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WO2019057114A1 - 一种高强度q＆p钢热轧卷的软化方法 - Google Patents

一种高强度q＆p钢热轧卷的软化方法 Download PDF

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Publication number
WO2019057114A1
WO2019057114A1 PCT/CN2018/106703 CN2018106703W WO2019057114A1 WO 2019057114 A1 WO2019057114 A1 WO 2019057114A1 CN 2018106703 W CN2018106703 W CN 2018106703W WO 2019057114 A1 WO2019057114 A1 WO 2019057114A1
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Prior art keywords
steel
strength
hot rolled
hot roll
softening
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PCT/CN2018/106703
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English (en)
French (fr)
Inventor
高兴健
徐嘉春
王野
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Baoshan Iron and Steel Co Ltd
Baosteel Zhanjiang Iron and Steel Co Ltd
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Baoshan Iron and Steel Co Ltd
Baosteel Zhanjiang Iron and Steel Co Ltd
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Priority claimed from CN201710853613.3A external-priority patent/CN107470377A/zh
Priority claimed from CN201810631922.0A external-priority patent/CN110616302B/zh
Application filed by Baoshan Iron and Steel Co Ltd, Baosteel Zhanjiang Iron and Steel Co Ltd filed Critical Baoshan Iron and Steel Co Ltd
Priority to US16/648,781 priority Critical patent/US11981972B2/en
Priority to KR1020207010903A priority patent/KR102452598B1/ko
Priority to JP2020537824A priority patent/JP7320512B2/ja
Priority to EP18857665.6A priority patent/EP3686296B8/en
Publication of WO2019057114A1 publication Critical patent/WO2019057114A1/zh
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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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
    • C21D9/02—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for springs
    • 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
    • C21D1/84—Controlled slow cooling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B1/24—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process
    • B21B1/26—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process by hot-rolling, e.g. Steckel hot mill
    • 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
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/22—Martempering
    • 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
    • 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
    • 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
    • C21D9/0006—Details, accessories not peculiar to any of the following furnaces
    • C21D9/0025—Supports; Baskets; Containers; Covers
    • 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
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B11/00—Bell-type furnaces

Definitions

  • the invention belongs to the technical field of production of advanced high-strength steel for the third generation automobile, and particularly relates to a softening method for hot-rolled high-strength Q&P steel.
  • the first generation of high-strength steel U T is 15 ⁇ 10GPa%, and the light weight and safety indicators are low;
  • the second-generation high-strength steel U T is 60 ⁇ 10GPa%, and the strength and plasticity are ideal. However, the process is complicated, the alloy content is high, and the production cost is high, which is difficult to be accepted by the market;
  • the third-generation high-strength steel U T is 30 ⁇ 10GPa%.
  • the light weight and safety index is better than the first-generation high-strength steel, and the production cost is significantly lower than that of the second-generation high-strength steel, which has caused widespread concern in the automotive and metallurgical industries.
  • Q&P Quality and Partitioning steel, which uses C, Si, Mn and other inexpensive elements as the main alloying elements, has been recognized as an important representative of the third-generation advanced high-strength steel for automobiles.
  • C, Si, Mn and other inexpensive elements as the main alloying elements
  • a class of hot-rolled Q&P steels such as China Patent Publication No. CN105177415A, CN105441814A, CN103215516A, CN103805851A, CN104532126A, CN103233161A, CN103805869A, CN102226248A, etc., are produced through smelting and hot rolling, which are characterized by short process flow and low production cost, but High requirements are placed on the hot rolling laminar cooling control, which is difficult to achieve in the industry and the surface quality of the product is difficult to guarantee.
  • cold-rolled Q&P steel such as China Patent Publication No. CN105734213A, CN104988391A, CN105648317A, etc.
  • cold-rolled Q&P steel needs to add an intermediate annealing process (hood furnace annealing or continuous annealing) between hot rolling and cold rolling, that is, reheating the hot rolled coil to austenitizing. The temperature is maintained for a sufficient period of time, and then cooled to room temperature at a suitable rate to soften the hot rolled coil of the Q&P steel to reduce the rolling force of the cold rolling mill to achieve the purpose of cold rolling.
  • intermediate annealing process hood furnace annealing or continuous annealing
  • the Q&P steel of the invention is quickly covered with an independent and closed heat insulating cover device on the line, thereby controlling cooling of the steel coil and utilizing coiling waste heat for effective self-tempering softening treatment.
  • the microstructure of Q&P steel hot rolled coil is adjusted online to decompose martensite and achieve the purpose of reducing the strength of the coil.
  • the present invention relates to a method for softening a high-strength Q&P steel hot rolled coil, which is characterized in that a Q&P steel slab is heated and then subjected to rough rolling, finish rolling, laminar cooling and coiling to a hot rolled coil, after unwinding
  • the thermal cover is placed on the wire and moved into the coil store with the transport chain. After the heat preservation time, the heat shield is removed and cooled to room temperature; wherein the coiling temperature is 400-600 ° C, and the thermal cover on the wire cover refers to each hot rolling.
  • the independent, sealed heat-insulating device is separately covered within 60 minutes after the unwinding of the roll; the holding time of the steel coil in the heat-insulating cover is ⁇ 60 minutes.
  • the slab heating temperature is ⁇ 1150 ° C
  • the soaking time is ⁇ 60 minutes.
  • the slab heating temperature is 1200-1300 ° C and the soaking time is 1-3 hours.
  • the rough rolling and the finish rolling are performed in a complete austenitizing temperature range, the entire hot rolling reduction ratio is ⁇ 90%, and the finishing rolling temperature is 800-1000 °C.
  • each of the hot rolled coils is individually covered with a heat shield within 20 minutes after unwinding.
  • the cooling speed of the steel coil in the heat preservation cover is ⁇ 15 ° C / hour.
  • the holding time of the steel coil in the heat preservation cover is 1-24 hours.
  • an exemplary insulative cover is a steel strip manufacturing line in-line thermal insulation chiller disclosed in any of the embodiments of CN 107470377 A, which is incorporated herein by reference in its entirety.
  • the heating temperature of the slab is lower than 1200 ° C, it is not conducive to the homogenization of the alloying elements; and when the temperature is higher than 1300 ° C, not only the manufacturing cost is increased, but also the heating quality is lowered. Therefore, it is suitable that the heating temperature of the slab is generally controlled at 1200 to 1300 °C.
  • the soaking time also needs to be controlled within a certain range.
  • the soaking time that is, the slab is heated to a set heating temperature and then kept for a while.
  • the soaking time is too short, the diffusion of solute atoms such as Si, Mn, etc. is insufficient, and the heating quality of the slab is not guaranteed; while the soaking time is too long, the austenite grains are coarse and the manufacturing cost is increased. Therefore, the soaking time is generally controlled to be suitable for 1-3 hours, and the higher the heating temperature, the corresponding soaking time can be appropriately shortened.
  • the alloying elements in the composition of Q&P steel are mainly C, Si, Mn, and the C content is generally greater than 0.15%, the Si content is generally greater than 1.0%, and the Mn content is generally greater than 1.5%. After the casting billet is heated, these alloying elements are solid-solubilized. In austenite, not only the stability of austenite is improved, but also the high temperature strength is improved. Therefore, rough rolling and finish rolling should be carried out in the complete austenitizing temperature range in order to reduce the hot rolling rolling force and ensure the stability of the through sheet.
  • the coiling temperature should not be designed to exceed 600 ° C. The lower the coiling temperature, the thinner the scale. However, as the coiling temperature decreases, the content of the horse's mass and martensite in the Q&P steel hot rolled coil increases gradually, which will lead to a significant increase in strength, which is not conducive to stable coiling and post-process cold rolling, so the coiling temperature is The design should not be lower than 400 °C.
  • the Q&P steel hot rolled coil After the Q&P steel hot rolled coil is coiled, its microstructure is mainly composed of bainite and martensite, and the martensite volume percentage is ⁇ 20%, and the tensile strength exceeds 1000 MPa.
  • the hot rolled coil of Q&P steel After unwinding the hot rolled coil of Q&P steel, a separate, closed heat insulating cover device is quickly placed on the wire (preferably within 20 minutes) to control the cooling of the steel coil, and the self-tempering treatment is performed by using the residual heat of coiling.
  • the martensite gradually decomposes and transforms into cementite and a small amount of ferrite, so that the strength of the coil is lowered.
  • the residual heat is self-tempered; in the "offline” mode, the temperature drop of the inner/outer ring and the edge is significantly greater than that of the middle during the transportation of the coil before entering the heat shield, and the temperature uniformity of the steel coil is poor.
  • 3 "offline” mode steel coil phase change uniformity is poor, local area martensite volume fraction is too high, is not conducive to uniform temper softening.
  • the invention is designed by a reasonable rolling process, and at the same time, with the innovative "single roll” heat preservation slow cooling process after hot rolling, the Q&P steel hot rolled coil can be controlled online, low cost and high efficiency. Cool and adjust its microstructure.
  • the Q&P steel hot rolled coil produced by the invention has a yield strength drop of ⁇ 85 MPa, a tensile strength drop of ⁇ 150 MPa, and a good elongation ( ⁇ 15%). ), the softening effect is remarkable, which can replace the intermediate annealing process in the traditional process and reduce the production cost of cold-rolled Q&P steel.
  • Figure 1 is a typical metallographic photograph of a test steel according to Example 1 of the present invention.
  • Example 2 is a typical metallographic photograph of a test steel according to Example 2 of the present invention.
  • Figure 3 is a typical metallographic photograph of the test steel of Comparative Example 1 of the present invention.
  • Figure 4 is a typical metallographic photograph of the test steel of Comparative Example 2 of the present invention.
  • Table 1 shows the key process parameters of the examples of the present invention
  • Table 2 shows the key process parameters of the comparative examples of the present invention
  • Table 3 shows the performance of the examples and comparative steel coils of the present invention.
  • the process flow of the embodiment of the invention is: Q&P steel slab heating ⁇ rough rolling ⁇ finishing rolling ⁇ laminar cooling ⁇ winding ⁇ on-line cover thermal insulation cover ⁇ moving the heat preservation cover, wherein the key process parameters are shown in Table 1.
  • the comparative process of the invention is: Q&P steel slab heating ⁇ rough rolling ⁇ finishing rolling ⁇ laminar cooling ⁇ coiling ⁇ steel coil stacking and slow cooling, wherein the key process parameters are shown in Table 2.
  • Example Yield strength (MPa) Tensile strength (MPa) Elongation rate (%) 1 644 816 20 2 692 840 16 3 726 859 18 4 849 970 17 5 885 1056 16 Comparative example Yield strength (MPa) Tensile strength (MPa) Elongation rate (%) 1 740 966 16 2 928 1063 14 3 1021 1184 14 4 1024 1257 15 5 970 1296 14
  • Figures 3 and 4 show typical metallographic photographs of the test steels of Comparative Examples 1 and 2. It can be clearly seen from the photograph that the microstructure of the coil is mainly bainite + cementite after the heat shield treatment.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • General Engineering & Computer Science (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Metal Rolling (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

一种高强度Q&P钢热轧卷的软化方法，将Q&P钢铸坯加热后经粗轧、精轧、层流冷却和卷取得到热轧卷，卸卷后在线盖上保温罩并随运输链移动进入钢卷库，达到保温时间后移出保温罩空冷至室温；其中，卷取温度为400～600℃，所述在线盖上保温罩是指每个热轧卷卸卷后60分钟内单独盖上独立的、密闭的保温罩装置；所述钢卷在保温罩内的保温时间≥60分钟。该软化方法取代冷轧Q&P钢生产过程中的中间退火工序，低成本、高效率、并且不受周围环境影响。

Description

一种高强度Q＆P钢热轧卷的软化方法 技术领域
本发明属于第三代汽车用先进高强钢生产技术领域，具体涉及一种高强度Q&P钢热轧卷的软化方法。
背景技术
随着汽车行业对轻量化和防撞安全性要求的提高，先进高强钢在白车身上的应用比例呈增长趋势。按汽车用钢的综合力学性能-强塑积U T(抗拉强度×伸长率)指标分类：
第一代高强钢U T为15±10GPa％，轻量化和安全性指标较低；
第二代高强钢U T为60±10GPa％，强度和塑性都很理想，但工艺复杂、合金含量高、生产成本居高不下，很难被市场接受；
第三代高强钢U T为30±10GPa％，轻量化和安全性指标优于第一代高强钢，而生产成本显著低于第二代高强钢，引起了汽车及冶金行业的广泛关注。
近年来，以C、Si、Mn等廉价元素为主要合金元素的淬火-配分钢即Q&P(Quenching and Partitioning)钢已经被公认为第三代汽车用先进高强钢的重要代表，其工业生产流程分为两类：
一类如中国专利公告号CN105177415A、CN105441814A、CN103215516A、CN103805851A、CN104532126A、CN103233161A、CN103805869A、CN102226248A等公开的热轧Q&P钢，通过冶炼、热轧完成生产，其特点是工艺流程短、生产成本低，但是对热轧层流冷却控制提出很高的要求，工业上难以实现，并且产品表面质量难以保证。
另一类如中国专利公告号CN105734213A、CN104988391A、CN105648317A等公开的冷轧Q&P钢，通过冶炼、热轧、中间退火、冷轧和最终Q&P热处理完成生产，其特点是产品具有高强度、高应变硬化率、较好的塑性、表面质量好，但工艺流程长、生产成本相对较高。与普通冷 轧产品的生产流程相比，冷轧Q&P钢在热轧和冷轧之间需要增加一道中间退火工序(罩式炉退火或者连续退火)，即将热轧卷重新加热至奥氏体化温度并保持足够时间，然后以适宜的速度冷却至室温，达到软化Q&P钢热轧卷从而降低冷轧机组轧制力实现冷轧轧制的目的。
发明内容
本发明的目的在于提供一种新的、低成本、高效率的高强度Q&P钢热轧卷的软化方法，并利用自回火软化取代冷轧Q&P钢生产过程中的中间退火工序。
为达到上述目的，本发明的技术方案是：
本发明Q&P钢经过热轧轧制、淬火、卷取后，在线快速地盖上独立的、密闭的保温罩装置，从而对钢卷进行控制冷却，利用卷取余热进行有效的自回火软化处理，在线调整Q&P钢热轧卷的微观组织结构，使马氏体分解，达到降低钢卷强度的目的。
具体的，本发明一种高强度Q&P钢热轧卷的软化方法，其特征是，将Q&P钢铸坯加热后经粗轧、精轧、层流冷却和卷取得到热轧卷，卸卷后在线盖上保温罩并随运输链移动进入钢卷库，达到保温时间后移出保温罩空冷至室温；其中，卷取温度为400～600℃，所述在线盖上保温罩是指每个热轧卷卸卷后60分钟内单独盖上独立的、密闭的保温罩装置；所述钢卷在保温罩内的保温时间≥60分钟。
进一步地，所述铸坯加热温度≥1150℃，均热时间≥60分钟。
优选地，铸坯加热温度为1200-1300℃，均热时间为1-3小时。
进一步地，所述粗轧和精轧在完全奥氏体化温度区间进行，整个热轧压下率≥90％，终轧温度为800-1000℃。
优选的，每个热轧卷卸卷后20分钟内单独盖上保温罩。
进一步地，所述钢卷在保温罩内的冷却速度≤15℃/小时。
优选的，钢卷在保温罩内的保温时间为1-24小时。
进一步地，示例性的保温罩为CN 107470377 A中任一实施方案所公开的钢带制造流水线在线保温缓冷装置，本文将其全部内容以引用的方式纳入本文。
本发明的制造方法中：
铸坯的加热温度若低于1200℃，则不利于合金元素的均匀化；而当温度高于1300℃时，不仅提高了制造成本，而且使得加热质量有所下降。因此，铸坯的加热温度一般控制在1200-1300℃比较合适。
类似地，均热时间也需要控制在一定范围内。均热时间即铸坯加热到设定的加热温度后保温一段时间。均热时间过短，溶质原子如Si、Mn等的扩散不够充分，铸坯的加热质量得不到保证；而均热时间过长则使得奥氏体晶粒粗大，并提高了制造成本。因此，均热时间一般控制在1-3小时比较合适，加热温度越高，相应的均热时间可适当缩短。
由于Q&P钢的成分中合金元素主要有C、Si、Mn，并且C含量一般大于0.15％、Si含量一般大于1.0％、Mn含量一般大于1.5％，铸坯经过加热后，这些合金元素固溶于奥氏体中，不仅提高了奥氏体的稳定性，而且提高了其高温强度。因此，粗轧和精轧应在完全奥氏体化温度区间进行，以便降低热轧轧制力，确保通板稳定性。
虽然热轧前一般采用高压除鳞的方式将加热过程形成的氧化铁皮去除干净，但在轧制过程及随后的冷却还是会在带钢表面形成一层氧化铁皮。为了减少氧化铁皮、避免或减轻内氧化问题，卷取温度的设计不宜超过600℃，卷取温度越低，氧化铁皮越薄。但随着卷取温度降低，Q&P钢热轧卷中的马奥组织和马氏体含量逐渐增加，将导致强度大幅上升，不利于稳定卷取和后工序冷轧轧制，因此卷取温度的设计不宜低于400℃。
Q&P钢热轧卷卷取后，其微观组织主要由贝氏体和马氏体组成，并且马氏体体积百分比≥20％，抗拉强度超过1000MPa。为了提高后工序冷轧的可制造性，减小冷轧轧制力，需对Q&P钢热轧卷进行软化处理。本发明中，Q&P钢热轧卷卸卷后，在线(优选20分钟内)快速地盖上独立的、密闭的保温罩装置，从而对钢卷进行控制冷却，利用卷取余热进行自回火处理，马氏体在保温罩内缓冷的过程中，逐渐发生分解，转变为渗碳体和少量铁素体，使得钢卷强度降低。所谓“在线”，即要求钢卷卸卷后第一时间盖上保温罩，与钢卷入库后再盖上保温罩的“离线”模式相比：①保证了入罩温度，可以充分利用卷取余热进行自回火处理；②“离线”模式下，钢卷在进入保温罩之前的运输过程中，内/外圈和边部的温降显著大于 中部，钢卷整体的温度均匀性较差；③“离线”模式下，钢卷相变均匀性较差，局部区域马氏体体积分数过高，不利于均匀回火软化。
本发明的有益效果：
(1)本发明通过合理的轧制工艺设计，同时配合创新性的热轧卷取后“单卷式”保温缓冷工艺，可在线、低成本、高效率地对Q&P钢热轧卷进行控制冷却，并调整其微观组织结构。
(2)采用本发明制造出的Q&P钢热轧卷，与常规堆垛缓冷工艺相比，屈服强度下降幅度≥85MPa、抗拉强度下降幅度≥150MPa，同时具有良好的延伸率(≥15％)，软化效果显著，可以取代传统流程中的中间退火工序，降低冷轧Q&P钢的生产成本。
附图说明
图1为本发明实施例1的试验钢典型金相照片。
图2为本发明实施例2的试验钢典型金相照片。
图3为本发明对比例1的试验钢典型金相照片。
图4为本发明对比例2的试验钢典型金相照片。
具体实施方式
下面结合实施例和附图对本发明做进一步说明。
表1为本发明实施例的关键工艺参数，表2为本发明对比例的关键工艺参数，表3为本发明实施例和对比例钢卷的性能。
本发明实施例工艺流程为：Q&P钢铸坯加热→粗轧→精轧→层流冷却→卷取→在线盖上保温罩→移出保温罩，其中关键工艺参数见表1。
本发明对比例工艺流程为：Q&P钢铸坯加热→粗轧→精轧→层流冷却→卷取→钢卷堆垛缓冷，其中关键工艺参数见表2。
表1
Figure PCTCN2018106703-appb-000001
Figure PCTCN2018106703-appb-000002
表2
Figure PCTCN2018106703-appb-000003
表3
实施例 屈服强度(MPa) 抗拉强度(MPa) 延伸率(％)
1 644 816 20
2 692 840 16
3 726 859 18
4 849 970 17
5 885 1056 16
对比例 屈服强度(MPa) 抗拉强度(MPa) 延伸率(％)
1 740 966 16
2 928 1063 14
3 1021 1184 14
4 1024 1257 15
5 970 1296 14
从表3中实施例和对比例的数据可以看出：采用本发明提出的方法生产Q&P钢热轧卷，与采用钢卷堆垛缓冷的方法相比，其屈服强度下降幅 度≥85MPa、抗拉强度下降幅度≥150MPa、断裂延伸率提高幅度≥2％，说明本发明提出的方法可以有效软化Q&P钢热轧卷，同时提高材料的塑性指标，有利于降低后工序冷轧轧制力。
图1、图2给出了实施例1和2试验钢的典型金相照片。从照片上可以清楚地看出，未经保温罩处理，钢卷的显微组织主要为贝氏体+马氏体。
图3、图4给出了对比例1和2试验钢的典型金相照片。从照片上可以清楚地看出，经过保温罩处理，钢卷的显微组织主要为贝氏体+渗碳体。
本发明的实施方式并不受上述实施例的限制，其他的任何未背离本发明的精神实质与原理下所作的改变、修饰、替代、组合、简化，均应为等效的置换方式，都包含在本发明的保护范围之内。

Claims (7)

  1. 一种高强度Q&P钢热轧卷的软化方法，其特征是，将Q&P钢铸坯加热后经粗轧、精轧、层流冷却和卷取得到热轧卷，卸卷后在线盖上保温罩并随运输链移动进入钢卷库，达到保温时间后移出保温罩空冷至室温；其中，卷取温度为400～600℃，所述在线盖上保温罩是指每个热轧卷卸卷后60分钟内单独盖上独立的、密闭的保温罩装置；所述钢卷在保温罩内的保温时间≥60分钟。
  2. 如权利要求1所述的高强度Q&P钢热轧卷的软化方法，其特征是，所述铸坯加热温度≥1150℃，均热时间≥60分钟。
  3. 如权利要求1所述的高强度Q&P钢热轧卷的软化方法，其特征是，所述铸坯加热温度为1200～1300℃，均热时间为1～3小时。
  4. 如权利要求1所述的高强度Q&P钢热轧卷的软化方法，其特征是，所述粗轧和精轧在完全奥氏体化温度区间进行，整个热轧压下率≥90％，终轧温度为800～1000℃。
  5. 如权利要求1所述的高强度Q&P钢热轧卷的软化方法，其特征是，所述热轧卷卸卷后20分钟内单独盖上保温罩。
  6. 如权利要求1所述的高强度Q&P钢热轧卷的软化方法，其特征是，所述钢卷在保温罩内的冷却速度≤15℃/小时。
  7. 如权利要求1所述的高强度Q&P钢热轧卷的软化方法，其特征是，所述钢卷在保温罩内的保温时间为1～24小时。
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