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WO2020108595A1 - 一种高表面质量、低屈强比热轧高强度钢板及制造方法 - Google Patents

一种高表面质量、低屈强比热轧高强度钢板及制造方法 Download PDF

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WO2020108595A1
WO2020108595A1 PCT/CN2019/121864 CN2019121864W WO2020108595A1 WO 2020108595 A1 WO2020108595 A1 WO 2020108595A1 CN 2019121864 W CN2019121864 W CN 2019121864W WO 2020108595 A1 WO2020108595 A1 WO 2020108595A1
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hot
strength steel
surface quality
yield ratio
steel sheet
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PCT/CN2019/121864
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English (en)
French (fr)
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张建苏
柏明卓
庞厚君
胡兆辉
华骏山
郁锋
王明
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宝山钢铁股份有限公司
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Priority to DE112019005950.5T priority Critical patent/DE112019005950T5/de
Priority to BR112021008309-0A priority patent/BR112021008309B1/pt
Publication of WO2020108595A1 publication Critical patent/WO2020108595A1/zh

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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
    • C21D8/0205—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
    • 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
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/02—Making non-ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
    • C21D2211/005—Ferrite
    • 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
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium

Definitions

  • the invention belongs to automobile steel, and particularly relates to a hot-rolled high-strength steel plate with high surface quality and low yield ratio and a manufacturing method, and is particularly suitable for automobile exterior parts such as car wheels.
  • Hot rolled steel plate is mainly used for car chassis, wheels, suspension and its surrounding parts, and its weight accounts for more than 25% of the total weight of the car body. Due to the increase in strength, the capacity of equipment used in the manufacture of many parts is also facing increased pressure. Therefore, it is hoped that materials with low yield strength and high tensile strength can be obtained to solve the contradictions faced. At the same time, many parts used in these parts have both appearance parts such as wheels and coated parts, which require good coatability of the steel plate surface.
  • the traditional dual-phase steel has a structure of ferrite + martensite. It has a low yield ratio, no yield platform, high work hardening rate, high baking hardening, long fatigue life, good welding performance, etc. Excellent performance, in order to obtain the desired structure and good performance, usually add Si to the ingredients to expand the ferrite formation area. But at the same time, the addition of Si also caused the formation of sharp olivine crystals composed of FeO-Fe 2 SiO 4 on the surface of the hot-rolled steel sheet. This crystal cannot be removed cleanly during descaling, leaving the surface of the steel sheet in the rolling direction One by one "red iron sheet” defects, see Figure 1. Therefore, there is an urgent need for a steel grade that not only has the advantages of low yield ratio, high work hardening rate, etc. unique to dual-phase steel, but also has high surface quality to meet the requirements of the appearance and coating of automobile chassis and automobile wheels.
  • Taiwanese patent TWI300443B proposes a hot-rolled steel plate manufacturing process with a composition of 0.01-0.08% C, Si ⁇ 0.9%, Mn 0.5-1.6%, A1 1.2%, Cr 0.3-1.2%, which is cooled in two stages. In the first stage, the steel plate is cooled at a speed of 2-15°C/s from 8-40s to 730°C, and then the steel plate is cooled to a temperature below 300°C at a cooling rate of 20-150°C/s.
  • German patent DE10327383C5 discloses a method for producing hot-rolled dual-phase steel plate, the composition of the steel is: 0.01-0.08% C, ⁇ 0.9% Si, 0.5-1.9% Mn, ⁇ 1.2% Al, 0.3- 1.2% Cr, the rest is Fe, finish rolling under A3 at 50-100°C, then cool to ferrite area at 30-150°C/s, and cool for 5 seconds, then cool at 30-150°C/s To 300°C.
  • the purpose of the present invention is to provide a hot-rolled high-strength steel plate with high surface quality and low yield ratio and a manufacturing method, which does not require heat treatment and can be directly produced by a general hot-rolling production line.
  • the high-strength steel plate has a simple cooling process after hot rolling, uniform performance, good shape, good cold workability and welding performance, low production cost, and good surface quality, which can meet the requirements of the appearance and coating of automobile chassis and automobile wheels.
  • the "high surface quality" mentioned in the present invention means that the surface has no defects of red iron skin.
  • the structure of the hot-rolled high-strength steel plate of the present invention is ferrite and martensite, wherein the volume fraction content of martensite is 15-20%, and the aspect ratio of ferrite of more than 80% in ferrite ⁇ 1.5.
  • the hot-rolled high-strength steel sheet of the present invention has a tensile strength ⁇ 590 MPa, preferably ⁇ 600 MPa; an elongation ⁇ 20%, preferably ⁇ 24%; a yield ratio ⁇ 0.6, preferably ⁇ 0.58.
  • the tensile strength of the hot-rolled high-strength steel sheet of the present invention is in the range of 590-900 MPa.
  • C It is used to form sufficient carbide strengthening phase to ensure the strength level of steel. If the C content is less than 0.045%, the strength cannot meet the requirements, and if the C content is more than 0.085%, it is detrimental to the welding performance and formability. Preferably, the C content is 0.045-0.082%.
  • the conventional dual-phase steel As a material for automobile chassis and wheels, the conventional dual-phase steel must have sufficient strength and excellent elongation, but due to the high Si content in the conventional dual-phase steel, red iron skin defects appear on the surface. In order to avoid this defect in dual-phase steel, a low Si composition is required. In the present invention, it is required to control the Si content to 0.15% or less. In some embodiments, preferably, the Si content is 0.05-0.14%.
  • Mn It is a solid solution strengthening element. If the Mn content is less than 1.0%, the strength of the steel is insufficient; if the Mn content is more than 1.5%, the plasticity of the steel is reduced. Preferably, the Mn content is 1.06-1.5%
  • Mn+20C 2.2-3.2%, below 2.2%, the volume fraction content of martensite is less than 15%, and above 3.2%, the volume fraction content of martensite exceeds 20%.
  • Mn+20C 2.3-3.1%.
  • P It is an impurity element in steel, and the content should be as low as possible. Preferably, P ⁇ 0.015%.
  • S It is also an impurity element in steel, and the content of S in steel is usually required to be 0.001% or less.
  • Al It is a deoxidizing element in steel, reducing oxide inclusions in steel and pure steel, which is beneficial to improve the formability of steel plates. At the same time, adding higher content of Al can partially replace the role of Si. Therefore, in the present invention, the Al content is 0.5-2.0%. In some embodiments, the Al content is 1.0-2.0%.
  • Ti It is an element that effectively refines grains and improves strength and toughness. It exists in steel in the form of carbides and carbonitrides. However, too much elements such as Ti and carbonitrides in low-carbon steel will affect the subsequent phase transformation, so the content of alloying elements needs to be controlled at the upper limit, preferably Ti ⁇ 0.03%. In some embodiments, the steel sheet of the present invention contains 0.01-0.03% Ti.
  • the grain boundary strengthening element can effectively increase the strength of the ferrite matrix.
  • the B content if the B content is too high, it will cause hot embrittlement and affect the welding performance and hot workability of the steel. Therefore, the B content needs to be strictly controlled.
  • the boron content in the low alloy high strength wear-resistant steel of the present invention is ⁇ 0.0005%.
  • the manufacturing method of the hot-rolled high-strength steel plate with high surface quality and low yield ratio according to the present invention includes the following steps:
  • the steel sheet is cooled to 600 to 750°C at a cooling rate of 50 to 150°C/s or more, and then cooled in the air at a cooling rate of 1 to 10°C/s for 2 to 10 seconds, and then again at 50 -The cooling speed of -200°C/s is cooled to 50 ⁇ 300°C and coiled, then air-cooled to room temperature.
  • the heating temperature is lower than 1150°C, the micro-alloying element is not sufficiently dissolved, and the effect of the micro-alloying element is not fully utilized, and the strength is reduced. If the heating temperature is higher than 1250°C, the grains are likely to be coarsened, which is detrimental to improving the toughness of the steel plate.
  • the slab is rough-rolled in the austenite re-grain boundary area, and the austenite grains are refined by recrystallization after rolling deformation.
  • the deformation of the steel plate is 80-95%, and the final rolling temperature is controlled at austenite.
  • the crystallization zone 780 ⁇ 850°C through the rolling deformation of the austenite low temperature zone, the deformation zone is formed in the austenite grains and the carbon nitride of the microalloy element is induced by the strain to refine the phase transformation product of the austenite To improve the toughness of the steel plate.
  • the steel plate is cooled to 600-750°C at a cooling rate of 50-150°C/s or more (two-phase region of ferrite + austenite), and cooled at a cooling rate of 1-10°C/s in air for 2-10 Seconds, such as 3 to 10 seconds, part of the austenite is transformed into equiaxed ferrite in this temperature range (over 80% ferrite aspect ratio ⁇ 1.5), and then the steel plate is at 50-200°C/s
  • the cooling rate is cooled to 50-300°C, preferably 70-300°C, and the material is passed through the bainite zone into the martensite zone, and finally about 15-20% of martensite is formed.
  • the Si content in the composition is less than 0.10%.
  • 0.5-2.0% Al needs to be added to make up, which can effectively improve the surface quality of the steel plate. See Figure 2. If the coiling temperature is higher than 300°C, a large amount of bainite is likely to appear in the microstructure of the steel plate, making the strength of the high-strength steel lower than 590MPa.
  • the hot-rolled high-strength steel plate of the invention adopts a relatively simple composition design, substitutes Al for Si to improve the surface quality of the steel plate, does not use the more expensive elements such as Nb, Mo, Cr, etc., and the alloy cost is low; in the production process, A relatively simple production process is adopted. After hot rolling, a segmented cooling mode is added to the conventional laminar cooling process, which is easy to produce.
  • the steel plate of the present invention produced according to the above composition design and process design has high strength ( ⁇ 590MPa), low yield strength (yield ratio ⁇ 0.6) and good surface quality, so that the steel plate of the present invention needs good appearance and good in manufacturing
  • the coating performance of automobile chassis and wheel parts has unique advantages.
  • Fig. 1 is a photograph of "red iron skin” defects on the surface of the steel sheet of Comparative Example 1.
  • Fig. 2 is a photograph of the surface of a steel plate in Example 1 of the present invention.
  • Figure 3 is a metallographic photograph of Example 3 of the present invention.
  • Table 1 is the chemical composition of steels A to G of the present invention, and H steel is a comparative steel of JPH09263885A.
  • the slab is heated at 1150-1250°C and then rolled in the austenite zone with a rolling deformation of 80-95%; the steel sheet after the final rolling is 50-150°C/s or more
  • the cooling rate is cooled to 600 ⁇ 750°C, and then air-cooled for 3-10 seconds.
  • the air cooling rate is controlled within the range of 1 ⁇ 10°C/s, and then cooled to 50 ⁇ 300°C again at a cooling rate of 50-200°C/s. Take up and cool to room temperature.
  • Table 2 shows the process control during rolling and the mechanical properties of the obtained steel plate with a thickness of 3 mm. The mechanical properties were tested according to the GB6397-86 standard.
  • the comparative example is the dual-phase steel plate of Japanese Patent JPH09263885A.
  • the steel plate of the present invention has a clean surface without the defects of “red iron skin” shown in FIG. 1, and the surface quality is high, which can meet the requirements of the appearance and coating of automobile chassis and automobile wheels.
  • the structure of the steel plate of Example 3 is ferrite and martensite, wherein the dark color is martensite, and the volume percentage thereof is in the range of 15-20%.
  • the tensile lengths of the tensile samples of the examples and the comparative examples are both 50 mm; Comparative Example 1 corresponds to Comparative Example 8 of JPH09263885A; Comparative Example 2 corresponds to Example 6 of JPH09263885A

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Abstract

一种高表面质量、低屈强比热轧高强度钢板及其制备方法，其成分重量百分比为：C 0.045-0.085％、Si≤0.15％、Mn 1.0～1.5％、P≤0.05％、S≤0.001％、Al 0.5～2.0％、N≤0.0060％；Ti≤0.03％、B≤0.0005％，其余是Fe和不可避免的杂质；且，Mn+20C＝2.2-3.2％。该高强度钢板热轧后冷却工艺较简单、性能均匀、板形好，具有良好冷加工性和焊接性能，生产成本低，同时具有良好的表面质量，能够满足汽车底盘和汽车车轮外观和涂覆的要求。

Description

一种高表面质量、低屈强比热轧高强度钢板及制造方法 技术领域
本发明属于汽车用钢，特别涉及一种高表面质量、低屈强比热轧高强度钢板及制造方法，特别适合用作轿车的车轮等汽车外观部件。
背景技术
近年来，由于人类环境保护意识日益增强，降低汽车的油耗及减少CO 2的排放已经成为了一个全球共同的呼声，在为了达到这一目标的多种措施中，汽车减重则是一个非常有效的手段。这一全球性的趋势以及对汽车安全性重视，带来了对各种先进的高强度、加工性能良好的新型钢铁材料的需求。
热轧钢板主要用于轿车底盘、车轮、悬挂及其周围部件，它的重量大约占车体总重量的25％以上。由于强度的提高，用于许多零件制造的设备能力也面临提升的压力，因此，希望能够得到屈服强度低、抗拉强度高的材料，从而解决面临的矛盾。与此同时，用于这些部位上的许多零部件既有外观件如车轮，也有涂覆件，需要钢板表面有良好的可涂覆性能。
传统意义上的双相钢，其组织为铁素体+马氏体，它具有屈强比低、无屈服平台、加工硬化率高、烘烤硬化高、疲劳寿命长、焊接性能好等多种优异性能，为了获得希望的组织构成和良好的性能，通常要在成分中添加Si，以扩大铁素体形成区域。但与此同时，Si的加入也造成了在热轧钢板表面形成由FeO-Fe 2SiO 4构成的尖橄榄石晶体，这种晶体在除鳞时无法去除干净，使钢板表面沿轧向留下一条条“红铁皮”缺陷，参见图1。因此，迫切需要一种既具有双相钢所特有的低屈强比、加工硬化率高等诸多优点、又具有较高表面质量的钢种，以满足汽车底盘和汽车车轮外观和涂覆的要求。
中国台湾专利TWI300443B提出了一个成分为C 0.01-0.08％，Si<0.9％，Mn 0.5-1.6％，A1 1.2％，Cr 0.3-1.2％的热轧钢板制造工艺，分两个阶段冷却，在第一阶段先以2-15℃/s的速度冷却8-40s至730℃，而后以20-150℃/s的冷速将钢板冷却 到300℃以下。
德国专利DE10327383C5公开了一种生产的热轧双相钢板的方法，钢的成分为：0.01-0.08％的C、≤0.9％的Si、0.5-1.9％的Mn、≤1.2％的Al、0.3-1.2％的Cr，其余为Fe，在A3之下50-100℃开始终轧，随后以30-150℃/s冷却到铁素体区域，并冷却5秒，再以30-150℃/s冷却到300℃。
发明内容
本发明的目的在于提供一种高表面质量、低屈强比热轧高强度钢板及制造方法，不需用热处理、仅用一般热轧生产线就能直接生产的590MPa以上级高强度钢板，这种高强度钢板热轧后冷却工艺较简单、性能均匀、板形好，具有良好冷加工性和焊接性能，生产成本低，同时具有良好的表面质量，能够满足汽车底盘和汽车车轮外观和涂覆的要求。本发明所述的“高表面质量”指表面无红铁皮缺陷。
为达到上述目的，本发明的技术方案是：
一种高表面质量、低屈强比热轧高强度钢板，其成分重量百分比为：C 0.045-0.085％、Si≤0.15％、Mn 1.0～1.5％、P≤0.05％、S≤0.001％、Al 0.5～2.0％、N≤0.0060％、Ti≤0.03％、B≤0.0005％，其余是Fe和不可避免的杂质；且，Mn+20C＝2.2-3.2％。
本发明所述热轧高强度钢板的组织为铁素体和马氏体，其中，马氏体的体积分数含量为15-20％，铁素体中80％以上的铁素体的长宽比≤1.5。
本发明的热轧高强度钢板的抗拉强度≥590MPa，优选≥600MPa；延伸率≥20％，优选≥24％；屈强比≤0.6，优选≤0.58。在一些实施方案中，本发明热轧高强度钢板的抗拉强度在590-900MPa的范围内。
在本发明钢成分设计中：
C：用于形成足够碳化物强化相，以保证钢的强度级别，C含量低于0.045％，则强度达不到要求，C含量高于0.085％则对焊接性能和成形性能不利。优选地，C含量为0.045-0.082％。
Si：在钢中的作用有如下三个：
1)起固溶强化作用，提高钢的强度；
2)可以对奥氏体向铁素体的转变起加速的作用，使奥氏体向铁素体的转变速 度加快。
3)阻止碳化物的析出，避免珠光体相的出现。
作为汽车底盘和车轮用材料，传统双相钢必须有足够的强度以及优良的延伸率，但由于传统双相钢中包含较高的Si，造成表面出现红铁皮缺陷。为了避免在双相钢中出现这一缺陷，需要采用低Si成分。在本发明中要求将Si含量控制在0.15％以下。在一些实施方案中，优选地，Si含量为0.05-0.14％。
Mn：是固溶强化元素。Mn含量低于1.0％，则钢的强度不足；Mn含量高于1.5％，则会使钢的塑性下降。优选地，Mn含量为1.06-1.5％
另外，Mn+20C＝2.2-3.2％，低于2.2％则马氏体的体积分数含量不足15％，高于3.2％则马氏体的体积分数含量会超20％。优选地，Mn+20C＝2.3-3.1％。
P：是钢中的杂质元素，含量应越低越好。优选地，P≤0.015％。
S：也是钢中的杂质元素，通常要求钢中S含量在0.001％以下。
Al：是钢中的脱氧元素，减少钢中的氧化物夹杂、纯净钢质，有利于提高钢板的成形性能。同时，加入较高含量的Al，可以部分代替Si的作用。因此，本发明中，Al含量为0.5-2.0％。在一些实施方案中，Al含量为1.0-2.0％。
Ti：是有效细化晶粒、提高强度和韧性的元素，以碳化物和碳氮化物的形式存在于钢中。但在低碳钢中Ti等碳氮化物生成元素太多会影响后续的相变，所以合金元素含量需要控制上限，优选控制在Ti≤0.03％。在一些实施方案中，本发明的钢板中含有0.01-0.03％的Ti。
B：晶界强化元素，可以有效提高铁素体基体的强度。但B含量过高将导致热脆现象，影响钢的焊接性能及热加工性能，因此需要严格控制B含量，本发明低合金高强度耐磨钢中控制硼含量为≤0.0005％。
本发明所述的高表面质量、低屈强比热轧高强度钢板的制造方法，其包括如下步骤：
1)按上述成分冶炼、铸造成铸坯；
2)铸坯经1150～1250℃加热后，在奥氏体区进行轧制，轧制变形量80-95％，终轧温度780～850℃；
3)终轧后的钢板以50～150℃/s以上的冷却速度冷到600～750℃，随后以1～10℃/s的冷却速度在空气中冷却2～10秒钟，随后再次以50-200℃/s的冷却速度冷 却至50～300℃并卷取，然后空冷至室温。
在本发明制造工艺中：
加热温度低于1150℃，微合金元素溶解不充分，未能充分利用微合金元素的作用，强度降低。加热温度高于1250℃，则晶粒容易粗化，对提高钢板韧性不利。
板坯在奥氏体再晶界区进行粗轧，通过轧制变形后的再结晶细化奥氏体晶粒，钢板的变形量在80-95％，终轧温度控制在奥氏体未再结晶区780～850℃，通过奥氏体低温区的轧制变形，使奥氏体晶粒内形成变形带并因应变诱发微合金元素的碳氮化物沉淀，细化奥氏体的相变产物，提高钢板的韧性。
终轧后钢板以50～150℃/s以上冷却速度冷却到600～750℃(铁素体+奥氏体两相区)，在空气中以1～10℃/s的冷却速度冷却2～10秒、如3～10秒，使部分奥氏体在此温度范围转变成等轴状铁素体(80％以上的铁素体长宽比≤1.5)，随后钢板以50-200℃/s的冷却速度冷却到50～300℃、优选70～300℃卷取，使材料穿过贝氏体区进入马氏体区，最终形成大约15-20％的马氏体。为了保证钢板表面无红铁皮缺陷，必须确保成分中Si含量低于0.10％。同时，为了弥补Si含量降低所造成的强度下降、铁素体形成困难等问题，需要添加0.5-2.0％Al进行弥补，从而能够有效改善钢板表面质量。参见图2。若卷取温度高于300℃，钢板微观组织中容易出现大量的贝氏体，使高强度钢的强度低于590MPa。
本发明的有益效果：
本发明热轧高强度钢板，采用了比较简单的成分设计，以Al代Si，以改善钢板表面质量，不使用较为昂贵的Nb、Mo、Cr等元素，合金成本较低；在生产过程中，采用了相对简单的生产工艺，热轧后在常规层流冷却工序上增加了一个分段冷却模式，易于生产。
按照上述成分设计和工艺设计所生产的本发明钢板，具有高强度(≥590MPa)、低屈服强度(屈强比≤0.6)以及良好的表面质量，使得本发明钢板在制造需要良好的外观以及良好的涂覆性能的汽车底盘和车轮部件时，具有独到的优势。
附图说明
图1为比较例1钢板表面的“红铁皮”缺陷照片。
图2为本发明实施例1的钢板表面的照片。
图3为本发明实施例3的金相照片。
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是本发明实施例A～G钢的化学成分，H钢是JPH09263885A的比较钢。
表1
Figure PCTCN2019121864-appb-000001
本发明实施例和比较例中，铸坯经1150～1250℃加热后，在奥氏体区进行轧制，轧制变形量80-95％；终轧后的钢板以50～150℃/s以上的冷却速度冷到600～750℃，然后空冷3～10秒，空冷速度控制在1～10℃/s的范围内，随后再次以50-200℃/s的冷却速度冷却至50～300℃并卷取，然后空冷至室温。表2是轧制时工艺控制和所得厚度为3mm的钢板的力学性能，力学性能的测试按GB6397－86标准进行，比较例是日本专利JPH09263885A的双相钢板。
参见图2，本发明钢板表面干净，没有图1中所示的一条条“红铁皮”缺陷，表面质量高，可以满足汽车底盘和汽车车轮外观和涂覆的要求。参见图3，实施例3的钢板的组织为铁素体和马氏体，其中深色为马氏体，其体积百分数在15-20％的范围内。
表2
Figure PCTCN2019121864-appb-000002
注：实施例和比较例拉伸试样标距均为50mm；比较例1对应于JPH09263885A的比较例8；比较例2对应于JPH09263885A的实施例6

Claims (8)

  1. 一种高表面质量、低屈强比热轧高强度钢板，其成分重量百分比为：C 0.045-0.085％、Si≤0.15％、Mn 1.0～1.5％、P≤0.05％、S≤0.001％、Al 0.5～2.0％、N≤0.0060％；Ti≤0.03％、B≤0.0005％，其余是Fe和不可避免的杂质；且，Mn+20C＝2.2-3.2％。
  2. 如权利要求1所述的高表面质量、低屈强比热轧高强度钢板，其特征在于，所述热轧高强度钢板的抗拉强度≥590MPa，屈强比≤0.6。
  3. 如权利要求1所述的高表面质量、低屈强比热轧高强度钢板，其特征在于，所述热轧高强度钢板的抗拉强度≥600MPa，屈强比≤0.58。
  4. 如权利要求1所述的高表面质量、低屈强比热轧高强度钢板，其特征在于，其成分重量百分比为：C，0.045-0.082％；Si，0.05-0.14％；Mn，1.06～1.5％；P≤0.015％；S≤0.001％；Al，0.5～2.0％；N≤0.0060％；Ti≤0.03％、B≤0.0005％，其余是Fe和不可避免的杂质；且，Mn+20C＝2.3-3.1％。
  5. 如权利要求1-4中任一项所述的高表面质量、低屈强比热轧高强度钢板，其特征在于，所述热轧高强度钢板的组织为铁素体和马氏体，其中，马氏体的体积百分数为15-20％，铁素体中80％以上的铁素体的长宽比≤1.5。
  6. 如权利要求1所述的高表面质量、低屈强比热轧高强度钢板，其特征在于，所述热轧高强度钢板的延伸率≥20％。
  7. 如权利要求1所述的高表面质量、低屈强比热轧高强度钢板的制造方法，其特征是：包括如下步骤：
    1)按权利要求1所述成分冶炼、铸造成铸坯；
    2)铸坯经1150～1250℃加热后，在奥氏体区进行轧制，轧制变形量80-95％，终轧温度780～850℃；
    3)终轧后的钢板以50～150℃/s以上的冷却速度冷到600～750℃，随后以1～10℃/s的冷却速度在空气中冷却2～10秒钟，随后再次以50～200℃/s的冷却速度冷却至50～300℃并卷取，然后空冷至室温。
  8. 如权利要求7所述的高表面质量、低屈强比热轧高强度钢板的制造方法，其特征是：所述钢板的成分重量百分比为：C，0.045-0.082％；Si，0.05-0.14％； Mn，1.06～1.5％；P≤0.015％；S≤0.001％；Al，0.5～2.0％；N≤0.0060％；Ti≤0.03％、B≤0.0005％，其余是Fe和不可避免的杂质；且，Mn+20C＝2.3-3.1％。
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