WO2024011713A1 - 一种超细晶钢板及其制备方法 - Google Patents

一种超细晶钢板及其制备方法 Download PDF

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WO2024011713A1
WO2024011713A1 PCT/CN2022/113888 CN2022113888W WO2024011713A1 WO 2024011713 A1 WO2024011713 A1 WO 2024011713A1 CN 2022113888 W CN2022113888 W CN 2022113888W WO 2024011713 A1 WO2024011713 A1 WO 2024011713A1
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steel plate
temperature
cooling
ultra
stage
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English (en)
French (fr)
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谯明亮
邱保文
钦祥斗
赵晋斌
邓阳
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南京钢铁股份有限公司
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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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/78—Combined heat-treatments not provided for above
    • C21D1/785—Thermocycling
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • 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
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • 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
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • the present invention relates to a steel plate and a preparation method thereof, in particular to an ultra-fine grain steel plate and a preparation method thereof.
  • Grain refinement is a recognized technical means to simultaneously improve the strength and low-temperature toughness of steel plates.
  • metallurgists usually use deformation-induced ferrite phase transformation to obtain an ultra-fine ferrite structure of ⁇ 3 ⁇ m, which can double the tensile strength based on the composition of ordinary carbon steel, and can be used at low temperatures. Excellent impact performance.
  • the principle of using deformation-induced ferrite phase transformation to produce steel plates has many strict limitations. For example, in low-temperature large-deformation rolling, the total strain must be large. To sum up, it requires that the thickness of the cast billet or steel ingot ⁇ the finished steel plate. 10 times the thickness. This results in that under the current production conditions of the metallurgical industry, there are almost no ultra-fine grain steel plates with a thickness >30mm. At the same time, the transformation rate of deformation-induced ferrite phase transformation is difficult to reach more than 95%. In the final microstructure of the steel plate, it is easy to find grains with an intercept size larger than 5 ⁇ m, and even grains larger than 10 ⁇ m, which seriously damages the low-temperature impact toughness. .
  • CN 101397625 B discloses a 420MPa ultra-fine grain steel plate with a maximum thickness of 20mm and a ferrite grain size of 3-5 ⁇ m.
  • the patent with the announcement number "CN 109518071 B” discloses an ultra-fine grained steel plate and its manufacturing method: the rough rolling single pass reduction rate is >20%, the final pass reduction rate is ⁇ 30%, and the rough rolling is performed for 5 times Pass; cumulative reduction rate of finishing rolling is 78-88%. Calculated based on the thickest blank of 320mm, it can be known that the thickness of the steel plate is less than 20mm.
  • the microstructure of the final steel plate has an average ferrite grain size of 3.0-4.0 ⁇ m.
  • the patent with the announcement number "CN 102011045 B” discloses an ultra-fine grained steel plate and its manufacturing method: when performing three-stage controlled rolling, the first stage deforms, the deformation temperature is 1000 ⁇ 1100°C, and the nominal deformation amount is 20 ⁇ 50% ; In the second stage of deformation, the deformation temperature is 830 to 950°C, and the nominal deformation amount is 30 to 50%; in the third stage of deformation, the deformation temperature is set near the Ar 3 temperature, and the nominal deformation amount is 30 to 50%.
  • An ultra-fine grained ferrite steel plate is prepared with a ferrite grain size of ⁇ 3.0 ⁇ m. However, from its published microstructure figures 2 and 3, many ferrite grains with an intercept size greater than 10 ⁇ m can be measured, and there are many pearlite particles with an intercept size greater than 20 ⁇ m. It can be considered that the low temperature impact toughness is poor.
  • the patent with the announcement number "CN 113073262 A” discloses a dual-gradient ultra-fine grain steel plate with excellent ultra-low temperature toughness and its preparation method.
  • the grain size of the steel plate changes in a gradient direction in the thickness direction.
  • the grain size of the surface layer of the steel plate is ⁇ 1.5 ⁇ m, and the grain size of the core of the steel plate is ⁇ 5 ⁇ m.
  • the thickness ratio of the blank to the steel plate is still >10, and it does not get rid of the compression ratio limitation of deformation-induced phase transformation.
  • the thickness of the steel plate is less than 30mm, which severely limits its application in the construction of large cryogenic pressure vessels, steel structure manufacturing in arctic and extremely cold conditions, and shipbuilding.
  • the present invention aims to provide an ultra-fine-grained steel plate that increases the thickness of the steel plate; another purpose of the present invention is to provide a method for preparing the ultra-fine-grained steel plate.
  • the chemical composition of an ultra-fine grained steel plate according to the present invention includes, in terms of mass percentage: C 0.04% ⁇ 0.10%, Mn 1.20% ⁇ 1.60%, Ni 0.30% ⁇ 0.60%, Nb 0.01% ⁇ 0.05 %, Ti 0.005% ⁇ 0.02%, Alt 0.015% ⁇ 0.050%, Cr 0.01% ⁇ 0.25%, Cu 0.10% ⁇ 0.35%, Si 0.10% ⁇ 0.40%, P ⁇ 0.010%, S ⁇ 0.004%, the balance is Fe and other inevitable impurities; the thickness of the steel plate is 40 ⁇ 60mm.
  • the chemical composition of the steel plate includes, in terms of mass percentage, C 0.04% ⁇ 0.009%, Mn 1.40% ⁇ 1.60%, Ni 0.30% ⁇ 0.50%, Nb 0.01% ⁇ 0.045%, Ti 0.007% ⁇ 0.020%, Alt 0.02% ⁇ 0.050%, Cr 0.03% ⁇ 0.25%, Cu 0.1% ⁇ 0.35%, Si 0.10% ⁇ 0.25%, P ⁇ 0.010%, S ⁇ 0.004%, the balance is Fe and other inevitable impurities.
  • the ferrite grains in the steel plate are less than 5 ⁇ m, and more than 50% of them are less than 3 ⁇ m.
  • the preparation method of ultra-fine grained steel plate of the present invention includes the following steps:
  • the continuous casting slab is heated, and after phosphorus removal, rough rolling;
  • C is the most effective strengthening alloy element. While improving the hardenability, it also increases the ductile-brittle transition temperature. Under the condition of ensuring strength, reducing the C content as much as possible is beneficial to reducing the ductile-brittle transition. Temperature; (2) Mn is the most effective element in improving strength under low carbon conditions.
  • the intermediate billet is cooled to 300-400°C, and a microstructure dominated by bainite structure can be obtained within the full thickness range.
  • the fine bainite strips are used as nucleation points to prepare for the next step. Preparation for thermally refining austenite.
  • step S3 incomplete austenitization occurs, a small amount of ultrafine ferrite exists, and the grain size after austenitization will be further refined than the austenite grain size after rough rolling; wherein Ae 3 is the ⁇ /( ⁇ + ⁇ ) phase boundary equilibrium temperature.
  • step S4 when the surface temperature of the steel plate is 760 ⁇ 10°C, which is slightly higher than the ferrite transformation temperature under continuous cooling conditions, the core temperature of the intermediate blank is still maintained at the reheating temperature, and is obtained within the full thickness range. Temperature conditions that are prone to deformation inducing ferrite; the cumulative reduction rate of the core is 40% to 50%, and more than 60% of ultra-fine ferrite grains with a diameter of ⁇ 3.0 ⁇ m will be obtained.
  • the heating temperature is 1080-1180°C
  • the rough rolling temperature is 1000-1150°C
  • the reduction rate is 45-55%.
  • the cooling rate of the controlled cooling is 2.0-4.0°C/second, cooling to 550-600°C for pile cooling, and the steel plate is pile-cooled for 24 to 40 hours.
  • Mechanism of invention Through thermal cycling, austenite grains that are more refined than conventional rolling processes are obtained, and deformation-induced ferrite is obtained under small reduction rates to create favorable conditions; through pre-formed ultra-fine deformation-induced ferrite The body band divides the austenite grains, providing more nucleation sites for the subsequent ferrite phase transformation of the remaining austenite, and finally obtains ferrite grains with a diameter less than 5.0 ⁇ m.
  • the ultra-fine grained steel plate has a thickness of 40-60mm, has a yield strength greater than 460MPa, excellent low-temperature toughness, and achieves an impact energy of greater than 120J at -101°C. , can be used in the construction of ultra-large low-temperature pressure vessels of 10,000 cubic meters or in the manufacturing fields of steel structures and ships in arctic and extremely cold weather;
  • the preparation of 40-60mm thick ultra-fine-grained steel plates by this method is better than the deformation-induced ferrite phase. By changing the process, the compression ratio is greatly reduced, and an ultra-fine ferrite structure can be obtained.
  • Figure 1 is a picture of the microstructure at 1/2 the thickness of the steel plate in Example 3.
  • the chemical composition of the ultra-fine grained steel plate of the present invention includes, in terms of mass percentage: C 0.04%, Mn 1.40%, Ni 0.30%, Nb 0.010%, Ti 0.007%, Alt 0.050%, Cr 0.01%, Cu 0.35%, Si 0.40%, P 0.009%, S 0.004%, the balance is Fe and other inevitable impurities; the thickness of the steel plate is 40mm.
  • Its preparation method includes the following steps:
  • the chemical composition of the ultra-fine grain steel plate of the present invention includes, in terms of mass percentage: C 0.09%, Mn 1.25%, Ni 0.50%, Nb 0.050%, Ti 0.005%, Alt 0.015%, Cr 0.03%, Cu 0.20%, Si 0.10%, P 0.004%, S 0.002%, the balance is Fe and other inevitable impurities; the thickness of the steel plate is 50mm.
  • Its preparation method includes the following steps:
  • the chemical composition of the ultra-fine grained steel plate of the present invention includes, in terms of mass percentage: C 0.10%, Mn 1.60%, Ni 0.60%, Nb 0.045%, Ti 0.020%, Alt 0.020%, Cr 0.25%, Cu 0.10%, Si 0.25%, P 0.006%, S 0.001%, the balance is Fe and other inevitable impurities; the thickness of the steel plate is 60mm.
  • Its preparation method includes the following steps:
  • the 260mm thick cast slab is heated to 1180°C, and after phosphorus removal, it is rough rolled at 1150°C.
  • the reduction rate after rough rolling is 55%;
  • steps S2 and S3 are not performed, and other conditions remain unchanged.
  • the thickness of the obtained steel plate was 60mm.
  • the 1/2 thickness of the steel plate in Example 3 was observed and characterized, as shown in Figure 1.
  • Ultra-fine grains can be obtained by cooling the intermediate billet, reheating it, austenitizing it, and rolling it.
  • the microstructure of the steel plate is dominated by ultrafine ferrite grains, plus a very small amount of ultrafine bainite grains.
  • the statistical characteristics of ferrite grain diameter are: 20% for ⁇ 1.5 ⁇ m, 45% for 1.5 ⁇ m-3.0 ⁇ m, 35% for 3.0 ⁇ m-5.0 ⁇ m, and no particles >5.0 ⁇ m have been found. grains.
  • the yield strength, tensile strength, elongation and core impact energy of the ultra-fine-grained steel plates prepared in Examples 1 to 3 were tested.
  • the test methods refer to GB/T 228 and GB/T 229.
  • the test results are shown in Table 1.
  • the steel plate prepared by the present invention improves the -101°C impact toughness of the steel plate and meets the -101°C impact toughness requirements of 3.5Ni low-temperature steel, with a maximum thickness of 60mm.
  • the yield strength of the steel plate is ⁇ 460MPa
  • the tensile strength is >570MPa
  • the Charpy impact energy at -101°C in the center of the plate thickness is ⁇ 120J.
  • the thickness of the steel plate is usually greater than 30mm.
  • the steel plate prepared by the present invention can meet the large thickness requirement.
  • Comparative Example 1 lacks the thermal cycle process consisting of steps S2 and S3, so a more refined austenite structure cannot be obtained.
  • the grains In the final transformation process from austenite to ferrite, the grains cannot be completely refined to less than 5 ⁇ m. It is very unfavorable for low-temperature impact toughness.
  • the -101°C impact energy is in the very low lower plateau area, making it difficult to meet the use requirements in the construction of large-scale low-temperature pressure vessels, steel structure manufacturing under extremely cold conditions in polar regions, and shipbuilding.

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Abstract

一种超细晶钢板及其制备方法，其化学成分以质量百分比计包括：C 0.04％～0.10％，Mn 1.20％～1.60％，Ni 0.30％～0.60％，Nb 0.01％～0.05％，Ti 0.005％～0.02％，Alt 0.015％～0.050％，Cr 0.01％～0.25％，Cu 0.10％～0.35％，Si 0.10％～0.40％，P≤0.010％，S≤0.004％，余量为Fe及其他不可避免的杂质；所述钢板厚度为40～60mm；其制备方法包括以下步骤：S1、将连铸板坯在加热，经除磷后，粗轧；S2、将中间坯在200～300秒冷却至300～400℃；S3、再将中间坯在加热炉内加热到Ae 3-10℃～Ae 3，保温30±10min；S4、将出炉的再热中间坯待温到760±10℃进行第二阶段精轧，心部累计压下率40～50％；S5、第二阶段精轧完毕后控冷，堆冷，获得超细晶钢板；该超细晶钢板厚度40～60mm，具有大于460MPa屈服强度，优异的低温韧性，实现了-101℃冲击功大于120J。

Description

一种超细晶钢板及其制备方法 技术领域
本发明涉及一种钢板及其制备方法，特别涉及一种超细晶钢板及其制备方法。
背景技术
细化晶粒是公认的同时提高钢板强度和低温韧性的技术手段。为追求优良的性能，冶金工作者通常采用形变诱导铁素体相变来获得≤3μm的超细铁素体组织，可以在普通碳素钢的成分基础上提高一倍的拉伸强度，并且低温冲击性能优良。
但是利用形变诱导铁素体相变来生产钢板，其原理自身有很多严苛的限制，如低温大变形轧制，总应变量要大，归结起来，就是要求铸坯或钢锭的厚度≥成品钢板厚度的10倍。这就导致在目前冶金行业生产条件下，几乎没有厚度＞30mm的超细晶钢板。同时形变诱导铁素体相变的转变率很难达到95％以上，最终钢板微观组织中很容易发现截距尺寸大于5μm的晶粒，甚至有10μm以上的晶粒，严重有损于低温冲击韧性。
公告号为“CN 101397625 B”的专利公开了一种最大厚度为20mm的420MPa级超细晶钢板，其铁素体晶粒尺寸3-5μm。
公告号为“CN 109518071 B”的专利公开了一种超细晶钢板及其制造方法：粗轧单道次压下率＞20％，末道次压下率≥30％，粗轧进行5个道次；精轧累计压下率78-88％。按最厚坯料320mm计算，可以知道该钢板厚度小于20mm。最终钢板的微观组织铁素体晶粒尺寸平均为3.0-4.0μm。
公告号为“CN 102011045 B”的专利公开了一种超细晶钢板及其制造方法：进行三阶段控制轧制时，第一阶段变形，变形温度1000～1100℃，名义变形量20～50％；第二阶段变形，变形温度830～950℃，名义变形量30～50％；第三阶段变形，变形温度设定在Ar 3温度附近变形，名义变形量30～50％。制备出超细晶粒铁素体钢板，铁素体晶粒尺寸＜3.0μm。但从其公布的微观组织图2和图3，可以测量出许多截距尺寸＞10μm的铁素体晶粒，并且存在很多截距尺寸大于20μm的珠光体颗粒。可以认为低温冲击韧性不佳。
公告号为“CN 113073262 A”的专利公开了一种具有优异超低温韧性的双梯度超细晶钢板及其制备方法。该钢板厚度方向上晶粒尺寸呈梯度变化，钢板表层晶粒尺寸≤1.5μm，钢板心部晶粒尺寸≤5μm。其应用实例中坯料与钢板厚度比依然＞10，没有摆脱形变诱导相变的压缩比限制。
钢板厚度小于30mm，在大型低温压力容器建造、极地极寒条件下的钢结构制造、船舶建造等领域的应用受到严重制约。
发明内容
发明目的：本发明旨在提供一种提高钢板厚度的超细晶钢板；本发明的另一目的是提供该超细晶钢板的制备方法。
技术方案：本发明所述的一种超细晶钢板，其化学成分以质量百分比计包括：C 0.04％～0.10％，Mn 1.20％～1.60％，Ni 0.30％～0.60％，Nb 0.01％～0.05％，Ti 0.005％～0.02％，Alt 0.015％～0.050％，Cr 0.01％～0.25％，Cu 0.10％～0.35％，Si 0.10％～0.40％，P≤0.010％，S≤0.004％，余量为Fe及其他不可避免的杂质；所述钢板厚度为40～60mm。
所述钢板化学成分以质量百分比计包括，C 0.04％～0.009％，Mn 1.40％～1.60％，Ni 0.30％～0.50％，Nb 0.01％～0.045％，Ti 0.007％～0.020％，Alt 0.02％～0.050％，Cr 0.03％～0.25％，Cu 0.1％～0.35％，Si 0.10％～0.25％，P≤0.010％，S≤0.004％，余量为Fe及其他不可避免的杂质。
所述钢板中铁素体晶粒小于5μm，其中小于3μm的大于50％。
本发明的超细晶钢板的制备方法，包括以下步骤：
S1、将连铸板坯在加热，经除磷后，粗轧；
S2、将中间坯在200～300秒冷却至400～300℃；
S3、再将中间坯在加热炉内加热到Ae 3-10℃～Ae 3，保温30±10min；
S4、将出炉的再热中间坯待温到760±10℃进行第二阶段精轧，心部累计压下率40％～50％；
S5、第二阶段精轧完毕后控冷，堆冷，获得超细晶钢板。
所述钢板成分中：(1)C是最有效的强化合金元素，提高淬透性的同时，也提高韧脆转变温度，在保证强度的条件下，尽量降低C含量，有利于降低韧脆转变温度；(2)Mn是在低碳情况下提高强度最有效的元素，超过一定含量时稳定过冷奥氏体作用强烈，将铁素体转变温度向低温区推移，减小有效晶粒尺寸；含量再进一步提高，铸坯中Mn偏析将加重，导致局部材料相变后出现异常的低韧性组织；利用Mn元素的成分起伏，配合适当的非再结晶温区和变形量，在相对贫Mn区诱导出超细铁素体，C元素以碳化物形式在晶粒内析出一部分，其它C元素以短程扩散形式在铁素体晶界析出弥散细小的碳化物；(3)Cr、Cu、Ni也是稳定过冷奥氏体元素，在铁素体相变中减小铁素体长大速率，为获得超细铁素体组织提供合适的冷却速率；(4)P、S元素作为有害元素，从洁净钢的角度考虑越低越好，综合经济性考虑，P含量0.008％以下，S含量0.002％以下为佳。
所述步骤S2中，中间坯冷却至300～400℃，在全厚度范围内可以获得以贝氏体组织为主导的微观组织，利用细小的贝氏体条束作为形核点，为下一步再热细化奥氏体做 好准备工作。
所述步骤S3中，发生不完全奥氏体化，有少量超细铁素体存在，并且奥氏体化后晶粒尺寸将比粗轧后的奥氏体晶粒尺寸得到进一步细化；其中Ae 3为γ/(α+γ)相界平衡温度。
所述步骤S4中，在钢板表面温度760±10℃时，略微高于连续冷却条件下的铁素体相变温度，中间坯的心部温度仍然保持在再热温度，在全厚度范围内获得易于形变诱导铁素体的温度条件；心部累计压下率40％～50％，将获得超过60％的直径＜3.0μm超细铁素体晶粒。
优选的，所述S1中，加热温度为1080～1180℃，粗轧的温度为1000～1150℃，压下率为45～55％。
优选的，所述控冷的冷却速度为2.0～4.0℃/秒，冷却至550～600℃进行堆冷，钢板堆冷24～40小时。
发明机理：通过热循环，获得比常规轧制工艺更加细化的奥氏体晶粒，在小压下率条件下获得形变诱导铁素体创造有利条件；通过预先形成的超细形变诱导铁素体带分割奥氏体晶粒，为剩余奥氏体随后发生的铁素体相变提供更多形核位置，最终获得直径小于5.0μm的铁素体晶粒。
有益效果：与现有技术相比，本发明具有如下显著优点：(1)本超细晶钢板厚度40～60mm，具有大于460MPa屈服强度，优异的低温韧性，实现了-101℃冲击功大于120J，可以应用于万立方米级超大型低温压力容器建造或极地极寒天气下钢结构、船舶等制造领域；(2)本方法制备40～60mm厚超细晶钢板相对于形变诱导铁素体相变工艺，大大降低压缩比，可以获得超细铁素体组织。
附图说明
图1为实施例3的钢板厚度1/2处的微观组织图片。
具体实施方式
下面结合实施例对本发明的技术方案作进一步说明。
实施例1
本发明的超细晶钢板，其化学成分以质量百分比计包括：C 0.04％，Mn 1.40％，Ni 0.30％，Nb 0.010％，Ti 0.007％，Alt 0.050％，Cr 0.01％，Cu 0.35％，Si 0.40％，P 0.009％，S 0.004％，余量为Fe及其他不可避免的杂质；所述钢板厚度为40mm.
其制备方法包括以下步骤：
S1、将150mm厚铸坯加热至1080℃，经除磷后，1000℃粗轧，粗轧后压下率45％；
S2、将中间坯在200秒冷却至399℃；
S3、再将中间坯在加热炉内加热到842.6℃(Ae 3-10℃～Ae 3)，保温30min；
S4、将出炉的再热中间坯待温到770℃进行第二阶段精轧，该阶段心部累计压下率48％；
S5、第二阶段精轧完毕后，控冷，冷却速度为2.0℃/秒，冷却至599℃堆冷24小时，获得超细晶钢板。
实施例2
本发明的超细晶钢板，其化学成分以质量百分比计包括：C 0.09％，Mn 1.25％，Ni 0.50％，Nb 0.050％，Ti 0.005％，Alt 0.015％，Cr 0.03％，Cu 0.20％，Si 0.10％，P 0.004％，S 0.002％，余量为Fe及其他不可避免的杂质；所述钢板厚度为50mm。
其制备方法包括以下步骤：
S1、将220mm厚铸坯加热至1100℃，经除磷后，1050℃粗轧，粗轧后压下率50％；
S2、将中间坯在280秒冷却至380℃；
S3、再将中间坯在加热炉内加热到816.5℃(Ae 3-10℃～Ae 3)，保温30min；
S4、将出炉的再热中间坯待温到760℃进行第二阶段精轧，该阶段心部累计压下率50％；
S5、第二阶段精轧完毕后，控冷，冷却速度为3.0℃/秒，冷却至550℃堆冷32小时，获得超细晶钢板。
实施例3
本发明的超细晶钢板，其化学成分以质量百分比计包括：C 0.10％，Mn 1.60％，Ni 0.60％，Nb 0.045％，Ti 0.020％，Alt 0.020％，Cr 0.25％，Cu 0.10％，Si 0.25％，P 0.006％，S 0.001％，余量为Fe及其他不可避免的杂质；所述钢板厚度为60mm。
其制备方法包括以下步骤：
S1、将260mm厚铸坯加热至1180℃，经除磷后，1150℃粗轧，粗轧后压下率55％；
S2、将中间坯在300秒冷却至350℃；
S3、再将中间坯在加热炉内加热到816.1℃(Ae 3-10℃～Ae 3)，保温30min；
S4、将出炉的再热中间坯待温到750℃进行第二阶段精轧，该阶段心部累计压下率40％；
S5、第二阶段精轧完毕后，控冷，冷却速度为4.0℃/秒，冷却至500℃堆冷40小时，获得超细晶钢板。
对比例1
在实施例3的基础上，不进行步骤S2和步骤S3，其他条件不变。
得到的钢板的厚度为60mm。
微观结构表征
对实施例3钢板厚度1/2处进行围观表征，如图1所示。通过中间坯冷却、再热奥氏体化后轧制，可以获得超细晶粒。钢板的显微组织以超细铁素体晶粒为主，加上极少量超细贝氏体晶粒。铁素体晶粒直径的统计特征为：≤1.5μm的百分比20％，1.5μm-3.0μm之间的百分比45％，3.0μm-5.0μm之间的百分比35％，未发现＞5.0μm以上的晶粒。
性能测试
对实施例1～3制备的超细晶钢板的屈服强度、拉伸强度、延伸率和心部冲击功进行测试，测试方法参照GB/T 228和GB/T 229，测试结果见表1。
表1 实施例1～3钢板性能测试结果
Figure PCTCN2022113888-appb-000001
由表1可以看出，本发明制备的钢板提高了钢板-101℃冲击韧性，获得了满足3.5Ni低温钢的-101℃冲击韧性要求，最大厚度60mm。钢板的屈服强度≥460MPa，抗拉强度＞570MPa，板厚中心部位-101℃的夏比冲击功≥120J。在大型低温压力容器建造、极地极寒条件下的钢结构制造、船舶建造等领域，因结构体对刚性的严格要求，建造钢板的厚度通常大于30mm，本发明制备的钢板能够满足大厚度要求。
对比例1因缺少步骤S2和S3组成的热循环过程，得不到更加细化的奥氏体组织，在最后进行奥氏体到铁素体转变过程，晶粒不能全部细化到5μm以下，对低温冲击韧性十分不利，-101℃冲击功处于很低的下平台区，难以满足大型低温压力容器建造、极地极寒条件下的钢结构制造、船舶建造等领域的使用要求。

Claims (7)

  1. 一种超细晶钢板，其特征在于，其化学成分以质量百分比计包括：C 0.04％～0.10％，Mn 1.20％～1.60％，Ni 0.30％～0.60％，Nb 0.01％～0.05％，Ti 0.005％～0.02％，Alt 0.015％～0.050％，Cr 0.01％～0.25％，Cu 0.10％～0.35％，Si 0.10％～0.40％，P≤0.010％，S≤0.004％，余量为Fe及其他不可避免的杂质；所述钢板厚度为40～60mm。
  2. 根据权利要求1所述的钢板，其特征在于，所述钢板化学成分以质量百分比计包括，C 0.04％～0.009％，Mn 1.40％～1.60％，Ni 0.30％～0.50％，Nb 0.01％～0.045％，Ti 0.007％～0.020％，Alt 0.02％～0.050％，Cr 0.03％～0.25％，Cu 0.1％～0.35％，Si 0.10％～0.25％，P≤0.010％，S≤0.004％，余量为Fe及其他不可避免的杂质。
  3. 根据权利要求1所述的钢板，其特征在于，所述钢板中铁素体晶粒小于5μm，其中小于3μm的大于50％。
  4. 一种权利要求1所述的钢板的制备方法，其特征在于，包括以下步骤：
    S1、将连铸板坯在加热，经除磷后，粗轧；
    S2、将中间坯在200～300秒冷却至300～400℃；
    S3、再将中间坯在加热炉内加热到Ae 3-10℃～Ae 3，保温30±10min；
    S4、将出炉的再热中间坯待温到760±10℃进行第二阶段精轧，该阶段心部累计压下率40～50％；
    S5、第二阶段精轧完毕后控冷，冷堆，获得超细晶钢板。
  5. 根据权利要求4所述的钢板的制备方法，其特征在于，所述S1中，加热温度为1080～1180℃，粗轧的温度为1000～1150℃，压下率为45～55％。
  6. 根据权利要求4所述的钢板的制备方法，其特征在于，所述控冷的冷却速度为2.0～4.0℃/秒。
  7. 根据权利要求4所述的钢板的制备方法，其特征在于，所述堆冷温度为550～600℃，堆冷时间为24～40小时。
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