CN117677717A - 高强度的涂覆双相钢带材及其生产方法 - Google Patents
高强度的涂覆双相钢带材及其生产方法 Download PDFInfo
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- CN117677717A CN117677717A CN202280047903.8A CN202280047903A CN117677717A CN 117677717 A CN117677717 A CN 117677717A CN 202280047903 A CN202280047903 A CN 202280047903A CN 117677717 A CN117677717 A CN 117677717A
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- 229910000885 Dual-phase steel Inorganic materials 0.000 title claims abstract description 37
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- 239000010959 steel Substances 0.000 claims abstract description 83
- 238000001816 cooling Methods 0.000 claims description 40
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- 238000000137 annealing Methods 0.000 claims description 31
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- 229910052791 calcium Inorganic materials 0.000 claims description 13
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- 238000003466 welding Methods 0.000 description 5
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 4
- 238000009844 basic oxygen steelmaking Methods 0.000 description 4
- 239000012467 final product Substances 0.000 description 4
- AMWRITDGCCNYAT-UHFFFAOYSA-L hydroxy(oxo)manganese;manganese Chemical compound [Mn].O[Mn]=O.O[Mn]=O AMWRITDGCCNYAT-UHFFFAOYSA-L 0.000 description 4
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- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 3
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- 229910001338 liquidmetal Inorganic materials 0.000 description 3
- 229910052749 magnesium Inorganic materials 0.000 description 3
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 3
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- AGVJBLHVMNHENQ-UHFFFAOYSA-N Calcium sulfide Chemical class [S-2].[Ca+2] AGVJBLHVMNHENQ-UHFFFAOYSA-N 0.000 description 1
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- 229910000532 Deoxidized steel Inorganic materials 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 238000005269 aluminizing Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
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- 229910017052 cobalt Inorganic materials 0.000 description 1
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- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 230000008094 contradictory effect Effects 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
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Classifications
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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
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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
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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
- 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
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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
- 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
- C21D8/0236—Cold rolling
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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
- 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
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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
- 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
- C21D8/0273—Final recrystallisation annealing
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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
- 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
- C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface 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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0426—Hot rolling
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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
- 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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0436—Cold rolling
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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
- 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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0473—Final recrystallisation annealing
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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
- 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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0478—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing involving a particular surface 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
- 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
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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
- C22C38/001—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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/06—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
- C22C38/46—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
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Abstract
本发明涉及一种经涂覆和任选地平整轧制的双相钢带材,该双相钢带材强度高且具有改善的成形性,其拉伸强度Rm为580‑720MPa以及屈服强度Rp为310‑430MPa。本发明还涉及一种用于生产此类钢带材的方法及其用途。
Description
技术领域
本发明涉及一种高强度的涂覆双相钢带材,其具有改善的成形性,例如用于汽车工业。本发明还涉及用于生产此类钢带材的方法。
背景技术
近年来,(先进)高强度钢板材,AHSS,越来越多地用于轿车零件以减少重量和燃油消耗。为了满足日益增长的需求,人们开发出一系列(先进)高强度钢,如HSLA、双相钢(DP)、铁素体-贝氏体钢(FB),涵盖了拉伸翻边性(SF)、复相(CP)、相变诱导塑性(TRIP)、热成形、孪晶诱导塑性(TWIP)。
然而,由于成形性相对较差,所以AHSS钢板不易应用于各种各样的轿车零件。产品优选以卷材形式供应给最终客户,由最终客户切割坯料并将其成型为最终部件。
随着钢材变得越来越强,它们同时越来越难以成形为汽车部件。实际上,AHSS钢(DP、CP和TRIP)在轿车零件中的实际应用仍然受限于其成形性。因此,改善成形性和可制造性成为AHSS应用的一个重要问题。另一方面,经济性也是一个重要问题。这限制了使用昂贵的合金化元素来达到钢材不得不满足、往往是相互矛盾的要求的能力:腐蚀防护、各种机械性能、可焊接性、光学性质、可加工性和成本。
双相钢由于其显微组织能够提供强度和冲压性(或可压性)的良好结合,其中硬马氏体和/或贝氏体相(的混合物)的主要组分分散于延性铁素体基体中。可能存在少量残余奥氏体(1-3%)和渗碳体。这些钢的应变硬化性高。这使它们不仅具有良好的应变再分布能力以及由此具有良好的冲压性,而且成品部件的机械性能,包括屈服强度,远远优于扁平金属(flat metal)。双相钢的屈服强度通过烤漆(paint baking)工艺(也称作烘烤硬化,BH)进一步增加。这些双相钢在VDA 239-100中被称作CR330Y590T-DP或DH,其中330指的是最小屈服(Y)强度(在本发明的背景下Rp=Rp0.2),单位为MPa,590指的是最小拉伸(T)强度(Rm),单位为MPa。DP代表双相以及DH代表较高成形性的DP(DH=Dehnung Hoch)。
表1:根据VDA 239-100的机械性质。
A80mm(%):使用规格长度L0=80mm(ISO 6892-1类型2(EN20×80))的样品断裂后的伸长率。
A50mm(%):使用规格长度L0=50mm(ISO 6892-1类型1(ASTM12.5×50)或类型3(JIS25×50))的样品断裂后的伸长率。
A(%):使用L0=5.65√S0的比例(proportional)样品断裂后的伸长率,其中S0是样品的起始横截面,单位为mm2。
Ag(%):均匀伸长率(最大力下的塑性伸长率)。
BH2(MPa):在2%塑性预应变的参比条件和热处理(170℃-20分钟)后获得的条件之间屈服应力的增加。
n10-20(-):由10至20%之间的塑性应变或Ag(如果Ag<20%)确定的应变硬化指数。
n4-6(-):由4至6%之间的塑性应变确定的应变硬化指数。
Rm(MPa):拉伸强度。
Rp0.2(MPa):在塑性延伸率为0.2%下的屈服强度(MPa)。这是在平整轧制后获得的。
发明目的
本发明的目的是找到一种高强度热浸镀锌钢带材的组成,在带材的成形性、均匀性和可加工性之间达成平衡。
本发明的另一个目的是通过热浸镀锌提供一种具有良好涂覆性的高强度热浸镀锌钢带材。
本发明还有另一个目的是提供一种具有良好可焊接性的高强度热浸镀锌钢带材。
本发明的另一个目的是提供一种具有良好表面质量的高强度热浸镀锌钢带材。
本发明还有另一个目的是提供一种成本价格尽可能低的高强度热浸镀锌钢带材。
本发明还有另一个目的是贯穿卷材或在整个卷材宽度和长度上以及卷材与卷材之间获得CR330Y590T特性。
发明内容
按重量%计组成为如下的双相钢带材可达到一个或多个所述目的:
C:0.090-0.140 B:0.0010-0.0050
Mn:1.200-1.900 S:至多0.050
Si:0.200-0.800 P:至多0.050
Al:0.200-0.800 N:至多0.015
以及可选地一种或多种元素,选自:
Cr:至多0.500 Nb:至多0.060
Mo:至多0.400 Ti:至多0.060
V:至多0.200 Ca:至多0.0050
其余为铁和不可避免的杂质,
其中该钢的拉伸强度Rm为580-720MPa,屈服强度Rp为310-430MPa。任选地,对钢带材进行热浸镀锌、电镀锌或电镀。
优选实施方案由从属权利要求提供。
双相钢(DP)具有多相显微组织。马氏体岛嵌在铁素体基体中,其比例用于调整相应等级的强度。就改善了成形性的双相钢(DH)而言,显微组织主要由铁素体和马氏体以及少量的贝氏体和残余奥氏体组成。显微组织和理想的机械性能可通过化学组成和退火工艺,任选地结合热浸镀锌进行调整。双相钢表现出很低的屈服强度与抗拉强度比率(Rp/Rm),结合了高抗拉强度以及强加工硬化能力。因此,这些双相钢很适合高拉伸要求的成形操作。显微组织优选没有渗碳体。
在本发明的背景下,热浸镀锌(锌或锌合金的热浸涂覆)包括热浸镀铝(商业纯铝或铝合金的热浸涂覆)。或者,可通过电沉积为退火的带材提供金属涂层。在本发明的背景下,电镀和电沉积是同义词,是通过在另一种金属上沉积金属涂层的电解工艺。电镀锌是电沉积的一种,通常与锌或锌合金涂覆于另一种金属上的电沉积有关。
使用主要合金化元素C-Mn-Si-Al-B,以及任选元素的任选添加,是达到欧洲标准VDA 239-100中规定的CR330Y590T-DH等级的一种划算的解决方案。VDA 239-100对该等级的一些要求如表1所示。根据本发明的钢符合VDA 239-100。在冷成形操作(如拉拔)过程中成形关键部件的情况下,增强的成形性提供了附加价值,同时保留了等同于常规双相钢种的焊接性能。由于其机械性能,这些钢种适用于抗碰撞的汽车安全部件。通过限制取代元素(如锰)的量,可获得良好的扩孔系数(HEC)值。锰的这种限制也对均匀伸长后的量具有有益效果。通过硼和硅的添加进一步实现了钢的加强。使用硅的一个劣势是点焊中开裂的风险,例如通过液态金属脆化(LME)或通过热收缩压力产生,因此铝的添加对于抑制点焊过程中的开裂是必要的。这是非常令人惊讶的,因为一般认为铝促进LME,但在这种仔细平衡的化学组成中,作为铁素体形成元素(ferrite former),铝对相转变的有益效果占优势。
发明人发现,通过仔细选择钢的主要组成元素(即碳、锰、硅、铝、铬和硼)的量,可以生产出高强度热浸镀锌钢带材,其具有所需的成形性、均匀性、可加工性、强度和伸长率,而同时提供了足够的可焊接性、涂覆性和表面质量。
根据本发明,对于钢中主要组成元素的量的理由如下所述(所有组成均以重量百分比(重量%)表示,除非另有说明)。据指出,尽管必须以平衡的方式应用下面给出的合金化元素以达到想要的结果,但这些元素可在如下文所述的单个元素的范围内相互独立地变化。
C:0.090-0.140重量%。碳是钢种中必要的具有成本效益的合金化元素,以获得传统的连续退火/镀锌生产线中的强度水平。碳必须以确保所需强度和伸长率的量存在。发现在传统退火/镀锌生产线中可用的冷却速率下,要确保淬透性并最终形成马氏体,需要至少0.090重量%。发现为确保足够的可焊接性和伸长率,0.140重量%的最大含量是必要的。优选地,C至少为0.094重量%,更优选为0.098重量%,更优选为0.104重量%,甚至更优选为至少0.110重量%。碳含量优选至多为0.130重量%,以及更优选至多为0.125重量%。在优选实施方案中,C为0.090重量%至0.130重量%。
Mn:1.200-1.900重量%。锰改善钢的淬透性,以使其促进贝氏体和马氏体的形成。锰通过固溶强化使铁素体基体增强且降低钢的转变温度范围,从而降低所需的退火温度。作为奥氏体稳定元素,其促进残余奥氏体的形成。众所周知,在热轧和冷轧过程中,锰对HEC值、通过卷材的延展性变化以及轧制力产生不利影响,因此Mn值应在1.900重量%以下,优选在1.800重量%以下。对于Mn合适的最大值为1.750重量%。在1.700重量%以下或者甚至在1.600重量%以下Mn值进一步改善HEC值和延展性。鉴于在铸造过程中较强的偏析以及在较高值时带材中的中心线偏析,也给出了这些最大含量。此外,产品应该是可在连续退火生产线上通过RTF加热和较快火焰加热加工的。在连续退火过程中,1.7重量%的过量严重延迟冷轧再结晶和随后的铁素体晶粒生长,尤其是如果较快火焰加热是在类似DFF(直接加热炉)或NOF(非氧化炉)或如感应加热的任何其他快速加热方法中进行的。考虑到在卷材宽度和长度上加热中不可避免的变化,这可对整个卷材宽度和长度上的延展性产生不利影响。Mn的最小值为1.200重量%,优选至少为1.300重量%,更优选至少为1.400重量%以及最优选至少为1450重量%。如果Mn含量过低,则无法达到所需的强度水平,同时具有低Rp/Rm比的DP性质也无法在较低值时获得。鉴于其他元素(如硼)的添加,这一较低限制是可能的。在较高锰值下,达到这些值较为容易,但成本和伸长率值变差,因此必须选择适当的平衡。在优选实施方案中,Mn为1.400重量%至1.750重量%。
Si:0.200-0.800重量%。硅抑制最终产品中渗碳体形成且稳定残余奥氏体形成从而改善产品的延展性。硅通过固溶有效地强化了钢的基体,以达到所需的强度水平和增加铁素体组分的加工硬化速率,这改善了局部成形性(HEC)和高的总伸长率。根据本发明,钢中Si含量最大值为0.800重量%。然而,据观察,Si对点焊性产生不利影响且可能容易使涂覆带材液态金属致脆,因此最大值优选限制在0.750或甚至0.700重量%或最优选至多0.650重量%。另外,过量的硅在卷材冷却过程中可导致内部和晶界氧化程度过高。这可通过使用很低的卷取温度和批量退火来规避,但是就工艺步骤而言,这超出了具有成本效益的解决方案的范围。
为了达到最小的强化效果,至少需要0.200重量%,以及优选至少0.250重量%。通过平衡Si与其他元素(如Al),可优选Si含量的最小值至少为0.400重量%,甚至更优选至少为0.450重量%。在优选实施方案中,Si为0.500重量%至0.700重量%。
Al:0.200-0.800重量%。为脱氧的目的,主要将相对少量的铝添加到液态钢中。过量的Al还与氮发生反应并形成AlN沉淀,从而阻止硼与氮发生反应。因此,硼在晶界上偏析,从而作为一种淬透性元素。为了至少实现游离氧和氮的结合,建议至少0.060重量%的较低Al含量。
较高含量的Al减缓贝氏体转变,从而决定了在由连续退火/镀锌生产线的退火阶段所规定的时间限制内最佳的贝氏体形成。Al以总的铝含量表示。铝还延缓碳化物的形成从而将碳保持在溶体中,这反过来在过时效过程中导致碳分配到奥氏体中并提升了奥氏体的稳定性。与硅不同,铝几乎不增加在连续退火生产线的过时效工段(section)中奥氏体碳富集的分配时间。这改善了伸长值和淬透性,还使连续退火生产线的过时效时间为最小值或没有过时效时间,同时仍然实现所需。0.800重量%的最大含量是对于铸造性规定的,因为高铝含量导致铸模熔渣中毒以及由此模具熔渣粘度的增加,导致铸造过程中不当的传热和润滑。
铸造过程中,铝偏析导致碳、硅和锰富集的偏析带以及中间的较低Mn高铝富集偏析带。两种效应增加了最终产品的伸长率和淬透性值(n4_6(其为在4-6%应变范围内的应变硬化指数)和n值(其为应变硬化系数)),同时保持低的屈服应力。此外,由于Al导致Mn和Si的偏析,因此也增加强度。铝的另一个有益效果是,其在锌(合金)涂覆的带材等的焊接过程中对裂纹形成不太敏感并因此降低了对液态金属致脆的敏感性。因此,它可以有限的程度替代Si。
铝的量影响着亚临界退火和亚临界退火过程中的相分布。这可以通过铝是铁素体形成元素来理解。基于上述原因,铝含量优选0.200重量%以上,更优选铝含量的最小值为0.25重量%。优选地,铝含量至多为0.750重量%,更优选至多为0.650重量%,以及甚至更优选至多为0.400重量%。在优选实施方案中,Al为0.200重量%至0.400重量%。
铝和硅的总和优选在Al+Si=0.350-1.200重量%之间且更优选在0.600-1.200重量%之间。这两种元素的组合抑制最终产品中碳化物的形成并使足够的奥氏体稳定化。众所周知,硅增加过时效段残余奥氏体形成的最佳时间,而铝则几乎不影响残余奥氏体形成的分配时间。使用恰当的组成,铝和硅的总和允许获得所需成形性的扩展。由于硅也决定热轧非再结晶温度(TNR),因此应平衡其使用。硅降低TNR而铝提高TNR。优选地,TNR尽可能低以允许热机械轧制,从而通过改善的r值确保更期望的成形性扩展。优选地,Al+Si在0.650-1.100之间,更优选在0.700-1.100之间,更优选在0.750-1.050重量%之间,最优选在0.800-0.950重量%之间。
B:0.0010-0.0050重量%(按重量计为5-50ppm)。添加作为淬透性元素的硼以达到所需的强度水平。硼的添加允许节省较昂贵合金化元素的使用。相较于较昂贵的固溶体合金化元素,硼对再结晶能力的影响少得多。这允许在热轧生产线上增加静态或动态再结晶,减少平均流动应力积累。它还提高了在连续退火的加热段期间的冷轧再结晶能力,从而允许充分的晶粒生长且在直接加热和慢管加热退火生产线上均达到DH600性能。因为硼影响最终产品的性质但不影响轧制力,所以使用硼而不是固溶硬化元素如Mn和Si,这改善了钢带材的尺寸窗口,意思是较高的宽度与厚度的比率,同时钢在钢带材宽度上保持适当的机械性能。硼细化残余奥氏体,从而稳定已形成的残余奥氏体。硼改善焊接性,因为它偏析到晶界并部分取代磷,这使钢中磷的量稍高而不牺牲焊接性成为可能。
硼的量为0.0010-0.0050重量%(10-50ppm)。合适的下限含量为0.0012重量%或甚至0.0015重量%。在一定的硼含量以上,锌涂覆受到不利影响同时淬透性降低。合适的上限含量为0.0040重量%,优选为0.0035重量%,更优选为0.0030重量%或甚至是0.0025重量%。在优选实施方案中,B为0.0015至0.0025重量%。
N:至多0.015重量%(150ppm)。氮在铸造过程存在。钢中游离氮应该避免,由于它可以导致严重的时效(ageing)并影响硼作为淬透性元素发挥作用的能力。然而,在根据本发明的钢的化学组成中有过剩的铝和硼,因此所有氮与Al或B结合为AlN或BN。氮含量限制在0.015重量%,其对于BOS炼钢厂和连铸机是典型的。然而,优选将氮减小到至多为0.012重量%,优选至多0.010重量%的值。更优选的最大含量为0.008重量%或者甚至0.006重量%。从钢中去除所有的氮是不经济的,因此在优选实施方案中,N为0.0001重量%至0.006重量%(10-60ppm)。
P:至多0.050。磷干扰碳化物的形成,因此一些磷在钢中可以是有益的。此外,磷对酸洗性产生积极影响并强化钢。允许的最大含量为0.050重量%。然而,磷能够使钢在焊接时变脆,因此磷的量优选限制在0.040重量%以保持足够的热延展性并避免在对点焊组件开展拉伸-剪切试验过程中由于剥离而失效。磷的最大含量优选为0.030重量%,甚至优选为0.020质量%。在优选实施方案中,P至多为0.015重量%。
S:至多0.050重量%。硫(S)的最大值为0.050重量%,优最大值选为0.020重量%,甚至0.010重量%。尽管硫可在一定程度上改善酸洗性,优选完全避免硫,但由于炼钢工艺和其中所用的原材料,硫不可避免地存在。硫以锰和/或钙硫化物的形式沉淀,显著降低了成形性。硫的量优选在0.0001-0.005重量%之间,更优选为至多0.003重量%或者更优选为至多0.002重量%。合适的最小量为0.0002重量%。在优选实施方案中,S为0.0001重量%至0.002重量%。
任选地,选自Ti、V、Cr、Mo、Nb、Ni、Cu、Ca的一种或多种元素可添加到钢组成或作为杂质存在。
钙(Ca)的添加改变了硫化锰夹杂物的形态。当加入钙时,夹杂物成为球状而非细长形状。细长的夹杂物也称为发纹(stringer),可作为薄弱面,沿其能够发生层状撕裂和剥落断裂。避免产生发纹有利于钢板材的成形工艺,该成形工艺需要扩孔或拉伸翻边并促进各向同性的成形行为。钙处理还防止在铝脱氧钢类别中形成坚硬、有棱角、有磨损性的氧化铝夹杂物,而是在轧制温度下形成较软和球状的铝酸钙夹杂物,从而改善材料的加工特性。在连铸机中,钢液中出现的一些夹杂物有堵塞喷嘴的倾向,导致产量损失和成本增加。钙处理通过促进不会堵塞铸机喷嘴的低熔点物质的形成而降低堵塞倾向。当硫含量很低时,不加钙也是可能的。Ca元素的最大值设定为0.0050重量%(=50ppm),优选为0.0030重量%,更优选为0.0020重量%或者甚至为0.0010重量%。在一个优选实施方案中,Ca至多为0.0010重量%。出于与钙类似的原因可加入镁或稀土金属(REM)。这些元素的最大值设定为Mg为500ppm以及REM为50ppm。
添加铬(Cr)以提高淬透性。它促进铁素体的形成。规定0.500重量%的最大含量以确保不以残余奥氏体为代价形成过多的马氏体。不添加铬也是可能的,在这种情况下,其完全不存在或至多以残余元素或杂质水平存在。Cr相当昂贵。从该角度来看,Cr的量优选至多为0.300重量%,更优选至多为0.250重量%以及甚至更优选至多为0.200重量%。从机械性质角度来看,如果添加Cr作为合金化元素,优选的范围在0.020-0.400重量%之间。当Cr在0.020-0.150重量%之间,优选在0.020和0.120重量%之间时,可在获得理想的显微组织、理想的机械性能和成本之间取得良好的平衡。如果作为合金化元素添加,铬合适的最小量为0.030重量%,或甚至为0.040重量%。低于0.020的值被视为处于残余元素含量。当元素处于残余元素水平时,该元素被认为不对钢的性质或加工性能以显著的方式产生影响,在这种情况下,即使进一步降低含量在技术上是可行的,进一步去除这些元素的成本超出进一步降低元素含量的预期效益。
添加钛(Ti)主要是为了强化钢,允许含量至多为0.060重量%。不添加钛也是可能的,在这种情况下,其完全不存在或至多以残余元素或杂质水平存在。如果添加,那么优选地,钛的量在0.010-0.060重量%之间,更优选在0.02-0.050重量%之间。低于0.010重量%的值会被视为处于残余元素水平。
可添加至多0.200重量%的钒。如果添加,优选的范围为0.005-0.200重量%。当钒的含量小于0.005重量%时,钒的沉淀强化作用不充分。当钒的含量大于0.200重量%时,在热轧过程中的早期阶段或热轧后会以微细沉淀物的形式发生沉淀,这降低了在连续退火过程中的尺寸窗口或粗化,降低了沉淀强化作用。钒的量为0.005-0.200重量%,优选为0.010-0.200重量%,更优选为0.030-0.200重量%,最优选为0.040-0.150重量%。不添加V也是可能的,在这种情况下,V完全不存在或至多以残余元素或杂质水平存在。低于0.010重量%的值被视为处于残余元素水平。
任选地,元素如钼延缓贝氏体转变并促进固溶硬化,可添加量不超过0.40重量%。Mo的量优选为0.005-0.20重量%,更优选为0.005-0.10重量%,以便限制钢的成本并保持尽可能大的尺寸窗口。添加Mo可以改善强度并改善锌基涂层的质量。Mo还通过沉淀物形成有助于钢强化。然而,不添加Mo也是可能的,在这种情况下,其完全不存在或至多以残余元素或杂质水平存在。低于0.015重量%的值被视为处于残余元素水平。
可添加铌(Nb)的量优选为0.001-0.060重量%,更优选为0.001-0.050重量%,以及最优选为0.001-0.030重量%。Nb的添加通过补充碳氮化物沉淀提高了强度,但增加热轧力,这减小尺寸窗口。如果添加,那么优选Nb的量在0.010-0.060重量%之间,更优选至多为0.050,或至多为0.030重量%。低于0.010重量%的值被视为处于残余元素水平。
因此,在实施方案中,根据前述权利要求中的任一项所述的双相钢带材,其中Cr、Mo、V、Nb和Ti中的一种或多种或全部仅作为杂质存在,这意味着,如果适用,一种或多种或全部的含量分别为,Cr低于0.020重量%,Ti低于0.010重量%,V低于0.010重量%,Mo低于0.015重量%,Nb低于0.010重量%。
根据本发明,钢中没有加入镍和铜,这些元素要么完全不存在、要么至多以残余元素或杂质水平存在。低于0.060重量%的值被认为处于残余元素水平。
在实施方案中,根据本发明的双相钢带材的拉伸强度Rm为590-720MPa和/或屈服强度Rp为320-430MPa。根据本发明,优选钢的屈服强度Rp至少为330MPa。根据本发明,优选钢的拉伸强度Rm至多为700MPa且屈服强度Rp至多为430MPa。
根据本发明的第二方面,提供了一种用于生产经涂覆和任选地经平整轧制的根据权利要求1至11中任一项的双相钢带材的方法,该双相钢带材的拉伸强度Rm为580-720MPa,屈服强度Rp为310-430MPa,包含以下步骤:
·通过热轧连铸板坯至厚度为2.0-4.5mm的热轧带材而提供热轧钢带材,该板坯的组成按重量%计为如下:
C:0.090-0.140 B:0.0010-0.0050
Mn:1.200-1.900 S:至多0.050
Si:0.200-0.800 P:至多0.050
Al:0.200-0.800 N:至多0.015
以及任选地一种或多种元素,选自:
Cr:至多0.500 Nb:至多0.060
Mo:至多0.400 Ti:至多0.060
V:至多0.200 Ca:至多0.0050
其余为铁和不可避免的杂质,
其中在带材有奥氏体显微组织的同时进行精轧;
·将精轧后的热轧带材冷却,冷却速率至少为30℃/s;
·将经冷却的带材进行卷取,卷取温度CT在500-650℃范围内,其中奥氏体的量大于60%且使卷取的带材后续冷却至环境温度;
·将卷取的热轧带材进行开卷,随后进行酸洗和以40-80%的压下率进行冷轧;
·通过如下连续退火经冷轧的带材
i.以至少3℃/s的加热速率HR1,将带材加热至在550-710℃范围内的温度T1,以使得冷轧带材的再结晶在奥氏体形成的开始前进行至少60%;
ii.以平均加热速率HR2,将带材进一步加热至在(Ac1+50℃)至(Ac3-30℃)范围内的温度T2,以形成部分奥氏体化的显微组织,优选地,其中HR2在2-20℃/s范围内。
iii.随后,或者
a.将带材在T2保持至多为90s的时间段t2,随后以0.5-12℃/s范围内的冷却速率CR1将带材缓慢冷却至在600-790℃范围内,优选为620-790℃的温度T3,使得在缓慢冷却的带材中存在16-30%的奥氏体,或者
b.以0.5-12℃/s范围内的冷却速率CR1,将带材从T2立即缓慢冷却至在600-790℃范围内,优选为620-790℃的温度T3,使得在缓慢冷却的带材中存在16-30%的奥氏体;
iv.以在5-70℃/s范围内的平均冷却速率CR2,对包含16-30%奥氏体的经缓慢冷却的带材进行快速冷却,或者
a.至在范围330-470℃的温度T4,或者
b.至过时效温度T_oa持续在5-100s范围内的时间t_oa,其中T_oa在390-465℃之间;
v.以至少4℃/s的冷却速率CR3,冷却钢带材至低于300℃的温度;
·其中带材为:a).在步骤iv.和步骤v.之间通过热浸涂覆而提供有金属涂层,任选地,随后对热浸涂覆后的带材进行镀锌层退火,或b).在步骤v.后通过电沉积而提供有金属涂层;
·任选地,以至多0.70%的压下率对涂覆的钢带材进行平整轧制或张力平整;
·其中,经涂覆及任选平整轧制的钢带材具有580-720MPa的抗拉强度Rm和310-430MPa的屈服强度Rp;
·卷取经涂覆的钢带材或者将涂覆的钢带材切割为板材或坯料;
·任选地,通过如冲压、弯曲、深拉的冷成形操作或通过温压成形或热压成形使涂覆的钢带材、板材或坯料成型。
优选实施方案由从属权利要求提供。
炼钢和铸造
钢熔体优选采用BOS工艺(碱性氧气炼钢)生产。由于其控制化学组成的能力,该工艺相比电弧(EA)工艺更优选,而且相比EA工艺,在BOS工艺中能达到不可避免的杂质的更低含量。在本发明的背景下,不可避免的杂质和残余元素的含义相同,因为不可避免的杂质的水平和残余元素的水平是由技术或经济上不能将元素水平降至低于这些水平所决定的。
将钢熔体在传统铸机上连续铸造为板坯。铸造后,将带材在连铸机中冷却。在连铸的冷却过程中板坯达到特定的温度范围,同时被弯曲,其中钢的延展性降低,这就是所谓的温度延展性低谷。在该温度范围内可形成沉淀。沉淀形成元素之一是Al,其在晶界处形成AlN。这应该部分地抑制,由于它可此后在加工过程中导致裂隙(sliver)的形成。通过加入B,部分地抑制AlN,因为优先形成BN。
铸造板坯可为厚板坯(150-350mm厚)或薄板坯(50-150mm)。BN和/或AlN(混合)沉淀的形成能抑制不均匀的过度晶粒生长。部分的BN沉淀溶解同时形成AlN沉淀。
热轧
随后热轧板坯。将厚板坯在传统带钢热轧机(HSM)中热轧。通常在薄板坯连铸(直接)连轧设备(TSCR)中铸造后将薄板坯进行直接热轧。在HSM中热轧厚连铸板坯前,不得不将板坯再加热至1150℃或更高的温度。在TSCR中热轧薄连铸板坯前,不得不将板坯在约1150℃的温度下进行温度均匀化。这两种热轧工艺同样适用于热轧根据本发明的钢。
尽管并非必要,但发明人发现,大多数从铸造板坯开始的热轧压下率优选在高于TNR时应用。
优选地,在从铸造厚板坯(150-350mm)开始时,至少50%、更优选至少75%以及甚至更优选至少80%或甚至85%的总热轧压下率(板坯厚度至热轧带材厚度)在高于非再结晶温度(TNR)下进行。从铸造薄板坯(50-150mm)开始,优选地,至少50%、更优选至少60%以及甚至更优选70%或甚至75%的总热轧压下率在高于非再结晶温度(TNR)下进行且在精轧机的首个机架(stand)中发生完全再结晶。优选地,至少40%以及更优选至少50%的热轧压下率(将棒材厚度转换为热轧带材厚度)在连续式精轧机中在高于TNR下进行。由于重复的静态或动态再结晶,高于TNR的较高压下率导致较细的奥氏体组织,从而导致热轧卷材的最终组织较细,以及铁素体基体中的残余奥氏体的部分较均匀分布。对于所发明的合金,所用公式为(组成以重量%计):
TNR(℃)=887+464*[C]+363*[Al]-357*[Si]
TNR优选低于1050℃,精轧温度(FRT)优选至少为880℃。在最后一个热轧压下步骤中,钢必须仍处于奥氏体状态(即高于Ac3),以便由此通过优化最终的铁素体晶体学晶粒取向而提升r值和局部延展性。
在热轧结束后,将带材在出料台上以优选高于50℃/s的平均冷却速度冷却至卷取温度。本发明中规定的卷取温度涉及到带材主体的目标卷取温度。由于冷却经卷取的热轧带材的效果,带材的头部和尾部在卷材上的冷却速度比带材主体快。头部和尾部形成了卷材的内部和外部卷(wrap)。为了补偿热轧带材头部和尾部的较快冷却,可优选通过使用所谓的U型冷却模式,力求头部和尾部较高的卷取温度。
热轧后主体卷取温度优选低于610℃以避免表面晶界氧化,优选低于600℃,或甚至低于590或580℃。卷取温度越低,表面晶界氧化的风险越低。另外,珠光体/渗碳体开始形成为带状形态,优选避免之。此外,中部卷材的强度显示出大幅下降且合金组成可具有无法在卷材中部位置达到适当强度的风险。另一方面,过低的卷取温度导致边缘硬和在卷材头部与尾部的边缘处伸长率降低。因此,主体卷取温度为500℃或更高,优选为520℃或更高。任何不利的尾部和头部的影响可通过适当选择较高的头部和/或尾部卷取温度来补偿。
冷轧
酸洗并随后冷轧带材。由于固溶体中的合金化元素,轧制力相当大。冷轧压下率因此为至多80%、优选地至多75%且更优选至多70%以及甚至更优选至多65%。较高的压下率导致高轧制力,并因此导致较高的成型缺陷的风险以及较小的尺寸窗口。越小的尺寸窗口意味着越低的宽度与厚度比,而在带材宽度上钢的机械性质保持合适。冷轧压下率还影响了退火后最终的显微组织。如果冷轧压下率超出某个(取决于组成的)阈值,则显微组织发生形变到以至于在退火处理过程中显微组织损失形成残余奥氏体的可能性的程度。该少量残余奥氏体对于获得期望的成形性是重要的,由此冷轧压下率是重要的。另外,高的冷轧压下率导致铁素体晶粒较小,这可能对n4_6值产生消极影响。
连续退火
尽管所有先前的工艺步骤都对钢的最终性质作出贡献,但连续退火步骤是获得期望的最终性质的最后的和重要的一步。
将冷轧带材以3-30℃/s之间的平均加热速率在非氧化炉(NOF)、直接加热炉(DFF)、感应加热炉、辐射管式炉(RTF)中进行加热或由热气体进行加热。在加热过程中,重要的是:冷轧显微组织的再结晶和奥氏体形成之间的重叠是低的。在开始向奥氏体转变之前,至少有相当一部分且优选全部的变形的显微组织中已经再结晶。这是因为未再结晶的铁素体晶粒在再结晶之前回复,这些回复的晶粒中的碳倾向于向回复晶粒中的低角度晶界扩散。再结晶晶粒不会"抓住"它的碳,且碳扩散到已形成的奥氏体中,由于铁素体中的碳含量较低,再结晶晶粒倾向于先于未再结晶晶粒转变。由于退火循环是亚临界退火循环,因此这意味着最后剩余的铁素体是具有较高碳含量的未再结晶的铁素体。这些碳在退火后的冷却过程中对马氏体的形成没有贡献,碳也无助于稳定残余奥氏体,而残余奥氏体被认为对于成形性是必要的。此外,未再结晶的铁素体对成形性产生不利影响。
在炉段中预氧化带材表面,以使得在表面上形成具有足够附着力的氧化物层,这适用于镀锌。根据本发明的钢的组成遭受在热浸镀锌过程中不佳的熔融金属润湿性。通过使用例如蒸汽、HNX、水蒸气或以受控露点来氧化表面。氧化铁膜还含有一些氧化锰。其他来自合金化元素(如Si和Al)的氧化物,不溶于铁/锰氧化物,在钢/氧化物界面被排斥(rejected)。然后,在以还原性气氛还原的炉段中还原氧化物后,氧化的合金化元素不完全覆盖表面,而是位于球粒(nodule)中,这可实现较好的润湿性和涂层附着力。
最大退火温度(T_最高(T2))选在(Ac1+50℃)至(Ac3-30℃)之间。再加热过程中相转变温度(Ac1和Ac3)和冷却过程中(例如贝氏体和马氏体转变温度)能以在膨胀计中模拟热曲线的方式简单地确定,如图5至8中所示意性描述的。T_最高(T2)的优选温度范围在790℃-880℃之间。可将带材保持在T_最高(T2)持续至多300秒的均热期。优选地,均热期至多为90s。或者,T_最高(T2)可以是峰值温度,其中该温度保持高于790℃持续至多300秒的均热期,其中该温度缓慢升高到T_最高并从T_最高(T2)缓慢下降。在均热期后,将带材缓慢冷却至T_缓慢(T3),其比最高温度低9℃至100℃。在冷却过程中形成外延铁素体同时残余奥氏体富集碳。重要的是,T_缓慢(T3)(由T2冷却至T3为慢冷段)高于650℃,以便保留足够的奥氏体,其能转变为贝氏体、马氏体或进一步富集于残余奥氏体中。至少15-20%的奥氏体的最小量确保达到所需的590MPa。缓冷段(CR2)后的冷却速率在5至70℃/s之间,优选地至少30℃/秒,以防止奥氏体形成碳化物。
本发明中,有或没有进行过时效,均应实现所述性质。可采用从T_缓慢(T3)直接冷却到熔融金属浴(见图8),后续进行热浸镀锌、气体喷嘴擦拭和冷却至环境温度。任选地,热浸镀锌带材可在冷却至环境温度之前退火(镀锌层退火)。镀锌后可进行退火处理,又称镀锌层退火。
过时效可具有形成额外的贝氏体并对现有的显微组织进行回火的优点。可发生碳分配用于残余奥氏体形成。还可至少部分释放溶解在带材中的氢,带材张力也可得到部分缓解。
在替代方案中,在370至470℃之间以至少15℃/s的冷却速率(CR2),将带材从T_缓慢(T3)冷却至过时效温度(T_oa)并保持至多50秒的过时效时间,任选地,随后加热或冷却至熔融金属浴温度,通过将带材浸入熔融金属浴中热浸镀锌(如图5、6和7所示)。浸入后,将镀锌带材冷却至环境温度,或任选地退火并冷却至环境温度。
熔融金属浴可含有熔融锌、熔融锌合金、熔融铝或熔融铝合金。锌合金可包含0.3-4.0重量%的Mg和0.3-6.0重量%的Al;任选至多0.2重量%的一种或多种另外的元素、不可避免的杂质;其余为锌。优选地,锌合金涂覆层中的合金化元素含量应为1.0-2.0%的Mg和1.0-3.0%的Al,任选至多0.2%的一种或多种另外的元素、不可避免的杂质,其余为锌。在甚至更优选实施方案中,锌合金涂层包含至多1.6%Mg和1.6-2.5%Al,任选至多0.2%的一种或多种另外的元素、不可避免的杂质,其余为锌。
在另一实施方案中,为钢带材、板材或坯料提供(市售纯)铝层或铝合金层。用于热浸涂覆此种铝层的典型金属浴包含与硅合金化的铝,例如与8-11重量%的硅和至多为4重量%的铁合金化的铝,任选至多为0.2重量%的一种或多种另外的元素(如钙),不可避免的杂质,其余为铝。硅的存在是为了防止形成厚的铁金属间化合物层,其降低了黏附性和成形性。优选地,铁以1-4重量%之间的量存在,更优选至少为2重量%。
也可以以锌或锌合金涂层对经退火的带材进行电镀锌来替代热浸镀锌。任选地,可以以镍、钴或铬及其组合电镀经退火的带材。
可任选以至多0.70%的涂覆钢带材的厚度压下率将涂覆的钢带材进行平整轧制或张力平整。优选地,压下率至多为0.45%。优选地,压下率至少为0.05%。确保足够高的n4_6值的需求支配压下率最大值。压下率最小值可用于改善涂覆带材的表面质地和/或抑制屈服点伸长率(YPE)和/或提高材料的屈服强度(Rp)。
实施例
表2中显示了比较性(C)钢和本发明(I)钢的组成。表3至5提供了实验的工艺设置。应指出,表4涉及工业规模试验以及表5涉及实验室规模试验。
表2:比较性(C)和本发明(I)实施例(按质量%计,B和N按ppm计)。
*LT:实验室试验,IT:工业级试验
表3a:实验室铸造合金的热轧和冷轧工艺设置。
合金 | 工艺 | T结束 | 冷却速率(℃/s) | T卷取 | 冷轧压下率(%) |
a | 1 | >900 | ~30 | 550 | 60 |
a | 2 | >900 | ~30 | 550 | 75 |
b | 3 | >900 | ~30 | 570 | 75 |
b | 4 | >900 | ~30 | 570 | 60 |
c | 5 | >900 | ~30 | 570 | 70 |
d | 6 | >900 | ~30 | 570 | 70 |
d | 7 | >900 | ~30 | 570 | 75 |
e | 8 | >900 | ~30 | 570 | 75 |
f | 9 | >900 | ~30 | 570 | 75 |
f | 10 | >900 | ~30 | 570 | 75 |
g | 11 | >900 | ~30 | 550 | 73 |
h | 12 | >900 | ~30 | 550 | 73 |
i | 13 | >900 | ~30 | 570 | 73 |
j | 14 | >900 | ~30 | 570 | 73 |
k | 15 | >900 | ~30 | 610 | 70 |
l | 16 | >900 | ~30 | 600 | 70 |
图3b:生产线试验(line-trialed)合金的热轧和冷轧工艺设置
合金 | 工艺 | T结束 | 冷却速率(℃/s) | T卷取 | 冷轧压下率(%) |
2 | p-a | >890 | >90 | 530 | 55 |
1 | p-b | >890 | >90 | 530 | 55 |
2 | p-c | >890 | >90 | 570 | 55 |
1 | p-d | >890 | >90 | 570 | 55 |
1 | p-e | >890 | >90 | 630 | 55 |
2 | p-f | >890 | >90 | 630 | 54 |
2 | p-g | >890 | >90 | 530 | 54 |
2 | p-h | >890 | >90 | 560 | 54 |
3 | p-i | >890 | >90 | 540 | 54 |
3 | p-j | >890 | >90 | 570 | 54 |
4 | p-k | >890 | >90 | 540 | 54 |
4 | p-l | >890 | >90 | 570 | 54 |
5 | p-m | >900 | >90 | 5 | 50 |
表4:生产线试验合金的工艺条件(%CR=55%,%TR=0.45%)
*-:未确定
表5:实验室铸造合金的工艺条件
*Y:使试样经受镀锌
表6和7给出了工业和实验室规模试验的结果。应该指出的是,本发明实施例的结果全部符合如表1显示的VDA-239的要求。Rp和Rm的值符合VDA-239的Rp在330至430MPa之间和Rm在590至700MPa之间的要求。
为确定作为拉伸翻边性的判据的扩孔系数,从每块板材切割三个方形试样(90x90mm2),随后在试样中冲压出一个10mm的孔。试样的扩孔试验用上部扩孔弯边(burring)完成。由下方向上推出60°的锥形孔,当贯穿厚度的裂纹形成时测量孔径df。HEC使用以下公式计算,其中d0=10mm:
拉伸翻边性在HEC最大值的基础上作评价,当HEC>35%被视作是满意的。
附图说明
本发明现在将用下列非限制性的图的方式进行解释。
图1显示了连续退火和热浸涂覆生产线的示意图,该生产线配备有用于容纳熔融金属(在此情况下为锌)的容器(pot)。标有星号的位置为任选镀锌层退火工段(section)所处的位置。在大多数这些生产线中,热浸涂覆是任选的,因此如果需要可以避开锌容器。
图2显示了位于锌容器和顶部翻转辊之间的镀锌层退火工段的示意图。镀锌层退火工段由加热段、保温段和冷却段组成。
图3显示了拉伸试验结果的比较,其中在与带材轧制方向成0°(即纵向)、90°(横向)和45°的条件下取样。Rm和Rp相对独立于该方向,但总应变和均匀应变不是。
图4显示了合金4(L)在1/4t下的显微组织。该显微组织由大于90%的铁素体(F)>90%(浅灰色基体)、4-6%的残余奥氏体(米白色)、一些马氏体(深灰色/黑色)、一些贝氏体(灰色)以及其余(如有)的渗碳体组成。
图5至8显示了对根据本发明钢进行退火的各种(非限制性的)选择:
5:以T2下的最大T的连续退火且没有平台,热浸镀锌以及热浸镀锌温度下的过时效;
6:CA&HDG以及低于熔融金属温度的过时效,包括加热至HDG温度;
7:在T2有平台的CA&HDG以及低于熔融金属温度的过时效,包括加热至HDG温度;
8:在T2有平台的CA&HDG,没有过时效;
图9显示了冷却前热轧带材的U型卷取温度曲线的简要表示。
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Claims (16)
1.双相钢带材,按重量%计由以下组成:
以及任选地,一种或多种选自以下的元素:
Cr:至多0.500 Nb:至多0.060
Mo:至多0.400 Ti:至多0.060
V:至多0.200 Ca:至多0.0050
其余为铁和不可避免的杂质,
其中所述钢的拉伸强度Rm为580-720MPa,屈服
强度Rp为310-430MPa,其中任选地,对所述钢带材进
行i)热浸镀锌或者ii)电镀锌或者iii)电镀。
2.根据权利要求1的双相钢带材,按重量%计由以下组成:
以及任选地,一种或多种选自以下的元素:
Cr:至多0.400 Nb:至多0.050
Mo:至多0.300 Ti:至多0.050
V:至多0.150 Ca:至多0.0050
其余为铁和不可避免的杂质。
3.根据权利要求1或2的双相钢带材,按重量%计由以下组成:
以及任选地,一种或多种选自以下的元素:
Cr:至多0.120 Nb:至多0.010
Mo:至多0.015 Ti:至多0.010
V:至多0.010 Ca:至多0.0050
其余为铁和不可避免的杂质。
4.根据权利要求1至3中任一项的双相钢带材,按重量%计由以下组成:
以及任选地,一种或多种选自以下的元素:
Cr:至多0.040 Nb:至多0.010
Mo:至多0.015 Ti:至多0.010
V:至多0.010 Ca:至多0.0050
其余为铁和不可避免的杂质。
5.根据权利要求1至4中任一项的双相钢带材,按重量%计由以下组成:
以及任选地,一种或多种选自以下的元素:
Mo:至多0.015 Ti:至多0.010
V:至多0.010 Ca:至多0.0050
Nb:至多0.010
其余为铁和不可避免的杂质。
6.根据权利要求1至3中任一项的双相钢带材,按重量%计由以下组成:
以及任选地,一种或多种选自以下的元素:
Cr:至多0.150 Nb:至多0.040
Mo:至多0.200 Ti:至多0.040
V:至多0.100 Ca:至多0.0050
其余为铁和不可避免的杂质。
7.根据前述任一项权利要求的双相钢带材,其中Cr、Mo、V、Nb和Ti的一种或多种或全部仅作为杂质存在,这意味着,如果适用,Cr低于0.020重量%,Ti低于0.010重量%,V低于0.010重量%,
Mo低于0.015重量%,Nb低于0.010重量%。
8.根据前述任一项权利要求的双相钢带材,其中所述钢的拉伸强度Rm为590-720MPa和/或屈服强度Rp为320-430Mpa。
9.根据前述任一项权利要求的双相钢带材,其中所述钢的均匀伸长率Ag至少为18%,优选至少19%,更优选至少20%,甚至更优选至少22%,最优选至少24%,和/或总伸长率A80为至少26%,优选至少28%,更优选至少29%,最优选至少30%。
10.根据前述任一项权利要求的双相钢带材,其中所述钢的扩孔能力HEC至少为35%。
11.根据前述任一项权利要求的双相钢带材,其中所述钢的平均应变硬化指数或n值至少为0.16,优选至少0.18,更优选至少0.20,甚至更优选至少0.22,最优选至少0.24。
12.根据前述任一项权利要求的双相钢带材,通过进行连续退火后立即热浸涂覆,或将连续退火的带材冷却至环境温度后通过电沉积,对所述双相钢带材提供金属涂层。
13.一种用于生产经涂覆且任选平整轧制的根据权利要求1至12中的任一项的双相钢带材的方法,所述双相钢带材的拉伸强度Rm为580-720MPa,屈服强度Rp为310-430Mpa,所述方法包含以下步骤:
·通过热轧连铸板坯至厚度为2.0-4.5mm的热轧带材来提供热轧钢带材,所述连铸板坯具有按重量%计由以下构成的组成:
以及任选地一种或多种选自以下的元素:
Cr:至多0.500 Nb:至多0.060
Mo:至多0.400 Ti:至多0.060
V:至多0.200 Ca:至多0.0050
其余为铁和不可避免的杂质,
其中在带材有奥氏体显微组织的同时进行精轧;
·在精轧后以至少30℃/s的冷却速率将热轧带材冷却;
·在500-650℃范围内的卷取温度CT下,将经冷却的带材进行卷取,其中奥氏体的量大于60%且后续使卷取的带材冷却至环境温度;
·将卷取的热轧带材进行开卷,随后进行酸洗和压下率为40-80%的冷轧;
·通过如下进行冷轧带材的连续退火:
i.以至少3℃/s的加热速率HR1,将带材加热至在550-710℃范围内的温度T1,以使冷轧带材的再结晶在奥氏体形成开始前进行至少60%;
ii.以平均加热速率HR2,将带材进一步加热至在(Ac1+50℃)至(Ac3-30℃)范围内的温度T2,以形成部分奥氏体化的显微组织,优选地,其中HR2在2-20℃/s范围内;
iii.随后,或者
a.将带材在T2保持至多为300s的时间段t2,随后以0.5-12℃/s范围内的冷却速率CR1将带材缓慢冷却至在600-790℃范围内,优选为620-790℃的温度T3,使得在缓慢冷却的带材中存在16-30%的奥氏体,或者
b.以0.5-12℃/s范围内的冷却速率CR1,立即将带材从T2缓慢冷却至在600-790℃范围内,优选为620-790℃的温度T3,使得在缓慢冷却的带材中存在16-30%的奥氏体;
iv.以在5-70℃/s范围内的平均冷却速率CR2,对包含16-30%奥氏体的经缓慢冷却的带材进行快速冷却,或者
a.至范围330-470℃的温度T4,或者
b.至过时效温度T_oa持续在5-100s范围内的时间t_oa,其中T_oa在390-465℃之间;
v.以至少4℃/s的冷却速率CR3,冷却钢带材至低于300℃的温度;
·其中带材为:a).在步骤iv.和步骤v.之间通过热浸涂覆而提供有金属涂层,任选地,随后对经热浸涂覆的带材进行镀锌层退火,或b),在步骤v.后通过电沉积而提供有金属涂层;
·任选地,以至多0.70%的压下率对涂覆的钢带材进行平整轧制或张力平整;
·将涂覆的钢带材进行卷取或者将涂覆的钢带材切割为板材或坯料;
·任选地,通过如冲压、弯曲、深拉的冷成形操作或通过温压成形或热压成形使涂覆的钢带材、板材或坯料成型。
14.根据权利要求13的方法,其中应用了一种或多种以下的工艺参数:
·卷取温度低于630℃,优选低于610℃,更优选低于600℃;
·卷取温度高于520℃,优选高于530℃;
·冷轧压下率至少44%,优选至少45%,且至多70%,优选至多67%;
·T3在400至470℃之间。
15.根据权利要求13或14的方法所生产的涂覆的钢带材、板材或坯料,具有以下中的一种或多种:
·均匀伸长率Ag为至少18%;
·总伸长率A80或JIS为至少26%;
·扩孔能力HEC为至少35%;
·总伸长率减去均匀伸长率为至少7.0%,优选至少7.5%。
16.一种轿车或卡车零件,如汽车底盘或安全零件、B柱、加固(防撞)部件、前防撞梁、座椅工件、保险杠部件、车门部件、白车身零件、车架或副车架零件、蓄电池支架或容器部件,所述零件由权利要求1至12中任一项所述的钢制成。
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