CN114875331A - 一种具有优良心部疲劳性能的610MPa级厚钢板及其生产方法 - Google Patents
一种具有优良心部疲劳性能的610MPa级厚钢板及其生产方法 Download PDFInfo
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Abstract
本发明涉及一种具有优良心部疲劳性能的610MPa级厚钢板及其生产方法,所述钢板是由下述质量百分比含量的元素组成:C:0.064~0.087%,Si:0.26~0.39%,Mn:1.05~1.24%,P:≤0.008%,S:≤0.002%,Als:0.028~0.058%,Nb:0.039~0.049%,Ti:0.021~0.035%,Ni:0.78~1.26%,La:0.017‑0.028%,Ca:0.0031~0.0055%,其余为铁及不可避免杂质;所述钢板中还添加有V:0.042~0.057%,B:0.0005~0.0008%;或者Cr:0.35~0.50%,Mo:0.26~0.41%;本发明钢板厚度60~90mm,屈服强度≥610MPa,抗拉强度≥700MPa,板厚中心部位疲劳强度≥400MPa,可用于建筑、工程机械、海洋工程等对钢板心部疲劳性能有一定需求的支撑件、构件;本发明具有制造工序简单等优点,在各冶金企业均可实施。
Description
技术领域
本发明涉及金属材料制造技术领域,特别是一种具有优良心部疲劳性能的610MPa级厚钢板及其生产方法。
背景技术
随着我国经济发展和装备设计、制造能力的不断进步,对大型构件用高强度钢需求越来越多,而且其主体结构用材向高强度、高韧化、大厚度方向不断发展。厚钢板是高层建筑、海洋开发、原油球罐、油气管线、船舶军舰等大型结构、设备、设施等重要的结构材料。
由于“板厚效应”,厚度中心部位的力学性能通常是厚钢板最差的部位,而且厚钢板往往采用大厚度铸坯轧制而成,绝大部分连铸坯受其凝固特性以及现有冶炼设备、工艺的限制,铸坯截面化学成分分布不均、内部偏析、疏松、缩孔等缺陷严重,都会对钢板强度、韧性、疲劳性能等指标造成较大影响。尤其是铸坯的中心偏析,会在轧制过程中“遗传”给钢板,造成钢板厚度中心部位组织异常、探伤不合,并在下一步加工或者使用过程中由于心部出现脆性区和提前开始损坏,影响钢结构构件的安全性,再加上国内现行检验标准往往以钢板厚度1/4处性能为代表,对相对较差的心部性能约束较少。因此,针对厚钢板,尤其是在一些对韧性、疲劳性能等有较高要求恶劣服役环境,如何改善中心部位的综合力学性能就显得十分必要。
经检索:
中国专利CN109112392A公开了一种TMCP型高强韧高疲劳性能耐候桥梁钢板及制备方法,该钢板化学成分按重量百分比为:C:0.05~0.08%、Si:0.12~0.18%、Mn:1.4~1.6%、Nb:0.045~0.058%、Ti:0.01~0.02%、Cu:0.30~0.35%、Cr:0.22~0.30%、Ni:0.45~0.55%、Al:0.02~0.04%、Mo:0.05~0.12%、P≤0.009%、S≤0.005%,其余为Fe和其他不可避免的杂质。该发明的优点在于产品性能优异,屈服强度大于500MPa、-60℃裂纹尖端张开位移指数不低于0.3mm,1000万次下疲劳强度不低于170MPa,腐蚀失重速率≤3.0g/(m2·h )。
中国专利CN113957346A公开了一种屈服强度不小于500MPa高性能桥梁钢及其制备方法和应用。桥梁钢包括如下成分:C:0.03~0.06%,Si:0.10~0.25%,Mn:1.30~1.50%,P≤0.015%,S≤0.003%,Als:0.010~0.040%,Cr:0.25~0.45%,Mo:0.05~0.20%,Cu:0.20~0.30%,Ni:0.25~0.40%,Nb:0.030~0.040%,Ti:0.010~0.040%,其余为Fe和杂质。该发明采用微合金化设计,配合TMCP工艺,降低了贵重元素,组织细小均匀,制得钢板具有强韧性、低屈强比、耐候性、焊接性及抗疲劳性能;该发明采用了浇铸末端采用重压下技术(压下比率12.3%),成品厚度8~60mm。
上述两项发明均涉及了一种高疲劳性能耐候桥梁钢,但成品厚度仅为≤60mm,且强度仅为500MPa。此外,两项发明均未明确显示钢种心部疲劳性能要求。特别是,CN113957346A文件未显示钢板疲劳性能指标。
中国专利CN109097702A公开了一种具有良好疲劳性能和焊接性能的高强桥壳钢及其制备方法,该钢的化学成分及重量百分比如下:C:0.04~0.07%,Si:0.05~0.15%,Mn:1.3~1.6%,P:≤0.013%,S:≤0.004% ,Nb:0.045~0.07% ,Ti:0.01~0.02%,N:≤0.003%,Alt:0.010~0.030%,O:0.001~0.002%,且Ti-2×O-3 .4×N<0 .007,其余为Fe及不可避免的杂质。该发明钢的力学性能达到了ReL≥530MPa,Rm≥600MPa,A≥20%,经用户加工成零件,成型合格率100%,经台架试验,零件垂直弯曲疲劳寿命≥85万次,具有良好疲劳性能的易焊接性能。该发明采用了连铸电磁搅拌工艺,冷却模式采用强冷模式。
中国专利CN113025897A公开了一种具有优异疲劳性能的600MPa级热轧高扩孔钢,其化学成分及wt%为:C为0.03~0.06%,Si为0.10~0.30%,Mn为1.30~1.70%,P≤0.009%,S≤0.003%,Ti为0.08~0.13%,Mo为0.18~0.22%,Nb为0.015~0.035%,V为0.08~0.12%;生产方法:经转炉冶炼后进行真空处理;连铸成坯后对铸坯加热;粗轧;精轧;前段式冷却;卷取。该发明铁素体晶粒度等级≥10级;铁素体基体内含有大量的纳米级簇团析出物,其尺寸在1~10nm,密度可达1.5×103/μm2;钢板的抗拉强度≥600MPa、延伸率≥25%,屈强比≥0.90,扩孔率≥150%,且由于含有大量纳米级析出物,钢板的条件疲劳强度由原来的不超过135MPa达到170MPa以上。该发明热轧钢板厚度为2.0-8.0mm。
上述两项专利CN109097702A、CN113025897A产品均采用且采用热连轧、卷取工艺生产,厚度不超过9.0mm,不适用于大厚度、单张轧制模式钢板生产。
发明内容
本发明的目的在于提供一种610MPa级心部疲劳性能优良的厚钢板及其生产方法。本发明钢板厚度60~90mm,屈服强度≥610MPa,抗拉强度≥700MPa,而且板厚中心部位疲劳强度≥400MPa。
本发明的一种具有优良心部疲劳性能的610MPa级厚钢板,所述钢板是由下述质量百分比含量的元素组成:C:0.064~0.087%,Si:0.26~0.39%,Mn:1.05~1.24%,P:≤0.008%,S:≤0.002%,Als:0.028~0.058%,Nb:0.039~0.049%, Ti:0.021~0.035%,Ni:0.78~1.26%,La:0.017-0.028%,Ca:0.0031~0.0055%,其余为铁及不可避免杂质。
优选地,所述钢板中还添加有V:0.042~0.057%,B:0.0005~0.0008%;或者Cr:0.35~0.50%,Mo:0.26~0.41%。
本发明制得的成品钢板厚度60~90mm,屈服强度≥610MPa,抗拉强度≥700MPa,板厚中心部位疲劳强度≥400MPa。
本发明的一种具有优良心部疲劳性能的610MPa级厚钢板的生产方法,包括下述步骤:
(1)进行铁水脱硫,并控制铁水中S≤0.002%;
(2)真空处理时间≥23min,连铸拉速不高于0.95m/ min,过热度控制不高于15℃,采用两段式电磁搅拌,其电流参数分别为443A、455A;采用三段式动态轻压下方案,压下量为分别控制为2mm,4mm,1mm;
(3)常规连铸成坯并对铸坯加热,控制加热温度在 1201~1235℃,出炉温度不低于1185℃;
(4)采用两阶段式轧制,第一阶段开轧温度不低于1083℃,单道次压下量≥22mm;第二阶段开轧温度不高于900℃,轧制道次压下率控制在8~10%,终轧温度在801~834℃;终轧后快速冷却,控制返红温度500~550℃;
(5)进行离线淬火热处理:控制淬火温度在908~936℃,保温时间为:(h+55)min,h是以mm为单位的产品厚度;控制淬火出炉辊速为7m/min并在高压水冷却段摇摆5min保证钢板完全水冷至室温;
(6)进行工业炉回火热处理,回火温度在601~621℃,在炉时间为:(h×2)min,到温后持续保温时间不低于(h×1.2)min,回火结束后空冷至室温。
本发明钢中主要化学成分限定理由如下:
C、Mn是提高钢材强度非常有效的元素。一方面,碳含量的增加钢的抗拉强度和屈服强度随之提高,但延伸率和冲击韧性下降,而且钢材的焊接热影响区还会出现淬硬现象,导致焊接冷裂纹的产生。随着Mn含量的增加,钢的强度明显增加,而冲击转变温度几乎不发生变化。Mn也是扩大奥氏体区元素,Mn含量增加可提高奥氏体稳定性,降低临界冷却速度,强化铁素体,显著提高淬透性,同时可使淬火后回火过程中组织分解转变速度减慢,提高回火组织稳定性。而另一方面,C、Mn元素又是铸坯中心极易偏聚、引发中心偏析的元素。因此,本发明将C、Mn控制在较低的水平(C:0.064~0.087%,Mn:1.05~1.24%),采用其他合金元素平衡钢板强度、韧性,减轻中心偏析对心部性能的不利影响。
Si元素可以提高钢中固溶体硬度和强度,不仅可以增加钢的淬透性,而且还可以增加淬火钢的抗回火性,使钢能在较高温度下回火,从而改善钢的韧性和耐延迟断裂性能;Si能显著提高钢的弹性极限、屈服强度和屈强比。Si含量过高会使钢的导热性变差,钢锭、钢坯表面易出现开裂或裂纹缺陷。本发明钢的Si含量设计为0.26~0.39%。
P、S是钢中的杂质元素,也是易于偏析的元素,可在钢的局部形成严重偏析、夹杂物,降低塑性及韧性。本发明钢,在冶金质量方面严格控制了硫、磷含量水平,即P≤0.008%,S≤0.002%。
Al是钢中的主要脱氧元素,另外,Al的熔点较高,在生产中,钢中Al可与N形成AlN,而AlN可阻碍高温奥氏体长大,起到细化晶粒的作用。本发明钢的Als含量控制为0.028~0.058%。
Nb、Ti是两种强烈的碳化物和氮化物形成元素,与氮、碳有极强的亲合力,可与之形成极其稳定的碳氮化物。弥散分布的Nb的碳氮化物第二相质点沿奥氏体晶界的分布,可大大提高原始奥氏体晶粒粗化温度,在轧制过程中的奥氏体再结晶温度区域内,Nb的碳氮化析出物可以作为奥氏体晶粒的形核核心,而在非再结晶温度范围内,弥散分布的Nb的碳氮化析出物可以有效钉扎奥氏体晶界,阻止奥氏体晶粒进一步长大,从而细化铁素体晶粒,达到提高强度和冲击韧性的目的;Ti的氮化物能有效地钉扎奥氏体晶界,有助于控制奥氏体晶粒的长大,大大改善焊接热影响区的低温韧性。因此,通过Nb、Ti微合金元素的细晶强化和沉淀强化作用,可以使钢板获得优良的强韧性。本发明钢Nb含量设计为0.039~0.049%,Ti含量设计为0.021~0.035%。
Ni在钢中能强化铁素体基体,抑制粗大的先共析铁素体,显著改善钢材的韧性,降低钢材的韧脆转变温度,提高钢的低温韧性。本发明将Ni的含量设计为0.78~1.26%。
La是稀土元素的一种,和氧、硫有很强的亲和力,在钢中有净化和明显的变质作用。固溶在钢中可以通过扩散机制富集于晶界,减少夹杂元素在晶界的偏聚,结果强化了晶界,改善了与晶界相关的性能,如低温脆性、韧性等。本发明Ce添加量为0.017~0.028%。
Ca在钢中有着脱硫、脱氧、减少夹杂物分布及改变夹杂物形状的作用,经过Ca处理可以明显提高钢板的脱氧和脱硫能力,达到良好的脱硫、脱氧以及控制夹杂物形态和分布的效果,提高钢的纯净度同时降低了夹杂物对组织性能的影响。在应力作用下,较高的夹杂物含量、集中分布,可形成裂纹源起点,对钢板疲劳性能造成不利影响。本发明Ca元素含量控制为0.0031~0.0055%。
V是一种相当强烈的碳化物形成元素,它可以通过细晶强化、沉淀强化和固溶强化来提高钢材的强度。此外在钢中,当V的质量分数低于0.1%时,随着V含量的增加,钢的韧脆转变温度降低。当V的质量分数超过0.1%时,V含量增加,韧脆转变温度反而升高。在含Si、Mn的钢中,加入少量的V就可以明显减轻这两种元素对晶粒长大和提高韧脆转变温度的影响。V与Nb复合添加时,既能提高钢的强度又能改善钢的韧性。添加时,本发明V元素含量0.042~0.057%。
B是强烈提高淬透性的元素,B的加入,可有效的抑制先共析铁素体的形核及生长,由于B在奥氏体晶界上的非平衡偏析,强烈抑制γ-α相变,促使奥氏体在淬火时形成细小的低碳马氏体,从而提高钢的屈服强度和抗拉强度。添加时,本发明的B含量选择在0.0005~0.0008%。
Cr在钢中与C具有较强的亲和力,同时可以显著增加钢的淬透性。在厚规格钢板中添加一定量的Cr元素,可以明显减轻“板厚效应”,改善钢板心部综合性能。添加时,本发明将Cr含量控制为0.35~0.50%。
Mo元素在钢中的主要作用是固溶强化,少量Mo可以形成难熔碳化物,阻碍加热时奥氏体晶粒长大,细化产品组织,提高强度、硬度和耐磨性。Mo可以提高淬透性,减轻或消除其他合金元素所导致的回火脆性而大大有利于钢的韧性,提高回火稳定性,有效消除或降低钢中的残余应力,但过高的Mo在快速冷却和焊接冷却过程中极易获得粗大马氏体,降低基材低温韧性和恶化焊接性能,因此,添加时本发明将Mo含量控制为0.26~0.41%。
本发明钢的主要工艺及工艺参数的设定理由如下:
控制连铸拉速、采用两段式电磁搅拌、控制各段动态轻压下量,可以最大程度的改善铸坯中心偏析等缺陷。
控制铸坯加热温度、出炉温度,是保证本发明钢足够的奥氏体化。
控制第一阶段开轧温度,配合单道次压下量,可以有效的将轧制压力传导到铸坯中心部位,充分细化奥氏体晶粒。
控制第二阶段开轧温度、限定轧制道次压下率、终轧温度,而非采用传统的大压下、少道次轧制工艺,可以对两个阶段的再结晶晶粒、铁素体形核晶粒叠加细化,进一步提升钢板韧性,并间接给予足够的时间减轻中心偏析、中心疏松。
轧后进行冷却,返红温度控制500~550℃。过高的返红温度不足以保证钢板获得足够的基础性能。
采用离线淬火热处理,控制足够的加热温度以及保温时间,以便钢中晶粒能够充分奥氏体化。在冷却阶段,匹配出炉辊速并在高压水冷却段摇摆一定时间,可以让钢板淬透,获得心部完全的马氏体组织,为后续钢板的强韧性提供基础条件。
控制回火温度在601~621℃,过低的回火加热温度会造成本发明钢回火时部分元素析出不充分,导致钢板强度不足,韧性不良;过高的温度会导致本发明钢强度下降。同时,由于钢板进入工业炉回火时,会引起炉温降低。因此,必须通过控制足够的回火到温后持续保温时间不低于(产品厚度/mm×1.2)min,以使钢板回火时元素析出、扩散充分,且内应力消除充分,从而获得优良的综合性能。
本发明相对现有技术,具有如下优点:本发明钢板厚度60~90mm,屈服强度≥610MPa,抗拉强度≥700MPa,而且板厚中心部位疲劳强度≥400MPa。可用于建筑、工程机械、海洋工程等对钢板心部疲劳性能有一定需求的支撑件、构件。本发明具有制造工序简单等优点,在各冶金企业均可实施。
具体实施方式
为了更好地解释本发明的技术方案,下面结合具体实施例对本发明的技术方案进行进一步的说明,下述实施例仅仅是示例性的说明本发明的技术方案,并不以任何形式限制本发明。
下表1为本发明各实施例及对比例钢板的化学成分(wt%)取值列表;
下表2为本发明各实施例及对比例钢板的主要工艺参数取值列表;
下表3为本发明各实施例及对比例钢板力学性能测试结果列表。
本发明各实施例的一种具有优良心部疲劳性能的610MPa级厚钢板的生产方法,包括下述步骤:
(1)进行铁水脱硫,并控制铁水中S≤0.002%;
(2)真空处理时间≥23min,连铸拉速不高于0.95m/ min,过热度控制不高于15℃,采用两段式电磁搅拌,其电流参数分别为443A、455A;采用三段式动态轻压下方案,压下量为分别控制为2mm,4mm,1mm;
(3)常规连铸成坯并对铸坯加热,控制加热温度在 1201~1235℃,出炉温度不低于1185℃;
(4)采用两阶段式轧制,第一阶段开轧温度不低于1083℃,单道次压下量≥22mm;第二阶段开轧温度不高于900℃,轧制道次压下率控制在8~10%,终轧温度在801~834℃;终轧后快速冷却,控制返红温度500~550℃;
(5)进行离线淬火热处理:控制淬火温度在908~936℃,保温时间为:(h+55)min,h是以mm为单位的产品厚度;控制淬火出炉辊速为7m/min并在高压水冷却段摇摆5min保证钢板完全水冷至室温;
(6)进行工业炉回火热处理,回火温度在601~621℃,在炉时间为:(h×2)min,到温后持续保温时间不低于(h×1.2)min,回火结束后空冷至室温。
表1 本发明各实施例及对比例钢板的化学成分(wt%)取值列表
表2 本发明各实施例及对比例钢板的主要工艺参数取值列表
表3 本发明各实施例及对比例钢板力学性能测试结果列表
由表可知,本发明实施例的疲劳强度均在400MPa以上,明显高于对比例,具有良好的心部疲劳性能。
本发明钢板是一种屈服强度≥610MPa,抗拉强度≥700MPa,板厚中心部位疲劳强度≥400MPa的60~90mm厚钢板。可用于建筑、工程机械、海洋工程等对钢板心部疲劳性能有一定需求的支撑件、构件。本发明具有制造工序简单等优点,在各冶金企业均可实施。
上述实施例仅仅是本发明为解释本发明而例举的具体实例,并不以任何形式限制本发明,任何人根据上述内容和形式做出的不偏离本发明权利要求保护范围的非实质性的改变,均应认为落入本发明权利要求的保护范围。
Claims (4)
1.一种具有优良心部疲劳性能的610MPa级厚钢板,其特征在于所述钢板是由下述质量百分比含量的元素组成:C:0.064~0.087%,Si:0.26~0.39%,Mn:1.05~1.24%,P:≤0.008%,S:≤0.002%,Als:0.028~0.058%,Nb:0.039~0.049%, Ti:0.021~0.035%,Ni:0.78~1.26%,La:0.017-0.028%,Ca:0.0031~0.0055%,其余为铁及不可避免杂质。
2.根据权利要求1所述的一种具有优良心部疲劳性能的610MPa级厚钢板,其特征在于,所述钢板中还添加有V:0.042~0.057%,B:0.0005~0.0008%;或者Cr:0.35~0.50%,Mo:0.26~0.41%。
3.根据权利要求1所述的一种具有优良心部疲劳性能的610MPa级厚钢板,其特征在于:制得的成品钢板厚度60~90mm,屈服强度≥610MPa,抗拉强度≥700MPa,板厚中心部位疲劳强度≥400MPa。
4.如权利要求1或2所述的一种具有优良心部疲劳性能的610MPa级厚钢板的生产方法,其特征在于包括下述步骤:
(1)进行铁水脱硫,并控制铁水中S≤0.002%;
(2)真空处理时间≥23min,连铸拉速不高于0.95m/ min,过热度控制不高于15℃,采用两段式电磁搅拌,其电流参数分别为443A、455A;采用三段式动态轻压下方案,压下量为分别控制为2mm,4mm,1mm;
(3)常规连铸成坯并对铸坯加热,控制加热温度在 1201~1235℃,出炉温度不低于1185℃;
(4)采用两阶段式轧制,第一阶段开轧温度不低于1083℃,单道次压下量≥22mm;第二阶段开轧温度不高于900℃,轧制道次压下率控制在8~10%,终轧温度在801~834℃;终轧后快速冷却,控制返红温度500~550℃;
(5)进行离线淬火热处理:控制淬火温度在908~936℃,保温时间为:(h+55)min,h是以mm为单位的产品厚度;控制淬火出炉辊速为7m/min并在高压水冷却段摇摆5min保证钢板完全水冷至室温;
(6)进行工业炉回火热处理,回火温度在601~621℃,在炉时间为:(h×2)min,到温后持续保温时间不低于(h×1.2)min,回火结束后空冷至室温。
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