CN116607075A - 薄坯生产厚规格355MPa高韧性管桩用钢及生产方法 - Google Patents
薄坯生产厚规格355MPa高韧性管桩用钢及生产方法 Download PDFInfo
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- 229910052758 niobium Inorganic materials 0.000 claims abstract description 6
- 239000000126 substance Substances 0.000 claims abstract description 5
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 4
- 239000012535 impurity Substances 0.000 claims abstract description 3
- 229910001562 pearlite Inorganic materials 0.000 claims description 8
- 238000001816 cooling Methods 0.000 claims description 5
- 238000010438 heat treatment Methods 0.000 claims description 4
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 abstract description 12
- 229910052742 iron Inorganic materials 0.000 abstract description 6
- 239000010955 niobium Substances 0.000 description 13
- 239000011572 manganese Substances 0.000 description 12
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Abstract
本发明涉及一种薄坯生产厚规格355MPa高韧性管桩用钢及生产方法,薄坯生产厚规格355MPa高韧性管桩用钢,钢中化学成分按重量百分比计为:C 0.069%~0.079%、Si0.10%~0.20%、Mn 1.02%~1.13%、P≤0.020%、S≤0.015%、Als 0.015%~0.030%、Nb0.032%~0.042%、Cr 0.20%~0.28%,其余为铁和不可避免的杂质。本发明可以实现薄板坯(135~170mm)连铸连轧生产厚规格(20~24mm)355MPa高强韧性管桩用钢热轧卷板。
Description
技术领域
本发明属于金属材料低合金热轧板卷技术领域,具体涉及一种薄坯生产厚规格355MPa高韧性管桩用钢及生产方法。
背景技术
近年来随着中国经济的发展和城镇化的推进,各种建筑和基础设施不断涌现完善,管桩作为常用建筑材料,得到了广泛应用,为保证建筑用管桩较大的承重能力和服役安全性,各大工程对管桩用钢的厚度和强韧性有了更高的要求。
目前各大钢厂热轧时所使用的连铸坯厚度普遍在200mm以上,而本发明所使用的连铸坯厚度为135~170mm,由于压缩比小,对厚规格管桩用钢的强韧性贡献小,因此生产厚规格355MPa级热轧板卷具有一定难度,公开资料表明,目前管桩用钢的韧性指标不高,其强韧性指标难以完全满足工程需求。
专利文件《一种高强度厚规格管桩用钢及其制造方法》,申请号CN200910251585.3,该钢种成分中C 0.12%~0.16%、Si 0.20%~0.50%、Mn 1.3%~1.5%、S≤0.010%、P≤0.015%、Nb 0.020%~0.030%、Al 0.015%~0.040%。该发明铸坯230mm,压缩比大,且采用Nb微合金化,合金成本高,此外C和Si含量高,对产品冲击韧性有害,产品屈服强度达到400MPa,但-40℃冲击功仅150J。
申请号CN201310489482.7的专利文件,公开了一种耐腐蚀桥梁管桩用钢及其生产方法,成分为(重量百分比):C 0.07%~0.13%,Si 0.3%~0.65%,Mn0.80%~1.30%,P0.025%~0.045%,S≤0.002%,V 0.035%~0.050%,Ti 0.008%~0.025%,Re 0.005%0~0.020%,Zr 0.006%~0.012%。该发明中S含量控制较低,炼钢成本较高;含有稀土元素Re和Zr,合金成本较高,产品屈服强度达到390MPa,但0℃冲击功仅为47J以上,实际工程使用易失效。
申请号CN201310407630.6的专利文件,公开了一种40~60mm厚管桩用钢板及其生产方法,该专利含描述的是中厚板,并不涉及板卷的生产方法。
论文“杭州湾大桥管桩用Q345C_Hq钢水冷焊接试验”(《钢铁研究》2004.4,p29-31)提到了管桩用钢板,C(1.34%)和Mn(1.25%~1.35%)含量高,偏析严重,韧性不高,其他元素添加和生产工艺未作描述。
论文“风力发电管桩S355钢多道焊横向裂纹产生原因”(《焊接》2011.10,p49-51)中提到了一种86mm厚度的管桩用钢,C(0.15%)、Si(0.3%)和Mn(1.56%)含量较高,且添加贵金属Ni,产品厚度、性能和生产工艺未作描述。
论文“水利工程用管桩钢的组织与耐蚀性”(《腐蚀与防护》2018.7,p501-502)中提到了3种管桩用钢,采用Cu和Cr单独或复合添加,屈服强度最高可达到339MPa,但0℃冲击功最高仅为90J,实际应用种易发生断裂失效,此外该论文对产品厚度和生产工艺未做描述。
论文“强度管桩钢的组织与耐蚀性研究”(《热加工工艺》2018.6,p56-57)中提到了3种不同Cr含量的管桩用钢,Cr含量分别为0.5、1.0和1.5%,Cr含量偏高,产品合金成本较高。此外,该论文也未对产品厚度、韧性指标和生产工艺进行描述。
上述公开资料中涉及的管桩用钢,包含中厚板和热轧板卷两种产品,其中热轧板卷产品的合金设计基本上采用高C、高Mn以保证产品强度,配合添加Nb、Ti、Cr、Ni和Cu中的一种或几种;虽然其产品强度级别均在300MPa以上,但冲击韧性都较差,冲击试验大部分在0℃,且冲击功不高;而为了保证钢板的强度和韧性,现有技术的生产工艺中,一般都是通过增大压缩比和添加大量合金元素来提高钢板的强韧性能,因此生产热轧板卷产品的板坯都较厚,厚度一般在200~230mm。经文献调研,目前现有公开资料没有能使用薄板坯生产厚规格355MPa级高韧性管桩用钢的方法。
发明内容
本发明的目的是通过采用经济合理的合金设计、匹配适当的生产工艺,提供一种厚规格高强韧性355MPa级高韧性管桩用钢及其生产方法,可以实现薄板坯(135~170mm)连铸连轧生产厚规格(20~24mm)355MPa高强韧性管桩用钢热轧卷板。
为了达到上述目的,本发明采用以下技术方案实现:
薄坯生产厚规格355MPa高韧性管桩用钢,其特征在于,钢中化学成分按重量百分比计为:C 0.069%~0.079%、Si 0.10%~0.20%、Mn 1.02%~1.13%、P≤0.020%、S≤0.015%、Als 0.015%~0.030%、Nb 0.032%~0.042%、Cr 0.20%~0.28%,其余为铁和不可避免的杂质。
本发明355MPa管桩用钢的成分采用C-Mn-Nb-Cr系合金设计,通过Nb微合金化细化晶粒,添加Cr提高管桩用钢服役安全性,在轧制工艺上采用低温加热和两阶段控轧控冷,获得均匀细小的铁素体-珠光体(F-P)组织,其中珠光体体积分数为5%~6%,以保证管桩用钢具有优异的强韧性,其主要元素的作用和选择理由如下:
C:是钢中仅次于铁的最主要元素,它直接影响钢材的强度、塑性、韧性和焊接性能等,C是最经济的提高钢材强度的元素,但随着C含量提高,钢的韧性和焊接性逐渐变差,由于本发明产品焊接后用于建筑行业的结合件中,因此低的碳含量设计是保证管桩用钢具有优异强韧性韧性和良好焊接性能的基本保障。本发明中,若C含量高于0.079%,损害成品韧性和焊接性,若C含量低于0.069%,形成Nb(CN)数量较少,细化晶粒的有益效果会降低,因此本发明将C含量控制为0.069%~0.079%。
Si:是炼钢过程中重要的还原剂和脱氧剂,对于碳钢中的很多材质来说,都含有0.5%以下的Si,Si可以显著提高铁素体-珠光体组织类型的强度,但高的Si含量会损失材料的塑性和韧性,所以本发明的Si控制在较低的含量。因此本发明的Si含量控制为0.10%~0.20%。
Mn:锰具有固溶强化作用,还可降低γ-α相变温度,进而细化铁素体晶粒,此外,本发明中添加Mn,还可推迟铁素体向珠光体转变,从而降低珠光体含量,对产品韧性有益,但锰含量过高会使偏析严重,损失材料的韧性。因此本发明将锰含量控制为1.02%~1.13%。
Nb:铌可通过析出强化、沉淀强化、相变强化等多种强化机制提高钢的性能,其细化晶粒的作用能提高屈服强度和冲击韧性,降低脆性转变温度,有益焊接性能。但Nb为贵重元素且加入到一定量后强化效果不再明显。因此本发明将Nb含量控制为0.032%~0.042%。
Cr:Cr对抗拉强度的贡献要大于屈服强度,所以可以降低屈强比,使钢带在打桩服役中表现良好,具有较高的结构安全性。此外,Cr还能够有效提高淬透性,提高厚规格产品厚度方向组织均匀性,从而提高韧性指标,本发明中若Cr含量过高,会形成M/A硬项,反而损失韧性指标,因此本发明的Cr含量为0.20%~0.28%。
Als:脱氧元素,添加适量的铝可形成细小弥散的AlN粒子,有利于细化晶粒,提高钢的强韧性能。因此本发明的Als含量为0.015%~0.030%。
P:极易在钢液凝固时高度偏析,会形成带状的F-P结构,P也会使管桩用钢中C降低带来的好处大打折扣,损失钢的韧性,钢中作为有害元素应尽量少,但要求过低会增加成本。因此本发明的P含量控制在0.020%以下。
S:是钢中不可避免的杂质元素,会降低刚材的韧性,一般希望越低越好,但要求过低会增加生产成本。因此本发明的S≤0.015%。
一种薄坯生产厚规格355MPa高韧性管桩用钢的生产方法,其生产工艺流程涉及:铁水预处理—转炉冶炼—炉外精炼(LF+Ca处理)—连铸—板坯加热-轧制-层流冷却—卷取。其中:
1)冶炼连铸工艺:铁水预处理,转炉冶炼采用顶吹或顶底复合吹炼;炉外精炼采用LF炉轻脱硫处理及钙处理控制夹杂物数量和形貌形;连铸采用动态轻压的方式,所得铸坯厚度为135~170mm;
2)轧制工艺:连铸板坯经步进式加热炉加热至1140~1150℃,添加的Nb完全固溶,且铸坯晶粒不过分长大而损失强韧性,随后经粗轧及精轧机组两阶段控制轧制,粗轧终轧温度≥960℃,精轧进入未再结晶区,终轧温度为800~820℃,随后采用层流冷却的方式以25.1~27.6℃/s的速度终冷至535~546℃卷取,最后空冷到室温。
本发明355MPa级打桩管用钢热轧板卷具有优异的强韧性:钢板屈服强度355~375MPa,抗拉强度≥480MPa,断后延伸率≥25%;-60℃夏比冲击功(3个试样平均值)Akv≥230J。
钢板成品厚度20~24mm。
与现有技术相比,由于本发明压缩比小,对厚规格管桩用钢的强韧性贡献小,因此生产厚规格355MPa级热轧板卷具有一定难度,通过下述第二和第三方面的技术工作弥补了压缩比不足对强韧性指标控制带来的缺失,本发明的有益效果是:
1)本发明采用135~170mm的薄板坯轧制厚规格(20~24mm)的高强韧性355MPa级管桩用钢板卷,能够提高生产效率,节约生产资源;
2)合金设计方面,本发明采用C-Mn-Nb-Cr系合金设计,低C、低Si设计保证优异的焊接性、添加Mn推迟珠光体转变发生从而提高其韧性、适量添加Nb主要发挥其细化晶粒作用而提高强韧性,而添加Cr提高厚规格产品厚度方向组织均匀性,进一步保障产品具有优异的强韧性指标。
3)轧制工艺方面,结合上述合金设计,铸坯加热至1140~1150℃,可使添加的Nb完全固溶的条件下具有最细小的原始奥氏体晶粒组织,960℃进入精轧区,产生更多的亚结构(位错和二项粒子)来保证强度,适宜的卷取温度和冷速不会产生过多的M/A硬项,保障产品具有优异的强韧性指标;
4)本发明所述产品的合金设计经济合理、工艺路线简单、稳定且易执行,产品实物质量优异,钢板屈服强度355~375MPa,抗拉强度≥480MPa,断后延伸率≥25%;-60℃夏比冲击功(3个试样平均值)Akv≥230J。
具体实施方式
为了使本发明的目的、技术方案及优点更加清楚明白,以下结合实施例,对本发明进行进一步详细说明。应当理解,此处所描述的具体实施例仅仅用以解释本发明,并不用于限定本发明。
下面结合实施例对本发明的具体实施方式作进一步说明,以下实施例用于具体说明本发明内容,这些实施例仅为本发明内容的一般描述,并不对本发明内容进行限制。本发明钢实施例的化学成分见表1,本发明钢实施例的轧制工艺制度见表2,本发明钢实施例的力学性能见表3。
表1实施例钢化学成分(wt,%)
实施例 | C | Si | Mn | P | S | Nb | Als | Cr |
1 | 0.078 | 0.10 | 1.10 | 0.018 | 0.015 | 0.040 | 0.016 | 0.20 |
2 | 0.077 | 0.15 | 1.03 | 0.017 | 0.012 | 0.032 | 0.030 | 0.27 |
3 | 0.069 | 0.17 | 1.12 | 0.020 | 0.011 | 0.036 | 0.028 | 0.28 |
4 | 0.078 | 0.13 | 1.12 | 0.019 | 0.014 | 0.038 | 0.022 | 0.23 |
5 | 0.069 | 0.20 | 1.13 | 0.017 | 0.012 | 0.042 | 0.024 | 0.22 |
6 | 0.074 | 0.11 | 1.11 | 0.018 | 0.013 | 0.041 | 0.015 | 0.28 |
7 | 0.079 | 0.12 | 1.02 | 0.020 | 0.011 | 0.034 | 0.018 | 0.21 |
8 | 0.070 | 0.19 | 1.08 | 0.019 | 0.015 | 0.041 | 0.020 | 0.20 |
9 | 0.071 | 0.14 | 1.04 | 0.020 | 0.012 | 0.035 | 0.026 | 0.21 |
10 | 0.077 | 0.18 | 1.02 | 0.019 | 0.013 | 0.033 | 0.017 | 0.22 |
表2实施例钢工艺制度
表3实施例钢主要力学性能
。
Claims (5)
1.薄坯生产厚规格355MPa高韧性管桩用钢,其特征在于,钢中化学成分按重量百分比计为:C 0.069%~0.079%、Si 0.10%~0.20%、Mn 1.02%~1.13%、P≤0.020%、S≤0.015%、Als 0.015%~0.030%、Nb 0.032%~0.042%、Cr 0.20%~0.28%,其余为Fe和不可避免的杂质。
2.根据权利要求1所述的薄坯生产厚规格355MPa高韧性管桩用钢,其特征在于,钢中组织为铁素体-珠光体,其中珠光体体积分数为5%~6%。
3.根据权利要求1所述的薄坯生产厚规格355MPa高韧性管桩用钢,其特征在于,钢板屈服强度355~375MPa,抗拉强度≥480MPa,断后延伸率≥25%;-60℃夏比冲击功Akv≥230J。
4.根据权利要求1所述的薄坯生产厚规格355MPa高韧性管桩用钢,其特征在于,钢板厚度20~24mm。
5.一种如权利要求1-4其中任意一项所述的薄坯生产厚规格355MPa高韧性管桩用钢的生产方法,其特征在于,包括:
连铸板坯厚度135~170mm,连铸板坯经加热炉加热至1140~1150℃,随后经粗轧及精轧机组两阶段控制轧制,粗轧终轧温度≥960℃;精轧终轧温度为800~820℃,随后采用层流冷却的方式以25.1~27.6℃/s的速度终冷至535~546℃卷取,最后空冷到室温。
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