WO2020019539A1 - 厚规格的420MPa级低屈强比低温桥梁钢及生产方法 - Google Patents

厚规格的420MPa级低屈强比低温桥梁钢及生产方法 Download PDF

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WO2020019539A1
WO2020019539A1 PCT/CN2018/110953 CN2018110953W WO2020019539A1 WO 2020019539 A1 WO2020019539 A1 WO 2020019539A1 CN 2018110953 W CN2018110953 W CN 2018110953W WO 2020019539 A1 WO2020019539 A1 WO 2020019539A1
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steel plate
thick
temperature
low
rolling
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PCT/CN2018/110953
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French (fr)
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李伟
丁叶
洪君
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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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following 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
    • C22C38/06—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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C21D2211/002—Bainite
    • 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 invention relates to the production of steel plates, and in particular to a 420 MPa grade low yield strength low temperature bridge steel plate with a thick specification and a production method.
  • Bridge design has taken low Ceq and low Pcm, low yield ratio, and high impact toughness as the basic design requirements for bridge steel.
  • the yield strength is mainly 370MPa, 420MPa, and 500MPa
  • the grade is D / E.
  • 370MPa is the main steel plate.
  • the 420MPa grade steel plate is mainly used in key parts.
  • the 500MPa grade is used in some large bridge structures. .
  • 420MPa class structural steel for bridges, thin gauge steel plates have been widely used, and their performance is stable in all aspects, but the use of thick gauge steel plates is relatively small, especially for 100mm thick steel plates, in terms of strength, low yield ratio, low temperature toughness and other stability. Research is inadequate.
  • the present invention provides a 420 MPa-grade low-yield-ratio low-temperature bridge steel plate with a thick specification and a production method thereof, which solve the problems of low strength and low-temperature impact instability of the current 420 MPa-grade thick steel plate.
  • the thick 420 MPa low-yield-temperature low-temperature bridge steel plate according to the present invention has a chemical composition in terms of mass percentage including: C 0.05-0.07%, Si 0.20-0.30%, Mn 1.50-1.60%, P ⁇ 0.012%, S ⁇ 0.005%, Ni 0.10-0.20%, Cr0.15-0.20%, Nb 0.025-0.035%, Al 0.025-0.050%, V 0.030-0.040%, Ti 0.01-0.02%, the balance is Fe and Inevitable impurities.
  • the tempered structure of the steel plate is a composite structure of bainite and a small amount of ferrite, and the maximum thickness of the steel plate is 100 mm.
  • the carbon equivalent of the steel sheet is 0.34-0.38%
  • the welding crack sensitivity coefficient is 0.14-0.18%
  • the yield strength is 430-500MPa
  • the tensile strength is 550-630MPa
  • the elongation is> 21%
  • the yield ratio is ⁇ 0.84.
  • the method for producing a thick-specified 420 MPa-grade low-yield-ratio low-temperature bridge steel plate includes the following steps:
  • the molten iron is subjected to desulfurization treatment, and then converted into a billet by continuous smelting, LF refining, and RH vacuum treatment;
  • the heated billet is rolled using a two-stage controlled rolling process in the austenite recrystallization zone and the non-recrystallized zone. After the rolling is completed, ultra-rapid cooling and laminar cooling are used for cooling.
  • the redness temperature is 400-480 °C;
  • the cooled steel sheet is heated to 480-550 ° C, and is subjected to tempering heat treatment.
  • the tempering time t (2.0-3.0) min / mm ⁇ steel sheet thickness + 50min.
  • the sulfur content after the molten iron desulfurization treatment in the step (1) is controlled to ⁇ 0.003%
  • the converter uses the double slag method to control the P content ⁇ 0.010%
  • the LF refining uses the white slag operation to desulfurize and deoxidize
  • the vacuum degree of the RH vacuum treatment ⁇ 3.0mbar
  • vacuum time ⁇ 25 minutes calcium treatment after vacuum completion, static stirring after calcium treatment, static stirring time ⁇ 12 minutes
  • the heating time in the step (2) is 9-16min / cm, and the soaking time is ⁇ 1.4min / cm.
  • the temperature of the first stage rough rolling and final rolling is controlled to be 1000 to 1100 ° C
  • the second stage opening rolling temperature is to be 840 to 870 ° C
  • the final rolling temperature is to be 780 to 830 ° C.
  • the present invention guarantees good welding performance of the steel plate through the design of a low carbon component, and applies appropriate controlled rolling and cooling and reasonable tempering heat treatment to ensure the uniformity of the structure and performance of the steel plate and obtain excellent performance indicators.
  • Structural steel for bridges After the rolling of the present invention is finished, the cooling method is combined with ultra-fast cooling and laminar cooling, which can remove the gas film formed between the residual water on the surface of the plate and the steel plate, thereby achieving full contact between the steel plate and the cooling water.
  • Comprehensive nuclear boiling in which the steel plate and the cooling water are in uniform contact not only improves the heat exchange between the steel plate and the cooling water to achieve a higher cooling rate, but also achieves uniform cooling of the steel plate and refines the structure of the steel plate.
  • the invention extends the heat treatment Time can ensure that the steel plate structure is fully homogenized, and the internal stress is reduced or eliminated as much as possible, which improves the stability of the steel plate's low-temperature impact performance.
  • FIG. 1 is a morphology of a quarter of the thickness of a hot-rolled sample of a 100 mm thick 420 MPa grade steel plate in Example 2;
  • FIG. 2 is a morphology of a quarter of the thickness of a tempered sample of a 100 mm thick 420 MPa grade steel plate in Example 2.
  • FIG. 2 is a morphology of a quarter of the thickness of a tempered sample of a 100 mm thick 420 MPa grade steel plate in Example 2.
  • 100mm thick 420MPa grade low yield strength low temperature bridge steel plate its chemical composition in mass percentage includes: C 0.05-0.07%, Si 0.20-0.30%, Mn 1.50-1.60%, P ⁇ 0.012%, S ⁇ 0.005%, Ni 0.10-0.20%, Cr 0.15-0.20%, Nb 0.025-0.035%, Al 0.025-0.050%, V 0.030-0.040%, Ti 0.01-0.02%, the balance is Fe and unavoidable impurities.
  • the production method of the above steel plate includes smelting, continuous casting, heating, controlled rolling and controlled cooling, and heat treatment processes. Specifically, the smelting and continuous casting processes are subjected to converter hot metal smelting, LF refining, RH vacuum treatment, and continuous casting, followed by hot metal desulfurization pretreatment. The sulfur content after hot metal desulfurization is controlled to ⁇ 0.003%, and the converter uses a double slag method to strictly control the P content.
  • LF refining adopts white slag operation for desulfurization and deoxidation, RH vacuum treatment, vacuum degree ⁇ 3.0mbar, vacuum time ⁇ 25 minutes, and calcium treatment after vacuum completion; static stirring after calcium treatment, static stirring time ⁇ 12 minutes;
  • the tundish temperature for continuous casting control is at the liquidus + (10-15) ° C, and no electromagnetic stirring is used.
  • the 320-mm-thick continuous casting slab is heated.
  • the total furnace time is 9-16min / cm
  • the soaking time is ⁇ 1.4min / cm
  • the tapping temperature is 1160-1200 ° C. After heating, rolling is carried out.
  • the two-stage controlled rolling process of austenite recrystallization zone + non-recrystallization zone is used for rolling.
  • the first stage rough rolling finish rolling temperature is controlled to 1000 ⁇ 1100 °C; the second stage rolling temperature is 840. -870 °C, final rolling temperature is 780 ⁇ 830 °C.
  • the redness temperature is 400-480 °C.
  • heat treatment is performed. The heat treatment is specifically 100mm thick.
  • the steel plate is heated to 480-550 ° C, and is subjected to tempering heat treatment, and the tempering time is controlled at (2.0-3.0) min / mm ⁇ 100mm (steel plate thickness) + 50min.
  • the tempered structure of the steel plate produced by the above method is a composite structure of bainite and a small amount of ferrite, and the maximum thickness of the steel plate is 100 mm.
  • the carbon equivalent of the steel plate is 0.34-0.38%
  • the welding crack sensitivity coefficient is 0.14-0.18%
  • the yield strength is 430-500MPa
  • the tensile strength is 550-630MPa
  • the elongation is> 21%
  • the yield ratio is ⁇ 0.84.
  • the controlled rolling, cooling, and tempering heat treatment process for 100 mm thick steel plates is controlled to solve the problem of unstable plate performance for a long time.
  • the tempering heat treatment can improve the low temperature impact toughness of the steel plate, but the tempering temperature point is not selected properly. Tempering brittleness can occur. When tempering brittleness occurs, the toughness of the steel sheet is significantly reduced.
  • the invention uses a low-carbon component design to ensure that the steel plate has good welding performance, and applies appropriate controlled rolling and cooling and reasonable tempering heat treatment to ensure the uniformity of the structure and performance of the steel plate and obtain a bridge structure with excellent performance indicators. steel.
  • the rolled steel sheet is air-cooled to room temperature before being subjected to tempering heat treatment.
  • the heat treatment process parameters are shown in Table 3:
  • the hot-rolled microstructures of Examples 1 and 2 are both B + F + a small amount of P, and the structure is mainly B + F after tempering heat treatment.
  • FIG. 1 is a metallographic structure at a thickness of 1/4 of a hot-rolled sample of a 100 mm thick 420 MPa low-yield-strength low-temperature bridge steel plate in Example 2, which is mainly B + acicular F + a small amount of P.
  • FIG. 2 is a metallographic structure at a thickness of 1/4 of the tempered sample of a 100 mm thick 420 MPa low-yield-temperature low-temperature steel plate for a bridge in Example 2. The structure is mainly a strip B + a small amount of F.
  • the tensile properties of the 100 mm thick 420 MPa grade low yield strength low temperature bridge steel sheet after tempering treatment are shown in Table 4, and the low temperature impact at -40 ° C is shown in Table 5.
  • the performance results of the steel plates of Examples 1 and 2 of the present invention are good.
  • the yield strength is between 430-500 MPa
  • the tensile strength is between 550-630 MPa
  • the elongation is> 21%
  • the yield ratio is ⁇ 0.84
  • the 1/4 plate thickness is -40.
  • Longitudinal impact energy at °C ⁇ 250J Excellent performance results and strong operability.

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
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  • Physics & Mathematics (AREA)
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Abstract

本发明公开了一种厚规格的420MPa级低屈强比低温桥梁用钢板及生产方法，本发明中通过对100mm厚钢板控制合适的控轧控冷及回火热处理工艺，解决长期以来厚板性能不稳定的问题，回火热处理可以改善钢板的低温冲击韧性，但回火温度点选择不当，可出现回火脆性，当产生回火脆性时，钢板韧性明显降低。本发明通过低碳成分设计，保证钢板具有良好的焊接性能，并施以适当的控轧控冷及合理的回火热处理，保证钢板组织及性能均匀性，获得各项性能指标优良的桥梁用结构钢。

Description

厚规格的420MPa级低屈强比低温桥梁钢及生产方法 技术领域
本发明涉及钢板的生产，具体涉及一种厚规格的420MPa级低屈强比低温桥梁用钢板及生产方法。
背景技术
近年来，铁路和公路建设里程逐年增长，大跨度、多车道、重载荷桥梁工程项目也明显增多，而且钢制桥梁越来越多地代替钢筋混凝土桥梁。因此，桥梁用钢板的需求量必然会大幅增长，高强度、高韧性特厚桥梁钢的使用成为必然选择。
桥梁设计已经将低Ceq和低Pcm、低屈强比、高冲击韧性作为桥梁用钢的基本设计要求。根据大桥钢板使用量来看，主要是屈服强度370MPa、420MPa和500MPa，级别为D/E级；且370MPa为主要用钢板，420MPa级钢板主要用在关键部位，500MPa级应用在部分大型桥梁结构中。420MPa级桥梁用结构钢，薄规格钢板已得到广泛应用，且各方面性能稳定，但厚规格钢板使用数量较少，尤其是100mm厚钢板，在强度、低屈强比、低温韧性等稳定性方面研究尚有不足。
发明内容
发明目的：本发明提供一种厚规格的420MPa级低屈强比低温桥梁用钢板及生产方法，解决目前420MPa级桥梁用厚板强度低、低温冲击不稳定的问题。
技术方案：本发明所述的厚规格的420MPa级低屈强比低温桥梁用钢板，其化学组成以质量百分数计包括：C 0.05-0.07％，Si 0.20-0.30％，Mn 1.50-1.60％，P≤0.012％，S≤0.005％，Ni 0.10-0.20％，Cr 0.15-0.20％，Nb 0.025-0.035％，Al 0.025-0.050％，V 0.030-0.040％，Ti 0.01-0.02％，余量为Fe和不可避免的杂质。
其中，所述钢板回火态组织为贝氏体和少量铁素体的复合组织，所述钢板的最大厚度为100mm。所述钢板的碳当量为0.34-0.38％，焊接裂纹敏感系数为0.14-0.18％，屈服强度为430-500MPa，抗拉强度为550-630MPa，延伸率＞21％，屈强比≤0.84。
本发明所述的厚规格的420MPa级低屈强比低温桥梁用钢板的生产方法，包括以下步骤：
(1)将铁水经过脱硫处理后转炉冶炼、LF精炼和RH真空处理后连铸成坯料；
(2)将坯料进行加热，加热出钢的温度为1160-1200℃；
(3)对加热后的坯料采用奥氏体再结晶区和未再结晶区两阶段控轧工艺进行轧制，轧钢结束后采用超快冷和层流冷却结合的方式进行冷却，返红温度为400-480℃；
(4)将冷却后的钢板加热到480-550℃，进行回火热处理，回火时间t＝(2.0-3.0)min/mm×钢板厚度+50min。
其中，所述步骤(1)中铁水脱硫处理后硫含量控制在≤0.003％，转炉采用双渣法控制P的含量≤0.010％，LF精炼采用白渣操作脱硫脱氧，RH真空处理的真空度≤3.0mbar,真空时间≥25分钟，真空结束后进行钙处理，钙处理结束后静搅，静搅时间≥12分钟，连铸控制中包温度在液相线+(10-15)℃。
所述步骤(2)中加热的时间为9-16min/cm，均热时间≥1.4min/cm。
所述步骤(3)中第一阶段粗轧终轧温度控制为1000～1100℃，第二阶段开轧温度为840-870℃，终轧温度为780～830℃。
有益效果：本发明通过低碳成分设计，保证钢板具有良好的焊接性能，并施以适当的控轧控冷及合理的回火热处理，保证钢板组织及性能均匀性，获得各项性能指标优良的桥梁用结构钢，本发明轧钢结束采用超快冷和层流冷却结合分方式进行冷却，能够将板面残存水与钢板之间形成的气膜清除，从而达到钢板与冷却水的完全接触，实现钢板和冷却水均匀接触的全面核沸腾，不仅提高了钢板和冷却水之间的热交换，达到较高的冷却速率，而且可以实现钢板的均匀冷却，细化钢板组织，本发明延长了热处理的时间，可保证钢板组织充分均匀化，并尽可能使内应力降低或消除，提高了钢板低温冲击性能稳定性。
附图说明
图1为实施例2的100mm厚420MPa级钢板热轧态试样厚度1/4处组织形貌；
图2为实施例2的100mm厚420MPa级钢板回火态试样厚度1/4处组织形貌。
具体实施方式
下面对本发明进行进一步说明。
100mm厚420MPa级低屈强比低温桥梁用钢板，其化学组成以质量百分数计包括：C 0.05-0.07％，Si 0.20-0.30％，Mn 1.50-1.60％，P≤0.012％，S≤0.005％，Ni 0.10-0.20％，Cr 0.15-0.20％，Nb 0.025-0.035％，Al 0.025-0.050％，V 0.030-0.040％，Ti 0.01-0.02％，余量为Fe和不可避免的杂质。
上述钢板的生产方法包括冶炼、连铸、加热、控轧控冷、热处理工序。具体为冶炼、连铸工艺依次经过铁水脱硫预处理后进行转炉冶炼、LF精炼、RH真空处理和连铸，铁水脱硫处理后硫含量控制在≤0.003％，转炉采用双渣法严格控制P的含量≤0.010％；LF精炼采用白渣操作脱硫脱氧，RH真空处理,真空度≤3.0mbar,真空时间≥25分钟，真空结束后进行钙处理；钙处理结束后静搅，静搅时间≥12分钟；连铸控制中包温度在液相线+(10-15)℃，不使用电磁搅拌。连铸成坯料后，将320mm厚度连铸坯进行加热，总在炉时间9-16min/cm，均热时间≥1.4min/cm，出钢温度1160-1200℃。加热后进行轧制，采用奥氏体再结晶区+未再结晶区两阶段控轧工艺进行轧制，第一阶段粗轧终轧温度控制为1000～1100℃；第二阶段开轧温度为840-870℃，终轧温度为780～830℃，轧制后采用超快冷和层流冷却结合的方式进行冷却，返红温度为400-480℃，冷却后进行热处理，热处理具体为将100mm厚钢板加热到480-550℃之间，进行回火热处理，回火时间控制在(2.0-3.0)min/mm×100mm(钢板厚度)+50min。
用上述方法生产的钢板回火态组织为贝氏体和少量铁素体的复合组织，钢板的最大厚度为100mm。钢板的碳当量为0.34-0.38％，焊接裂纹敏感系数为0.14-0.18％，屈服强度为430-500MPa，抗拉强度为550-630MPa，延伸率＞21％，屈强比≤0.84。1/4板厚-40℃纵向冲击功≥250J。本发明中通过对100mm厚钢板控制合适的控轧控冷及回火热处理工艺，解决长期以来厚板性能不稳定的问题，回火热处理可以改善钢板的低温冲击韧性，但回火温度点选择不当，可出现回火脆性，当产生回火脆性时，钢板韧性明显降低。本发明通过低碳成分设计，保证钢板具有良好的焊接性能，并施以适当的控轧控冷及合理的回火热处理，保证钢板组织及性能均匀性，获得各项性能指标优良的桥梁用结构钢。
采用上述生产方法生产下列化学组成的100mm厚420MPa级低屈强比低温桥梁用钢板，主要化学成分(wt％)如表1所示；
表1主要化学成分(wt％)
Figure PCTCN2018110953-appb-000001
采用高温加热，奥氏体再结晶区和奥氏体未再结晶区两阶段控制轧制技术。粗轧阶段采用全纵轧、道次间大压下量轧制，此阶段进行奥氏体再结晶；精轧阶段采用低温未再结晶区轧制，精轧结束后，进行超快冷快速冷却。实施例1和2的出钢温度、粗轧终轧 温度，精轧终轧温度和返红温度如表2所示；
表2加热热轧制冷却工艺参数
Figure PCTCN2018110953-appb-000002
轧制钢板空冷至室温后再进行回火热处理，热处理工艺参数如表3所示：
表3回火热处理工艺参数
实施例 成品厚度(mm) 回火温度(℃) 回火时间(min)
实施例1 100 510 275
实施例2 100 521 325
实施例1和2的热轧态组织均为B+F+少量P，回火热处理后组织主要是B+F。图1为实施例2的100mm厚420MPa级低屈强比低温桥梁用钢板热轧态试样厚度1/4处金相组织，主要为B+针状F+少量P。图2为实施例2的100mm厚420MPa级低屈强比低温桥梁用钢板回火态试样厚度1/4处金相组织，组织主要为板条B+少量F。
本发明100mm厚的420MPa级低屈强比低温桥梁用钢板回火热处理后拉伸性能如表4所示，-40℃低温冲击如表5所示。本发明实施例1和2的钢板性能结果较好，屈服强度在430-500MPa，抗拉强度在550-630MPa之间，延伸率＞21％，屈强比≤0.84，1/4板厚-40℃纵向冲击功≥250J。性能结果优异且具有较强的可操作性。
表4回火态拉伸性能
Figure PCTCN2018110953-appb-000003
表5回火态低温冲击性能
Figure PCTCN2018110953-appb-000004

Claims (7)

  1. 一种厚规格的420MPa级低屈强比低温桥梁用钢板，其特征在于，其化学组成以质量百分数计包括：C 0.05-0.07％，Si 0.20-0.30％，Mn 1.50-1.60％，P≤0.012％，S≤0.005％，Ni 0.10-0.20％，Cr 0.15-0.20％，Nb 0.025-0.035％，Al 0.025-0.050％，V 0.030-0.040％，Ti 0.01-0.02％，余量为Fe和不可避免的杂质。
  2. 根据权利要求1所述的厚规格的420MPa级低屈强比低温桥梁用钢板，其特征在于，所述钢板回火态组织为贝氏体和少量铁素体的复合组织，所述钢板的最大厚度为100mm。
  3. 根据权利要求1所述的厚规格的420MPa级低屈强比低温桥梁用钢板，其特征在于，所述钢板的碳当量为0.34-0.38％，焊接裂纹敏感系数为0.14-0.18％，屈服强度为430-500MPa，抗拉强度为550-630MPa，延伸率＞21％，屈强比≤0.84。
  4. 如权利要求1所述的厚规格的420MPa级低屈强比低温桥梁用钢板的生产方法，其特征在于，包括以下步骤：
    (1)将铁水经过脱硫处理后转炉冶炼、LF精炼和RH真空处理后连铸成坯料；
    (2)将坯料进行加热，加热出钢的温度为1160-1200℃；
    (3)对加热后的坯料采用奥氏体再结晶区和未再结晶区两阶段控轧工艺进行轧制，轧钢结束后采用超快冷和层流冷却结合的方式进行冷却，返红温度为400-480℃；
    (4)将冷却后的钢板加热到480-550℃，进行回火热处理，回火时间t＝(2.0-3.0)min/mm×钢板厚度+50min。
  5. 根据权利要求4所述的厚规格的420MPa级低屈强比低温桥梁用钢板的生产方法，其特征在于，所述步骤(1)中铁水脱硫处理后硫含量控制在≤0.003％，转炉采用双渣法控制P的含量≤0.010％，LF精炼采用白渣操作脱硫脱氧，RH真空处理的真空度喜爱≤3.0mbar,真空时间≥25分钟，真空结束后进行钙处理，钙处理结束后静搅，静搅时间≥12分钟，连铸控制中包温度在液相线+(10-15)℃。
  6. 根据权利要求4所述的厚规格的420MPa级低屈强比低温桥梁用钢板的生产方法，其特征在于，所述步骤(2)中加热的时间为9-16min/cm，均热时间≥1.4min/cm。
  7. 根据权利要求4所述的厚规格的420MPa级低屈强比低温桥梁用钢板的生产方法，所述步骤(3)中第一阶段粗轧终轧温度控制为1000～1100℃，第二阶段开轧温度为840-870℃，终轧温度为780～830℃。
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