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WO2018227740A1 - 一种低屈强比高强韧厚规格钢板及其制造方法 - Google Patents

一种低屈强比高强韧厚规格钢板及其制造方法 Download PDF

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Publication number
WO2018227740A1
WO2018227740A1 PCT/CN2017/096430 CN2017096430W WO2018227740A1 WO 2018227740 A1 WO2018227740 A1 WO 2018227740A1 CN 2017096430 W CN2017096430 W CN 2017096430W WO 2018227740 A1 WO2018227740 A1 WO 2018227740A1
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temperature
strength
steel plate
steel sheet
low
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PCT/CN2017/096430
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English (en)
French (fr)
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孙超
李强
单以刚
王从道
党军
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南京钢铁股份有限公司
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Priority to JP2019555528A priority Critical patent/JP6798041B2/ja
Priority to AU2017418679A priority patent/AU2017418679B2/en
Publication of WO2018227740A1 publication Critical patent/WO2018227740A1/zh
Priority to AU2019100570A priority patent/AU2019100570A4/en

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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
    • 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
    • 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
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • 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
    • C21D2211/001—Austenite
    • 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
    • C21D2211/008—Martensite

Definitions

  • the invention relates to a steel plate and a manufacturing method thereof, in particular to a low-yield ratio high-strength and toughness-thickness steel plate and a manufacturing method thereof.
  • the yield ratio is the ratio of yield strength to tensile strength, reflecting the work hardening ability of the material. The higher the yield ratio, the more likely the local stress concentration or local large deformation occurs during the deformation of the steel plate. The absorption of a small amount of energy in the steel structure will lead to material fracture or structural instability. The lower the yield ratio, the plastic deformation from the steel plate to the final fracture.
  • the yield ratio of the high-strength steel sheet produced by the existing quenching and tempering process is generally not less than 0.92. A higher yield ratio limits the range of applications of the steel sheet.
  • steels of a single structure type such as bainite and martensite tend to achieve high yield strength and high tensile strength, but the values of yield strength and tensile strength are not much different, and thus the yield is relatively high.
  • Obtaining multiphase structure by improving the process is an effective method to achieve high strength and low yield ratio, including ferrite + martensite, ferrite + bainite, bainite + martensite.
  • Prior art processes for obtaining low yield ratio multiphase structures are generally based on sub-temperature quenching, such as reheat quenching-sub-temperature quenching-tempering, normalizing-sub-temperature quenching-tempering, direct quenching-sub-temperature quenching-tempering , TMCP - sub-temperature quenching - tempering, sub-temperature zone direct quenching - tempering and other processes.
  • this type of process has the disadvantage of a long production cycle.
  • the process based on rapid heating on-line heat treatment can flexibly control the multi-phase structure, and the production cycle is short and the efficiency is high.
  • the production equipment is extremely demanded and difficult to be popularized.
  • the patent publication CN104789892A discloses a low yield strength with excellent low temperature impact toughness. Compared with the high-strength and toughness thick steel plate and the manufacturing method thereof, the low-yield ratio high-strength and tough-thickness steel plate contains 3.6% or more of Ni in the chemical composition, and thus the cost is high.
  • the publication No. CN106399840A discloses a low-cost low yield ratio quenched and tempered Q690E steel sheet and a production method thereof, and the low yield ratio quenched and tempered Q690E steel sheet has a thickness of only 8-40 mm.
  • the patent publication CN103352167A discloses a low-strength ratio high-strength bridge steel and a manufacturing method thereof, and the low-yield ratio high-strength bridge steel has a yield strength of not more than 600 MPa and can only guarantee a -40 ° C impact. toughness.
  • the publication No. CN102277539A discloses a low yield ratio high plasticity ultrafine grain high strength steel and a method for producing the same, and the low yield ratio high plasticity ultrafine grain high strength steel has a bainite structure.
  • the object of the present invention is to provide a low to high strength ratio high strength toughness and thick gauge steel sheet which has outstanding characteristics of high strength, high toughness, thick gauge and low yield ratio.
  • Another object of the present invention is to provide a method for producing a low-yield ratio high-strength and tough-thickness steel sheet, by which a thick gauge steel sheet having a low yield ratio and high toughness can be obtained.
  • a low-yield ratio high-strength and tough-thickness specification steel plate the mass percentage content of the chemical composition of the steel plate is: C: 0.060-0.080%, Mn: 5.5-6.0%, Si: 0.10-0.30%, Al: 0.015-0.040%, Mo: 0.15-0.30%, Cr: 0.20-0.40%, Ni: 0.15-0.40%, Ti: 0.01-0.03%, S ⁇ 0.006%, P ⁇ 0.010%, the balance is Fe and cannot be avoided Impurity element.
  • the C element can significantly increase the strength of the matrix by solid solution strengthening while stabilizing the austenite phase, but in order to reduce the ductile-brittle transition temperature of the material, the C content should be minimized. In addition, C is also detrimental to the welding properties of the material. Therefore, the present invention controls the C content to a lower level of 0.060-0.080%.
  • Mn is a main alloying element of the steel sheet according to the present invention, and is both a ferrite strengthening element and an austenite stabilizing element.
  • increasing the Mn/C ratio can significantly reduce the ductile-brittle transition temperature. Therefore, Mn can replace the higher-priced Ni to a certain extent, but too high Mn content will increase the degree of segregation and increase the difficulty of smelting. And the cost of materials has increased. Therefore, the present invention controls the Mn content to be 5.5 to 6.0%.
  • Si is a deoxidizing element in the steel making process, and an appropriate amount of Si can inhibit the segregation of Mn and P, while the O content Excessively high, Mn and P segregation can damage toughness. Si can also produce solid solution strengthening, but when the content exceeds 0.3%, the ductile-brittle transition temperature is increased, so the content cannot be too high.
  • the present invention controls Si from 0.10 to 0.30%.
  • Al is a deoxidizing element in the steel making process, which can also reduce the amount of solid solution N atoms, thereby improving the toughness and time effect resistance, and the formed AlN can also refine the grains, thereby further reducing the ductile-brittle transition temperature.
  • the present invention controls the Al content to be 0.015 to 0.040%.
  • Mo can increase the strength of martensite after tempering, and can also weaken the grain boundary segregation of Mn to improve toughness. Excessive Mo content will deteriorate weldability and increase material costs. Therefore, the present invention controls the Mo content to be 0.15-0.30%.
  • the present invention controls the Cr content to be 0.20-0.40%.
  • Ni can stabilize the austenite phase, improve the hardenability, lower the ductile-brittle transition temperature, and improve the deformation properties, and also contribute to weldability.
  • excessive addition of Ni elements can significantly increase costs. Therefore, the present invention controls the Ni content to be 0.15-0.40%.
  • Ti can refine high-temperature austenite grains, which is beneficial to improve strength and toughness. A small amount of addition can work, and excessive addition will result in an increase in inclusions. Therefore, the present invention controls the Ti content to be from 0.010 to 0.030%.
  • the present invention requires S ⁇ 0.006% and P ⁇ 0.010%.
  • the microstructure under the microstructure of the steel plate is a multiphase structure of tempered martensite and rotating austenite.
  • the tempered martensite as the matrix structure determines the yield strength of the material.
  • the rotating austenite can improve the toughness of the material on the one hand, and can also change the tensile strength and reduce the yield ratio during the deformation process on the other hand.
  • the volume fraction of the rotated austenite was measured by an X-ray diffractometer to be 5-15%.
  • the thickness of the steel plate is 50-100 mm, the yield strength is ⁇ 690 MPa, the yield ratio is ⁇ 0.80, and the transverse impact absorption energy of the -60 ° C Charpy impact test is ⁇ 60 J.
  • the method for manufacturing a low-yield-ratio high-strength and tough-thickness steel plate according to the present invention comprises the steps of heating, rolling, and heat treatment, as follows:
  • Heating heating a billet having the same chemical composition as the above-mentioned low yield ratio high strength toughness and thickness gauge steel sheet, The heating temperature of the billet is controlled at 1070-1150 ° C, and the temperature is maintained for 90-150 min after the billet center reaches the temperature.
  • the heating temperature is controlled at 1070-1150 ° C, and the temperature is maintained for 90-150 min after the billet center reaches the temperature.
  • the billet is heated, a high-temperature austenite structure is obtained, and the alloy elements are homogenized by diffusion. If the heating temperature is too high or the holding time is too long, the high-temperature austenite grains will be too coarse, and the heating temperature is too low or the holding time is too short, which is not conducive to the homogenization of the alloying elements. Therefore, the present invention controls the heating temperature at 1070-1150 ° C.
  • the holding time is controlled at 90-150 min.
  • the final cooling temperature is ⁇ 130 °C lower than the martensite transformation end point, the austenite is transformed into lath martensite, and the microstructure is further refined; wherein the final cooling temperature after water cooling is room temperature to 130 ° C.
  • the steel plate is heated to 605-645 ° C, after the temperature reaches the temperature in the center of the steel plate, the temperature is kept for 50-120 min, and then air-cooled to room temperature.
  • the heat treatment temperature of 605-645 °C is located in the ferrite-austenite two-phase region, which can form a rotating austenite with a volume fraction of 5-15%.
  • the austenite is enriched during the heating process and the heat preservation process of 50-120 min. Alloying elements such as C and Mn have sufficient thermal stability to maintain a face-centered cubic structure when cooled to -60 °C.
  • martensite undergoes moderate recovery at high temperatures, and the strength is lowered and the plastic toughness is improved.
  • the air is cooled to room temperature to obtain a multiphase structure of tempered martensite + rotating austenite.
  • the low yield ratio high strength and toughness thick gauge steel plate of the present invention has high yield strength and low yield ratio, yield strength ⁇ 690 MPa, yield ratio ⁇ 0.80; -60 ° C Charpy impact test transverse direction
  • the impact absorption energy is ⁇ 60J, which has good low temperature impact toughness; and the thickness specification of the steel plate reaches 50-100mm.
  • the method for manufacturing a low-yield ratio high-strength and tough-thickness steel sheet according to the present invention can produce a high-strength steel sheet having high strength, high toughness, and low yield ratio; and the manufacturing process requires only one heat treatment, and the process is simple and easy to implement.
  • Fig. 1 is a transmission electron micrograph of the structure of a steel sheet having a low yield ratio and a high toughness and thickness gauge in Example 1.
  • Example 1 Production of a low yield ratio high toughness steel plate having a thickness of 50 mm was carried out according to the following procedure:
  • the total deformation is 75%, water-cooled after the end of rolling, and the final cooling temperature is 25 °C;
  • the chemical composition of the steel sheet and its mass percentage content are: C: 0.060%, Mn: 5.5%, Si: 0.22%, Al: 0.030%, Mo: 0.15%, Cr: 0.20%, Ni: 0.15%, Ti: 0.010 %, S: 0.003%, P: 0.006%, and the balance is Fe and impurity elements.
  • the steel plate structure is a multiphase structure of tempered martensite + rotary austenite, as shown in Fig. 1, which is a transmission electron micrograph of the steel plate structure, and the tempered martensite and the rotary oscillating
  • the body is a tempered martensite in the light part and a rotating austenite in the dark part.
  • the yield strength of the steel plate was 752 MPa, the yield ratio was 0.80, and the lateral impact absorption energy of the -60 °C Charpy impact test was 155 J.
  • Example 2 A low to high strength toughness steel plate having a thickness of 70 mm was produced, and the following steps were carried out:
  • the total deformation is 65%, water-cooled after the end of rolling, and the final cooling temperature is 68 ° C;
  • the chemical composition and mass fraction of the steel sheet are C: 0.065%, Mn: 5.6%, Si: 0.20%, Al: 0.027%, Mo: 0.18%, Cr: 0.22%, Ni: 0.24%, Ti: 0.026%, S: 0.006%, P: 0.010%, the balance being Fe and inevitable impurity elements.
  • the microstructure of the steel plate is a multiphase structure of tempered martensite + rotary austenite, the yield strength is 743 MPa, the yield ratio is 0.75, and the transverse impact energy of the Charpy impact test is -102 J.
  • Example 3 Production of a low yield ratio high toughness steel plate having a thickness of 80 mm was carried out according to the following procedure:
  • the total deformation is 75%, water cooling after the end of rolling, and the final cooling temperature is 72 ° C;
  • the chemical composition and mass fraction of the steel sheet are C: 0.073%, Mn: 5.8%, Si: 0.10%, Al: 0.040%, Mo: 0.22%, Cr: 0.27%, Ni: 0.40%, Ti: 0.030%, S: 0.002%, P: 0.008%, and the balance is Fe and an unavoidable impurity element.
  • the microstructure of the steel plate is a multiphase structure of tempered martensite + rotating austenite, the yield strength is 708 MPa, the yield ratio is 0.71, and the transverse impact energy of the Charpy impact test is -93 J.
  • Example 4 Production of a low yield ratio high toughness steel plate having a thickness of 100 mm was carried out according to the following procedure:
  • the chemical composition of the billet and its mass percentage are C: 0.080%, Mn: 6.0%, Si: 0.30%, Al: 0.015%, Mo: 0.30%, Cr: 0.40%, Ni: 0.31%, Ti: 0.021%, S : 0.001%, P: 0.008%, the balance being Fe and inevitable impurity elements;
  • the total deformation is 69%, water cooling after the end of rolling, and the final cooling temperature is 130 ° C;
  • the chemical composition of the steel sheet and its mass percentage are C: 0.080%, Mn: 6.0%, Si: 0.30%, Al: 0.015%, Mo: 0.30%, Cr: 0.40%, Ni: 0.31%, Ti: 0.021%, S : 0.001%, P: 0.008%, the balance being Fe and inevitable impurity elements.
  • the microstructure of the steel plate is a multiphase structure of tempered martensite + rotating austenite, the yield strength is 690 MPa, the yield ratio is 0.74, and the transverse impact energy of the Charpy impact test is 60 J at -60 °C.

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Abstract

一种低屈强比高强韧厚规格钢板，其化学组分的质量百分比含量为：C:0.060-0.080％、Mn:5.5-6.0％、Si:0.10-0.30％、Al:0.015-0.040％、Mo:0.15-0.30％、Cr:0.20-0.40％、Ni:0.15-0.40％、Ti:0.01-0.03％、S≤0.006％、P≤0.010％，余量为Fe和不可避免的杂质元素；该钢板具有较高的屈服强度、较低的屈强比和良好的低温冲击韧性。钢板的制造方法包括：加热、轧制和热处理；该方法仅需要一次热处理，工艺简单。

Description

一种低屈强比高强韧厚规格钢板及其制造方法 技术领域
本发明涉及一种钢板及其制造方法，特别是一种低屈强比高强韧厚规格钢板及其制造方法。
背景技术
随着船体、桥梁、建筑、压力容器以及海洋平台对结构材料要求的不断提高，高强度、高韧性的厚规格钢板的研发受到了广泛关注。但是，高强度钢板存在一个显著的问题，那就是屈强比难以降低。屈强比是屈服强度与抗拉强度之比，反映材料的加工硬化能力。屈强比越高，钢板形变过程中越容易发生局部应力集中或者局部大变形，钢结构吸收少量能量就会导致材料断裂或者结构失稳；屈强比越低，从钢板开始发生塑性形变到最终断裂所经历的形变容量越大、吸收能量越多，钢结构的抗震性能就越好。因此，在对钢结构稳定性要求高的场合，应采用较低屈强比的钢板。然而，采用现有淬火、回火工艺生产的高强度钢板的屈强比一般不低于0.92。较高的屈强比限制了钢板的应用范围。
通常情况下，如贝氏体、马氏体等单一组织类型的钢容易达到高屈服强度和高抗拉强度，但屈服强度和抗拉强度的数值差别不大，因而屈强比较高。通过改进工艺获得复相组织是实现高强度、低屈强比的有效方法，包括铁素体+马氏体、铁素体+贝氏体、贝氏体+马氏体等。复相组织形变时，软相先发生屈服，硬相在进一步的变形过程中提供抗拉强度，因此屈强比得以降低。现有技术获得低屈强比复相组织的工艺通常基于亚温淬火，例如再加热淬火-亚温淬火-回火、正火-亚温淬火-回火、直接淬火-亚温淬火-回火、TMCP-亚温淬火-回火、亚温区直接淬火-回火等工艺。但是，这一类工艺存在生产周期长的缺点。与基于亚温淬火的工艺相比，基于快速加热在线热处理的工艺能够灵活地调控复相组织，且生产周期短、效率高，但是，对生产设备要求极高，难以普遍推广。
另外，除了低屈强比与高强度之间的矛盾，高强度与高韧性也难以同时获得，而且，在厚规格条件下获得高强度也有很大难度。因此，通过简单工艺在厚规格钢板上同时实现高强度、高韧性以及低屈强比是亟待解决的难题。
公开号为CN104789892A的专利公开了一种具有优异低温冲击韧性的低屈强 比高强韧厚钢板及其制造方法，该低屈强比高强韧厚钢板化学成分中含有3.6％以上的Ni，因而成本高昂。
公开号为CN106399840A的专利公开了一种低成本低屈强比调质型Q690E钢板及生产方法，该低屈强比调质型Q690E钢板的厚度仅有8-40mm。
公开号为CN103352167A的专利公开了一种低屈强比高强度桥梁用钢及其制造方法，该低屈强比高强度桥梁用钢的屈服强度不高于600MPa，且仅能保证-40℃冲击韧性。
公开号为CN102277539A的专利公开了一种低屈强比高塑性超细晶粒高强钢及其制造方法，该低屈强比高塑性超细晶粒高强钢的组织为贝氏体。
发明内容
发明目的：本发明目的是提供一种低屈强比高强韧厚规格钢板，该钢板兼具高强度、高韧性、厚规格以及低屈强比的突出特点。
本发明的另一目的是提供一种低屈强比高强韧厚规格钢板的制造方法，通过该方法可以制得低屈强比、高强韧性的厚规格钢板。
技术方案：一种低屈强比高强韧厚规格钢板，所述钢板化学组分的质量百分比含量为：C:0.060-0.080％、Mn:5.5-6.0％、Si:0.10-0.30％、Al:0.015-0.040％、Mo:0.15-0.30％、Cr:0.20-0.40％、Ni:0.15-0.40％、Ti:0.01-0.03％、S≤0.006％、P≤0.010％，余量为Fe和无法避免的杂质元素。
本发明所述的低屈强比高强韧厚规格钢板中各化学组分质量百分比含量的限定理由如下：
C元素能够通过固溶强化显著增加基体强度，同时能够稳定奥氏体相，但为了降低材料韧脆转变温度，应当尽量降低C含量。此外，C也不利于材料的焊接性能。因此，本发明将C含量控制在0.060-0.080％的较低水平。
Mn作为本发明所述钢板的主要合金元素，既是铁素体强化元素，又是奥氏体稳定元素。在改善材料低温韧性方面，提高Mn/C比能够显著降低韧脆转变温度，因此Mn能够在一定程度上取代价格较高的Ni，但是过高的Mn含量将使偏析程度加重、冶炼难度加大以及材料成本提高。因此，本发明将Mn含量控制在5.5-6.0％。
Si在炼钢过程中为脱氧元素，适量Si能够抑制Mn和P的偏聚，而O含量 过高、Mn和P偏聚都会损害韧性。Si还能够产生固溶强化，但含量超过0.3％时会引起韧脆转变温度升高，因此含量不能过高。本发明将Si控制在0.10-0.30％。
Al在炼钢过程中为脱氧元素，也能够降低固溶N原子数量，从而提高韧性和时效应变抗力，且形成的AlN还能够细化晶粒，从而进一步降低韧脆转变温度。但是，过量添加会形成大尺寸的Al3O2和AlN并损害韧性。因此，本发明将Al含量控制在0.015-0.040％。
Mo能够提高马氏体回火后的强度，还能够减弱Mn的晶界偏聚从而提高韧性。Mo含量过高将恶化焊接性能并增加材料成本。因此，本发明将Mo含量控制在0.15-0.30％。
Cr能够产生固溶强化，但是Cr含量过高则会降低焊接性。因此，本发明将Cr含量控制在0.20-0.40％。
Ni能够稳定奥氏体相、提高淬透性、降低韧脆转变温度并能够改善变形性能，此外还有利于焊接性。但是过多添加Ni元素会显著增加成本。因此，本发明将Ni含量控制在0.15-0.40％。
Ti能够细化高温奥氏体晶粒，有利于提高强度和韧性。微量添加就能够发挥作用，过量添加将导致夹杂物增多。因此，本发明将Ti含量控制在0.010-0.030％。
S易与Mn形成MnS，P容易在晶界偏聚并降低晶界抗裂纹扩展能力，为提高材料韧性，需要将S、P控制在最低限度。因此，本发明要求S≤0.006％，P≤0.010％。
其中，该钢板显微结构下的微观组织为回火马氏体和回转奥氏体的复相组织。回火马氏体作为基体组织，决定了材料的屈服强度。回转奥氏体作为弥散分布的第二相，一方面能够提高材料的韧性，另一方面也能够在形变过程中发生相变并提高抗拉强度，从而降低屈强比。其中，通过X射线衍射仪测得回转奥氏体体积分数为5-15％。
所述钢板的厚度为50-100mm，屈服强度≥690MPa，屈强比≤0.80，-60℃夏比冲击试验横向冲击吸收能量≥60J。
本发明所述的低屈强比高强韧厚规格钢板的制造方法，包括步骤：加热、轧制、热处理，如下：
(1)加热：加热与上述低屈强比高强韧厚规格钢板相同化学成分的坯料， 控制坯料的加热温度1070-1150℃，在坯料中心达到该温度后保温90-150min。坯料加热时得到高温奥氏体组织，同时合金元素通过扩散方式均匀化。加热温度过高或保温时间过长将导致高温奥氏体晶粒过于粗大，而加热温度过低或保温时间过短不利于合金元素均匀化，因此本发明将加热温度控制在1070-1150℃，保温时间控制在90-150min。
(2)轧制：加热后对坯料进行轧制，控制开轧温度≤1020℃，终轧温度≥820℃，总变形量≥65％，轧制结束后水冷，终冷温度≤130℃。轧制温度区间位于奥氏体相区，开轧温度过高不利于晶粒细化，终轧温度过低则使变形困难，因此本发明控制开轧温度≤1020℃、终轧温度≥820℃。总变形量≥65％能够保证足够的应变积累并细化奥氏体组织。轧制后水冷，终冷温度≤130℃低于马氏体转变结束点，奥氏体转变为板条马氏体，组织进一步细化；其中，轧制结束后水冷的终冷温度为室温至130℃。
(3)热处理：将钢板加热至605-645℃，在钢板中心达到该温度后，保温50-120min，然后空冷至室温。热处理温度605-645℃位于铁素体-奥氏体两相区，能够形成体积分数为5-15％的回转奥氏体，回转奥氏体在升温过程及50-120min的保温过程中富集C、Mn等合金元素以获得足够的热稳定性，能够在冷却至-60℃时仍然保持面心立方结构。此外，马氏体在高温下发生适度回复，强度降低而塑韧性提高。保温后空冷至室温，得到回火马氏体+回转奥氏体的复相组织。
有益效果：本发明所述的低屈强比高强韧厚规格钢板具有较高的屈服强度和较低的屈强比，屈服强度≥690MPa，屈强比≤0.80；-60℃夏比冲击试验横向冲击吸收能量≥60J，具有良好的低温冲击韧性；并且，该钢板的厚度规格达到50-100mm。通过本发明所述的低屈强比高强韧厚规格钢板的制造方法能够生产高强度、高韧性、低屈强比的厚规格钢板；并且制造工艺仅需要一次热处理，工艺简单，易于生产实施。
附图说明
图1是实施例1中低屈强比高强韧厚规格钢板组织的透射电镜显微照片。
具体实施方式
实施例1：制造厚度为50mm的低屈强比高强韧钢板，按照以下步骤进行：
(1)加热：将200mm厚的坯料放入加热炉中加热至1110℃并保温120min， 坯料的化学组分成分及其质量百分比为C:0.060％、Mn:5.5％、Si:0.22％、Al:0.030％、Mo:0.15％、Cr:0.20％、Ni:0.15％、Ti:0.010％、S:0.003％、P:0.006％，余量为Fe和不可避免的杂质元素；
(2)轧制：对加热后的坯料进行轧制，开轧温度1020℃，终轧温度845℃，轧机压下规程按照表1制定：
表1 实施例1压下规程
道次 1 2 3 4 5 6 7 8
入料厚度mm 200 176 155 132 112 89 72 59
出料厚度mm 176 155 132 112 89 72 59 50
总变形量75％，轧制结束后水冷，终冷温度25℃；
(3)热处理：将钢板放入加热炉中加热至645℃并保温50min，钢板出炉后空冷至室温。
该钢板化学组分及其质量百分比含量为：C:0.060％、Mn:5.5％、Si:0.22％、Al:0.030％、Mo:0.15％、Cr:0.20％、Ni:0.15％、Ti:0.010％、S:0.003％、P:0.006％，余量为Fe和杂质元素。该钢板组织为回火马氏体+回转奥氏体的复相组织，如图1所示，为该钢板组织的透射电镜显微照片，可观察到间隔分布的回火马氏体和回转奥氏体，其中浅色部分为回火马氏体，深色部分为回转奥氏体。该钢板的屈服强度为752MPa，屈强比为0.80，-60℃夏比冲击试验横向冲击吸收能量为155J。
实施例2：制造厚度为70mm的低屈强比高强韧钢板，按照以下步骤进行：
(1)加热：将200mm厚的坯料放入加热炉中加热至1115℃并保温110min，坯料的化学成分及其质量分数分别为C:0.065％、Mn:5.6％、Si:0.20％、Al:0.027％、Mo:0.18％、Cr:0.22％、Ni:0.24％、Ti:0.026％、S:0.006％、P:0.010％,余量为Fe和不可避免的杂质元素；
(2)轧制：对加热后的坯料进行轧制，开轧温度1006℃，终轧温度827℃，轧机压下规程按照表2制定：
表2 实施例2压下规程
道次 1 2 3 4 5 6 7 8
入料厚度mm 200 181 162 143 122 101 86 77
出料厚度mm 181 162 143 122 101 86 77 70
总变形量65％，轧制结束后水冷，终冷温度68℃；
(3)热处理：将钢板放入加热炉中加热至625℃并保温90min，钢板出炉后空冷至室温。
该钢板化学成分及其质量分数分别为C:0.065％、Mn:5.6％、Si:0.20％、Al:0.027％、Mo:0.18％、Cr:0.22％、Ni:0.24％、Ti:0.026％、S:0.006％、P:0.010％,余量为Fe和不可避免的杂质元素。该钢板微观组织为回火马氏体+回转奥氏体的复相组织，屈服强度743MPa，屈强比0.75，-60℃夏比冲击试验横向冲击吸收能量为102J。
实施例3：制造厚度为80mm的低屈强比高强韧钢板，按照以下步骤进行：
(1)加热：将320mm厚的坯料放入加热炉中加热至1150℃并保温90min，坯料的化学成分及其质量分数分别为C:0.073％、Mn:5.8％、Si:0.10％、Al:0.040％、Mo:0.22％、Cr:0.27％、Ni:0.40％、Ti:0.030％、S:0.002％、P:0.008％,余量为Fe和不可避免的杂质元素；
(2)轧制：对加热后的坯料进行轧制，开轧温度1005℃，终轧温度820℃，轧机压下规程按照表3制定：
表3 实施例3压下规程
道次 1 2 3 4 5 6 7 8
入料厚度mm 320 282 248 211 179 143 115 95
出料厚度mm 282 248 211 179 143 115 95 80
总变形量75％，轧制结束后水冷，终冷温度72℃；
(3)热处理：将钢板放入加热炉中加热至620℃并保温90min，钢板出炉后空冷至室温。
该钢板化学成分及其质量分数分别为C:0.073％、Mn:5.8％、Si:0.10％、Al:0.040％、Mo:0.22％、Cr:0.27％、Ni:0.40％、Ti:0.030％、S:0.002％、P:0.008％,余量为Fe和不可避免的杂质元素。该钢板微观组织为回火马氏体+回转奥氏体的复相组织，屈服强度708MPa，屈强比0.71，-60℃夏比冲击试验横向冲击吸收能量为93J。
实施例4：制造厚度为100mm的低屈强比高强韧钢板，按照以下步骤进行：
(1)加热：将320mm厚的坯料放入加热炉中加热至1070℃并保温150min， 坯料的化学成分及其质量百分比为C:0.080％、Mn:6.0％、Si:0.30％、Al:0.015％、Mo:0.30％、Cr:0.40％、Ni:0.31％、Ti:0.021％、S:0.001％、P:0.008％，余量为Fe和不可避免的杂质元素；
(2)轧制：对加热后的坯料进行轧制，开轧温度1002℃，终轧温度837℃，轧机压下规程按表4制定：
表4 实施例4压下规程
道次 1 2 3 4 5 6 7 8 9
入料厚度mm 320 282 248 218 192 169 149 131 114
出料厚度mm 282 248 218 192 169 149 131 114 100
总变形量69％，轧制结束后水冷，终冷温度130℃；
(3)热处理：将钢板放入加热炉中加热至605℃并保温120min，钢板出炉后空冷至室温。
该钢板化学成分及其质量百分比为C:0.080％、Mn:6.0％、Si:0.30％、Al:0.015％、Mo:0.30％、Cr:0.40％、Ni:0.31％、Ti:0.021％、S:0.001％、P:0.008％，余量为Fe和不可避免的杂质元素。该钢板微观组织为回火马氏体+回转奥氏体的复相组织，屈服强度690MPa，屈强比0.74，-60℃夏比冲击试验横向冲击吸收能量为60J。

Claims (5)

  1. 一种低屈强比高强韧厚规格钢板，其特征在于，化学组分的质量百分比含量为：C:0.060-0.080％、Mn:5.5-6.0％、Si:0.10-0.30％、Al:0.015-0.040％、Mo:0.15-0.30％、Cr:0.20-0.40％、Ni:0.15-0.40％、Ti:0.01-0.03％、S≤0.006％、P≤0.010％，余量为Fe和不可避免的杂质元素；
    其中，所述钢板的微观组织包括回火马氏体和回转奥氏体。
  2. 根据权利要求1所述的低屈强比高强韧厚规格钢板，其特征在于，所述钢板的厚度为50-100mm。
  3. 根据权利要求1所述的低屈强比高强韧厚规格钢板，其特征在于，所述钢板的微观组织中回转奥氏体的体积分数为5-15％。
  4. 根据权利要求1-3中任意一项所述的低屈强比高强韧厚规格钢板的制造方法，其特征在于，包括下述步骤：
    (1)加热：控制坯料的加热温度1070-1150℃，在坯料中心达到该温度后保温90-150min；
    (2)轧制：控制开轧温度≤1020℃，终轧温度≥820℃；总变形量≥65％，轧制结束后水冷，终冷温度≤130℃；
    (3)热处理：将钢板加热至605-645℃，在钢板中心达到该温度后，保温50-120min，然后空冷至室温。
  5. 根据权利要求4所述的制造方法，其特征在于，所述步骤(2)中，轧制结束后水冷的终冷温度为室温到130℃。
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