极寒环境作为一类典型的极端自然条件，会显著改变材料的腐蚀动力学过程与疲劳失效模式，对寒区装备及工程结构的服役安全性与耐久性构成严峻挑战[1~3]。传统认知普遍认为低温环境会通过抑制化学反应活性降低金属腐蚀速率，但近年来的系列研究证据表明，极寒条件下金属材料的锈蚀现象仍普遍存在且作用机理更为复杂[4~7]。Dychko等[8]通过低温腐蚀试验表明，当环境温度高于-25 ℃时，寒冷气候对腐蚀反应的抑制效应并不显著，金属表面仍可发生持续的电化学腐蚀过程。White等[9]进一步揭示了冰/液界面的特殊作用机制，指出冷却过程中产生的Workman-Reynolds效应会导致冰相中金属表面形成显著的阳极极化现象，产生约100 mV的电位差，这一电位梯度会极大加速腐蚀电化学反应的进行。Fu等[10]的研究则从介质导电性角度阐明，固态NaCl体系中存在晶界导电、冰层导电及复合导电3种传输路径，为极寒环境下腐蚀电流的持续传导提供了关键条件。
本文选取A588耐候钢作为研究对象，结合南极中山站与高纬度寒冷地区典型极寒大气环境特征，开展室外暴露试验，通过扫描电子显微镜(SEM)、X射线衍射(XRD)及能谱分析(EDS)等表征手段解析腐蚀形貌特征与产物组成，系统揭示A588耐候钢在极端低温-高盐协同作用下的腐蚀行为机理，为其在极寒地区工程结构中的长效安全应用提供理论支撑与技术参考。
1 实验方法
本文使用A588耐候钢进行室外暴露试验，其化学成分(质量分数，%)如下：C 0.15，Mn 1.00，Si 0.03，P 0.03，Cr 0.50，Ni 0.50，Mo 0.25，Cu 0.25，Nb 0.03，V 0.05，Fe余量。试样尺寸为150 mm × 75 mm × 3 mm。使用400#到2000#的砂纸进行打磨抛光，乙醇溶液清洗除油。采用游标卡测量尺寸，电子天平称重。
户外暴露试验在极寒大气环境下进行，试样准备完毕后放置在南极中山站大气试验场(69°22ʹ24ʺ S, 76°22ʹ40ʺ E)进行现场暴露试验，暴露期间南极中山站的气象数据如表1所示。南极气候独特，气温低，金属表面大部分时间都被冰层所覆盖。试验样品与水平面成45°进行暴晒，时间共12个月，到预定时间后取下试样，表面进行充分风干处理后进行性能测试。
表1 暴露期间南极中山站的环境参数
Table 1
| Environmental parameters | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Maximum temperature / ℃ | 4.8 | 4.9 | -1.3 | -3.6 | -8.4 | -6.0 | -2.3 | -5.6 | -5.3 | 1.2 | 1.1 | 5.7 |
| Minimum temperature / ℃ | -4.0 | -9.3 | -17 | -27.9 | -26.6 | -33.2 | -32.1 | -36.4 | -25.4 | -21.6 | -12.7 | -4.7 |
| Average temperature / ℃ | -0.2 | -2.0 | -7.3 | -13.3 | -16.7 | -16.4 | -17.5 | -13.4 | -13.6 | -11.2 | -3.5 | 0.5 |
| Maximum humidity / RH% | 89% | 85% | 90% | 82% | 78% | 93% | 78% | 89% | 88% | 89% | 75% | 87% |
| Minimum humidity / RH% | 49% | 45% | 40% | 46% | 40% | 47% | 40% | 44% | 43% | 40% | 44% | 51% |
| Average humidity / RH% | 61.4% | 60.6% | 63.9% | 63.3% | 54% | 68% | 62.1% | 64% | 67.3% | 54.5% | 54.7% | 63.4% |
| TOW / h (King) | 672 | 528 | 504 | 192 | 24 | 120 | 144 | 216 | 48 | 240 | 408 | 696 |
| Freeze-thaw time / d | 7 | 2 | - | - | - | - | - | - | - | 2 | 7 | 10 |
| Snowfall time / d | 7 | 7 | 13 | 14 | 5 | 14 | 5 | 12 | 11 | 5 | 8 | 5 |
从户外暴露环境中取回试样之后，采用特定配方的除锈液(500 mL HCl + 500 mL去离子水+ 0.3 g六次甲基四胺)，借助超声技术对试样进行除锈处理。完成除锈后，采用去离子水对试样进行冲洗，随后利用吹风机将其吹干。为了降低实验过程中的误差，在对每个试样进行称重时，均进行3次称重操作，最终取其平均值作为该试样的质量数据。腐蚀失重速率的计算公式如
式中，V为腐蚀速度(μm/a)，w0和w1分别为试样原始和除锈后质量(g)，S为试样腐蚀面积(m2)，t为腐蚀时间(a)，ρ为材质密度(g/cm3)。
将带锈试样切割为10 mm × 10 mm后进行形貌表征，使用数码相机(Canon 6D Mark II)观察试样宏观形貌。使用SEM (Gemini SEM 300)观察试样微观形貌、截面形貌和去除腐蚀产物后的表面锈蚀形貌，使用SEM配套EDS测试锈层的元素组成和分布。使用激光共聚焦显微镜(CLSM，VK-X260K)观测腐蚀坑分布和深度。
将锈层从试样表面用小刀刮除，收集不小于5 mg的锈层粉末。使用XRD (D8 advance)分析物相组成，测试角度为10°~90°，扫描速度为5 (°)/min。使用Raman光谱仪(Renishaw in Via)检测锈层物相组成和分布，扫描范围100~1700 cm-1。
2 结果与分析
2.1 腐蚀速率测试
A588耐候钢在极寒大气环境下暴露12个月的腐蚀速率为11.0 μm/a。该腐蚀速率显著低于温带海洋环境下碳钢及普通耐候钢的腐蚀水平，相关研究表明，温带海洋大气中Q235碳钢的年腐蚀速率通常为25~30 μm/a，而普通耐候钢的年腐蚀速率约为18~22 μm/a[16,17]。这种差异主要源于极寒环境特定的腐蚀条件。暴露12个月时，极寒地区处于寒季，金属表面被持续性冰层覆盖，一方面冰层通过物理阻隔作用减少了氧与腐蚀介质向金属表面的传质效率，另一方面低温环境降低了电化学腐蚀反应的动力学速率；同时，A588耐候钢自身形成的致密氧化层在低温下稳定性增强，进一步抑制了腐蚀进程。相较之下，温带海洋环境中持续的高湿度、盐雾沉积及较高温度，更有利于腐蚀电化学反应的持续进行，导致碳钢和普通耐候钢的腐蚀速率维持在较高水平。
2.2 腐蚀形貌分析
A588耐候钢暴露于极寒大气环境后形成的腐蚀产物表面宏观形貌如图1所示。暴露12个月后，试样表面完全被腐蚀产物所覆盖，锈层存在轻微脱落的痕迹，呈现出均匀腐蚀的形貌。正面锈层更加致密平整，表现出较为均匀的棕褐色，在钢材打孔处以及边缘处黄色的锈更多。背面锈层十分粗糙，表面均匀分布着黑色点状腐蚀产物。
图1
图1
A588耐候钢暴露极寒大气环境下12个月后宏观形貌
Fig.1
Macroscopic morphologies of the sunny side (a) and shady side (b) of A588 weathering steel after 12 month exposure to extremely cold atmospheric environment
图2为极寒大气环境下A588耐候钢暴露12个月后的SEM表面微观形貌特征。观察可见，试样正反表面的腐蚀产物在微观形貌上无显著差异，整体呈现显著的粗糙化与不规则起伏特征。在低放大倍数视野下，表面分布有大量贯穿性裂纹，这些裂纹形成的贯通性缝隙为Cl-等侵蚀性离子提供了传输通道，使其能够穿透腐蚀产物层抵达金属基体界面，成为驱动基体持续腐蚀的重要因素[18]。从高倍放大图像可见，表面腐蚀产物以块状堆积形态为主，且在局部区域形成典型的鸟巢状多孔结构，经物相分析证实该特征产物为γ-FeOOH。这种鸟巢状结构虽在一定程度上覆盖了金属表面，但裂纹的存在破坏了产物层的完整性，导致腐蚀介质仍可通过缝隙持续作用于基体，这与极寒环境下长期冰层覆盖与冻融循环引发的腐蚀产物层力学损伤机制密切相关。
图2
图2
A588耐候钢暴露极寒大气环境下12个月后的表面微观形貌
Fig.2
Surface micro-morphologies of A588 weathering steel after 12 month exposure to extremely cold atmospheric environment: (a1-a3) sunny side, (b1-b3) shady side
图3展示了在极寒大气环境中暴露12个月后的A588耐候钢腐蚀产物正面与背面锈层的截面形貌及EDS元素分布特征。正面锈层的平均厚度约为70 μm，形貌整体较为连续且厚度分布均匀，表明该侧在服役过程中经历了相对充分的腐蚀产物生长过程。相比之下，背面锈层的平均厚度约为40 μm，呈现出明显的非均匀分布特征，局部区域锈层显著减薄，反映该侧腐蚀行为处于锈蚀初期或不完全发展阶段，尚未形成均一稳定的腐蚀产物层。EDS元素分布分析表明，Cl在正、背两侧锈层中均有广泛分布，说明大气环境中Cl-能够穿透锈层并持续参与金属基体的腐蚀过程，锈层对Cl-的屏蔽作用较为有限，可能影响其长期耐腐蚀性能。此外，锈层中合金元素的空间分布亦具有显著差异：正面锈层内层检测到少量Cr与Mn的富集，背面锈层则表现为Cr富集于中间层，Mn主要分布于内层区域。相关研究表明，Cr有助于形成稳定致密的保护性锈层，从而提高耐腐蚀性；Mn则可能通过促进难溶氧化物的生成降低腐蚀反应速率，二者在锈层结构稳定性和保护性能中的协同效应不容忽视。
图3
图3
极寒大气环境下A588耐候钢暴露12个月截面微观形貌及Cl元素分布图
Fig.3
Cross-sectional micro-morphologies and Cl element distribution maps of the sunny side (a) and shady side (b) of A588 weathering steel after 12-month exposure to extremely cold atmospheric environment
图4显示了去除腐蚀产物后A588耐候钢表面的微观形貌特征。试样正面表面整体较为平整，缺乏明显的深坑状腐蚀特征，说明该区域腐蚀过程相对均衡。相比之下，背面则呈现出多个腐蚀凹坑及连片状的浅腐蚀区，表明该区域腐蚀存在更明显的空间不均一性。上述差异与截面观察中锈层厚度与结构的非均匀性相一致，说明正反两侧在极寒暴露条件下的腐蚀行为具有一定差异性。这一腐蚀分布特征可能与极寒环境下的微气候条件密切相关。试样正面长时间暴露于阳光照射，其表面温度相对更高，有助于液态腐蚀介质(如Cl-富集的液膜)在其表面更长时间停留，从而增强腐蚀反应的活跃性。同时，主导风向可能促使盐粒子在正面沉积更集中，进一步加剧Cl-的局部富集。相对而言，背面温度更低，表面水分更易冻结，液态介质存在时间短，对腐蚀反应形成一定抑制。
图4
图4
极寒大气环境下A588耐候钢去除腐蚀产物后的表面腐蚀形貌和CLSM图
Fig.4
Surface corrosion morphologies and CLSM images of A588 weathering steel after removing corrosion products in extremely cold atmospheric environment: (a, c) sunny side, (b, d) shady side
2.3 腐蚀产物成分分析
图5展示了A588耐候钢在极寒大气环境中暴露12个月后锈蚀产物的XRD图谱及其物相组成的相对含量分布。由于X射线衍射技术难以有效区分Fe3O4与γ-Fe2O3，且二者在一定条件下可相互转化，因此本文将其合并表示为Fe3O4/γ-Fe2O3[19]。为进一步评估锈层的防护性能，本文引入锈层保护性指数α/γ*，其中α表示保护性锈相α-FeOOH的含量，γ*表示促腐锈相(包括γ-FeOOH、β-FeOOH和Fe3O4/γ-Fe2O3)之和。该指数越高，通常表明锈层越具致密性和防护性。分析结果显示，A588耐候钢在该服役条件下的腐蚀产物主要由α-FeOOH、γ-FeOOH、β-FeOOH以及Fe3O4/γ-Fe2O3组成。其中，β-FeOOH占据主导地位，分别在正面与背面锈层中占比约为68%与63%，为主要腐蚀产物。α-FeOOH含量相对较低，正面约为8%，背面约为10%，导致α/γ*指数整体处于较低水平，表明锈层整体防护能力有限。值得注意的是，背面锈层中α-FeOOH的相对含量略高于正面，可能与正面锈层中较高的Cl-含量有关。已有研究表明[20]，Cl-的存在可能抑制α-FeOOH等致密锈相的形成，进而影响锈层结构的致密性与稳定性。这一差异或可部分解释正反两面腐蚀行为的差异性。
图5
图5
A588耐候钢暴露于极寒大气环境12个月后的腐蚀产物物相组成及百分比
Fig.5
Phase composition (a) and percentage (b) of corrosion products of A588 weathering steel after 12-month exposure to extremely cold atmospheric environment
为确定A588耐候钢在极寒大气环境暴露12个月后锈层的物相分布特征，采用Raman光谱对试样正面锈层的内层、中间层及外层进行了逐层检测，结果如图6所示。
图6
图6
A588耐候钢暴露于极寒大气环境下12个月后的腐蚀产物物相分布
Fig.6
Phase distribution of corrosion products of A588 weathering steel after 12-month exposure to extremely cold atmospheric environment
锈层内层的Raman光谱中，最强特征峰位于710 cm-1，另在310和385 cm-1处出现弱峰，且在1360 cm-1处出现一较宽峰。这些峰位共同对应于α-FeOOH和Fe3O4/γ-Fe2O3。中间层Raman谱图呈现出310、385、538及721 cm-1的特征峰，表明该区域主要由β-FeOOH构成。锈层外层的Raman谱图则在248 cm-1处出现最强峰，其他较弱峰位于380、528、650及1300 cm-1，对应于γ-FeOOH[21]。上述结果显示，A588耐候钢锈层存在明显的物相分布差异：α-FeOOH及Fe3O4/γ-Fe2O3主要富集于内层，β-FeOOH集中分布于中间层，而γ-FeOOH主要出现在锈层表面。α-FeOOH主要分布于靠近金属基体的区域，表明锈层内层具有更高的致密性与较强的防护性能。锈层不同层位物相的形成，与钢中合金元素的加入及腐蚀介质中Cl-浓度变化密切相关[22]。在极寒大气环境中，含盐颗粒的沉积可能导致A588耐候钢表面Cl-浓度的空间差异，从而促进了β-FeOOH的选择性生成。特别是在暖季期间，由于冰雪的融化—冻结交替过程以及高氧含量，有利于β-FeOOH的快速生成；而在冰层覆盖阶段，液态水中溶解氧浓度降低，可能促进Fe3O4/γ-Fe2O3等低氧条件下的腐蚀产物形成。
2.4 A588耐候钢在极寒大气环境下腐蚀行为分析
在极寒大气环境中，A588耐候钢仍表现出一定的腐蚀活性，表明即便在低温条件下，其腐蚀过程并未完全被抑制。特别是在夏季暖周期，受较大昼夜温差、强日照及冰雪反复冻融等环境条件影响，金属表面更容易形成持久存在的Cl-富集液膜，为腐蚀反应提供了连续的电解质环境。在腐蚀初期，由于水膜中氧浓度的空间不均，易在金属表面形成氧浓差电池，进而引发点蚀。Cl-在点蚀坑内不断富集，增强电化学反应的局部性，加速金属阳极溶解[23]。随着腐蚀产物的逐渐积累，锈层在一定程度上限制了腐蚀介质的扩散，导致腐蚀由局部向横向扩展，最终形成更为均匀的腐蚀形貌。
锈蚀产物的物相分析显示，A588钢在极寒环境中生成的腐蚀产物主要包括α-FeOOH、β-FeOOH、γ-FeOOH及Fe3O4/γ-Fe2O3等。其中β-FeOOH含量较高，尤其在试样正面，由于Cl-迁移作用显著，α-FeOOH的生成受到抑制，使锈层整体保护性能下降。此外，反复冻融作用不仅易诱导锈层结构微裂纹的形成，还加剧了Cl-和O的渗透与再分布，进一步促进了腐蚀的进行[24]。锈层中物相的分层结构与合金元素分布的不均及表面环境差异密切相关，是导致其局部腐蚀难以转化为完全保护性锈层的关键因素之一。
与其他钢材的腐蚀行为对比可揭示A588耐候钢的优势与局限。研究表明，在NaCl飞溅或盐雾环境下，A588钢表现出较好的耐蚀性。在相同的环境条件下，Q235钢的腐蚀速率可高达0.20 mm/a，而A588钢的腐蚀速率仅为0.12 mm/a，这反映了A588钢在抗腐蚀能力方面的显著优势，特别是在湿润和盐雾条件下，其锈层结构稳定且具有较强的保护性[25]。这一优势归因于A588钢在其合金化过程中添加了Cu、Cr、Ni等元素，这些元素有助于促进稳定致密的锈层形成，有效阻止了腐蚀介质的渗透。然而，尽管A588钢在一般大气环境中表现出较好的耐蚀性，但在低温高湿度环境下，其腐蚀稳定性仍存在一定局限性。与A588钢相比，含有较高比例Cr和Ni的高合金钢表现出更低的腐蚀速率。特别是在极寒环境中，如极地低温大气条件下，Ni-Cr-Mo-V低合金高强钢的腐蚀速率仅为0.02 mm/a，远低于A588钢的腐蚀速率[4]。这种差异主要源于含有Cr和Ni的高合金钢在极寒环境下能够形成更加致密、均匀的氧化物层(如α-FeOOH)，而这些氧化物层能够有效隔绝腐蚀介质，减少腐蚀反应的发生。
此外，环境因素在影响钢材腐蚀速率方面起着关键作用。极寒环境中的低温、高湿度、频繁的冻融循环以及Cl-等腐蚀介质的高浓度共同作用，显著改变了锈层的结构特征与腐蚀反应机制。已有研究表明，在低温高湿条件下，Cl-的持续富集与反复冻融过程会诱导锈层产生裂纹，破坏其连续性和致密性，从而加速腐蚀进程。值得关注的是，本研究中试样正面的腐蚀程度普遍高于背面，这一趋势与部分热带海洋环境中阴极面腐蚀速率高于阳极面的常见现象存在差异。该差异可能源于极寒气候下特有的微环境条件。试样正面长期暴露于太阳辐射下，表面温度通常高于背面，有利于液态腐蚀介质(尤其是Cl-富集的液膜)在其表面更长时间滞留，从而维持活跃的电化学腐蚀过程[26]。此外，风向主导也可能导致盐粒子在正面沉积更集中，进一步加剧Cl-的局部浓度。而相较之下，背面温度更低，表面水分易于冻结，限制了液态介质的存在与扩散，从而抑制了腐蚀反应的发生。
综合来看，A588钢在极寒大气环境下的腐蚀行为受锈层结构演化、腐蚀介质渗透性以及环境载荷的多重影响。尽管其在常规大气环境中表现出良好的耐腐蚀能力，但在极寒地区服役时仍存在锈层不致密、裂纹多发、Cl-富集显著等问题。
3 结论
(1) A588耐候钢在极寒大气环境中暴露12个月后的年腐蚀速率为11.0
μm/a，明显低于温带海洋环境中普通碳钢和耐候钢。
(2) SEM形貌观察表明，锈层存在较多裂纹及孔隙，局部区域形成鸟巢状结构，腐蚀产物层连续性较差，且正面腐蚀程度高于背面，显示出服役方向与环境耦合作用的影响。
(3) EDS分析显示，Cl在锈层中广泛富集，正面Cl-含量更高，是导致点蚀加剧和锈层劣化的重要因素。
(4) XRD分析表明，腐蚀产物主要包括β-FeOOH、γ-FeOOH、α-FeOOH和Fe3O4/γ-Fe2O3，其中β-FeOOH占主导地位，保护性较强的α-FeOOH含量偏低，导致α/γ*保护性指数整体处于较低水平。
(5) Raman光谱进一步揭示锈层具有显著的分层特征，α-FeOOH集中分布于内层，γ-FeOOH分布于外层，β-FeOOH主要富集在中间层，体现出锈层物相演化受腐蚀介质浓度和环境动态影响的协同作用。
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[J].为探究海工钢极地环境适用性，本工作基于室外暴露实验，通过腐蚀速率测试、腐蚀形貌分析以及腐蚀产物分析等方法，研究了Q460和Q690低合金钢在南极大气环境下暴露1个月和12个月的腐蚀行为。结果表明，南极低温环境冰层、雪层覆盖下电化学腐蚀过程依然可以发生。暴露初期，冰雪冻-融环境导致液膜长周期存在，促进了腐蚀的进行并且加速了局部腐蚀，Q460和Q690钢的腐蚀速率分别为29.7和77.0 μm/a。暴露12个月后，腐蚀速率分别降低至10.7和18.7 μm/a，腐蚀产物主要由α-FeOOH、γ-FeOOH、β-FeOOH和Fe<sub>3</sub>O<sub>4</sub>/γ-Fe<sub>2</sub>O<sub>3</sub>组成。由于Cl<sup>-</sup>的存在，Q460钢和Q690钢的锈层产生了较多的β-FeOOH和裂纹。长周期暴露时，金属表面被冰雪所覆盖，冰层以及锈层对溶解氧及侵蚀性离子的阻挡使得腐蚀的发生受到了抑制,并且局部腐蚀向均匀腐蚀演变。
