CN111902552B - 合金化热浸镀锌钢板 - Google Patents

合金化热浸镀锌钢板 Download PDF

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Publication number
CN111902552B
CN111902552B CN201880091618.XA CN201880091618A CN111902552B CN 111902552 B CN111902552 B CN 111902552B CN 201880091618 A CN201880091618 A CN 201880091618A CN 111902552 B CN111902552 B CN 111902552B
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steel
steel sheet
less
layer
ferrite
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CN111902552A (zh
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佐野幸一
川田裕之
山口裕司
内田智史
今井义典
冈本力
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Nippon Steel Corp
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Nippon Steel and Sumitomo Metal Corp
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/60Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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    • C21D9/00Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C21D9/48Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00Layered products comprising a layer of metal
    • B32B15/01Layered products comprising a layer of metal all layers being exclusively metallic
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00Layered products comprising a layer of metal
    • B32B15/01Layered products comprising a layer of metal all layers being exclusively metallic
    • B32B15/013Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
    • BPERFORMING OPERATIONS; TRANSPORTING
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    • B32B15/00Layered products comprising a layer of metal
    • B32B15/04Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • BPERFORMING OPERATIONS; TRANSPORTING
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    • BPERFORMING OPERATIONS; TRANSPORTING
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    • B32B15/00Layered products comprising a layer of metal
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    • C21D1/00General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
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Abstract

一种钢板,该钢板以质量%计由下述成分构成:C:0.06%~0.22%、Si:0.50%~2.00%、Mn:1.50%~2.80%、Al:0.01%~1.00%、P:0.001%~0.100%、S:0.0005%~0.0100%、N:0.0005%~0.0100%、剩余部分:Fe和杂质,在钢板表面具有热浸镀锌层或合金化热浸镀锌层,其中,以从钢板表面起算的板厚方向的1/4板厚为中心的1/8板厚~3/8板厚的显微组织以面积率计由铁素体:15%~85%、残留奥氏体:低于5%、马氏体:15%~75%、珠光体:5%以下和剩余部分(包括为0%在内):贝氏体构成,板厚方向的厚度为20μm以下的铁素体块的数量是铁素体块的总数的50%以上,在钢板表层部形成有厚度为10μm~150μm的脱C层,所述脱C层中的铁素体的粒径为30μm以下,马氏体中的纵横比为5以上的马氏体的比例为50%以下。

Description

合金化热浸镀锌钢板
技术领域
本发明涉及适合用作压制加工的汽车用钢板的具有590MPa(优选为980MPa)以上的强度并且伸长性、扩孔性和疲劳特性也优良的高强度的合金化热浸镀锌钢板。
背景技术
近年来,对环境问题的意识提高,在汽车业界为了提高燃油效率,车体的轻量化变得重要。另一方面,为了确保碰撞时的安全,还需要提高车体强度。为了兼顾该车体轻量化和安全性的提高,使用高强度材料即可,但强度变得越高,压制成型就变得越困难。另外,为了提高压制性能,优选钢板的宽度方向的特性是均质的。
这是因为一般来说随着钢材强度增高,屈服强度增大,伸长性和扩孔性下降的缘故。另外,越是高强度,疲劳极限比越是下降,所以进一步的高强度化变得困难。
在高强度热浸镀锌钢板中,在以往的退火工序的缓慢冷却中会生成贝氏体。因此,例如在专利文献1中公开的含有以马氏体为主体的铁素体的钢板是以往已知的,但并未实现具有充分的成型性的热浸镀锌钢板。
在专利文献2中,公开了将奥氏体低温相变相的尺寸优化以改善伸长性和凸缘性的技术,但并未达到强度和伸长性的兼顾。另外,有关伸长性的改善,利用了残留奥氏体的加工诱发相变的钢板(以下称为TRIP钢)等例如公开于专利文献3和4中。
可是,就通常的TRIP钢板而言,为了抑制渗碳体的生成,大量的Si是必要的,但如果添加大量的Si,则钢板表面的热浸镀锌性恶化,所以能够适用的钢材受到限制。进而,为了确保高强度,大量的C是必要的,但如果添加大量的C,则会发生熔核开裂等焊接方面的问题。
有关钢板表面的热浸镀锌性,在专利文献5中公开了在TRIP钢中减少Si的内容,但尽管能期待热浸镀锌性和延展性的提高,但在前述的焊接性方面还存在课题。
在用比TRIP钢少的C量就能够制造的DP钢中,当Si量多时,如后述那样延展性变高。可是,与TRIP钢的情况同样,镀覆性存在课题。作为因高Si而引起的镀覆性下降的课题的解決方法,例如在专利文献6中,公开了:控制退火时的气氛,将钢板表层脱C。通过将钢板表层脱C,则Si即使超过1质量%,也能够镀覆,但由于钢板表层变软,所以会产生疲劳特性大幅劣化的问题。此外,就强度为980MPa以上的超高强度级的钢板而言,由于显微组织的强度高,所以制造时容易受到冷却和压下等宽度方向的变动的影响,存在着难以制作在宽度方向上具有均匀特性的钢板的课题。
现有技术文献
专利文献
专利文献1:日本特许第5305149号公报
专利文献2:日本特许第4730056号公报
专利文献3:日本特开昭61-157625号公报
专利文献4:日本特开2007-063604号公报
专利文献5:日本特许2000-345288号公报
专利文献6:日本特许第5370104号公报
专利文献7:国际公开第2013/047755号
发明内容
发明所要解决的课题
本发明鉴于以往技术的现状,目的是针对具有590MPa以上(优选为980MPa以上)的强度的合金化热浸镀锌钢板,以提高伸长性、扩孔性和疲劳特性以及使钢板的宽度方向的特性均匀化为课题,提供解决该课题的合金化热浸镀锌钢板。
用于解决课题的手段
本发明者们对解决上述课题的方法进行了深入研究,得到了以下的认识。
(w)冷轧后,在2相区或单相区进行热处理后,进行冷却,或者在比贝氏体的生成温度高的温度下保持以抑制贝氏体相变,贝氏体分率低,并且通过形成铁素体与马氏体的复合组织而能够实现延展性的提高。
(x)通过Si的添加而稳定地提高铁素体分率,提高延展性,与此同时通过固溶强化而能够实现强度的提高,因而能够确保优良的强度-延展性平衡。
(y)对于Si添加所引起的镀覆性的下降,是通过以往的气氛控制来处理,如果将气氛控制中生成的阻碍疲劳特性的脱C层中的马氏体设定为纵横比小的马氏体,则能够提高疲劳特性。在热轧钢板的酸洗前后,如果对热轧钢板实施平整(leveller),则能够将脱C层中的马氏体设定为纵横比小的马氏体。
(z)在实施平整的同时,在冷轧后的退火工序中,将所需要的温度范围的加热速度控制为所需要的范围以抑制铁素体的分布不均,并且将铁素体粒子聚集而成的铁素体块均质化达到无害的形态,则扩孔性就能提高,伸长性和扩孔性能够兼顾,并且能够使包括镀覆状态在内的钢板的宽度方向的特性均匀化。
本发明是基于上述认识而完成的,其要旨如下所述。
(1)一种合金化热浸镀锌钢板,钢板的成分组成以质量%计由下述成分构成:
C:0.06%~0.22%、
Si:0.50%~2.00%、
Mn:1.50%~2.80%、
Al:0.01%~1.00%、
P:0.001%~0.100%、
S:0.0005%~0.0100%、
N:0.0005%~0.0100%、
Ti:0%~0.10%、
Mo:0%~0.30%、
Nb:0%~0.050%、
Cr:0%~1.00%、
B:0%~0.0050%、
V:0%~0.300%、
Ni:0%~2.00%、
Cu:0%~2.00%、
W:0%~2.00%、
Ca:0%~0.0100%、
Ce:0%~0.0100%、
Mg:0%~0.0100%、
Zr:0%~0.0100%、
La:0%~0.0100%、
REM:0%~0.0100%、
Sn:0%~1.000%、
Sb:0%~0.200%、
剩余部分:Fe和杂质,
在钢板表面具有合金化热浸镀锌层,其特征在于,
以从钢板表面起算的板厚方向的1/4板厚为中心的1/8板厚~3/8板厚的范围的显微组织以面积率计由铁素体:15%~85%、残留奥氏体:低于5%、马氏体:15%~75%、珠光体:5%以下和剩余部分(包括为0%在内):贝氏体构成,
所述板厚方向的厚度为20μm以下的铁素体块的数量是铁素体块的总数的50%以上,
在钢板表层部形成有厚度为10μm~150μm的脱C层,
所述脱C层中的铁素体的粒径为30μm以下,马氏体中的纵横比为5以上的马氏体的比例为50%以下。
(2)根据前述(1)所述的合金化热浸镀锌钢板,其特征在于,在所述合金化热浸镀锌层与所述脱C层之间还具有平均厚度为0.1μm~5.0μm的微细化层。
(3)根据前述(1)或(2)所述的合金化热浸镀锌钢板,其特征在于,所述合金化热浸镀锌层中的宽度方向的Fe浓度之差以质量%计为低于1.0%,并且宽度方向的所述纵横比为5以上的马氏体的比例之差为10%以下。
(4)根据前述(1)~(3)中任一项所述的合金化热浸镀锌钢板,其特征在于,所述成分组成以质量%计含有下述成分中的1种或2种以上:
Ti:0.01%~0.10%、
Mo:0.01%~0.30%、
Nb:0.005%~0.050%、
Cr:0.01%~1.00%、
B:0.0002%~0.0050%、
V:0.001%~0.300%、
Ni:0.01%~2.00%、
Cu:0.01%~2.00%、
W:0.01%~2.00%、
Ca:0.0001%~0.0100%、
Ce:0.0001%~0.0100%、
Mg:0.0001%~0.0100%、
Zr:0.0001%~0.0100%、
La:0.0001%~0.0100%、
REM:0.0001%~0.0100%、
Sn:0.001%~1.000%、
Sb:0.001%~0.200%。
发明效果
根据本发明,可以提供伸长性、扩孔性和疲劳特性优良并且钢板的宽度方向的特性被均匀化的高强度的合金化热浸镀锌钢板。
具体实施方式
就本实施方式的合金化热浸镀锌钢板而言,钢板的成分组成以质量%计由下述成分构成:
C:0.06%~0.22%、
Si:0.50%~2.00%、
Mn:1.50%~2.80%、
Al:0.01%~1.00%、
P:0.001%~0.100%、
S:0.0005%~0.0100%、
N:0.0005%~0.0100%、
Ti:0%~0.10%、
Mo:0%~0.30%、
Nb:0%~0.050%、
Cr:0%~1.00%、
B:0%~0.0050%、
V:0%~0.300%、
Ni:0%~2.00%、
Cu:0%~2.00%、
W:0%~2.00%、
Ca:0%~0.0100%、
Ce:0%~0.0100%、
Mg:0%~0.0100%、
Zr:0%~0.0100%、
La:0%~0.0100%、
REM:0%~0.0100%、
Sn:0%~1.000%、
Sb:0%~0.200%、
剩余部分:Fe和杂质,
在钢板表面具有合金化热浸镀锌层,其特征在于,
以从钢板表面起算的板厚方向的1/4板厚为中心的1/8板厚~3/8板厚的范围的显微组织以面积率计由铁素体:15%~85%、残留奥氏体:低于5%、马氏体:15%~75%、珠光体:5%以下和剩余部分(包括为0%在内):贝氏体构成,
所述板厚方向的厚度为20μm以下的铁素体块的数量是铁素体块的总数的50%以上,
在钢板表层部形成有厚度为10μm~150μm的脱C层,
所述脱C层中的铁素体的粒径为30μm以下,马氏体中的纵横比为5以上的马氏体的比例为50%以下。
以下,对本实施方式的合金化热浸镀锌钢板和本实施方式制造方法依次进行说明。
在以往的DP(Dual Phase[二相])型的超高强度钢(DP钢)中,一般是通过适当调整铁素体和马氏体等的组织分率来控制钢的材质。获知:如果提高铁素体分率,则延展性提高,但铁素体如果增加,则(a)软质组织的分率的增加引起的强度下降、进而(b)铁素体粒的块状化引起的延展性的下降会成为原因,而不能获得所需要的强度-延展性平衡。
就本实施方式的合金化热浸镀锌钢板而言,本发明者们为了提高伸长性、扩孔性和疲劳特性,着眼于铁素体的特性和存在形态以及其它组织的特性和存在状态而进行了深入研究。结果发现,就DP钢(还包括含有少量残留奥氏体的情况)而言,通过软质的铁素体的硬质化和形态控制,从而即使提高强度,延展性和扩孔性也不会下降。以下进行说明。
获知:为了减小上述(a)的强度下降的程度,如果将钢的Si量设定为0.5%,则强度-延展性-扩孔性平衡提高。尽管其理由还不明确,但据认为其要因如下:(a1)将铁素体固溶强化了,相应地可以降低马氏体分率,裂纹的起点减少,局部延展性提高;和(a2)通过铁素体的固溶强化,塑性不稳定区域减少,均匀伸长性提高等。
可是,另一方面,因Si的增量而使表层的氧化皮增加,镀覆性下降,镀覆钢板的制造变得困难。因此,使用了进行气氛控制、不是在钢板表层而是在钢板内部形成氧化物、确保良好的镀覆性的方法。可是,该方法中,由于在钢板内部形成氧化物的同时,在钢板表层进行脱C,所以钢板表层软质化,疲劳亀裂变得容易传播,疲劳极限比大幅减少。
本发明者们在对解决本发明的课题的方法进行深入研究的过程中发现:关于热轧结束后供给平整的钢板和对钢板表层进行了研削的钢板,疲劳特性良好。另外判明,在退火工序中,如果对钢板实施弯曲加工,则疲劳特性进一步提高。
其理由还不明确,但据认为要因如下:在钢板表层形成的脱C层中存在的马氏体的纵横比变小、以及表层组织微细化,疲劳的龟裂传播变得不易发生。
如上所述,Si的添加使得强度-延展性平衡提高,但即使铁素体分率增加,强度-延展性平衡的提高程度和强度-扩孔性平衡的提高程度也小。
一般来说,软质相的铁素体在DP钢中作为承担变形的存在,在低形变区域有大的变形量。不过,存在于马氏体附近的铁素体在变形时,受到马氏体的约束,变形量小。
本发明者们着眼于该现象,对约束铁素体的变形的最优条件进行了研究。于是,通过在维持能够获得伸长性的提高的铁素体分率的同时,将铁素体受到的来自相邻的硬质相(马氏体)的变形约束状态优化,获得伸长性和扩孔性的兼顾。
迄今为止,显微组织控制的主流是研究结晶晶界与特性的相关性。如果是单相钢,显然特性不同的晶界的影响大,但本发明者们在对铁素体和马氏体那样的特性差异大的组织共存的复合组织研究扩孔性的提高的情况下,想到单个组织中的结晶粒径没有大的意义,而同一相的存在形态才对特性有大的贡献。
于是,本发明者们基于上述想法,确认了用与硬质相(贝氏体、马氏体)相邻的铁素体的块(具有多个铁素体粒子的被硬质相包围的铁素体粒子的集合体,以下有时称作“铁素体块”。)进行评价的重要性,发现了约束铁素体的变形的最优条件。
在上述优化条件下材质得到改善的机理还不明确,但据认为,铁素体块的板厚方向的厚度如果薄的话,则通过硬质相的变形拘束,铁素体的变形被更加约束,铁素体疑似硬化,对强度的维持起到有意义的作用,并且局部的巨大变形可抑制裂纹的发生,对扩孔性的提高起到有效的作用。
铁素体块的厚度是在被硬质相包围的各个铁素体块中与板面的垂直方向的厚度的最大值。
而且,由于伸长性依赖于铁素体的变形能力,与铁素体分率成线性相关性,所以通过控制铁素体分率和铁素体的存在形态,就能够使伸长性和扩孔性兼顾。
本实施方式的合金化热浸镀锌钢板是根据本发明者们发现的以上的认识而完成的,以下对本实施方式的合金化热浸镀锌钢板的特征要件进行说明。
首先,对成分组成的限定理由进行说明。以下,成分组成中的%是指质量%。
成分组成
C:0.06%~0.22%
C是提高马氏体的硬度、有助于强度的提高的元素。C如果低于0.06%,则无法充分获得添加效果,因此C设定为0.06%以上。优选为0.07%以上。另一方面,C如果超过0.22%,则会促进渗碳体的生成,扩孔性和焊接性下降,因此C设定为0.22%以下。C优选为0.17%以下。
Si:0.50%~2.00%
Si是通过固溶强化而在不会使延展性下降的情况下有助于强度和疲劳强度的提高的元素。Si如果低于0.50%,则无法充分获得添加效果,因此Si设定为0.50%以上。优选为0.80%以上,更优选为1.00%以上。另一方面,Si如果超过2.00%,则延展性和点焊性下降,因此Si设定为2.00%以下。Si优选为1.80%以下,更优选为1.60%以下。
Mn:1.50%~2.80%
Mn是通过固溶强化和淬透性的提高而有助于强度提高的元素。Mn如果低于1.50%,则无法充分获得添加效果,因此Mn设定为1.50%以上。优选为1.80%以上。另一方面,Mn如果超过2.80%,则焊接性下降,并且铁素体的生成受到抑制而延展性下降,另外,偏析扩大,扩孔性也下降,因此Mn设定为2.80%以下。Mn优选为2.50%以下。
Al:0.01%~1.00%以下
Al是脱氧所必要的元素,并且是抑制有害的碳化物的生成、有助于伸长性和扩孔性的提高的元素。特别是在低Si系的成分体系中,是在不会使延展性下降的情况下有助于化成处理性的提高的元素。
Al如果低于0.01%,则无法充分获得添加效果,因此Al设定为0.01%以上。另一方面,Al如果超过1.00%,则添加效果饱和,并且化成处理性和点焊接性下降,因此Al设定为1.00%以下。从化成处理的提高的观点出发,优选为0.80%以下。
P:0.001%~0.100%
P是有助于强度的提高的元素,并且是通过与Cu的共存而提高耐蚀性的元素。P如果低于0.001%,则无法充分获得添加效果,另外,制钢成本大幅上升,因此P设定为0.001%以上。从制钢成本的观点出发,P优选为0.010%以上。另一方面,P如果超过0.100%,则焊接性和加工性下降,因此P设定为0.100%以下。当耐蚀性不成问题、而重视加工性时,P优选为0.050%以下。
S:0.0005%~0.0100%
S是形成作为裂纹的起点的硫化物(MnS等)、阻碍扩孔性和全伸长性的元素。S越少越好,但如果将S减少至低于0.0005%,则制钢成本大幅上升,因此S设定为0.0005%以上。另一方面,S如果超过0.0100%,则扩孔性和全伸长性显著下降,因此S设定为0.0100%以下。S优选为0.0060%以下。
N:0.0005%~0.0100%
N是阻碍加工性的元素。另外,N是如下的元素:如果与Ti和/或Nb共存,则会形成阻碍伸长性和扩孔性的氮化物(TiN和/或NbN),从而减少Ti和/或Nb的有效量。
N越少越好,但如果将N减少至低于0.0005%,则制钢成本大幅上升,因此N设定为0.0005%以上。另一方面,N如果超过0.0100%,则加工性、伸长性和扩孔性显著下降,因此N设定为0.0100%以下。N优选为0.0060%以下。
本发明的镀覆钢板的成分组成中,以特性提高为目的,还可以适当含有下述成分中的1种或2种以上:Ti:0.01%~0.10%、Mo:0.01%~0.30%、Nb:0.005%~0.050%、Cr:0.01%~1.00%、B:0.0002%~0.0050%、V:0.001%~0.300%、Ni:0.01%~2.00%、Cu:0.01%~2.00%、W:0.01%~2.00%、Ca:0.0001%~0.0100%、Ce:0.0001%~0.0100%、Mg:0.0001%~0.0100%、Zr:0.0001%~0.0100%、La:0.0001%~0.0100%、REM:0.0001%~0.0100%、Sn:0.001%~1.000%、Sb:0.001%~0.200%。
Ti:0.01%~0.10%
Ti是使再结晶延迟、有助于未再结晶铁素体的形成、并且形成碳化物和/或氮化物、有助于强度的提高的元素。
Ti如果低于0.01%,则无法充分获得含有效果,因此Ti优选为0.01%以上。另一方面,如果超过0.10%,则成型性下降,因此Ti设定为0.10%以下。Ti优选为0.05%以下。
Mo:0.01%~0.30%
Mo是使再结晶延迟、有助于未再结晶铁素体的形成、并且提高淬透性、有助于马氏体分率的控制的元素。另外,Mo是如下的元素:偏析于晶界,在焊接时抑制锌侵入焊接部的组织内,有助于焊接时的裂纹防止,并且还有助于退火工序的冷却中的珠光体的生成抑制。
Mo如果低于0.01%,则无法充分获得含有效果,因此Mo优选为0.01%以上。Mo更优选为0.04%以上。另一方面,Mo如果超过0.30%,则成型性劣化,因此Mo设定为0.30%以下。Mo优选为0.25%以下。
Nb:0.005%~0.050%
Nb是使再结晶延迟、有助于未再结晶铁素体的形成、并且形成碳化物和/或氮化物、有助于强度的提高的元素。Nb如果低于0.005%,则无法充分获得含有效果,因此Nb优选为0.005%以上。Nb更优选为0.010%以上。另一方面,Nb如果超过0.050%,则成型性下降,因此Nb设定为0.050%以下。Nb优选为0.030%以下。
Cr:0.01%~1.00%
Cr是使再结晶延迟、有助于未再结晶铁素体的形成、并且有助于退火工序的冷却中的珠光体的生成抑制的元素。Cr如果低于0.01%,则无法充分获得含有效果,Cr优选为0.01%以上。Cr更优选为0.05%以上。另一方面,Cr如果超过1.00%,则成型性下降,因此Cr设定为1.00%以下。Cr优选为0.50%以下。
B:0.0002%~0.0050%、
B是使再结晶延迟、有助于未再结晶铁素体的形成、并且提高淬透性、有助于马氏体分率的控制的元素。另外,B是如下的元素:偏析于晶界,在焊接时抑制锌侵入焊接部的组织内,有助于焊接时的裂纹防止,并且还有助于退火工序的冷却中的珠光体的生成抑制。
B如果低于0.0002%,则无法充分获得含有效果,因此B优选为0.0002%以上。B更优选为0.0010%以上。另一方面,B如果超过0.0050%,成型性下降,因此B设定为0.0050%以下。B优选为0.0025%以下。
V:0.001%~0.300%
V是通过析出物强化、由铁素体晶粒的生长抑制产生的细粒强化和由再结晶的抑制产生的位错强化而有助于强度提高的元素。V如果低于0.001%,则无法充分获得强度提高效果,因此V优选为0.001%以上。V更优选为0.010%以上。另一方面,V如果超过0.300%,则碳氮化物会过剩析出,成型性下降,因此V设定为0.300%以下。V优选为0.150%以下。
Ni:0.01%~2.00%
Ni是抑制高温下的相变、有助于强度提高的元素。Ni如果低于0.01%,则无法充分获得含有效果,因此Ni优选为0.01%以上。Ni更优选为0.10%以上。另一方面,Ni如果超过2.00%,则焊接性下降,因此Ni设定为2.00%以下。Ni优选为1.20%以下。
Cu:0.01%~2.00%
Cu是作为微细的粒子存在、并有助于强度提高的元素。Cu如果低于0.01%,则无法充分获得含有效果,因此Cu优选为0.01%以上。Cu更优选为0.10%以上。另一方面,Cu如果超过2.00%,则焊接性下降,因此Cu设定为2.00%以下。Cu优选为1.20%以下。
W:0.01%~2.00%
W是抑制高温下的相变、有助于强度提高的元素。W如果低于0.01%,则无法充分获得含有效果,因此W优选为0.01%以上。W更优选为0.10%以上。另一方面,W如果超过2.00%,则热加工性下降,生产率下降,因此W设定为2.00%以下。W优选为1.20%以下。
Ca:0.0001%~0.0100%
Ce:0.0001%~0.0100%
Mg:0.0001%~0.0100%
Zr:0.0001%~0.0100%
La:0.0001%~0.0100%
REM:0.0001%~0.0100%
Ca、Ce、Mg、Zr、La和REM是有助于成型性的提高的元素。Ca、Ce、Mg、Zr、La和REM分别如果低于0.0001%,则无法充分获得含有效果,因此任何元素都优选为0.0001%以上。更优选的是,任何元素都为0.0010%以上。
另一方面,Ca、Ce、Mg、Zr、La和REM分别如果超过0.0100%,则延展性有可能下降,任何元素都设定为0.0100%以下。优选任何元素都为0.0070%以下。
此外,REM是稀土金属的简写,是指属于镧系的元素。REM和Ce大多以混合稀土的形态含有,但除了La和Ce以外,有时还复合含有镧系元素。作为杂质,即使含有La和Ce以外的镧系元素,特性也不会受到阻碍。另外,也可以含有金属La和Ce。
Sn:0.001%~1.000%
Sn是抑制组织的粗大化、有助于强度提高的元素。Sn如果低于0.001%,则无法充分获得含有效果,因此Sn优选为0.001%以上。Sn更优选为0.010%以上。另一方面,Sn如果超过1.000%,则钢板过度脆化,轧制时钢板有可能断裂,因此Sn设定为1.000%以下。Sn优选为0.500%以下。
Sb:0.001%~0.200%
Sb是抑制组织的粗大化、有助于强度提高的元素。Sb如果低于0.001%,则无法充分获得含有效果,因此Sb优选为0.001%以上。Sb更优选为0.005%以上。另一方面,Sb如果超过0.200%,则钢板过度脆化,轧制时钢板有可能断裂,因此Sb设定为0.200%以下。Sb优选为0.100%以下。
在本实施方式的合金化热浸镀锌钢板的成分组成中,除上述元素外的剩余部分是Fe和杂质。杂质是从钢原料和/或在制钢过程中不可避免地混入的元素,是在不阻碍本实施方式的合金化热浸镀锌钢板的特性的范围内容许存在的元素。
例如,Ti、Mo、Nb、Cr、B、V、Ni、Cu、W、Ca、Ce、Mg、Zr、La、REM、Sn和Sb均只要是低于本实施方式的合金化热浸镀锌钢板的成分组成所规定的下限值的微量,就容许作为不可避免的杂质。
另外,作为杂质,H、Na、Cl、Sc、Co、Zn、Ga、Ge、As、Se、Y、Tc、Ru、Rh、Pd、Ag、Cd、In、Te、Cs、Ta、Re、Os、Ir、Pt、Au和Pb的合计容许在0.010%以下的范围。
下面,对本实施方式的合金化热浸镀锌钢板的显微组织进行说明。
本实施方式的合金化热浸镀锌钢板通过控制铁素体和马氏体的分率和形态,并且控制表层组织,能够以高水平获得强度与延展性、扩孔性和疲劳特性各自的平衡。
一般来说,如果提高铁素体分率,则延展性提高,但由于铁素体是软质的,所以强度和扩孔性下降。本实施方式中,由于用硬质相来约束软质相的变形,所以能够有效利用铁素体的特性和功能。
显微组织的限定范围:以从钢板表面起算的板厚方向的1/4板厚为中心的1/8板厚~3/8板厚
以从钢板表面起算的板厚方向的1/4板厚为中心的1/8板厚~3/8板厚的显微组织主要承担钢板全体的机械特性。因此,在本实施方式中,规定组织分率的板厚方向的范围设定为“以1/4板厚为中心的1/8板厚~3/8板厚”。此外,组织分率的%为面积率。
铁素体:15%~85%
铁素体如果低于15%,则难以确保所需要的伸长性,因此铁素体设定为15%以上。铁素体优选为20%以上。另一方面,铁素体如果超过85%,则难以确保所需要的强度,因此铁素体设定为85%以下。铁素体优选为75%以下。
珠光体:5%以下
珠光体如果超过5%,则伸长性和扩孔性下降,因此珠光体设定为5%以下。下限包括0%。
残留奥氏体:低于5%
从确保伸长性的观点出发,辅助地利用残留奥氏体是有效的,但残留奥氏体根据使用条件而有可能成为氢裂纹的原因,因此残留奥氏体设定为低于5%。下限包括0%。
马氏体:15%~75%
马氏体如果低于15%,则难以确保所需要的强度,因此马氏体设定为15%以上。马氏体优选为20%以上。另一方面,马氏体如果超过75%,则难以确保所需要的伸长性,因此马氏体设定为75%以下。马氏体优选为65%以下。
贝氏体:剩余部分
贝氏体作为调整马氏体的分率的组织,可以作为剩余部分组织而生成,也可以为0%。为了确保铁素体和马氏体各自的下限分率,剩余部分的上限为70%。
下面,对面积率的算出方法进行说明。
将平行于轧制方向的板厚断面作为观察面来采取试样,研磨观察面,进行硝酸乙醇腐蚀,用光学显微镜或扫描电子显微镜(scanning electron microscopy:SEM)进行观察。使用拍摄的图像、或机器内的图像解析软件来算出面积率。面积率以如下的方式得到:将图像中的1个视场设定为纵200μm、横200μm以上,对10个以上的不同视场分别进行图像解析,算出各组织的面积率并求出平均值,将平均值作为面积率。
使用上述图像,测定铁素体块的厚度。在上述视场中,将铁素体块的板厚方向上的最长的厚度作为铁素体块的厚度。
能够使用上述图像来算出后述的脱C层中的马氏体的纵横比。在马氏体的厚度上,测定长的部分和短的部分,将用长的部分的厚度除以短的部分的厚度而得到的值作为纵横比。进而,算出上述纵为200μm、横为200μm以上的面积的视场中的马氏体中的纵横比为5以上的马氏体的个数比例。
此外,马氏体在用硝酸乙醇腐蚀难以判别时,也可以利用平整蚀刻。
下面,对残留奥氏体的测定方法进行说明。
残留奥氏体的面积率可以用电子背散射衍射(electron backscatterdiffraction:EBSD)法或X射线衍射法来测定。当用X射线衍射法测定时,使用Mo-Kα射线,测定铁素体的(111)面的衍射强度(α(111))、残留奥氏体的(200)面的衍射强度(γ(200))、铁素体的(211)面的衍射强度(α(211))和残留奥氏体的(311)面的衍射强度(γ(311)),按照下式可以算出残留奥氏体的面积率(fA)。
fA=(2/3){100/(0.7×α(111)/γ(200)+1)}+(1/3){100/(0.78×α(211)/γ(311)+1)}
板厚方向的铁素体块的厚度:20μm以下
上述厚度为20μm以下的铁素体块的数量:铁素体块的总数的50%以上
在本实施方式的合金化热浸镀锌钢板中,在确保所需要的扩孔性方面,铁素体块的厚度和数量是重要的。
铁素体块的板厚方向的厚度如果超过20μm,则相邻的硬质相(马氏体、贝氏体)对铁素体块的约束不能充分发生作用,在铁素体块的中心部,发生过度的变形,容易达到变形极限,在钢板中发生局部的变形,不能获得扩孔性的提高效果,因此铁素体块的板厚方向的厚度设定为20μm以下。优选为16μm以下。
板厚方向的厚度为20μm以下的铁素体块的数量如果低于铁素体块的总数的50%,则难以以显著不同的水平获得上述扩孔性的提高效果,因此板厚方向的厚度为20μm以下的铁素体块的数量设定为铁素体块的总数的50%以上。优选为70%以上。
钢板表层部的脱C层的厚度:10μm~150μm
脱C层是通过钢板表层的C与气氛中的氧反应而形成CO或CO2,并逃逸到气氛中而形成的。在C减少的表层部,由于难以获得硬质组织,所以与钢板内部相比成为软质组织。
脱C层的厚度如下确定。
在板厚方向上,以1/4板厚为中心,在1/8板厚~3/8板厚的范围内测定硬度,将平均值设定为钢板的硬度的基准硬度。从钢板的1/8板厚朝着钢板表层测定硬度,插入基准硬度的0.9以下的点,将从0.9以下的点至钢板表面的距离设定为脱C层的厚度。
在本实施方式的合金化热浸镀锌钢板中,在确保所需要的扩孔性和疲劳特性的方面,钢板表层部中的厚度为10μm~150μm的脱C层的存在是重要的。后面对脱C层的形成进行叙述。
脱C层的厚度如果低于10μm,则镀覆性和扩孔性下降,因此脱C层的厚度设定为10μm以上。优选为20μm以上,更优选为30μm以上。另一方面,脱C层的厚度如果超过150μm,则即使控制脱C层中的马氏体的形态,疲劳特性也不会提高,而且疲劳特性和强度下降,因此脱C层的厚度设定为150μm以下。优选为120μm以下,更优选为100μm以下。
在上述脱C层中,从确保所需要的疲劳特性的观点出发,铁素体的粒径设定为30μm以下,并且马氏体中的纵横比为5以上的马氏体的比例设定为50%以下。以下进行说明。
脱C层中的铁素体的粒径:30μm以下
在脱C层中,铁素体的粒径如果超过30μm,则疲劳特性下降,因此铁素体的粒径设定为30μm以下。疲劳特性下降的理由还不明确,但据认为,这是因为铁素体的粒径如果大的话,则相邻的马氏体的分率变小,疲劳龟裂变得容易传播的缘故。铁素体的粒径越小越优选,优选为25μm以下,更优选为20μm以下。这里,铁素体的粒径表示平均粒径。例如,观察面积为40000μm2以上的区域,写入与轧制方向平行的线段,将用线段的长度的合计除以线段与晶界的交点的数量而得到的平均值作为铁素体粒径。
纵横比为5以上的马氏体的比例:50%以下
就纵横比为5以上的马氏体而言,据认为疲劳龟裂沿着马氏体发生,并且容易传播,所以就本实施方式的合金化热浸镀锌钢板而言,通过减少脱C层中的马氏体中的纵横比为5以上的比例来实现疲劳特性的进一步提高。
脱C层中的马氏体中的纵横比为5以上的比例如果超过50%,则疲劳特性显著下降,因此上述比例设定为50%以下。优选为40%以下、更优选为30%以下。另外,为了使宽度方向的特性更加均匀化,宽度方向的纵横比为5以上的马氏体的比例之差优选为10%以下。更优选为6%以下。
下面,对存在于脱C层与合金化热浸镀锌层之间的微细化层进行说明。微细化层是在如后述那样退火时在控制为特定的气氛的条件下通过进行氧化或脱碳反应而生成的层。因此,构成微细化层的组织除了氧化物和夹杂物粒子以外实质上铁素体相是主体。微细化层与脱C层的边界是微细化层中的铁素体的平均粒径为低于脱C层铁素体平均粒径的1/2时的边界。
微细化层的平均厚度优选设定为0.1μm~5.0μm。微细化层的平均厚度如果低于0.1μm,则无法获得抑制断裂发生和伸展的效果,无法得到镀覆粘附性的改善效果。如果超过5.0μm,则镀覆层的合金化(Zn-Fe合金生成)会发展,合金化热浸镀锌层中的Fe含量变大,镀覆粘附性下降。更优选的微细化层的平均厚度为0.2μm~4.0μm、进一步优选为0.3μm~3.0μm。
微细化层的平均厚度用以下所示的方法测定。从合金化热浸镀锌钢板上采取将平行于母材钢板的轧制方向的断面作为观察面的试样。将试样的观察面用CP(Cross sectionpolisher;剖面研磨仪)装置进行加工,用FE-SEM(Field Emission Scanning ElectronMicroscopy;场发射扫描电镜)在5000倍下观察反射电子图像,并进行测定。
在微细化层中含有Si和Mn中的1种以上的氧化物。作为氧化物,例如可以列举出选自SiO2、Mn2SiO4、MnSiO3、Fe2SiO4、FeSiO3、MnO中的1种以上。该氧化物如后所述在退火时在特定的温度区域形成于母材钢板内。由于利用氧化物粒子来使母材钢板的表层中的铁素体相结晶的生长被抑制,因而会形成微细化层。
下面,对合金化热浸镀锌层进行说明。
合金化热浸镀锌层是将在通常的镀覆条件下形成的热浸镀锌层(还包括将锌合金进行热浸镀而形成的镀覆层)在通常的合金化处理条件下进行合金化而得到的镀覆层。
合金化热浸镀锌层的镀覆附着量并不特别地限定为特定的量,但从确保所需要的耐蚀性的观点出发,单面附着量优选为5g/m2以上。
另外,为了减小外观的不均匀,合金化热浸镀锌层的宽度方向的Fe浓度之差以质量%计优选设定为低于1.0%。更优选为0.7%以下。
就本实施方式的合金化热浸镀锌钢板而言,以改善涂装性和焊接性为目的,在合金化热浸镀锌层的上面还可以实施上层镀覆(例如镀Ni)。另外,以改善合金化热浸镀锌层的表面性状为目的,还可以实施各种处理,例如铬酸盐处理、磷酸盐处理、润滑性提高处理、焊接性提高处理等。
本实施方式的合金化热浸镀锌钢板的拉伸强度优选为590MPa以上。拉伸强度为590MPa以上的高强度钢板适合作为汽车用构件的素材钢板。
本实施方式的合金化热浸镀锌钢板的板厚并不特别地限定为特定的板厚范围,但优选为0.1~11.0mm。板厚为0.1~11.0mm的高强度薄钢板适合作为通过压制加工而制造的汽车用构件的素材钢板。另外,上述板厚的高强度薄钢板可以用薄板制造生产线容易地制造。
下面,对本实施方式制造方法进行说明。
制造本实施方式的合金化热浸镀锌钢板的制造方法例如特征在于:
(a)将本实施方式的合金化热浸镀锌钢板的成分组成的铸造板坯加热至1100℃以上并供给至热轧,在Ar3点以上的最终温度下结束热轧,将热轧结束后的热轧钢板在680℃以下的温度区域进行卷取,
(b)将卷取的热轧钢板在酸洗前和/或后对热轧钢板实施平整,然后,供给至轧制率为30%~70%的冷轧,制成冷轧钢板,
(c)对冷轧钢板进行如下处理,
(c-1)在由H2为1~10体积%、以及剩余部分为N2、H2O和O2中的1种或2种以上构成的在预热带和均热带中的水分压与氢分压之比以log(PH2O/PH2)计为-1.7~-0.2的气氛中,
(c-2)将500℃以上至最高到达温度-50℃的温度区域的平均加热速度设定为1℃/秒以上,加热至720℃~900℃的最高到达温度并保持30秒~30分钟,保持后,
(c-3)实施下述的退火:从最高到达温度-50℃的温度开始,以满足下述式(A)的X(℃/秒)以上的平均冷却速度冷却至满足下述式(B)的冷却停止温度T(℃),同时进行1次以上的弯曲半径为800mm以下的弯曲加工,
(d)对退火后的钢板实施热浸镀锌,然后对热浸镀锌实施合金化处理。
X≥(Ar3-350)/10a (A)
a=0.6[C]+1.4[Mn]+1.3[Cr]+3.7[Mo]-100[B]-0.87
T≥730-350[C]-90[Mn]-70[Cr]-83[Mo] (B)
[元素]:元素的质量%
以下、对本实施方式制造方法的工序条件进行说明。
(a)工序
铸造板坯的加热温度:1100℃以上
最终热轧温度:Ar3点以上
卷取温度:680℃以下
按照常规方法准备本实施方式的合金化热浸镀锌钢板的成分组成的铸造板坯。在将铸造板坯暂时冷却的情况下,加热至1100℃以上,并供给至热轧。铸造板坯的加热温度如果低于1100℃,则铸造板坯的均质化和碳氮化物的溶解变得不充分,导致强度下降和加工性下降,因此铸造板坯的加热温度设定为1100℃以上。优选为1150℃以上。
另一方面,铸造板坯的加热温度如果超过1300℃,则制造成本上升,同时生产率下降,并且初期的奥氏体的粒径局部地变大而形成混粒组织,延展性有可能下降。因此,铸造板坯的加热温度优选为1300℃以下。更优选为1250℃以下。
铸造板坯也可以在刚刚铸造了铸造板坯后的高温(1100℃以上、优选为1300℃以下)下直接供给至热轧。
热轧在Ar3点以上的温度下结束。最终热轧温度如果低于Ar3点,则在下面的冷轧中,钢板有可能发生裂纹,材质下降,因此最终热轧温度设定为Ar3点以上。优选为(Ar3+15)℃以上。
最终热轧温度可以在Ar3点以上的温度范围内,按照热轧钢板的成分组成、材质等来适当设定,所以最终热轧温度的上限不特别设定。
此外,Ar3点可以按照下述式来算出。
Ar3=901-325×[C]+33×[Si]+287×[P]+40×[Al]-92([Mn]+[Mo])
[元素]:元素的质量%
将热轧结束后的热轧钢板在680℃以下的温度下卷取。卷取温度如果超过680℃,则渗碳体粗大化,退火时间变长,另外,表层脱C层中的铁素体的粒径会超过30μm,因此卷取温度设定为680℃以下。优选为630℃以下,更优选为580℃以下。
卷取温度的下限没有特别限定,但如果低于400℃,则热轧钢板的强度过度上升,冷轧中的轧制负荷上升,因此卷取温度优选为400℃以上。
(b)工序
轧制率:30%~70%
将热轧钢板进行酸洗,除去氧化皮层后,将热轧钢板供给至冷轧。轧制率如果低于30%,则难以形成再结晶核,由于回复粒的粗大化而使晶粒开始生长,再结晶变得不充分,延展性下降,另外,板厚方向的厚度为20μm以下的铁素体块的数量比例减少,因而轧制率设定为30%以上。
为了减小未再结晶铁素体的面积率,进一步提高钢板的伸长性,轧制率越高越为优选,但由于随着轧制率的上升轧制荷重也上升,所以轧制率设定为70%以下。轧制荷重如果高的话,则钢板的形状精度有可能下降,所以轧制率优选为65%以下。
另外,为了在宽度方向上提高组织的均匀性,在将热轧钢板进行酸洗前和/或后,对热轧钢板实施平整。通过该处理,可以减少脱C层中的马氏体中的纵横比为5以上的马氏体的数量比例。
通过实施平整,冷轧后平整的形变也加算到冷轧的形变中并残留。因钢板表层中积蓄的形变,铁素体在退火中回复并再结晶,接近于等轴状,然后,逆相变而形成纵横比小的奥氏体,通过冷却而变成纵横比小的马氏体,推测其分布也在宽度方向上变得均匀。因此,在不实施平整的情况下,纵横比为5以上的马氏体的比例变高,进而,宽度方向上的该比例之差变大(例如,宽度方向上的纵横比为5以上的马氏体的比例之差变得超过10%),因而疲劳极限比之差也变大,疲劳特性下降。
进而,如果如上述那样对宽度方向上变为均匀的表层组织实施镀覆处理和合金化处理,则容易均匀地合金化,合金化热浸镀锌层中的宽度方向的Fe浓度之差变小。
另外,通过实施平整,在宽度方向的1/4板厚附近的范围,尽管没有表层那种程度但也加算了平整的形变,因而与不实施平整的情况相比,升温时铁素体会进行微细再结晶。而且,保持时,奥氏体从微细的铁素体的晶界析出,因此大的铁素体粒的块会分散。结果是,板厚方向的厚度为20μm以下的铁素体块的数量达到铁素体块的总数的50%以上,能够确保所需要的扩孔性。另外,如果实施平整,则在接下来的冷轧中宽度方向的轧制变得均匀,并且平整的形变也在宽度方向上均匀地残留,因而在宽度方向的1/4厚度附近的范围内铁素体组织也被分散,组织的均匀性提高。例如,据认为,如果作为通过辊式平整导入钢板表层的形变量而言最大为0.2%以上的话,则能够对表层的组织变化产生影响。
(c)工序
退火工序是精密制造本实施方式的合金化热浸镀锌钢板的显微组织时最重要的工序。以下,对工序条件分别进行说明。
(c-1)退火气氛
气氛组成:H2为1~10体积%、以及剩余部分为N2、H2O和O2中的1种或2种以上
均热带中的水分压与氢分压之比:以log(PH2O/PH2)计为-1.7~-0.2
退火工序中,退火气氛由H2为1~10体积%、以及剩余部分为N2、H2O和O2中的1种或2种以上构成,均热带中的水分压与氢分压之比控制为以log(PH2O/PH2)计为-1.7~-0.2。
如果在上述退火气氛中将钢板退火,则钢板表层的氧化皮消失,在钢板内部生成氧化物。其结果是,能够确保钢板的镀覆性,在后述的镀覆工序中,能够粘附性良好地在钢板表面形成热浸镀锌层。
H2如果低于1体积%,则均热带中难以将log(PH2O/PH2)设定为-1.7~-0.2的范围内,钢板的镀覆性下降,因此H2设定为1体积%以上。优选为3体积%以上。H2如果超过10体积%,则气氛成本上升,因而H2设定为10体积%以下。优选为7体积%以下。
均热带中的log(PH2O/PH2)如果低于-1.7,则脱C层的厚度变得低于10μm,镀覆性下降,因而均热带中的log(PH2O/PH2)设定为-1.7以上。优选为-1.3以上,更优选为-1以上。均热带中的log(PH2O/PH2)如果超过-0.2,则脱C层的厚度超过150μm,疲劳特性下降,因而均热带中的log(PH2O/PH2)设定为-0.2以下。优选为-0.5以下、更优选为-0.7。
此外,只要能够控制脱C层的厚度,代替水分压与氢分压之比,例如也可以控制二氧化碳的分压与一氧化碳的分压之比。
上述退火气氛的条件是均热带中的条件,预热带中,log(PH2O/PH2)也控制为-1.7~-0.2。预热带中,调整水蒸气分压PH2O与氢分压PH2之比,会对脱C层的厚度、微细化层厚度、马氏体的纵横比、宽度方向的Fe浓度的均匀性和镀覆前的钢板的表面性状产生影响。
如前所述,冷轧后平整的形变在宽度方向上也加算到冷轧的形变中并残留。进而预热带中通过调整水蒸气分压PH2O与氢分压PH2之比,会抑制表层的C浓度的下降,从而抑制再结晶过度进行,因而升温时再结晶的铁素体会微细化。其结果是,在之后的均热带中的退火时,表层有奥氏体微细地析出,冷却后生成的马氏体的纵横比变小,铁素体也变得微细。如上所述地实施平整,进而在预热带中控制为以log(PH2O/PH2)计为-1.7~-0.2,由此可以改善脱C层中的马氏体的纵横比。
另外,预热带中,通过控制为以log(PH2O/PH2)计为-1.7~-0.2,会抑制钢板表面处的过剩的脱碳,在后续的镀覆工序和合金化工序中,会抑制钢板表面的晶界处的过剩的Fe-Zn合金反应。由此,在合金化热浸镀锌层中,会促进均匀的Fe-Al合金层的形成,宽度方向的Fe浓度均匀化,可以获得优良的镀覆粘附性、外观均匀化。
预热带中,log(PH2O/PH2)如果超过-0.2,则钢板表面处的脱碳变得过剩,脱C层的厚度超过150μm,疲劳特性下降。因此,预热带中的log(PH2O/PH2)设定为-0.2以下。优选为-0.5以下、更优选为-0.7。另一方面,预热带中,log(PH2O/PH2)如果低于-1.7,则在钢板表面形成碳浓度高的部分,在表面不形成微细化层,因而宽度方向的Fe浓度容易变得不均匀,进而镀覆粘附性下降。因此,预热带中的log(PH2O/PH2)设定为-1.7以上。优选为-1.3以上,更优选为-1以上。
(c-2)加热和保持
500℃~最高达到温度-50℃的温度区域的平均加热速度:1℃/秒以上
最高到达温度:720℃~900℃
最高到达温度下的保持:30秒~30分钟
退火工序中,500℃~最高到达温度-50℃的温度区域的平均加热速度在形成所需要形态的铁素体这点上是重要的。
加热钢板时,在500℃以上开始生成铁素体,因而将规定平均加热速度的温度区域的下限设定为500℃。最终将钢板加热至720℃~900℃的最高到达温度,并保持30秒~30分钟,但以1℃/秒以上的平均加热速度进行加热的温度区域设定为直到最高到达温度-50℃为止。
在控制铁素体的形态方面,上述温度区域的平均加热速度快者更好。平均加热速度如果低于1℃/秒,则从优先的核生成位置开始核生成,铁素体块变大,板厚方向的厚度为20μm以上的铁素体块的数量比例会超过50%,从而扩孔性下降,因而上述温度区域的平均加热速度设定为1℃/秒以上。优选为5℃/秒以上。
在钢板含有形成碳化物的Ti、Nb、V等的情况下,如果在加热钢板时,在550~760℃的温度区域停留30秒,然后加热至最高到达温度-50℃,在最高到达温度为720~900℃下进行退火,则可以使TiC、NbC、VC等碳化物在钢板组织中微细地析出。
退火工序中的最高到达温度设定为720~900℃。最高到达温度如果低于720℃,则不能充分形成奥氏体,不能充分确保马氏体,另外,渗碳体残留有不溶的部分,拉伸强度(TS)和扩孔性(λ)下降,因而最高到达温度设定为720℃以上。从充分形成奥氏体、并且充分溶解渗碳体、确保所需要的拉伸强度(TS)和扩孔性(λ)的观点出发,最高到达温度优选为770℃以上。
最高到达温度如果超过900℃,则奥氏体粒子粗大化,之后的铁素体的形成延迟,延展性下降,因而最高到达温度设定为900℃以下。从确保所需要的延展性、进一步提高强度-延展性平衡的观点出发,最高到达温度优选为850℃以下。
最高到达温度下的保持时间设定为30秒~30分钟。保持时间如果低于30秒,则不能充分形成奥氏体,不能充分确保马氏体,另外,渗碳体残留有不溶的部分。由于马氏体的下降而使得拉伸强度(TS)下降,并且由于不溶残留的渗碳体的存在,延展性和扩孔性(λ)尽管强度下降也不会上升,所以TS×λ下降。保持时间设定为30秒以上。优选为60秒以上。
保持时间如果超过30分钟,则奥氏体粒子粗大化,铁素体块厚度比规定的范围变大,因此扩孔性下降,强度×λ的值变低。因而保持时间设定为30分钟以下。优选为20分钟以下。
此外,保持时间是在最高到达温度~最高到达温度-50℃的温度区域保持的时间。
(c-3)冷却和弯曲加工
冷却温度区域:最高到达温度-50℃~满足下述式(B)的冷却停止温度T(℃)
平均冷却速度:满足下述式(A)的X(℃/秒)以上
冷却中的半径为800mm以下的弯曲加工:1次以上
继上述保持之后,将钢板从最高到达温度-50℃的温度开始,以满足下述式(A)的X(℃/秒)以上的平均冷却速度冷却至满足下述式(B)的冷却停止温度T(℃),并且对钢板实施1次以上的弯曲半径为800mm以下的弯曲加工。
下述式(A)是与成分组成相关联地规定能够抑制珠光体的生成的平均冷却速度(℃/秒)的经验式。下述式(B)是与成分组成相关联地规定能够抑制贝氏体的生成、确保充分量的马氏体的温度区域的下限的经验式。
冷却停止温度T(℃)如果不满足下述式(B)式,则生成大量的贝氏体,无法得到充分量的马氏体,不能确保所需要的强度,因而冷却停止温度T(℃)设定为满足下述式(B)的温度。
直到冷却停止温度T(℃)为止的平均冷却速度如果慢的话,则冷却中会生成阻碍伸长性和扩孔性的珠光体,因而为了将珠光体的分率抑制为5%以下,直到冷却停止温度T(℃)为止的平均冷却速度X(℃/秒)设定为满足下述式(A)的平均冷却速度。
X≥(Ar3-350)/10a(A)
a=0.6[C]+1.4[Mn]+1.3[Cr]+3.7[Mo]-100[B]-0.87
T≥730-350[C]-90[Mn]-70[Cr]-83[Mo](B)
[元素]:元素的质量%
在冷却钢板的过程中,对钢板实施1次以上的弯曲半径为800mm以下的弯曲加工。通过该弯曲加工,可以使钢板表层的粒径变得微细,可以将脱C层中的铁素体的粒径设定为30μm以下。其理由还不明确,但据认为结晶方位不同的晶粒的核生成被促进,退火后得到的钢板表层的结晶粒径变小。
弯曲半径如果超过800mm,则向钢板表层的导入形变量少,不会发生晶粒的核生成,无法获得晶粒微细化效果,因而弯曲半径设定为800mm以下。弯曲量(加工量)越多,核生成越被促进,能够进一步获得晶粒微细化效果,因而弯曲半径优选为730mm以下。更优选为650mm以下。
弯曲半径可以根据钢板的板厚和设备的荷重规格来适当设定,因而弯曲半径的下限不特别设定。
(d)工序
热浸镀锌
镀浴温度:440~480℃
钢板温度:430~490℃
将结束了退火工序的钢板浸渍于镀覆浴中,对钢板表面实施包括锌合金热浸镀的热浸镀锌。
镀浴是以熔融锌为主体的镀浴,可以含有Al、Pb、Sb、Si、Sn、Mg、Mn、Ni、Cr、Co、Ca、Cu、Li、Ti、Be、Bi、Sc、I、Cs、REM中的1种或2种以上。Al量可以根据合金化的容易性来适当调整。
镀浴温度优选为440~480℃。镀浴温度如果低于440℃,则镀浴的粘度过多地上升,难以适当地控制镀层的厚度,钢板的外观和镀覆粘附性下降,因而镀浴温度优选为440℃以上。更优选为450℃以上。
另一方面,镀浴温度如果超过480℃,则会发生大量的烟气,作业环境恶化,安全作业受到阻碍,因而镀浴温度优选为480℃以下。更优选为470℃以下。
镀浴中浸入的钢板的温度如果低于430℃,则难以将镀浴温度稳定地维持在450℃以上,因而镀浴中浸入的钢板的温度优选为430℃以上。更优选为450℃以上。
另一方面,镀浴中浸入的钢板的温度如果超过490℃,则难以将镀浴温度稳定地维持在470℃以下,因而镀浴中浸入的钢板的温度优选为490℃以下,更优选为470℃以下。
镀覆后,还可以对冷却至室温的热浸镀锌钢板实施压下率为3%以下的冷轧。通过该冷轧,可以矫正热浸镀锌钢板的形状,另外,可以调整该钢板的屈服强度(也称为耐力或屈服点)和延展性。此外,压下率如果超过3%,则延展性下降,因而压下率优选为3%以下。
热浸镀合金化
加热温度:470~620℃
加热时间:2~200秒
对将钢板浸渍于镀浴中而形成的热浸镀锌层实施合金化处理,在钢板表面形成合金化热浸镀锌层。
合金化处理温度如果低于470℃,则合金化不能充分进行,因此合金化处理温度优选为470℃以上。更优选为490℃以上。另一方面,合金化处理温度如果超过620℃,则在生成粗大的渗碳体的同时生成珠光体,强度下降,因而合金化处理温度设定为620℃以下。更优选为600℃以下。
合金化处理时间如果低于2秒,则热浸镀锌层的合金化不能充分进行,因而合金化处理时间优选为2秒以上。更优选为5秒以上。另一方面,合金化处理时间如果超过200秒,则在生成珠光体的同时,镀覆层会过合金化,因而合金化处理时间优选为200秒以下。更优选为150秒以下。
另外,合金化处理可以在将钢板从镀浴中提起后立即进行,也可以暂时将镀覆钢板冷却至室温后,再加热来进行。
合金化处理后,对冷却至室温后的合金化热浸镀锌钢板也可以实施压下率为3%以下的冷轧。通过该冷轧,可以矫正合金化热浸镀锌钢板的形状,另外,可以调整该钢板的屈服强度和延展性。此外,压下率如果超过3%,则延展性下降,因而压下率优选为3%以下。
实施例
下面,对本发明的实施例进行说明,但实施例中的条件是为了确认本发明的可实施性和效果而采用的一个条件例,本发明不受该一个条件例的限定。只要不超出本发明的要旨,能够实现本发明的目的,则本发明就能够采用各种条件。
(实施例1)
按照常规方法连续铸造表1所示的成分组成的钢液,制成铸造板坯。在表1中,符号A~T的成分组成满足本发明的成分组成。
符号a的成分组成中C和Mo不满足本发明的成分组成,符号b的成分组成中Mn和P不满足本发明的成分组成,符号c的成分组成中Al和Nb不满足本发明的成分组成,符号d的成分组成中C和Mn不满足本发明的成分组成。
符号e的成分组成中Si和S不满足本发明的成分组成,符号f的成分组成中N和Ti不满足本发明的成分组成,符号g的成分组成中Si、N和Ti不满足本发明的成分组成,符号h的成分组成中,Cr不满足本发明的成分组成,符号i的成分组成中,B不满足本发明的成分组成。
Figure GDA0002694378240000271
将表1所示的成分组成的铸造板坯进行加热,并供给至热轧,酸洗、平整后,供给至冷轧,制造板厚为1.6mm的钢板,将该钢板在表2~6所示的条件下进行退火、冷却,冷却后实施镀覆。
表2
Figure GDA0002694378240000281
表3
处理编号 加热速度 到达温度 保持时间 式(A)右边 冷却速度 式(B)右边 冷却停止温度T 备注
℃/秒 ℃/秒 ℃/秒
A1 10 780 160 0.2 2.5 443 520 比较钢
A2 10 780 160 0.2 2.5 443 520 发明钢
A3 10 780 160 0.2 2.5 443 520 发明钢
A4 10 780 160 0.2 2.5 443 520 发明钢
A5 10 780 160 0.2 2.5 443 520 发明钢
A6 10 780 160 0.2 2.5 443 520 比较钢
A7 10 780 160 0.2 2.5 443 520 发明钢
A8 10 780 160 0.2 2.5 443 520 发明钢
A9 10 780 160 0.2 2.5 443 520 比较钢
A10 10 780 160 0.2 2.5 443 520 发明钢
A11 10 780 160 0.2 2.5 443 520 比较钢
A12 10 780 160 0.2 50.0 443 520 比较钢
A13 10 780 160 0.2 50.0 443 520 比较钢
A14 10 780 160 0.2 50.0 443 520 发明钢
A15 10 780 160 0.2 50.0 443 520 发明钢
B1 20 820 200 1.9 1.0 490 500 比较钢
B2 20 820 200 1.9 5.0 490 500 发明钢
B3 20 820 200 1.9 50.0 490 500 发明钢
B4 20 820 200 1.9 50.0 490 500 比较钢
B6 20 820 200 1.9 50.0 490 500 比较钢
C1 15 785 15 1.8 2.0 483 490 比较钢
C2 15 785 180 1.8 2.0 483 490 发明钢
C3 15 785 2400 1.8 2.0 483 490 比较钢
C4 15 785 180 1.8 2.0 483 490 发明钢
C5 15 785 180 1.8 2.0 483 490 比较钢
C6 15 785 180 1.8 2.0 483 490 比较钢
C7 15 785 180 1.8 2.0 483 490 发明钢
C8 15 785 180 1.8 2.0 483 490 发明钢
C9 15 785 180 1.8 2.0 483 490 比较钢
D1 100 710 100 0.8 1.0 469 460 比较钢
D2 100 800 100 0.8 1.0 469 500 发明钢
D3 100 800 100 0.8 1.0 469 540 发明钢
D4 100 800 100 0.8 1.0 469 500 比较钢
D5 100 800 100 0.8 1.0 469 500 比较钢
D6 100 800 100 0.8 1.0 469 500 发明钢
D7 100 800 100 0.8 1.0 469 500 发明钢
D8 100 800 100 0.8 1.0 469 500 比较钢
E1 0.5 800 90 0.5 2.5 465 500 比较钢
E2 3 800 90 0.5 2.5 465 500 发明钢
E3 10 800 90 0.5 2.5 465 500 发明钢
E4 100 800 90 0.5 2.5 465 500 发明钢
E5 10 800 90 0.5 2.5 465 430 比较钢
F1 10 920 120 1.6 5.8 512 525 比较钢
F2 10 780 120 1.6 5.8 512 525 发明钢
F3 10 800 120 1.6 5.8 512 525 发明钢
F4 10 820 120 1.6 5.8 512 525 发明钢
F5 10 800 120 1.6 5.8 512 525 比较钢
F6 10 800 120 1.6 5.8 512 525 比较钢
F7 10 800 120 1.6 5.8 512 525 比较钢
G1 0.7 750 300 1.3 30.0 493 510 比较钢
G2 35 810 180 1.3 30.0 493 510 发明钢
G3 20 810 200 1.3 50.0 493 500 比较钢
G5 35 810 90 1.3 30.0 493 510 比较钢
G9 35 810 180 1.3 30.0 493 510 比较钢
H1 35 800 60 2.2 5.0 516 530 发明钢
H2 35 800 60 2.2 5.0 516 530 比较钢
I1 35 800 60 1.8 5.0 501 520 发明钢
J1 35 780 60 0.1 5.0 397 430 发明钢
K1 35 800 60 1.7 5.0 522 540 发明钢
L1 20 840 60 1.9 4.0 515 520 发明钢
L2 20 840 60 1.9 4.0 515 520 比较钢
M1 10 780 160 2.6 5.0 501 520 发明钢
N1 10 780 160 0.8 5.0 476 520 发明钢
O1 10 780 160 3.4 5.0 508 520 发明钢
P1 10 780 160 1.9 5.0 495 520 发明钢
Q1 10 780 160 0.6 5.0 460 520 发明钢
R1 10 780 160 1.5 5.0 493 520 发明钢
S1 10 780 160 2.4 5.0 501 520 发明钢
T1 10 780 160 3.6 5.0 511 520 发明钢
a1 10 800 160 0.1 2.0 433 500 比较钢
b1 10 800 160 0.1 2.0 402 500 比较钢
c1 10 800 160 1.5 2.0 496 500 比较钢
d1 10 800 160 22.3 30.0 603 650 比较钢
e1 10 800 160 4.0 30.0 523 550 比较钢
f1 10 800 160 7.0 30.0 519 550 比较钢
g1 10 780 160 6.5 30.0 519 550 比较钢
h1 10 800 160 0.0 30.0 382 450 比较钢
i1 10 800 160 1.1 30.0 522 550 比较钢
表4
处理编号 弯曲半径 次数 镀锌浴温度 进入板温 合金化处理温度 合金化处理时间 冷轧率(退火后) 备注
mm 次数
A1 500 5 460 470 520 60 0.4 比较钢
A2 500 5 460 470 520 60 0.4 发明钢
A3 500 5 460 470 520 60 0.4 发明钢
A4 500 5 460 470 520 60 0.4 发明钢
A5 500 5 460 470 520 60 0.4 发明钢
A6 500 5 460 470 520 60 0.4 比较钢
A7 680 5 460 470 520 60 0.4 发明钢
A8 780 5 460 470 520 60 0.4 发明钢
A9 850 5 460 470 520 60 0.4 比较钢
A10 775 5 460 470 520 60 0.4 发明钢
A11 - 0 460 470 520 60 0.4 比较钢
A12 500 5 460 470 520 60 0.4 比较钢
A13 500 5 460 470 520 60 0.4 比较钢
A14 500 5 460 470 520 60 0.4 发明钢
A15 500 5 460 470 520 60 0.4 发明钢
B1 460 2 460 470 520 30 0.6 比较钢
B2 460 2 460 470 520 30 0.6 发明钢
B3 460 2 460 470 520 30 0.6 发明钢
B4 460 2 460 470 520 30 0.6 比较钢
B6 - 0 460 470 520 30 0.6 比较钢
C1 460 3 460 470 520 30 0.2 比较钢
C2 460 3 460 470 520 30 0.2 发明钢
C3 460 3 460 470 520 30 0.2 比较钢
C4 460 3 460 470 520 30 0.2 发明钢
C5 460 3 460 470 520 30 0.2 比较钢
C6 460 3 460 470 520 30 0.2 比较钢
C7 460 5 460 470 520 30 0.2 发明钢
C8 460 5 460 470 520 30 0.2 发明钢
C9 460 3 460 470 520 30 0.2 比较钢
D1 460 5 460 470 560 30 0.4 比较钢
D2 460 5 460 470 560 30 0.4 发明钢
D3 460 5 460 470 560 30 0.4 发明钢
D4 460 5 460 470 630 30 0.4 比较钢
D5 460 5 460 470 560 1 0.4 比较钢
D6 460 5 460 470 560 6 0.4 发明钢
D7 460 5 460 470 560 99 0.4 发明钢
D8 460 5 460 470 560 500 0.4 比较钢
E1 460 5 460 470 520 30 0.4 比较钢
E2 460 5 460 470 520 30 0.4 发明钢
E3 460 5 460 470 520 30 0.4 发明钢
E4 460 5 460 470 520 30 0.4 发明钢
E5 460 5 460 470 520 30 0.4 比较钢
F1 460 4 460 470 540 30 0.4 比较钢
F2 460 4 460 470 540 30 0.4 发明钢
F3 460 4 460 470 540 30 0.4 发明钢
F4 460 4 460 470 540 30 0.4 发明钢
F5 460 4 460 470 540 30 0.4 比较钢
F6 850 4 460 470 540 30 0.4 比较钢
F7 460 4 460 470 540 30 0.4 比较钢
G1 460 5 460 470 520 30 0.4 比较钢
G2 460 5 460 470 520 30 0.4 发明钢
G3 460 5 460 470 520 30 0.4 比较钢
G5 460 5 435 470 520 30 0.4 比较钢
G9 460 5 460 470 520 30 0.4 比较钢
H1 460 5 460 470 520 30 0.4 发明钢
H2 460 5 435 470 520 30 0.4 比较钢
I1 460 5 460 470 520 30 0.4 发明钢
J1 460 5 460 470 520 30 0.4 发明钢
K1 460 5 460 470 520 30 0.4 发明钢
L1 460 5 460 470 520 30 0.4 发明钢
L2 460 5 460 470 520 30 0.4 比较钢
M1 500 5 460 470 520 30 0.4 发明钢
N1 500 5 460 470 520 30 0.4 发明钢
O1 500 5 460 470 540 30 0.4 发明钢
P1 500 5 460 470 560 30 0.4 发明钢
Q1 500 5 460 470 540 30 0.4 发明钢
R1 500 5 460 470 520 30 0.4 发明钢
S1 500 5 460 470 520 30 0.4 发明钢
T1 500 5 460 470 540 30 0.4 发明钢
a1 460 5 460 470 540 30 0.4 比较钢
b1 460 5 460 470 540 30 0.4 比较钢
c1 460 5 460 470 540 30 0.4 比较钢
d1 460 5 460 470 540 30 0.4 比较钢
e1 460 5 460 470 540 30 0.4 比较钢
f1 460 5 460 470 540 30 0.4 比较钢
g1 460 5 460 470 540 30 0.4 比较钢
h1 460 5 460 470 540 30 0.4 比较钢
i1 460 5 460 470 540 30 0.4 比较钢
表2~表4和后面的表5~表7中所示的处理编号(字母+数字)中,字母表示表1所示的成分组成的钢,数字表示实施例的编号。例如,处理编号“A1”是表示使用表1所示成分组成的钢A实施的第1个实施例。
表2~表4中示出了铸造板坯加热温度、Ar3、热轧的最终温度、卷取温度、酸洗前的热轧钢板的处理、冷轧的轧制率、退火的炉内气氛、退火工序的加热速度、到达温度(最高温度)、保持时间、冷却工序中的平均冷却速度、冷却停止温度。另外,式(A)、式(B)的右边的值也一并示出。在发明例和一部分比较例中,通过平整而对表面施加了最大0.2%以上的形变。
进而,示出了退火中的弯曲加工的弯曲半径和弯曲的次数、镀锌浴温度、向镀浴中的进入板温。另外,进行了合金化处理者示出了其合金化处理温度和合金化处理时间。
对钢板实施了表2~表4中所示的条件的处理后,测定并评价显微组织的形态和机械特性。
显微组织中的各组织的分率、铁素体块的厚度、脱C层的厚度通过前述的方法来求出。脱C层中的铁素体粒径、和脱C层中的马氏体的纵横比为5以上的数量密度用扫描电子显微镜如下所述地观察并算出。
在脱C层中的脱C层的一半厚度的外侧的区域,观察面积为40000μm2以上的区域,写入与轧制方向平行的线段,将用线段的长度的合计除以线段与晶界的交点的数量而得到的平均值设定为铁素体粒径。
求出马氏体的个数、和各个马氏体的短轴和长轴的长度,将用长轴的长度除以短轴的长度而得到的值设定为纵横比,用纵横比为5以上的马氏体的数量除以全体马氏体的数量以算出数量密度。另外,作为宽度方向组织的差,用脱C层中的马氏体的纵横比为5以上的马氏体的数量除以全体马氏体的数量而得到的数量密度的差也一并算出。
镀覆外观的评价如下进行:用目视来判断评价镀覆层中的宽度方向上的Fe浓度之差、和未镀覆的发生状况。“×”是观察到直径为0.5mm以上的未镀覆、并且超出了外观上的容许范围的情况。“○”是未观察到直径为0.5mm以上的未镀覆,但宽度方向的Fe浓度之差为1.0%以上,产生了不均匀的情况。另外,“◎”是这以外的情况。
施加了压缩形变的加工时的镀覆粘附性用60°V弯曲试验后的剥离状况来评价。“×”是剥离宽度为7.0mm以上、实用上不能容许的情况;“○”是其以外的情况。
根据JIS Z 2241进行试验,评价机械特性(屈服应力、拉伸强度、伸长性、屈服点伸长性)。有关扩孔性,根据JIS Z 2256进行试验。通过平面弯曲疲劳试验测定疲劳特性。试验片使用JIS1号试验片,应力比设定为-1。重复频率设定为25Hz、最大重复数设定为2×106次。将用疲劳极限的强度除以拉伸最大强度而得到的值设定为疲劳极限比。另外,作为钢板的宽度方向的特性是否均匀化的指标,还算出宽度方向上的疲劳极限比之差。
表5~表7中示出了测定结果和评价结果。
表5
Figure GDA0002694378240000331
表6
处理编号 脱C层中马氏体的纵横比≥5(f-MC)的数量密度 宽度方向f-MC差 疲劳极限比之差 Fe 宽度方向的Fe浓度差 备注
A1 21 3 0.03 11.6 0.3 比较钢
A2 23 4 0.04 11.9 0.3 发明钢
A3 20 3 0.04 12.0 0.1 发明钢
A4 19 4 0.04 11.5 0.1 发明钢
A5 21 5 0.05 11.4 0.3 发明钢
A6 18 4 0.05 11.5 0.3 比较钢
A7 18 5 0.04 11.1 0.4 发明钢
A8 19 4 0.05 11.9 0.4 发明钢
A9 20 5 0.05 11.0 0.2 比较钢
A10 19 5 0.04 11.4 0.2 发明钢
A11 18 5 0.05 11.7 0.4 比较钢
A12 16 5 0.05 12.2 0.4 比较钢
A13 60 3 0.03 9.8 1.2 比较钢
A14 20 4 0.05 12.0 0.4 发明钢
A15 48 3 0.03 10.2 0.7 发明钢
B1 19 3 0.03 11.5 0.3 比较钢
B2 20 4 0.04 11.6 0.2 发明钢
B3 19 6 0.04 11.6 0.2 发明钢
B4 60 14 0.13 10.6 1.0 比较钢
B6 28 5 0.04 11.6 0.3 比较钢
C1 30 3 0.03 11.6 0.3 比较钢
C2 25 6 0.07 11.7 0.3 发明钢
C3 30 4 0.03 11.6 0.3 比较钢
C4 28 5 0.05 10.0 0.7 发明钢
C5 30 4 0.04 8.9 0.7 比较钢
C6 30 3 0.04 12.1 0.3 比较钢
C7 30 4 0.04 11.8 0.3 发明钢
C8 29 3 0.04 11.6 0.3 发明钢
C9 62 13 0.13 10.9 1.1 比较钢
D1 无法测定 4 0.03 11.3 0.4 比较钢
D2 34 3 0.04 11.4 0.4 发明钢
D3 33 3 0.04 11.7 0.2 发明钢
D4 35 6 0.06 15.3 0.1 比较钢
D5 30 6 0.05 8.5 1.6 比较钢
D6 30 4 0.03 11.2 0.4 发明钢
D7 30 6 0.05 11.9 0.2 发明钢
D8 35 6 0.07 11.6 0.1 比较钢
E1 35 6 0.06 11.3 0.1 比较钢
E2 37 3 0.03 11.9 0.1 发明钢
E3 34 5 0.05 11.6 0.4 发明钢
E4 35 5 0.06 11.9 0.4 发明钢
E5 35 3 0.03 11.9 0.4 比较钢
F1 10 5 0.04 11.5 0.1 比较钢
F2 26 3 0.02 11.8 0.1 发明钢
F3 25 6 0.05 11.4 0.4 发明钢
F4 23 5 0.04 11.2 0.3 发明钢
F5 29 3 0.04 11.9 0.4 比较钢
F6 26 4 0.05 11.8 0.3 比较钢
F7 47 4 0.03 12.0 0.3 比较钢
G1 31 5 0.06 11.6 0.2 比较钢
G2 26 3 0.04 11.6 0.2 发明钢
G3 65 13 0.12 10.8 1.2 比较钢
G5 31 3 0.04 7.5 0.7 比较钢
G9 65 13 0.12 10.8 1.0 比较钢
H1 28 4 0.05 11.1 0.1 发明钢
H2 31 3 0.02 11.6 0.3 比较钢
I1 35 6 0.07 12.0 0.3 发明钢
J1 24 6 0.06 12.0 0.4 发明钢
K1 23 3 0.02 11.2 0.3 发明钢
L1 28 5 0.06 11.2 0.4 发明钢
L2 27 5 0.04 11.4 0.3 比较钢
M1 28 6 0.05 11.3 0.1 发明钢
N1 29 4 0.03 11.2 0.4 发明钢
O1 30 3 0.04 11.6 0.1 发明钢
P1 21 4 0.03 11.9 0.4 发明钢
Q1 31 5 0.05 11.7 0.4 发明钢
R1 31 5 0.05 11.3 0.2 发明钢
S1 30 3 0.03 11.3 0.2 发明钢
T1 32 3 0.03 11.1 0.2 发明钢
a1 33 6 0.06 12.0 0.2 比较钢
b1 34 5 0.06 11.2 0.4 比较钢
c1 40 6 0.05 11.0 0.2 比较钢
d1 30 5 0.06 11.4 0.2 比较钢
e1 30 3 0.04 12.0 0.2 比较钢
f1 31 6 0.07 11.8 0.1 比较钢
g1 33 5 0.04 11.5 0.2 比较钢
h1 35 5 0.04 11.2 0.2 比较钢
i1 33 3 0.02 11.0 0.2 比较钢
表7
处理编号 外观 镀覆剥离 微细化层厚度 拉伸强度 伸长率 扩孔性 TS×EL TS×EL×λ 疲劳极限比 备注
μm N/mm<sup>2</sup> MPa% MPa%%
A1 2.7 989 16.3 23 16,121 370,776 0.45 比较钢
A2 2.1 980 16.5 33 16,170 533,610 0.46 发明钢
A3 3.2 1112 16.7 41 18,570 761,386 0.48 发明钢
A4 2.7 993 16.8 40 16,682 667,296 0.50 发明钢
A5 2.5 1108 16.7 41 18,504 758,648 0.46 发明钢
A6 2.7 978 17.5 42 17,115 718,830 0.36 比较钢
A7 2.7 1126 16.8 41 18,917 775,589 0.48 发明钢
A8 2.7 1246 16.9 43 21,057 905,468 0.47 发明钢
A9 2.1 1110 17.0 42 18,870 792,540 0.37 比较钢
A10 3.2 1250 16.2 43 20,250 870,750 0.46 发明钢
A11 2.1 1258 16.5 41 20,757 851,037 0.37 比较钢
A12 4.2 979 17.0 37 16,643 615,791 0.37 比较钢
A13 × <0.1 998 16.7 39 16,667 649,997 0.39 比较钢
A14 4.0 982 16.9 38 16,596 630,640 0.50 发明钢
A15 0.3 995 16.7 39 16,617 648,044 0.43 发明钢
B1 3.2 1040 9.0 19 9,360 177,840 0.47 比较钢
B2 2.7 1150 14.0 38 16,100 611,800 0.49 发明钢
B3 2.5 1190 14.0 40 16,660 666,400 0.52 发明钢
B4 2.5 1199 14.0 20 16,786 335,720 0.39 比较钢
B6 2.7 1182 14.1 36 16,666 599,983 0.36 比较钢
C1 3.4 888 11.0 40 9,768 390,720 0.51 比较钢
C2 2.7 1138 15.0 35 17,070 597,450 0.51 发明钢
C3 2.3 1120 15.0 30 16,800 403,200 0.47 比较钢
C4 0.3 1130 15.5 35 17,515 613,025 0.55 发明钢
C5 × × <0.1 1150 14.1 30 16,215 486,450 0.55 比较钢
C6 2.7 1090 15.0 28 16,350 457,800 0.34 比较钢
C7 2.7 1105 16.2 30 17,901 537,030 0.42 发明钢
C8 2.1 1111 15.8 29 17,554 509,060 0.41 发明钢
C9 2.7 1125 14.5 22 16,313 358,875 0.39 比较钢
D1 2.7 600 10.7 20 6,420 128,400 0.52 比较钢
D2 2.7 1030 17.0 38 17,510 665,380 0.46 发明钢
D3 2.1 1065 16.5 35 17,573 615,038 0.46 发明钢
D4 × 2.5 970 10.0 33 9,700 320,100 0.47 比较钢
D5 × 2.7 1,035 16.8 31 17,388 539,028 0.47 比较钢
D6 2.7 1,031 16.5 30 17,012 510,345 0.47 发明钢
D7 2.1 1,040 16.2 30 16,848 505,440 0.47 发明钢
D8 × 3.2 978 10.3 31 10,073 312,275 0.47 比较钢
E1 2.7 820 17.0 25 13,940 348,500 0.46 比较钢
E2 2.9 823 20.0 30 16,460 493,800 0.46 发明钢
E3 2.5 835 22.0 30 18,370 551,100 0.47 发明钢
E4 2.9 842 21.8 29 18,356 532,312 0.48 发明钢
E5 3.4 770 20.0 25 15,400 385,000 0.47 比较钢
F1 2.7 1345 6.2 42 8,339 350,238 0.39 比较钢
F2 2.3 983 18.6 30 18,284 548,514 0.50 发明钢
F3 2.5 992 18.3 35 18,154 635,376 0.51 发明钢
F4 2.7 1035 17.5 37 18,113 670,163 0.50 发明钢
F5 2.7 982 17.8 37 17,480 646,745 0.36 比较钢
F6 2.1 980 18.0 38 17,640 670,320 0.36 比较钢
F7 3.2 979 16.0 14 15,664 219,296 0.48 比较钢
G1 3.2 938 18.5 20 17,353 347,060 0.53 比较钢
G2 2.9 942 20.5 36 19,311 695,196 0.52 发明钢
G3 2.5 952 20.1 20 19,135 382,704 0.35 比较钢
G5 × 2.9 943 20.3 33 19,143 631,716 0.48 比较钢
G9 2.9 950 20.3 20 19,285 385,700 0.38 比较钢
H1 2.7 1280 13.0 35 16,640 582,400 0.46 发明钢
H2 × 2.5 1269 13.2 34 16,751 569,527 0.46 比较钢
I1 2.9 1200 15.0 31 18,000 558,000 0.47 发明钢
J1 2.5 1230 14.2 30 17466 523980 0.48 发明钢
K1 2.9 1280 13.8 29 17664 512256 0.50 发明钢
L1 2.1 983 17.0 34 16711 568174 0.46 发明钢
L2 3.2 871 6.0 12 5228 62734 0.55 比较钢
M1 2.1 1084 15.5 31 16802 520862 0.48 发明钢
N1 2.1 1080 16.0 29 17280 501120 0.48 发明钢
O1 3.2 1075 16.8 32 18060 577920 0.46 发明钢
P1 2.7 982 19.3 36 18953 682294 0.47 发明钢
Q1 2.5 1100 15.8 30 17380 521400 0.48 发明钢
R1 2.9 990 18.0 33 17820 588060 0.47 发明钢
S1 2.7 998 17.9 32 17864 571654 0.48 发明钢
T1 2.5 996 18.3 33 18227 601484 0.46 发明钢
a1 2.1 1,313 8.0 5 10,504 52,520 0.45 比较钢
b1 3.2 1,213 11.2 7 13,586 95,099 0.46 比较钢
c1 2.7 950 8.8 7 8,360 58,520 0.55 比较钢
d1 2.5 523 22.0 72 11,506 828,432 0.60 比较钢
e1 2.9 780 15.0 30 11,700 351,000 0.54 比较钢
f1 3.2 1,100 9.8 11 10,780 118,580 0.60 比较钢
g1 2.7 983 15.0 29 14,745 427,605 0.43 比较钢
h1 2.5 700 6.0 2 4,200 8,400 0.22 比较钢
i1 2.9 851 10.3 8 8,767 70,134 0.23 比较钢
实施例中,为了确认钢种的好坏,将TS×EL≥16000MP%、TS×EL×λ≥480000MP%%、疲劳极限比≥0.40、疲劳极限比之差≤0.10的情况表示为发明钢。
就处理编号A1和F7的钢板而言,轧制率低,“铁素体块的厚度为20μm以下率”低,TS×EL×λ变低。就处理编号A6的钢板而言,卷取温度高,脱C层中的铁素体粒径大,疲劳极限比变低。就处理编号A9的钢板而言,弯曲加工的弯曲半径大,脱C层中的铁素体粒径大,疲劳极限比变低。
就处理编号A11和B6的钢板而言,由于未进行弯曲加工,所以脱C层中的铁素体粒径大,疲劳极限比变低。就处理编号A12而言,预热带中的炉内气氛的log(PH2O/PH2)高,脱C层的厚度变厚,疲劳极限比变低。就处理编号A13而言,预热带中的炉内气氛的log(PH2O/PH2)低,表面产生不均匀,并且镀覆粘附性下降。另外,脱C层中由于纵横比为5以上的马氏体的比例超过50%,所以疲劳极限比下降。
就处理编号B1的钢板而言,由于冷却速度慢,所以珠光体分率高,TS×EL和TS×EL×λ变低。就处理编号C1的钢板而言,由于加热时的保持时间短,所以组织分率不在本发明的范围内,TS×EL和TS×EL×λ变低。
就处理编号C3的钢板而言,加热时的保持时间长,因此TS×EL×λ变低。就处理编号C5的钢板而言,由于均热带中的炉内气氛的log(PH2O/PH2)低,脱C层的厚度低于10μm,所以镀层的外观和镀覆粘附密着性下降。就处理编号C6的钢板而言,均热带中的炉内气氛的log(PH2O/PH2)高,脱C层的厚度变厚,TS×EL×λ和疲劳极限比变低。
就处理编号D1的钢板而言,最高达到温度低,组织分率不在本发明的范围内,TS×EL和TS×EL×λ变低。就处理编号D4的钢板而言,合金化处理温度高,镀层的外观下降,另外,由于珠光体量多,所以TS×EL和TS×EL×λ变低。就处理编号D5的钢板而言,合金化处理时间短,镀层的外观下降。
就处理编号D8的钢板而言,合金化处理时间长,镀层的外观下降。另外,由于珠光体量多,所以TS×EL和TS×EL×λ变低。就处理编号G1和E1的钢板而言,加热速度慢,“铁素体块的厚度为20μm以下率”低,TS×EL×λ变低。
就处理编号E5的钢板而言,冷却停止温度低,贝氏体相变过度进行,马氏体分率变低,TS×EL和TS×EL×λ变低。就处理编号F1的钢板而言,最高到达温度高,铁素体分率变少,TS×EL和TS×EL×λ变低。就处理编号F5的钢板而言,卷取温度高,脱C层中的铁素体粒径变大,疲劳极限比变低。
就处理编号F6的钢板而言,弯曲加工的弯曲半径大,脱C层中的铁素体粒径变大,疲劳极限比变低。就处理编号G5和H2的钢板而言,镀锌浴温度低,尽管镀层的外观下降,但伸长性、扩孔性和疲劳特性优良,进而钢板的宽度方向的特性也均匀化。就处理编号L2的钢板而言,加热温度低,马氏体分率超出本发明的范围,TS×EL和TS×EL×λ变低。
就处理编号B4、C9、G3、G9的钢板而言,均是在酸洗之前和/或之后未实施平整。因此,均是板厚方向的厚度为20μm以下的铁素体块的数量低于铁素体块的总数的50%,并且脱C层中纵横比为5以上的马氏体的比例超过了50%。其结果是,均是宽度方向上的纵横比为5以上的马氏体的比例之差超过10%,脱C层中的宽度方向上的组织之差变大,因而疲劳极限比之差也变大。另外,TS×EL×λ低,疲劳极限比小。
就处理编号a1、b1、c1、d1、e1、f1、g1、h1和i1的钢板而言,由于成分组成超出了本发明的范围,因此TS×EL、TS×EL×λ等变低。有关其它条件,变成本发明的范围内的组织,表面品位(外观、镀覆粘附性)、TS×EL、TS×EL×λ、疲劳极限比、疲劳极限比之差变得良好。
工业上的可利用性
如前所述,根据本发明,可以提供伸长性、扩孔性和疲劳特性优良、进而钢板的宽度方向的特性被均匀化的高强度的合金化热浸镀锌钢板。因此,本发明在钢板制造产业、汽车制造产业和其它的机械制造产业中的可利用性高。

Claims (5)

1.一种合金化热浸镀锌钢板,钢板的成分组成以质量%计由下述成分构成:
C:0.06%~0.22%、
Si:0.50%~2.00%、
Mn:1.50%~2.80%、
Al:0.01%~1.00%、
P:0.001%~0.100%、
S:0.0005%~0.0100%、
N:0.0005%~0.0100%、
Ti:0%~0.10%、
Mo:0%~0.30%、
Nb:0%~0.050%、
Cr:0%~1.00%、
B:0%~0.0050%、
V:0%~0.300%、
Ni:0%~2.00%、
Cu:0%~2.00%、
W:0%~2.00%、
Ca:0%~0.0100%、
Ce:0%~0.0100%、
Mg:0%~0.0100%、
Zr:0%~0.0100%、
La:0%~0.0100%、
REM:0%~0.0100%、
Sn:0%~1.000%、
Sb:0%~0.200%、
剩余部分:Fe和杂质,
在钢板表面具有合金化热浸镀锌层,其特征在于,
以从钢板表面起算的板厚方向的1/4板厚为中心的1/8板厚~3/8板厚的范围的显微组织以面积率计由铁素体:15%~85%、残留奥氏体:低于5%、马氏体:15%~75%、珠光体:5%以下和包括为0%在内的剩余部分:贝氏体构成,
所述板厚方向的厚度为20μm以下的铁素体块的数量是铁素体块的总数的50%以上,
在钢板表层部形成有厚度为10μm~150μm的脱C层,
所述脱C层中的铁素体的粒径为30μm以下,马氏体中的纵横比为5以上的马氏体的比例为50%以下,
所述脱C层中的宽度方向的所述纵横比为5以上的马氏体的比例之差为10%以下。
2.根据权利要求1所述的合金化热浸镀锌钢板,其特征在于,在所述合金化热浸镀锌层与所述脱C层之间还具有平均厚度为0.1μm~5.0μm的微细化层。
3.根据权利要求1或2所述的合金化热浸镀锌钢板,其特征在于,所述合金化热浸镀锌层中的宽度方向的Fe浓度之差以质量%计为低于1.0%。
4.根据权利要求1或2所述的合金化热浸镀锌钢板,其特征在于,所述成分组成以质量%计含有下述成分中的1种或2种以上:
Ti:0.01%~0.10%、
Mo:0.01%~0.30%、
Nb:0.005%~0.050%、
Cr:0.01%~1.00%、
B:0.0002%~0.0050%、
V:0.001%~0.300%、
Ni:0.01%~2.00%、
Cu:0.01%~2.00%、
W:0.01%~2.00%、
Ca:0.0001%~0.0100%、
Ce:0.0001%~0.0100%、
Mg:0.0001%~0.0100%、
Zr:0.0001%~0.0100%、
La:0.0001%~0.0100%、
REM:0.0001%~0.0100%、
Sn:0.001%~1.000%、
Sb:0.001%~0.200%。
5.根据权利要求3所述的合金化热浸镀锌钢板,其特征在于,所述成分组成以质量%计含有下述成分中的1种或2种以上:
Ti:0.01%~0.10%、
Mo:0.01%~0.30%、
Nb:0.005%~0.050%、
Cr:0.01%~1.00%、
B:0.0002%~0.0050%、
V:0.001%~0.300%、
Ni:0.01%~2.00%、
Cu:0.01%~2.00%、
W:0.01%~2.00%、
Ca:0.0001%~0.0100%、
Ce:0.0001%~0.0100%、
Mg:0.0001%~0.0100%、
Zr:0.0001%~0.0100%、
La:0.0001%~0.0100%、
REM:0.0001%~0.0100%、
Sn:0.001%~1.000%、
Sb:0.001%~0.200%。
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