and 20 ° C. or more lower than the highest temperature in the high temperature range. It is characterized by.
本開示の第２発明に係る高強度高延性鋼板の製造方法は、
上記第１発明において、
前記熱延板または冷延板の成分組成が、さらに、質量％で、
Ｃｒ、Ｍｏ、Ｎｉ、Ｃｕの１種または２種以上を合計量で０％超１．０％以下含むものである。 The manufacturing method of the high strength and high ductility steel sheet according to the second invention of the present disclosure is as follows:
In the first invention,
The component composition of the hot-rolled sheet or cold-rolled sheet is further mass%,
It contains one or more of Cr, Mo, Ni and Cu in a total amount of more than 0% and 1.0% or less.
上記第１発明において、
前記熱延板または冷延板の成分組成が、さらに、質量％で、
Ｃｒ、Ｍｏ、Ｎｉ、Ｃｕの１種または２種以上を合計量で０％超１．０％以下含むものである。 The manufacturing method of the high strength and high ductility steel sheet according to the second invention of the present disclosure is as follows:
In the first invention,
The component composition of the hot-rolled sheet or cold-rolled sheet is further mass%,
It contains one or more of Cr, Mo, Ni and Cu in a total amount of more than 0% and 1.0% or less.
本開示の第３発明に係る高強度高延性鋼板の製造方法は、
上記第１または第２発明において、
前記熱延板または冷延板の成分組成が、さらに、質量％で、
Ｖ、Ｎｂ、Ｔｉの１種または２種以上を合計量で０％超０．２％以下含むものである。 The manufacturing method of the high strength and high ductility steel sheet according to the third invention of the present disclosure is as follows:
In the first or second invention,
The component composition of the hot-rolled sheet or cold-rolled sheet is further mass%,
One or more of V, Nb, and Ti are included in a total amount of more than 0% and 0.2% or less.
上記第１または第２発明において、
前記熱延板または冷延板の成分組成が、さらに、質量％で、
Ｖ、Ｎｂ、Ｔｉの１種または２種以上を合計量で０％超０．２％以下含むものである。 The manufacturing method of the high strength and high ductility steel sheet according to the third invention of the present disclosure is as follows:
In the first or second invention,
The component composition of the hot-rolled sheet or cold-rolled sheet is further mass%,
One or more of V, Nb, and Ti are included in a total amount of more than 0% and 0.2% or less.
本開示によれば、Ｍｎを４～１０質量％含有する鋼において、焼鈍工程として、２相域の高温側ないしオーステナイト単相域に少し入った高温域でごく短時間加熱した後に、２相域の低温域で従来技術より短い時間加熱する２段階加熱方式を採用したことで、焼鈍工程での合計加熱時間は従来技術より大幅に短縮されたうえ、炭化物の溶解を促進しつつ、オーステナイト中へのＭｎの濃化を加速し、さらには、母相の回復（転位密度の低下）を抑制することが可能となり、その結果、目標の強度－延性バランスを確保しつつ、従来より高生産性で高強度高延性鋼板を製造できるようになった。
According to the present disclosure, in steel containing 4 to 10% by mass of Mn, as an annealing process, after heating for a short time in the high temperature side of the two-phase region or in the high-temperature region that slightly enters the austenite single-phase region, By adopting a two-step heating method that heats for a shorter time in the low temperature region than in the prior art, the total heating time in the annealing process is significantly shortened compared to the prior art, and in the austenite while promoting dissolution of carbides It is possible to accelerate the concentration of Mn in the steel and to further suppress the recovery of the parent phase (decrease in the dislocation density). As a result, while maintaining the target strength-ductility balance, the productivity is higher than before. High strength and high ductility steel sheets can be manufactured.
発明者らは、上記課題を解決するために、中Ｍｎ鋼において、炭化物の溶解を促進しつつ、オーステナイト中へのＭｎの濃化を加速させ、さらには母相の回復を抑制する手段について、以下の思考フローにより検討を行った。
In order to solve the above-mentioned problems, the inventors have promoted the dissolution of carbides in the medium Mn steel while accelerating the concentration of Mn in austenite and further suppressing the recovery of the parent phase. The following thought flow was used for examination.
・炭化物の溶解の促進
強度－伸びバランスを確保するために、フェライトとオーステナイトの分率を理想的な分率に調整しようとして２相域の中央付近の温度で加熱保持すると、炭化物（セメンタイト）からオーステナイトへの逆変態の駆動力が小さくなり、炭化物の溶解の進行が遅くなる。そこで、炭化物の溶解を促進させるため、まず、第１段階として、加熱温度を２相域の中央付近の温度より高める。 ・ Promoting the dissolution of carbides In order to ensure the strength-elongation balance, when the heat and temperature are maintained near the center of the two-phase region in an attempt to adjust the ferrite and austenite fractions to an ideal fraction, the carbides (cementite) The driving force for reverse transformation to austenite is reduced, and the progress of dissolution of carbide is slowed. Therefore, in order to promote the dissolution of carbides, first, as a first stage, the heating temperature is raised above the temperature near the center of the two-phase region.
強度－伸びバランスを確保するために、フェライトとオーステナイトの分率を理想的な分率に調整しようとして２相域の中央付近の温度で加熱保持すると、炭化物（セメンタイト）からオーステナイトへの逆変態の駆動力が小さくなり、炭化物の溶解の進行が遅くなる。そこで、炭化物の溶解を促進させるため、まず、第１段階として、加熱温度を２相域の中央付近の温度より高める。 ・ Promoting the dissolution of carbides In order to ensure the strength-elongation balance, when the heat and temperature are maintained near the center of the two-phase region in an attempt to adjust the ferrite and austenite fractions to an ideal fraction, the carbides (cementite) The driving force for reverse transformation to austenite is reduced, and the progress of dissolution of carbide is slowed. Therefore, in order to promote the dissolution of carbides, first, as a first stage, the heating temperature is raised above the temperature near the center of the two-phase region.
・オーステナイト中へのＭｎの濃化の加速
上記のように、炭化物の溶解を促進するために加熱温度を２相域の中央付近の温度より上昇させると、熱力学上の平衡関係より、オーステナイト中の平衡Ｍｎ濃度が低下するため、Ｍｎの濃化が起こりにくくなる。そこで、つぎに、第２段階として、２相域の中央付近の温度より低い温度で加熱することで、Ｍｎの拡散速度は低くなるものの、オーステナイト中の平衡Ｍｎ濃度を高めることによってフェライト中からオーステナイト中へのＭｎの分配を進行させることができる。また、低い温度での加熱によりオーステナイトの粗大化を抑制し、強度低下を防止できる。 ・ Acceleration of Mn concentration in austenite As described above, when the heating temperature is raised above the temperature near the center of the two-phase region in order to promote the dissolution of carbides, Therefore, the concentration of Mn is less likely to occur. Then, as a second stage, the Mn diffusion rate is lowered by heating at a temperature lower than the temperature near the center of the two-phase region, but the equilibrium Mn concentration in the austenite is increased to increase the equilibrium Mn concentration in the austenite. The distribution of Mn into it can proceed. Moreover, the coarsening of austenite can be suppressed by heating at a low temperature, and strength reduction can be prevented.
上記のように、炭化物の溶解を促進するために加熱温度を２相域の中央付近の温度より上昇させると、熱力学上の平衡関係より、オーステナイト中の平衡Ｍｎ濃度が低下するため、Ｍｎの濃化が起こりにくくなる。そこで、つぎに、第２段階として、２相域の中央付近の温度より低い温度で加熱することで、Ｍｎの拡散速度は低くなるものの、オーステナイト中の平衡Ｍｎ濃度を高めることによってフェライト中からオーステナイト中へのＭｎの分配を進行させることができる。また、低い温度での加熱によりオーステナイトの粗大化を抑制し、強度低下を防止できる。 ・ Acceleration of Mn concentration in austenite As described above, when the heating temperature is raised above the temperature near the center of the two-phase region in order to promote the dissolution of carbides, Therefore, the concentration of Mn is less likely to occur. Then, as a second stage, the Mn diffusion rate is lowered by heating at a temperature lower than the temperature near the center of the two-phase region, but the equilibrium Mn concentration in the austenite is increased to increase the equilibrium Mn concentration in the austenite. The distribution of Mn into it can proceed. Moreover, the coarsening of austenite can be suppressed by heating at a low temperature, and strength reduction can be prevented.
・母相の回復の抑制
上記のようにして実質的に高温での滞在時間を短くすることで、母相中における転位密度の低下を抑制し、強度の確保をしやすくする。 -Suppression of recovery of parent phase By substantially shortening the residence time at a high temperature as described above, it is possible to suppress a decrease in dislocation density in the parent phase and to ensure strength.
上記のようにして実質的に高温での滞在時間を短くすることで、母相中における転位密度の低下を抑制し、強度の確保をしやすくする。 -Suppression of recovery of parent phase By substantially shortening the residence time at a high temperature as described above, it is possible to suppress a decrease in dislocation density in the parent phase and to ensure strength.
発明者らは、上記思考フローに基づき、後記実施例に示す確証試験によってさらに検討を進めた結果、本開示の高強度高延性鋼板の製造方法を完成するに至った。
As a result of further investigations based on the above-described thought flow and the confirmation test shown in the examples below, the inventors have completed the method for producing a high-strength and high-ductility steel sheet of the present disclosure.
このようにして完成した、本開示に係る高強度高延性鋼板の製造方法は、
成分組成が、質量％で、
Ｃ：０．０５～０．３０％、
Ｓｉ：０～２．５％、
Ｍｎ：４．０～１０．０％、
Ａｌ：０～２．０％、
Ｐ：０％超０．０３％以下、
Ｓ：０％超０．０１％以下であり、
残部が鉄および不可避的不純物からなる、
熱延板または冷延板を、
（Ａｅ１＋Ａｅ３）／２以上［Ａｅ３＋５０℃］以下の高温域において、［最高到達温度－１０℃］以上の温度での滞在時間が３～２００ｓとなるように滞在させたのち、
引き続きＡｅ１以上（Ａｅ１＋２×Ａｅ３）／３以下で且つ前記高温域における最高到達温度から２０℃以上低い低温域において、±１℃／ｓ以内の温度変化で３０～３００ｓ滞在させる焼鈍工程
を備えたことを特徴とするものである。 The manufacturing method of the high-strength and high-ductility steel plate according to the present disclosure completed as described above is as follows.
Ingredient composition is mass%,
C: 0.05 to 0.30%
Si: 0 to 2.5%,
Mn: 4.0 to 10.0%,
Al: 0 to 2.0%,
P: more than 0% and 0.03% or less,
S: more than 0% and 0.01% or less,
The balance consists of iron and inevitable impurities,
Hot rolled or cold rolled
In a high temperature range of (Ae1 + Ae3) / 2 or more and [Ae3 + 50 ° C.] or less, the residence time at a temperature of [maximum reached temperature −10 ° C.] or more is 3 to 200 s,
An annealing step was further provided for staying for 30 to 300 s with a temperature change within ± 1 ° C./s in a low temperature range of Ae 1 or more (Ae1 + 2 × Ae3) / 3 or less and 20 ° C. or more lower than the highest temperature in the high temperature range. It is characterized by.
成分組成が、質量％で、
Ｃ：０．０５～０．３０％、
Ｓｉ：０～２．５％、
Ｍｎ：４．０～１０．０％、
Ａｌ：０～２．０％、
Ｐ：０％超０．０３％以下、
Ｓ：０％超０．０１％以下であり、
残部が鉄および不可避的不純物からなる、
熱延板または冷延板を、
（Ａｅ１＋Ａｅ３）／２以上［Ａｅ３＋５０℃］以下の高温域において、［最高到達温度－１０℃］以上の温度での滞在時間が３～２００ｓとなるように滞在させたのち、
引き続きＡｅ１以上（Ａｅ１＋２×Ａｅ３）／３以下で且つ前記高温域における最高到達温度から２０℃以上低い低温域において、±１℃／ｓ以内の温度変化で３０～３００ｓ滞在させる焼鈍工程
を備えたことを特徴とするものである。 The manufacturing method of the high-strength and high-ductility steel plate according to the present disclosure completed as described above is as follows.
Ingredient composition is mass%,
C: 0.05 to 0.30%
Si: 0 to 2.5%,
Mn: 4.0 to 10.0%,
Al: 0 to 2.0%,
P: more than 0% and 0.03% or less,
S: more than 0% and 0.01% or less,
The balance consists of iron and inevitable impurities,
Hot rolled or cold rolled
In a high temperature range of (Ae1 + Ae3) / 2 or more and [Ae3 + 50 ° C.] or less, the residence time at a temperature of [maximum reached temperature −10 ° C.] or more is 3 to 200 s,
An annealing step was further provided for staying for 30 to 300 s with a temperature change within ± 1 ° C./s in a low temperature range of Ae 1 or more (Ae1 + 2 × Ae3) / 3 or less and 20 ° C. or more lower than the highest temperature in the high temperature range. It is characterized by.
以下、本発明の実施形態をさらに詳しく説明するため、要件ごとに分説する。
Hereinafter, in order to describe the embodiment of the present invention in more detail, each requirement will be described.
〔熱延板または冷延板の成分組成〕
まず、本発明の実施形態に用いる熱延板または冷延板の成分組成、すなわち、最終製品としての鋼板（以下、単に「鋼板」ともいう。）の成分組成について説明する。以下、化学成分の単位はすべて質量％である。また、各成分の「含有量」を単に「量」と記載することもある。 [Component composition of hot-rolled or cold-rolled sheet]
First, the component composition of a hot-rolled sheet or cold-rolled sheet used in the embodiment of the present invention, that is, the component composition of a steel plate (hereinafter also simply referred to as “steel plate”) as a final product will be described. Hereinafter, all the units of chemical components are mass%. In addition, “content” of each component may be simply referred to as “amount”.
まず、本発明の実施形態に用いる熱延板または冷延板の成分組成、すなわち、最終製品としての鋼板（以下、単に「鋼板」ともいう。）の成分組成について説明する。以下、化学成分の単位はすべて質量％である。また、各成分の「含有量」を単に「量」と記載することもある。 [Component composition of hot-rolled or cold-rolled sheet]
First, the component composition of a hot-rolled sheet or cold-rolled sheet used in the embodiment of the present invention, that is, the component composition of a steel plate (hereinafter also simply referred to as “steel plate”) as a final product will be described. Hereinafter, all the units of chemical components are mass%. In addition, “content” of each component may be simply referred to as “amount”.
Ｃ：０．０５～０．３０％
Ｃは、鋼板中の残留オーステナイトの量に寄与することで、鋼板の強度と延性を確保するために必須の元素である。このような作用を有効に発揮させるためには、鋼板中にＣを０．０５％以上、好ましくは０．０６％以上、さらに好ましくは０．０７％以上含有させる必要がある。ただし、鋼板中のＣ量が過剰になると、溶接性を劣化させるので、鋼板中のＣ量は０．３０％以下、好ましくは０．２８％以下、さらに好ましくは０．２６％以下とする。 C: 0.05 to 0.30%
C contributes to the amount of retained austenite in the steel sheet, and is an essential element for ensuring the strength and ductility of the steel sheet. In order to effectively exhibit such an action, it is necessary to contain C in the steel sheet at 0.05% or more, preferably 0.06% or more, and more preferably 0.07% or more. However, since the weldability is deteriorated when the C content in the steel sheet becomes excessive, the C content in the steel sheet is 0.30% or less, preferably 0.28% or less, and more preferably 0.26% or less.
Ｃは、鋼板中の残留オーステナイトの量に寄与することで、鋼板の強度と延性を確保するために必須の元素である。このような作用を有効に発揮させるためには、鋼板中にＣを０．０５％以上、好ましくは０．０６％以上、さらに好ましくは０．０７％以上含有させる必要がある。ただし、鋼板中のＣ量が過剰になると、溶接性を劣化させるので、鋼板中のＣ量は０．３０％以下、好ましくは０．２８％以下、さらに好ましくは０．２６％以下とする。 C: 0.05 to 0.30%
C contributes to the amount of retained austenite in the steel sheet, and is an essential element for ensuring the strength and ductility of the steel sheet. In order to effectively exhibit such an action, it is necessary to contain C in the steel sheet at 0.05% or more, preferably 0.06% or more, and more preferably 0.07% or more. However, since the weldability is deteriorated when the C content in the steel sheet becomes excessive, the C content in the steel sheet is 0.30% or less, preferably 0.28% or less, and more preferably 0.26% or less.
Ｓｉ：０～２．５％
Ｓｉは、固溶強化により鋼板の強度上昇に寄与するとともに、残留オーステナイトの分解を抑制することで残留オーステナイト量を確保できるようにして延性の向上に寄与する元素であるので、鋼板中に含有させてもよい。これらの作用を効果的に発揮させるためには、鋼板中にＳｉを０．１％以上、好ましくは０．３％以上、さらに好ましくは０．５％以上含有させるのが好ましい。ただし、鋼板中のＳｉ量が過剰になると、母相の延性が劣化して鋼板の延性が却って劣化するので、鋼板中のＳｉ量は２．５％以下、好ましくは２．３％以下、さらに好ましくは２．１％以下に制限する必要がある。 Si: 0 to 2.5%
Si is an element that contributes to an increase in the strength of the steel sheet by solid solution strengthening and contributes to an improvement in ductility by ensuring the amount of retained austenite by suppressing the decomposition of the retained austenite. May be. In order to effectively exhibit these functions, it is preferable to contain Si in the steel sheet in an amount of 0.1% or more, preferably 0.3% or more, and more preferably 0.5% or more. However, when the amount of Si in the steel sheet becomes excessive, the ductility of the matrix phase deteriorates and the ductility of the steel sheet deteriorates, so the Si amount in the steel sheet is 2.5% or less, preferably 2.3% or less, Preferably, it should be limited to 2.1% or less.
Ｓｉは、固溶強化により鋼板の強度上昇に寄与するとともに、残留オーステナイトの分解を抑制することで残留オーステナイト量を確保できるようにして延性の向上に寄与する元素であるので、鋼板中に含有させてもよい。これらの作用を効果的に発揮させるためには、鋼板中にＳｉを０．１％以上、好ましくは０．３％以上、さらに好ましくは０．５％以上含有させるのが好ましい。ただし、鋼板中のＳｉ量が過剰になると、母相の延性が劣化して鋼板の延性が却って劣化するので、鋼板中のＳｉ量は２．５％以下、好ましくは２．３％以下、さらに好ましくは２．１％以下に制限する必要がある。 Si: 0 to 2.5%
Si is an element that contributes to an increase in the strength of the steel sheet by solid solution strengthening and contributes to an improvement in ductility by ensuring the amount of retained austenite by suppressing the decomposition of the retained austenite. May be. In order to effectively exhibit these functions, it is preferable to contain Si in the steel sheet in an amount of 0.1% or more, preferably 0.3% or more, and more preferably 0.5% or more. However, when the amount of Si in the steel sheet becomes excessive, the ductility of the matrix phase deteriorates and the ductility of the steel sheet deteriorates, so the Si amount in the steel sheet is 2.5% or less, preferably 2.3% or less, Preferably, it should be limited to 2.1% or less.
Ｍｎ：４．０～１０．０％
Ｍｎは、鋼板中に残留オーステナイトを多量に確保するために、非常に有効であるとともに、残留オーステナイトに濃化して残留オーステナイトの安定度を高めることができ、その結果鋼板の延性向上に寄与する必須の元素である。これらの作用を有効に発揮させるためには、鋼板中にＭｎを４．０％以上、好ましくは４．５％以上、さらに好ましくは５．０％以上含有させる必要がある。ただし、鋼板中のＭｎ量が過剰になると、Ａｅ１点が低下することで、Ａｅ１以上（Ａｅ１＋２×Ａｅ３）／３以下で且つ前記高温域における最高到達温度から２０℃以上低い低温域において滞在させる温度が低くなりすぎて、狙いとする短時間（３０～３００ｓの滞在時間）ではＭｎの拡散が十分に起こらず所望の効果が得られなくなるので、鋼板中のＭｎ量は１０．０％以下、好ましくは９．０％以下、さらに好ましくは８．０％以下とする。 Mn: 4.0 to 10.0%
Mn is very effective for securing a large amount of retained austenite in the steel sheet, and it can be concentrated in the retained austenite to increase the stability of the retained austenite, thereby contributing to the improvement of the ductility of the steel sheet. Elements. In order to exhibit these functions effectively, it is necessary to contain Mn in the steel sheet at 4.0% or more, preferably 4.5% or more, more preferably 5.0% or more. However, when the amount of Mn in the steel sheet becomes excessive, the Ae1 point is lowered, so that the temperature of Ae1 is not less than (Ae1 + 2 × Ae3) / 3 and the temperature is kept in a low temperature range that is 20 ° C. or more lower than the highest temperature in the high temperature range. The Mn content in the steel sheet is 10.0% or less, preferably because the Mn diffusion does not occur sufficiently and the desired effect cannot be obtained in the targeted short time (30 to 300 s residence time). Is 9.0% or less, more preferably 8.0% or less.
Ｍｎは、鋼板中に残留オーステナイトを多量に確保するために、非常に有効であるとともに、残留オーステナイトに濃化して残留オーステナイトの安定度を高めることができ、その結果鋼板の延性向上に寄与する必須の元素である。これらの作用を有効に発揮させるためには、鋼板中にＭｎを４．０％以上、好ましくは４．５％以上、さらに好ましくは５．０％以上含有させる必要がある。ただし、鋼板中のＭｎ量が過剰になると、Ａｅ１点が低下することで、Ａｅ１以上（Ａｅ１＋２×Ａｅ３）／３以下で且つ前記高温域における最高到達温度から２０℃以上低い低温域において滞在させる温度が低くなりすぎて、狙いとする短時間（３０～３００ｓの滞在時間）ではＭｎの拡散が十分に起こらず所望の効果が得られなくなるので、鋼板中のＭｎ量は１０．０％以下、好ましくは９．０％以下、さらに好ましくは８．０％以下とする。 Mn: 4.0 to 10.0%
Mn is very effective for securing a large amount of retained austenite in the steel sheet, and it can be concentrated in the retained austenite to increase the stability of the retained austenite, thereby contributing to the improvement of the ductility of the steel sheet. Elements. In order to exhibit these functions effectively, it is necessary to contain Mn in the steel sheet at 4.0% or more, preferably 4.5% or more, more preferably 5.0% or more. However, when the amount of Mn in the steel sheet becomes excessive, the Ae1 point is lowered, so that the temperature of Ae1 is not less than (Ae1 + 2 × Ae3) / 3 and the temperature is kept in a low temperature range that is 20 ° C. or more lower than the highest temperature in the high temperature range. The Mn content in the steel sheet is 10.0% or less, preferably because the Mn diffusion does not occur sufficiently and the desired effect cannot be obtained in the targeted short time (30 to 300 s residence time). Is 9.0% or less, more preferably 8.0% or less.
Ａｌ：０～２．０％
Ａｌは、Ｓｉと同様に、固溶強化により鋼板の強度上昇に寄与するとともに、残留オーステナイトの分解を抑制することで残留オーステナイト量を確保できるようにして延性の向上に寄与する元素であるので、鋼板中に含有させてもよい。これらの作用を効果的に発揮させるためには、鋼板中にＡｌを０．０２％以上、さらには０．１％以上、特に０．３％以上含有させるのが好ましい。ただし、鋼板中のＡｌ量が過剰になると、母相の延性が劣化して鋼板の延性が却って劣化するので、鋼板中のＡｌ量は２．０％以下、好ましくは１．８％以下、さらに好ましくは１．６％以下に制限する必要がある。 Al: 0 to 2.0%
Al, like Si, contributes to increasing the strength of the steel sheet by solid solution strengthening, and is an element that contributes to improving ductility by ensuring the amount of retained austenite by suppressing the decomposition of retained austenite. You may make it contain in a steel plate. In order to effectively exhibit these functions, it is preferable to contain Al in the steel sheet in an amount of 0.02% or more, further 0.1% or more, and particularly 0.3% or more. However, if the amount of Al in the steel sheet becomes excessive, the ductility of the matrix phase deteriorates and the ductility of the steel sheet deteriorates, so the Al content in the steel sheet is 2.0% or less, preferably 1.8% or less, Preferably, it should be limited to 1.6% or less.
Ａｌは、Ｓｉと同様に、固溶強化により鋼板の強度上昇に寄与するとともに、残留オーステナイトの分解を抑制することで残留オーステナイト量を確保できるようにして延性の向上に寄与する元素であるので、鋼板中に含有させてもよい。これらの作用を効果的に発揮させるためには、鋼板中にＡｌを０．０２％以上、さらには０．１％以上、特に０．３％以上含有させるのが好ましい。ただし、鋼板中のＡｌ量が過剰になると、母相の延性が劣化して鋼板の延性が却って劣化するので、鋼板中のＡｌ量は２．０％以下、好ましくは１．８％以下、さらに好ましくは１．６％以下に制限する必要がある。 Al: 0 to 2.0%
Al, like Si, contributes to increasing the strength of the steel sheet by solid solution strengthening, and is an element that contributes to improving ductility by ensuring the amount of retained austenite by suppressing the decomposition of retained austenite. You may make it contain in a steel plate. In order to effectively exhibit these functions, it is preferable to contain Al in the steel sheet in an amount of 0.02% or more, further 0.1% or more, and particularly 0.3% or more. However, if the amount of Al in the steel sheet becomes excessive, the ductility of the matrix phase deteriorates and the ductility of the steel sheet deteriorates, so the Al content in the steel sheet is 2.0% or less, preferably 1.8% or less, Preferably, it should be limited to 1.6% or less.
Ｐ：０％超０．０３％以下
Ｐは不純物元素として鋼板中に不可避的に存在し、固溶強化により強度の上昇に寄与するが、旧オーステナイト粒界に偏析し、粒界を脆化させることで伸びフランジ性を劣化させるので、鋼板中のＰ量は０．０３％以下、好ましくは０．０２％以下、さらに好ましくは０．０１５％以下とする。 P: more than 0% and 0.03% or less P is unavoidably present in the steel sheet as an impurity element and contributes to an increase in strength by solid solution strengthening, but segregates at the prior austenite grain boundaries and embrittles the grain boundaries. Therefore, the amount of P in the steel sheet is 0.03% or less, preferably 0.02% or less, and more preferably 0.015% or less.
Ｐは不純物元素として鋼板中に不可避的に存在し、固溶強化により強度の上昇に寄与するが、旧オーステナイト粒界に偏析し、粒界を脆化させることで伸びフランジ性を劣化させるので、鋼板中のＰ量は０．０３％以下、好ましくは０．０２％以下、さらに好ましくは０．０１５％以下とする。 P: more than 0% and 0.03% or less P is unavoidably present in the steel sheet as an impurity element and contributes to an increase in strength by solid solution strengthening, but segregates at the prior austenite grain boundaries and embrittles the grain boundaries. Therefore, the amount of P in the steel sheet is 0.03% or less, preferably 0.02% or less, and more preferably 0.015% or less.
Ｓ：０％超０．０１％以下
Ｓも不純物元素として鋼板中に不可避的に存在し、ＭｎＳ介在物を形成し、穴拡げ時に亀裂の起点となることで伸びフランジ性を低下させるので、鋼板中のＳ量は０．０１％以下、好ましくは０．００７％以下、さらに好ましくは０．００５％以下とする。 S: more than 0% and 0.01% or less S is also unavoidably present in the steel sheet as an impurity element, forms MnS inclusions, and becomes a starting point of cracks when expanding holes, thereby reducing stretch flangeability. The S content is 0.01% or less, preferably 0.007% or less, and more preferably 0.005% or less.
Ｓも不純物元素として鋼板中に不可避的に存在し、ＭｎＳ介在物を形成し、穴拡げ時に亀裂の起点となることで伸びフランジ性を低下させるので、鋼板中のＳ量は０．０１％以下、好ましくは０．００７％以下、さらに好ましくは０．００５％以下とする。 S: more than 0% and 0.01% or less S is also unavoidably present in the steel sheet as an impurity element, forms MnS inclusions, and becomes a starting point of cracks when expanding holes, thereby reducing stretch flangeability. The S content is 0.01% or less, preferably 0.007% or less, and more preferably 0.005% or less.
本発明の実施形態に係る製造方法で得られた鋼板は上記元素を基本成分とし、残部は鉄および不可避的不純物（Ｎ、Ｏ等）であるが、その他、本開示の作用を損なわない範囲で、下記の許容成分を含有させることができる。
The steel plate obtained by the manufacturing method according to the embodiment of the present invention has the above-mentioned elements as basic components, and the balance is iron and inevitable impurities (N, O, etc.), but within the scope not impairing the effects of the present disclosure. The following permissible components can be contained.
Ｃｒ、Ｍｏ、ＮｉおよびＣｕの１種または２種以上：合計量で０％超１．０％以下
これらの元素は、鋼板の焼入れ性を高めて、フェライトやパーライトといった拡散変態を抑制し、強度の確保、残留オーステナイトの確保に寄与することで鋼板の強度－延性バランスを改善するのに有用な元素である。これらの作用を効果的に発揮させるためには、これらの元素を鋼板中に合計量で０．０１％以上、さらには０．０２％以上、特に０．０３％以上含有させるのが好ましい。ただし、これらの元素を鋼板中に過剰に含有させるとコストが高くなりすぎるので、合計量で１．０％以下、さらには０．８％以下、特に０．６％以下に制限するのが好ましい。 One or more of Cr, Mo, Ni and Cu: Total amount of more than 0% and 1.0% or less These elements enhance the hardenability of the steel sheet and suppress the diffusion transformation such as ferrite and pearlite, and the strength It is an element useful for improving the strength-ductility balance of a steel sheet by contributing to the securing of retained austenite. In order to exhibit these functions effectively, it is preferable to contain these elements in the steel sheet in a total amount of 0.01% or more, further 0.02% or more, particularly 0.03% or more. However, if these elements are contained excessively in the steel sheet, the cost becomes too high, so the total amount is preferably 1.0% or less, more preferably 0.8% or less, and particularly preferably 0.6% or less. .
これらの元素は、鋼板の焼入れ性を高めて、フェライトやパーライトといった拡散変態を抑制し、強度の確保、残留オーステナイトの確保に寄与することで鋼板の強度－延性バランスを改善するのに有用な元素である。これらの作用を効果的に発揮させるためには、これらの元素を鋼板中に合計量で０．０１％以上、さらには０．０２％以上、特に０．０３％以上含有させるのが好ましい。ただし、これらの元素を鋼板中に過剰に含有させるとコストが高くなりすぎるので、合計量で１．０％以下、さらには０．８％以下、特に０．６％以下に制限するのが好ましい。 One or more of Cr, Mo, Ni and Cu: Total amount of more than 0% and 1.0% or less These elements enhance the hardenability of the steel sheet and suppress the diffusion transformation such as ferrite and pearlite, and the strength It is an element useful for improving the strength-ductility balance of a steel sheet by contributing to the securing of retained austenite. In order to exhibit these functions effectively, it is preferable to contain these elements in the steel sheet in a total amount of 0.01% or more, further 0.02% or more, particularly 0.03% or more. However, if these elements are contained excessively in the steel sheet, the cost becomes too high, so the total amount is preferably 1.0% or less, more preferably 0.8% or less, and particularly preferably 0.6% or less. .
Ｖ、ＮｂおよびＴｉの１種または２種以上：合計量で０％超０．２％以下
これらの元素は、析出強化により鋼板の強度を高めるのに有用な元素である。このような作用を効果的に発揮させるためには、これらの元素を鋼板中に合計量で０．０１％以上、さらには０．０２％以上、特に０．０５％以上含有させるのが好ましい。ただし、これらの元素を鋼板中に過剰に含有させるとコストが高くなりすぎるので、合計量で０．２％以下、さらには０．１８％以下、特に０．１５％以下に制限するのが好ましい。 One or more of V, Nb and Ti: Total amount of more than 0% and 0.2% or less These elements are useful elements for increasing the strength of the steel sheet by precipitation strengthening. In order to effectively exhibit such an action, it is preferable to contain these elements in the steel sheet in a total amount of 0.01% or more, further 0.02% or more, particularly 0.05% or more. However, if these elements are excessively contained in the steel sheet, the cost becomes too high, so the total amount is preferably 0.2% or less, more preferably 0.18% or less, and particularly preferably 0.15% or less. .
これらの元素は、析出強化により鋼板の強度を高めるのに有用な元素である。このような作用を効果的に発揮させるためには、これらの元素を鋼板中に合計量で０．０１％以上、さらには０．０２％以上、特に０．０５％以上含有させるのが好ましい。ただし、これらの元素を鋼板中に過剰に含有させるとコストが高くなりすぎるので、合計量で０．２％以下、さらには０．１８％以下、特に０．１５％以下に制限するのが好ましい。 One or more of V, Nb and Ti: Total amount of more than 0% and 0.2% or less These elements are useful elements for increasing the strength of the steel sheet by precipitation strengthening. In order to effectively exhibit such an action, it is preferable to contain these elements in the steel sheet in a total amount of 0.01% or more, further 0.02% or more, particularly 0.05% or more. However, if these elements are excessively contained in the steel sheet, the cost becomes too high, so the total amount is preferably 0.2% or less, more preferably 0.18% or less, and particularly preferably 0.15% or less. .
〔本発明の実施形態に用いる熱延板または冷延板〕
つぎに、本発明の実施形態に用いる中間材である、熱延板または冷延板について説明する。 [Hot rolled plate or cold rolled plate used in the embodiment of the present invention]
Next, a hot-rolled plate or a cold-rolled plate, which is an intermediate material used in the embodiment of the present invention, will be described.
つぎに、本発明の実施形態に用いる中間材である、熱延板または冷延板について説明する。 [Hot rolled plate or cold rolled plate used in the embodiment of the present invention]
Next, a hot-rolled plate or a cold-rolled plate, which is an intermediate material used in the embodiment of the present invention, will be described.
本発明の実施形態では、上記組成を有する中間材を用いるが、その中間材としては、熱延板を用いてもよく、冷延板を用いてもよい。熱延板としては、特にその製造条件を限定するものではなく、例えば上記成分組成を有する鋼材を常法により熱間圧延して得られたものを用いることができる。また、冷延板としても、特にその製造条件を限定するものではなく、例えば上記成分組成を有する鋼材を常法により熱間圧延した後、さらに常法により冷間圧延したものを用いることができる。なお、冷延板として、Ｍｎを高濃度に含有するものを用いる場合には、熱間圧延後の冷却により熱延板の強度が高くなり冷間圧延しにくくなるため、熱間圧延後に一旦軟化焼鈍を施してから冷間圧延したものを用いることも推奨される。
In the embodiment of the present invention, an intermediate material having the above composition is used. As the intermediate material, a hot-rolled plate or a cold-rolled plate may be used. The hot-rolled sheet is not particularly limited in the production conditions, and for example, a steel sheet obtained by hot rolling a steel material having the above component composition by a conventional method can be used. Further, the cold-rolled sheet is not particularly limited in its production conditions. For example, a steel sheet having the above component composition can be hot-rolled by a conventional method and further cold-rolled by a conventional method. . In addition, when using a sheet containing Mn at a high concentration as a cold-rolled sheet, the strength after hot-rolling increases the strength of the hot-rolled sheet and makes it difficult to cold-roll. It is also recommended to use one that has been annealed and then cold rolled.
〔焼鈍工程〕
つぎに、本発明の実施形態を特徴づける焼鈍工程について説明する。 [Annealing process]
Next, an annealing process characterizing the embodiment of the present invention will be described.
つぎに、本発明の実施形態を特徴づける焼鈍工程について説明する。 [Annealing process]
Next, an annealing process characterizing the embodiment of the present invention will be described.
上述したとおり、本発明の実施形態では、その焼鈍工程として、２相域の高温側ないしオーステナイト単相域に少し入った高温域でごく短時間加熱処理した後に、２相域の低温域で従来技術より短い時間加熱処理する２段階加熱処理方式を採用した点で、上記従来技術と異なる。
As described above, in the embodiment of the present invention, as the annealing process, after the heat treatment for a very short time in the high temperature side of the two-phase region or the austenite single-phase region for a short time, the conventional low temperature region of the two-phase region. It differs from the above-mentioned conventional technique in that a two-stage heat treatment method in which heat treatment is performed for a shorter time than the technique is adopted.
＜第１段階の加熱保持：（Ａｅ１＋Ａｅ３）／２以上［Ａｅ３＋５０℃］以下の高温域において、［高温域における最高到達温度－１０℃］以上の温度での滞在時間が３～２００ｓとなるように滞在＞
炭化物の溶解を促進するために、逆変態が進行しやすい、２相域の中間温度より高温側の温度域（高温域）で加熱保持する。このような作用を有効に発揮させるため、高温域の下限は（Ａｅ１＋Ａｅ３）／２、とする必要がある。ただし、加熱温度を高くしすぎたり、滞在時間を長くしすぎたりすると、オーステナイト分率が上昇する一方、フェライト分率が低下して、最終製品としての鋼板の強度－延性バランスが確保できなくなるので、加熱温度の上限はＡｅ３＋５０℃に制限する。 <First-stage heating and holding: In a high temperature range of (Ae1 + Ae3) / 2 to [Ae3 + 50 ° C.] or less, the residence time at a temperature of [the highest reached temperature in the high temperature range−10 ° C.] or higher is 3 to 200 s. Stay>
In order to promote dissolution of the carbide, the material is heated and held in a temperature range (high temperature range) higher than the intermediate temperature of the two-phase region where reverse transformation is likely to proceed. In order to effectively exhibit such an action, the lower limit of the high temperature range needs to be (Ae1 + Ae3) / 2. However, if the heating temperature is set too high or the staying time is set too long, the austenite fraction will increase while the ferrite fraction will decrease, making it impossible to secure the strength-ductility balance of the steel sheet as the final product. The upper limit of the heating temperature is limited to Ae3 + 50 ° C.
炭化物の溶解を促進するために、逆変態が進行しやすい、２相域の中間温度より高温側の温度域（高温域）で加熱保持する。このような作用を有効に発揮させるため、高温域の下限は（Ａｅ１＋Ａｅ３）／２、とする必要がある。ただし、加熱温度を高くしすぎたり、滞在時間を長くしすぎたりすると、オーステナイト分率が上昇する一方、フェライト分率が低下して、最終製品としての鋼板の強度－延性バランスが確保できなくなるので、加熱温度の上限はＡｅ３＋５０℃に制限する。 <First-stage heating and holding: In a high temperature range of (Ae1 + Ae3) / 2 to [Ae3 + 50 ° C.] or less, the residence time at a temperature of [the highest reached temperature in the high temperature range−10 ° C.] or higher is 3 to 200 s. Stay>
In order to promote dissolution of the carbide, the material is heated and held in a temperature range (high temperature range) higher than the intermediate temperature of the two-phase region where reverse transformation is likely to proceed. In order to effectively exhibit such an action, the lower limit of the high temperature range needs to be (Ae1 + Ae3) / 2. However, if the heating temperature is set too high or the staying time is set too long, the austenite fraction will increase while the ferrite fraction will decrease, making it impossible to secure the strength-ductility balance of the steel sheet as the final product. The upper limit of the heating temperature is limited to Ae3 + 50 ° C.
高温域においては、［高温域における最高到達温度－１０℃］以上の温度で、滞在時間３～２００ｓで鋼板を滞在させる。最高到達温度とは、実際に高温域で熱処理したときに、最も高くなったときの温度をいう。鋼板を加熱保持する間、加熱温度をほぼ一定に維持する。そのため、鋼板は、本質的には、最高到達温度で保持されることになる。しかしながら、保持中のわずかな温度変化、具体的には、１０℃以下の変動であれば許容される。これを言い換えれば、第１段階の加熱保持では、鋼板を［高温域における最高到達温度－１０℃］以上の温度で加熱保持する。これにより、熱処理時の保持温度は、［最高到達温度］～［最高到達温度－１０℃］の間に制御される。なお、最高到達温度は、高温域の上限である［Ａｅ３＋５０℃］以下であり、［高温域における最高到達温度－１０℃］は、高温域の下限である（Ａｅ１＋Ａｅ３）／２以上である。
In the high temperature range, the steel plate is allowed to stay at a temperature of [the highest temperature reached in the high temperature range −10 ° C.] or higher for a stay time of 3 to 200 s. The maximum attained temperature refers to the temperature at which the highest temperature is obtained when the heat treatment is actually performed in a high temperature range. While the steel sheet is heated and held, the heating temperature is kept substantially constant. Therefore, the steel sheet is essentially held at the highest temperature reached. However, a slight temperature change during holding, specifically, a fluctuation of 10 ° C. or less is allowed. In other words, in the first stage of heating and holding, the steel sheet is heated and held at a temperature equal to or higher than the [maximum reached temperature in the high temperature range−10 ° C.]. As a result, the holding temperature during the heat treatment is controlled between [maximum attained temperature] to [maximum attained temperature−10 ° C.]. The maximum temperature reached is [Ae3 + 50 ° C.] or less, which is the upper limit of the high temperature region, and [Maximum temperature reached in the high temperature region−10 ° C.] is equal to or higher than the lower limit (Ae1 + Ae3) / 2 of the high temperature region.
さらに、第１段階の加熱保持での保持温度（つまり、［高温域における最高到達温度－１０℃］以上の温度）での滞在時間が３ｓ未満であると、逆変態が十分に進行しない。そのため、最終製品の鋼板中における残留オーステナイト量が不足して、強度が低下するため、強度－伸びバランスを確保できない可能性がある。一方、保持温度での滞在時間が２００ｓを超えると、オーステナイト分率が上昇する。そのため、最終製品の鋼板中におけるマルテンサイト量が過剰となり、フェライト量が不足する。これにより、伸びが低下して、強度－伸びバランスを確保できない可能性がある。したがって、［高温域における最高到達温度－１０℃］以上の温度での滞在時間を３～２００ｓとした。
Furthermore, the reverse transformation does not proceed sufficiently if the residence time at the holding temperature in the first stage of heating and holding (that is, the temperature of [the highest temperature in the high temperature range−10 ° C.] or higher) is less than 3 s. For this reason, the amount of retained austenite in the steel plate of the final product is insufficient and the strength is lowered, so that there is a possibility that a strength-elongation balance cannot be ensured. On the other hand, when the staying time at the holding temperature exceeds 200 s, the austenite fraction increases. Therefore, the amount of martensite in the steel plate of the final product becomes excessive and the amount of ferrite is insufficient. As a result, the elongation may decrease and the strength-elongation balance may not be ensured. Therefore, the residence time at a temperature equal to or higher than the [maximum reached temperature in the high temperature range−10 ° C.] is set to 3 to 200 s.
＜第２段階の加熱保持：引き続きＡｅ１以上（Ａｅ１＋２×Ａｅ３）／３以下で且つ前記高温域における最高到達温度から２０℃以上低い低温域において、±１℃／ｓ以内の温度変化で３０～３００ｓ滞在＞
上記第１段階での加熱保持により炭化物を十分に溶解させた後、オーステナイト／フェライト分率を適切に制御するとともに、オーステナイト中へのＭｎの濃化を促進するため、引き続き上記第１段階での温度域（高温域）より低温側の２相域（低温域）で加熱保持する。このような作用を有効に発揮させるため、低温域は、Ａｅ１以上（Ａｅ１＋２×Ａｅ３）／３以下で且つ前記高温域における最高到達温度から２０℃以上低い温度域とし、その温度域にて±１℃／ｓ以内の温度変化で、すなわち、緩冷却、緩昇温、または一定温度に保持の状態で３０ｓ以上滞在させる必要がある。なお、上記温度変化は温度降下側をプラス（＋）で、温度上昇側をマイナス（－）でそれぞれ表示する。ただし、滞在時間を長くしすぎると、上記作用効果が飽和し、生産性が低下するだけであるので、その上限は３００ｓ以下に制限する。
なお、Ａｅ１（℃）およびＡｅ３（℃）は、熱力学計算ソフト（Ｔｈｅｒｍｏ－Ｃａｌｃ Ｓｏｆｔｗａｒｅ、ＡＢ社製Ｔｈｅｒｍｏ－Ｃａｌｃ）にて熱力学データベースとしてＴＣＦＥ７を用い、Ｃ、Ｍｎ、ＳｉおよびＡｌの含有量（質量％）から各温度におけるＦＣＣ、ＢＣＣおよびセメンタイト各相の相分率を求め、ＢＣＣ－セメンタイトの２相状態からＦＣＣ－ＢＣＣ－セメンタイトの３相状態に遷移する温度をＡｅ１（℃）、ＦＣＣ－ＢＣＣの２相状態からＦＣＣの単相に遷移する温度をＡｅ３（℃）と定義して求めた。 <Second-stage heating and holding: In a low temperature range of Ae1 or more (Ae1 + 2 × Ae3) / 3 or less and 20 ° C or more lower than the highest temperature in the high temperature range, the temperature change within ± 1 ° C / s is 30 to 300 seconds. Stay>
After sufficiently dissolving the carbide by heating and holding in the first stage, in order to appropriately control the austenite / ferrite fraction and promote the concentration of Mn in the austenite, the first stage is continued. Heat and hold in a two-phase region (low temperature region) on the lower temperature side than the temperature region (high temperature region). In order to effectively exhibit such an action, the low temperature range is Ae1 or more (Ae1 + 2 × Ae3) / 3 or less and a temperature range that is 20 ° C. or more lower than the highest temperature reached in the high temperature range, and ± 1 in that temperature range. It is necessary to stay for 30 s or more at a temperature change within ° C./s, that is, in a state of slow cooling, moderate temperature rise, or constant temperature. The temperature change is indicated by plus (+) on the temperature drop side and minus (-) on the temperature rise side. However, if the staying time is made too long, the above-described effects are saturated and productivity is lowered, so the upper limit is limited to 300 s or less.
Ae1 (° C.) and Ae3 (° C.) are obtained from thermodynamic calculation software (Thermo-Calc Software, Thermo-Calc manufactured by AB) using TCFE7 as a thermodynamic database, and the contents of C, Mn, Si and Al (Mass%), the phase fraction of each phase of FCC, BCC and cementite at each temperature is obtained, and the temperature at which transition from the two-phase state of BCC-cementite to the three-phase state of FCC-BCC-cementite is made Ae1 (° C.), FCC -The temperature at which the transition from the two-phase state of BCC to the single phase of FCC was defined as Ae3 (° C).
上記第１段階での加熱保持により炭化物を十分に溶解させた後、オーステナイト／フェライト分率を適切に制御するとともに、オーステナイト中へのＭｎの濃化を促進するため、引き続き上記第１段階での温度域（高温域）より低温側の２相域（低温域）で加熱保持する。このような作用を有効に発揮させるため、低温域は、Ａｅ１以上（Ａｅ１＋２×Ａｅ３）／３以下で且つ前記高温域における最高到達温度から２０℃以上低い温度域とし、その温度域にて±１℃／ｓ以内の温度変化で、すなわち、緩冷却、緩昇温、または一定温度に保持の状態で３０ｓ以上滞在させる必要がある。なお、上記温度変化は温度降下側をプラス（＋）で、温度上昇側をマイナス（－）でそれぞれ表示する。ただし、滞在時間を長くしすぎると、上記作用効果が飽和し、生産性が低下するだけであるので、その上限は３００ｓ以下に制限する。
なお、Ａｅ１（℃）およびＡｅ３（℃）は、熱力学計算ソフト（Ｔｈｅｒｍｏ－Ｃａｌｃ Ｓｏｆｔｗａｒｅ、ＡＢ社製Ｔｈｅｒｍｏ－Ｃａｌｃ）にて熱力学データベースとしてＴＣＦＥ７を用い、Ｃ、Ｍｎ、ＳｉおよびＡｌの含有量（質量％）から各温度におけるＦＣＣ、ＢＣＣおよびセメンタイト各相の相分率を求め、ＢＣＣ－セメンタイトの２相状態からＦＣＣ－ＢＣＣ－セメンタイトの３相状態に遷移する温度をＡｅ１（℃）、ＦＣＣ－ＢＣＣの２相状態からＦＣＣの単相に遷移する温度をＡｅ３（℃）と定義して求めた。 <Second-stage heating and holding: In a low temperature range of Ae1 or more (Ae1 + 2 × Ae3) / 3 or less and 20 ° C or more lower than the highest temperature in the high temperature range, the temperature change within ± 1 ° C / s is 30 to 300 seconds. Stay>
After sufficiently dissolving the carbide by heating and holding in the first stage, in order to appropriately control the austenite / ferrite fraction and promote the concentration of Mn in the austenite, the first stage is continued. Heat and hold in a two-phase region (low temperature region) on the lower temperature side than the temperature region (high temperature region). In order to effectively exhibit such an action, the low temperature range is Ae1 or more (Ae1 + 2 × Ae3) / 3 or less and a temperature range that is 20 ° C. or more lower than the highest temperature reached in the high temperature range, and ± 1 in that temperature range. It is necessary to stay for 30 s or more at a temperature change within ° C./s, that is, in a state of slow cooling, moderate temperature rise, or constant temperature. The temperature change is indicated by plus (+) on the temperature drop side and minus (-) on the temperature rise side. However, if the staying time is made too long, the above-described effects are saturated and productivity is lowered, so the upper limit is limited to 300 s or less.
Ae1 (° C.) and Ae3 (° C.) are obtained from thermodynamic calculation software (Thermo-Calc Software, Thermo-Calc manufactured by AB) using TCFE7 as a thermodynamic database, and the contents of C, Mn, Si and Al (Mass%), the phase fraction of each phase of FCC, BCC and cementite at each temperature is obtained, and the temperature at which transition from the two-phase state of BCC-cementite to the three-phase state of FCC-BCC-cementite is made Ae1 (° C.), FCC -The temperature at which the transition from the two-phase state of BCC to the single phase of FCC was defined as Ae3 (° C).
上記第２段階の加熱保持後は、組織を凍結するため、すなわち、当該加熱保持により得られた適切なオーステナイト／フェライト分率をそれ以上変化させないため、常識的な範囲の冷却速度で冷却を行えばよい。例えば、第２段階の加熱処理終了温度から［Ａｅ１－５０℃］以下までを１℃／ｓ以上の冷却速度で冷却することが推奨される。また、鋼板の靱性をより向上させるため、前記冷却後に、必要に応じてさらに焼戻し処理を行ってもよい。
After the second stage of heating and holding, cooling is performed at a cooling rate within a common sense range in order to freeze the structure, that is, not to change the appropriate austenite / ferrite fraction obtained by the heating and holding any further. Just do it. For example, it is recommended to cool from the end temperature of the second stage heat treatment to [Ae1-50 ° C.] or lower at a cooling rate of 1 ° C./s or higher. Moreover, in order to improve the toughness of a steel plate, you may perform a tempering process further as needed after the said cooling.
以下、実施例を挙げて本開示をより具体的に説明するが、本開示はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することももちろん可能であり、それらはいずれも本開示の技術的範囲に包含される。
Hereinafter, the present disclosure will be described in more detail with reference to examples. However, the present disclosure is not limited by the following examples as a matter of course, and appropriate modifications are made within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and both are included in the technical scope of the present disclosure.
下記表１に示す成分の冷延板に対して、下記表２に示す熱処理条件で焼鈍を施して鋼板を作製した。
なお、下記表２に示す全ての熱処理Ｎｏ．において、第１段階の加熱保持までの加熱速度は１０℃／ｓ一定とした。また、熱処理Ｎｏ．１－Ｔでは、第２段階の加熱保持後にさらに焼戻しを実施したが、その焼戻し条件は、冷却停止温度２０℃で５０ｓ保持した後、３０℃／ｓの加熱速度で４００℃まで再加熱してその温度で２０ｓ保持したのち、１０℃／ｓの冷却速度で冷却する条件とした。 A cold-rolled sheet having the components shown in Table 1 below was annealed under the heat treatment conditions shown in Table 2 below to produce a steel sheet.
All the heat treatment Nos. The heating rate up to the first stage of heating and holding was constant at 10 ° C./s. In addition, heat treatment No. In 1-T, tempering was further carried out after the second stage of heating and holding. The tempering conditions were that the cooling stop temperature was held at 20 ° C. for 50 s, and then reheated to 400 ° C. at a heating rate of 30 ° C./s. After maintaining at that temperature for 20 s, cooling was performed at a cooling rate of 10 ° C./s.
なお、下記表２に示す全ての熱処理Ｎｏ．において、第１段階の加熱保持までの加熱速度は１０℃／ｓ一定とした。また、熱処理Ｎｏ．１－Ｔでは、第２段階の加熱保持後にさらに焼戻しを実施したが、その焼戻し条件は、冷却停止温度２０℃で５０ｓ保持した後、３０℃／ｓの加熱速度で４００℃まで再加熱してその温度で２０ｓ保持したのち、１０℃／ｓの冷却速度で冷却する条件とした。 A cold-rolled sheet having the components shown in Table 1 below was annealed under the heat treatment conditions shown in Table 2 below to produce a steel sheet.
All the heat treatment Nos. The heating rate up to the first stage of heating and holding was constant at 10 ° C./s. In addition, heat treatment No. In 1-T, tempering was further carried out after the second stage of heating and holding. The tempering conditions were that the cooling stop temperature was held at 20 ° C. for 50 s, and then reheated to 400 ° C. at a heating rate of 30 ° C./s. After maintaining at that temperature for 20 s, cooling was performed at a cooling rate of 10 ° C./s.
そして、上記熱処理後の各鋼板について、以下の測定方法により、鋼組織中の各相の面積率および残留オーステナイト中のＭｎ濃度を測定した。
And about each steel plate after the said heat processing, the area ratio of each phase in steel structure and the Mn density | concentration in a retained austenite were measured with the following measuring methods.
まず、鋼板をナイタール腐食し、光学顕微鏡（倍率４００倍）で観察して残留オーステナイト以外の各相を同定し、画像解析により各相の面積率を測定した。
First, the steel plate was subjected to nital corrosion, observed with an optical microscope (400 magnifications) to identify each phase other than retained austenite, and the area ratio of each phase was measured by image analysis.
次いで、残留オーステナイトの面積率は、鋼板の１／４の厚さまで研削した後、化学研磨してからＸ線回折法により測定した（ＩＳＩＪ Ｉｎｔ．Ｖｏｌ．３３，（１９３３），Ｎｏ．７，ｐ．７７６）。
Next, the area ratio of retained austenite was measured by X-ray diffraction after grinding to a thickness of ¼ of the steel plate (ISIJＩＳInt. Vol. 33, (1933), No. 7, p. . 776).
残留オーステナイト中のＭｎ濃度については、薄膜の試料をＦＩＢ（ＦＥＩ製 Ｎｏｖａ２００）を用いて作製し、これを球面収差補正機能付き透過型電子顕微鏡（日本電子社製 ＪＥＭ－ＡＲＭ２００Ｆ）で像を観察しながら付属のＥＤＳ分析装置（日本電子製ＪＥＤ－２３００Ｔ）を用いてＭｎ濃度を測定した。
Regarding the Mn concentration in the retained austenite, a thin film sample was prepared using FIB (FEI Nova200), and this was observed with a transmission electron microscope with a spherical aberration correction function (JEOL JEM-ARM200F). However, the Mn concentration was measured using the attached EDS analyzer (JED-2300T manufactured by JEOL Ltd.).
また、上記各鋼板について、強度－延性バランスを評価するために、引張試験により、引張強度ＴＳおよび伸び（全伸び）ＥＬを測定した。なお、引張試験は、圧延方向と平行になるように、サンプルを採取し、ＪＩＳ １４Ｂ号試験片（ｔ＝２ｍｍ、ｗ＝７ｍｍ、ＧＬ＝２０ｍｍ）を用いて、ＪＩＳ Ｚ ２２４１に従って実施した。
Moreover, in order to evaluate the strength-ductility balance for each of the above steel plates, the tensile strength TS and the elongation (total elongation) EL were measured by a tensile test. The tensile test was conducted according to JIS Z 2241 using a JIS 14B test piece (t = 2 mm, w = 7 mm, GL = 20 mm) so as to be parallel to the rolling direction.
測定結果を下記表３に示す。同表において、鋼板の組織について、残留オーステナイトの面積率が、対応する標準条件の鋼板よりも高く、かつ、その残留オーステナイト中のＭｎ濃度ＭｎγＲと鋼板全体のＭｎ含有量［Ｍｎ］との比ＭｎγＲ／［Ｍｎ］が１．２０以上であり、さらに、鋼板の機械的特性について、ＴＳが７８０ＭＰａ以上であるとともに、ＴＳ×ＥＬが２５０００ＭＰａ％以上で、かつ標準条件の鋼板よりも２０００ＭＰａ％以上高くなっているものを発明例とし、それ以外のものを比較例とした。
The measurement results are shown in Table 3 below. In the same table, the ratio of the area ratio of retained austenite is higher than that of the corresponding standard condition steel sheet and the ratio of Mn concentration Mn γR in the retained austenite to the Mn content [Mn] of the entire steel sheet. Mn γR / [Mn] is 1.20 or more. Further, regarding the mechanical properties of the steel sheet, TS is 780 MPa or more, TS × EL is 25000 MPa% or more, and 2000 MPa% or more than the steel sheet under standard conditions. The higher ones were used as invention examples, and the others were used as comparative examples.
表３において、試験Ｎｏ．１、２２、２４、２６、２８、３０および３２は、表２に示すように、焼鈍を１段階のみの加熱保持で行う標準条件（それぞれ標準条件１～７）であり、従来技術に相当するものである。これに対し、試験Ｎｏ．２～２１、２３、２５、２７、２９、３１および３３は、上記各標準条件にそれぞれ対応する２段階の加熱保持について種々条件を変更して行った試験である。
In Table 3, test no. 1, 2, 24, 26, 28, 30 and 32 are standard conditions (standard conditions 1 to 7, respectively) in which annealing is performed by heating and holding in only one stage, as shown in Table 2, and correspond to the prior art. Is. In contrast, test no. Nos. 2 to 21, 23, 25, 27, 29, 31 and 33 are tests performed by changing various conditions for the two-stage heating and holding corresponding to the respective standard conditions.
表１～３に示すとおり、試験Ｎｏ．２～４、８、１１、１２、１４～１６、１９、２１、２３、２５、２７および３３は、本開示の要件を全て満たす発明例である。表３に示すとおり、いずれの発明例も、対応する標準条件に比べて、残留オーステナイト量が増加しているとともに、残留オーステナイト中へのＭｎの濃化が促進され、強度を確保しつつ、強度－延性バランスが向上していることがわかる。そして、いずれの発明例も、焼鈍工程における合計滞在時間が、対応する標準条件の合計滞留時間（３０ｓ＋２００ｓ＝２３０ｓ）と等しいか、あるいは短いので、対応する標準条件と同等の強度－延性バランスを確保するには、焼鈍工程における合計滞在時間を標準条件より短くできることが明らかである。
As shown in Tables 1-3, test no. 2 to 4, 8, 11, 12, 14 to 16, 19, 21, 23, 25, 27, and 33 are examples of the invention that satisfy all the requirements of the present disclosure. As shown in Table 3, in each of the inventive examples, the amount of retained austenite is increased as compared with the corresponding standard conditions, and the concentration of Mn in the retained austenite is promoted, while ensuring strength, -It can be seen that the ductility balance is improved. In each of the invention examples, the total residence time in the annealing process is equal to or shorter than the total residence time (30 s + 200 s = 230 s) of the corresponding standard condition, so that a strength-ductility balance equivalent to the corresponding standard condition is ensured. It is clear that the total residence time in the annealing process can be made shorter than the standard condition.
これに対し、試験Ｎｏ．５～７、９、１０、１３、１７、１８、２０、２９および３１は、本開示の要件いずれかを満たさない比較例である。
In contrast, test no. Reference numerals 5 to 7, 9, 10, 13, 17, 18, 20, 29, and 31 are comparative examples that do not satisfy any of the requirements of the present disclosure.
すなわち、試験Ｎｏ．５～７、９、１０、１３、１７、１８および２０は、本開示の成分規定の要件を満足する鋼種を用いているものの、焼鈍条件の要件を一部外れる条件で焼鈍しているため、組織規定の要件を充足せず、機械的特性が劣っている。
That is, test No. 5-7, 9, 10, 13, 17, 18, and 20 are steel types that satisfy the requirements of the component provisions of the present disclosure, but are annealed under conditions that partially deviate from the requirements of the annealing conditions. Organizational requirements are not met and mechanical properties are inferior.
例えば、試験Ｎｏ．５（熱処理Ｎｏ．１－Ｄ）は、第１段階加熱保持における加熱温度（最高到達温度）が本開示の規定範囲から外れて低すぎるため、逆変態が十分に進行せず、最終製品としての鋼板中の残留オーステナイト量が不足し、ＴＳおよびＴＳ×ＥＬが劣っている。
For example, test no. 5 (heat treatment No. 1-D), the heating temperature in the first stage heating and holding (maximum temperature reached) is too low outside the specified range of the present disclosure, so the reverse transformation does not proceed sufficiently, and the final product The amount of retained austenite in the steel sheet is insufficient, and TS and TS × EL are inferior.
一方、試験Ｎｏ．６（熱処理Ｎｏ．１－Ｅ）は、逆に第１段階加熱保持における加熱温度（最高到達温度）が本開示の規定範囲から外れて高すぎるため、オーステナイト分率が上昇して最終製品としての鋼板中のマルテンサイト分率が上昇する一方、フェライト分率が低下して、ＴＳ×ＥＬが劣っている。
On the other hand, test no. 6 (heat treatment No. 1-E), on the contrary, the heating temperature in the first stage heating and holding (maximum temperature reached) is too high outside the specified range of the present disclosure. While the martensite fraction in the steel sheet increases, the ferrite fraction decreases and TS × EL is inferior.
また、試験Ｎｏ．７（熱処理Ｎｏ．１－Ｆ）は、第１段階加熱保持における滞在時間が本開示の規定範囲から外れて短すぎるため、逆変態が十分に進行せず、最終製品としての鋼板中の残留オーステナイト量が不足し、ＴＳ×ＥＬが劣っている。
Also, test no. No. 7 (heat treatment No. 1-F), the residence time in the first stage heating and holding is too short outside the specified range of the present disclosure, so the reverse transformation does not proceed sufficiently, and the retained austenite in the steel sheet as the final product Insufficient quantity and TS × EL is inferior.
一方、試験Ｎｏ．９（熱処理Ｎｏ．１－Ｈ）は、逆に第１段階加熱保持における滞在時間が本開示の規定範囲から外れて長すぎるため、オーステナイト分率が上昇して最終製品としての鋼板中のマルテンサイト量が過剰となり、フェライト量が不足して、ＴＳ×ＥＬが劣っている。
On the other hand, test no. 9 (heat treatment No. 1-H), on the contrary, the residence time in the first stage heating and holding is too long outside the specified range of the present disclosure, so that the austenite fraction is increased and the martensite in the steel sheet as the final product is increased. The amount is excessive, the amount of ferrite is insufficient, and TS × EL is inferior.
また、試験Ｎｏ．１０（熱処理Ｎｏ．１－Ｉ）は、第２段階加熱保持における加熱温度（開始温度および終了温度）が本開示の規定範囲から外れて低すぎるため、最終製品としての鋼板中の残留オーステナイト量が不足し、ＴＳおよびＴＳ×ＥＬが劣っている。
Also, test no. 10 (heat treatment No. 1-I) has a heating temperature (starting temperature and ending temperature) in the second stage heating and holding that is too low outside the specified range of the present disclosure, so the amount of retained austenite in the steel sheet as the final product is Insufficient and TS and TS × EL are inferior.
一方、試験Ｎｏ．１３（熱処理Ｎｏ．１－Ｌ）は、逆に第２段階加熱保持における加熱温度（開始温度および終了温度）が本開示の規定範囲から外れて高すぎるため、最終製品としての鋼板のＴＳ×ＥＬが劣っている。
On the other hand, test no. 13 (heat treatment No. 1-L), on the contrary, the heating temperature (starting temperature and ending temperature) in the second stage heating and holding is too high outside the specified range of the present disclosure, so TS × EL of the steel sheet as the final product Is inferior.
また、試験Ｎｏ．１７（熱処理Ｎｏ．１－Ｐ）は、第２段階加熱保持における温度変化が本開示の規定範囲から外れて大きすぎるため、最終製品としての鋼板のΔＴＳ×ＥＬが不足している。
Also, test no. In No. 17 (heat treatment No. 1-P), the temperature change in the second stage heating and holding is too large outside the specified range of the present disclosure, so that ΔTS × EL of the steel sheet as the final product is insufficient.
また、試験Ｎｏ．１８（熱処理Ｎｏ．１－Ｑ）は、第２段階加熱保持における滞在時間が本開示の規定範囲から外れて短すぎるため、最終製品としての鋼板のＴＳ×ＥＬが劣っている。
Also, test no. No. 18 (heat treatment No. 1-Q) is inferior in TS × EL of the steel sheet as the final product because the residence time in the second stage heating and holding is too short outside the specified range of the present disclosure.
一方、試験Ｎｏ．２０（熱処理Ｎｏ．１－Ｓ）は、逆に第２段階加熱保持における滞在時間が本開示の規定範囲から外れて長すぎるため、最終製品としての鋼板の鋼組織および機械的特性は合格基準を満たすものの、生産性が劣っている。
On the other hand, test no. 20 (heat treatment No. 1-S), on the contrary, the stay time in the second stage heating and holding is out of the specified range of the present disclosure and is too long, so the steel structure and mechanical properties of the steel sheet as the final product are within the acceptance criteria. Although satisfied, productivity is inferior.
一方、試験Ｎｏ．２９および３１は、本開示で規定する焼鈍条件で焼鈍しているものの、本開示の成分規定の要件を一部外れる鋼種を用いているため、組織規定の要件を充足せず、機械的特性が劣っている。
On the other hand, test no. Although 29 and 31 are annealed under the annealing conditions specified in the present disclosure, they use steel types that partially deviate from the requirements of the component specifications of the present disclosure. Inferior.
例えば、試験Ｎｏ．２９（鋼種ｅ）は、Ｍｎ量が多すぎるため、残留オーステナイト中へのＭｎの濃化が不十分となり、Δ（ＴＳ×ＥＬ）が不足している。
For example, test no. Since 29 (steel type e) has too much Mn, the concentration of Mn in the retained austenite is insufficient, and Δ (TS × EL) is insufficient.
また、試験Ｎｏ．３１（鋼種ｆ）は、逆にＭｎ量が少なすぎるため、残留オーステナイト量が不足するとともに、残留オーステナイト中へのＭｎの濃化が不十分となり、ＴＳ×ＥＬが劣っている。
Also, test no. On the other hand, 31 (steel type f) has an excessively small amount of Mn, so that the amount of retained austenite is insufficient and the concentration of Mn in the retained austenite becomes insufficient, and TS × EL is inferior.
本出願は、出願日が２０１６年２月１９日である日本国特許出願、特願第２０１６－０２９６４７号を基礎出願とする優先権主張を伴う。特願第２０１６－０２９６４７号は参照することにより本明細書に取り込まれる。
This application is accompanied by a priority claim based on Japanese Patent Application No. 2016-029647, whose application date is February 19, 2016. Japanese Patent Application No. 2016-029647 is incorporated herein by reference.
Claims (3)
- 成分組成が、質量％で、
Ｃ：０．０５～０．３０％、
Ｓｉ：０～２．５％、
Ｍｎ：４．０～１０．０％、
Ａｌ：０～２．０％、
Ｐ：０％超０．０３％以下、
Ｓ：０％超０．０１％以下であり、
残部が鉄および不可避的不純物からなる、
熱延板または冷延板を、
（Ａｅ１＋Ａｅ３）／２以上［Ａｅ３＋５０℃］以下の高温域において、［前記高温域における最高到達温度－１０℃］以上の温度での滞在時間が３～２００ｓとなるように滞在させたのち、
引き続きＡｅ１以上（Ａｅ１＋２×Ａｅ３）／３以下で且つ前記高温域における最高到達温度から２０℃以上低い低温域において、±１℃／ｓ以内の温度変化で３０～３００ｓ滞在させる焼鈍工程
を備えたことを特徴とする高強度高延性鋼板の製造方法。 Ingredient composition is mass%,
C: 0.05 to 0.30%
Si: 0 to 2.5%,
Mn: 4.0 to 10.0%,
Al: 0 to 2.0%,
P: more than 0% and 0.03% or less,
S: more than 0% and 0.01% or less,
The balance consists of iron and inevitable impurities,
Hot rolled or cold rolled
In a high temperature range of (Ae1 + Ae3) / 2 or more and [Ae3 + 50 ° C.] or less, the residence time at a temperature of [the highest reached temperature in the high temperature range −10 ° C.] or more is made to stay for 3 to 200 s,
An annealing step was further provided for staying for 30 to 300 s with a temperature change within ± 1 ° C./s in a low temperature range of Ae 1 or more (Ae1 + 2 × Ae3) / 3 or less and 20 ° C. or more lower than the highest temperature in the high temperature range. A method for producing a high-strength, high-ductility steel sheet characterized by - 前記熱延板または冷延板の成分組成が、さらに、質量％で、
Ｃｒ、Ｍｏ、ＮｉおよびＣｕの１種または２種以上を合計量で０％超１．０％以下含む、
請求項１に記載の高強度高延性鋼板の製造方法。 The component composition of the hot-rolled sheet or cold-rolled sheet is further mass%,
Containing one or more of Cr, Mo, Ni and Cu in a total amount of more than 0% and 1.0% or less,
The manufacturing method of the high intensity | strength highly ductile steel plate of Claim 1. - 前記熱延板または冷延板の成分組成が、さらに、質量％で、
Ｖ、ＮｂおよびＴｉの１種または２種以上を合計量で０％超０．２％以下含む、
請求項１または２に記載の高強度高延性鋼板の製造方法。 The component composition of the hot-rolled sheet or cold-rolled sheet is further mass%,
Containing one or more of V, Nb and Ti in a total amount of more than 0% and 0.2% or less,
The manufacturing method of the high intensity | strength highly ductile steel plate of Claim 1 or 2.
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| WO2019134102A1 (en) | 2018-01-05 | 2019-07-11 | The University Of Hong Kong | An automotive steel and a method for the fabrication of the same |
| CN114375343A (en) * | 2019-09-17 | 2022-04-19 | 株式会社神户制钢所 | High-strength steel sheet and method for producing same |
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| CN111893393B (en) * | 2020-08-20 | 2021-11-23 | 山东华星新材料科技有限公司 | Mo-Ti alloy wear-resistant medium manganese steel and preparation method thereof |
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