金属材料的耐腐蚀评价怎么做

结论：不同类型的腐蚀，评价方法不同，不能一个盐雾试验打天下

医疗器械上的金属件面临多种腐蚀环境：体液、汗液、血液、清洁剂、消毒剂、以及潮湿空气。

而腐蚀有多种类型，各自的机理和评价方法不同：

均匀腐蚀。 表面均匀减薄，相对容易预测。

点蚀。 局部形成蚀孔，危害大于均匀腐蚀，因为局部穿透可能造成突然失效。

缝隙腐蚀。 在缝隙和遮蔽处发生，结构设计相关。

电偶腐蚀。 不同金属接触时的电化学作用。

应力腐蚀。 应力加腐蚀环境的共同作用。

微动腐蚀。 微小相对运动加腐蚀。

用一个盐雾试验评价所有类型，是不充分的。

各类腐蚀的特点

「点蚀」在含氯离子的环境中是主要关注，而人体体液和多数消毒剂都含氯离子。

评价方法的选择

盐雾试验。 加速的大气腐蚀评价，适合表面处理和涂层的评价。但它不能直接反映体内的腐蚀行为。

浸泡试验。 在模拟体液或实际介质中浸泡，测量失重和观察形貌。

电化学方法。 极化曲线、开路电位、阻抗。能定量评价腐蚀倾向和钝化能力，且周期短。

点蚀电位测量。 专门评价点蚀倾向。

缝隙腐蚀试验。 人为制造缝隙的试验。

电偶腐蚀试验。 不同金属组合的试验。

应力腐蚀试验。 施加应力的同时接触介质。

建议按实际的使用环境和关注的腐蚀类型选择方法，而不是默认用盐雾。

电化学方法的价值

这类方法在耐蚀评价中很实用：

周期短。 相比长期浸泡，电化学测量可以在较短时间得到结果。

定量。 能给出腐蚀电位、腐蚀电流、点蚀电位等定量指标。

可比性好。 不同材料或不同处理的对比清晰。

能反映钝化能力。 不锈钢等材料依靠钝化膜防护，钝化膜的稳定性可以通过电化学方法评价。

「点蚀电位」是不锈钢等材料的重要指标 ——电位越高，抗点蚀能力越强。

影响腐蚀的因素

材料成分。 合金元素对耐蚀性的影响。

表面状态。 粗糙度、加工痕迹、残留物。

热处理与加工。 影响组织和残余应力。

焊接。 热影响区可能耐蚀性下降。

钝化处理。 表面钝化能显著提高耐蚀性。

介质。 氯离子浓度、pH、温度、含氧量。

应力。 与腐蚀叠加。

「焊接热影响区」是常见的腐蚀起点，因为焊接改变了局部的组织和成分分布。

「钝化处理」对不锈钢件是有效且成本不高的措施，能明显提高耐点蚀能力。

结构设计上的应对

避免缝隙。 结构上减少不易排水的缝隙。

便于排水。 避免积液位置。

异种金属的隔离。 必须接触时用绝缘隔离。

降低应力集中。 减少应力腐蚀的风险。

表面处理。 钝化、涂层、电镀。

便于清洁。 残留的清洁剂和污物加速腐蚀。

「积液位置」是设计中要专门检查的 ——管件端口、凹陷、盲孔，这些位置的积液会形成缝隙腐蚀的条件。

结果的解读

失重数据。 反映均匀腐蚀速率，但不反映局部腐蚀。

形貌观察。 能看出腐蚀的类型和分布，比失重数据信息量大。

电化学参数。 反映腐蚀倾向和钝化能力。

与使用环境的对应。 试验介质与实际介质的关系。

加速的倍率。 加速试验与实际的对应关系，通常难以精确对应。

「形貌观察」建议作为必做内容 ——同样的失重，均匀腐蚀和点蚀的实际危害完全不同，而只看失重数据分辨不出来。

清洁消毒环境的腐蚀

医疗器械面临的一个特殊腐蚀环境是反复的清洁消毒：

消毒剂的种类。 含氯消毒剂对不锈钢的腐蚀性较强。

浓度与接触时间。 高浓度和长时间接触加剧腐蚀。

残留。 清洁后残留的消毒剂持续作用。

干燥。 未干燥的残留液体形成腐蚀条件。

反复循环。 累积的作用超过单次。

「消毒剂残留」是实际的腐蚀源，清洁后如果冲洗不净或未干燥，残留液体在缝隙中持续作用，这也是结构设计要便于冲洗和排水的原因。

送检准备的建议

提供材料牌号与成分；说明表面处理（钝化、涂层、电镀）；说明使用环境与接触介质；说明清洁消毒的方式与频次；以及提供有代表性的样品（含焊接区域如果有）。

常见的准备不足

信息不全。 材料、工艺、使用环境的信息缺失，导致方案设计缺乏依据。

样品不具代表性。 试制样品或挑选样品，与量产状态有差距。

条件未明确。 测试条件没说清楚，数据的适用范围就不明确。

只看初始值。 忽略了环境和时间作用后的性能变化。

项目不完整。 遗漏了必要的项目，提交时才发现。

这五项在实际委托中出现频率较高，建议在项目启动时逐项确认，因为它们造成的返工成本远高于事前确认所花的时间。

数据的组织与保存

记录的完整性。 条件、方法、设备、样品状态、实测值。

可追溯性。 数据与样品批次、生产批次的关联。

保存期限。 覆盖产品的生命周期。

检索的便利。 需要时能快速定位。

版本的管理。 数据更新时的版本控制。

建议建立统一的数据台账，记录每组数据的来源、条件、适用范围和有效期。数据积累起来之后，后续的产品开发和变更评估都能受益。

我们的做法

做金属件耐蚀评价时，我们会根据实际的使用环境和关注的腐蚀类型选择方法 ——接触体液的用模拟体液，接触消毒剂的用实际消毒剂，关注点蚀的做电化学测量。

形貌观察是我们必做的内容，因为腐蚀的类型比腐蚀的量更能说明问题，而类型只能通过观察判断。

对于有焊接的产品，焊接区域是我们重点关注的位置，因为热影响区的耐蚀性往往低于母材。

如果你有金属件需要做耐蚀评价，可以把材料、表面处理和使用环境发过来一起讨论方法，或者直接联系：132 4819 8029。能力范围见服务介绍，流程见检测流程，更多内容见知识库。

English version

Conclusion. Metal components in medical devices face several corrosive environments: body fluids, perspiration, blood, cleaning agents, disinfectants and humid air. Corrosion itself takes several forms with different mechanisms and assessment methods. Uniform corrosion thins the surface evenly and is comparatively predictable. Pitting forms localised cavities and is more dangerous than uniform corrosion, since local penetration can cause sudden failure. Crevice corrosion occurs in gaps and shielded areas and relates to structural design. Galvanic corrosion arises electrochemically where dissimilar metals meet. Stress corrosion arises from stress combined with a corrosive medium. And fretting corrosion arises from small relative movement combined with corrosion. Assessing every type with a single salt spray test is inadequate.

Characteristics of each type. Uniform corrosion occurs in general corrosive environments, is predictable and can be accommodated by margin. Pitting occurs in chloride-containing environments, penetrates locally and resists prediction. Crevice corrosion occurs in structural gaps and shielded areas, is concealed and develops quickly. Galvanic corrosion occurs where dissimilar metals contact and accelerates attack on the more active metal. Stress corrosion occurs under stress in specific media and produces sudden cracking. Fretting corrosion occurs with micromotion and is the concern for implants. And intergranular corrosion arises from microstructural problems and causes abrupt loss of strength. Pitting is the principal concern in chloride-containing environments, and body fluids and most disinfectants contain chloride.

Choosing assessment methods. Salt spray testing accelerates atmospheric corrosion and suits assessment of surface treatments and coatings, though it does not directly reflect corrosion behaviour in the body. Immersion testing places specimens in simulated body fluid or the actual medium and measures mass loss with morphological observation. Electrochemical methods including polarisation curves, open circuit potential and impedance quantify corrosion tendency and passivation capability in a short time. Pitting potential measurement specifically assesses pitting tendency. Crevice corrosion testing creates artificial crevices. Galvanic corrosion testing examines metal combinations. And stress corrosion testing applies stress while exposing to the medium. Choose the method from the actual service environment and the corrosion type of concern rather than defaulting to salt spray.

The value of electrochemical methods. These are practical in corrosion assessment. They are quick, giving results in far less time than prolonged immersion. They are quantitative, yielding corrosion potential, corrosion current and pitting potential. They compare well, distinguishing materials and treatments clearly. And they reflect passivation capability, which matters because stainless steels rely on a passive film whose stability electrochemical methods can assess. Pitting potential is an important indicator for stainless steels: the higher the potential, the greater the resistance to pitting.

Factors affecting corrosion. Material composition determines corrosion resistance through alloying elements. Surface condition covers roughness, machining marks and residues. Heat treatment and processing affect microstructure and residual stress. Welding may reduce corrosion resistance in the heat-affected zone. Passivation treatment markedly improves resistance. The medium matters through chloride concentration, pH, temperature and oxygen content. And stress combines with corrosion. Weld heat-affected zones are a common corrosion initiation site, since welding alters local microstructure and element distribution. Passivation is an effective and inexpensive measure for stainless steel components, markedly improving pitting resistance.

Design responses. Avoid crevices, reducing gaps that cannot drain. Enable drainage, avoiding places where fluid collects. Isolate dissimilar metals with insulation where contact is unavoidable. Reduce stress concentration to lower stress corrosion risk. Apply surface treatments including passivation, coating and plating. And design for cleaning, since residual cleaning agents and soil accelerate corrosion. Fluid-collecting locations deserve a specific design check: tube ends, recesses and blind holes collect fluid and create the conditions for crevice corrosion.

Interpreting results. Mass loss data reflect uniform corrosion rate but not localised attack. Morphological observation reveals the type and distribution of corrosion and carries more information than mass loss. Electrochemical parameters reflect corrosion tendency and passivation capability. Correspondence with the service environment concerns the relationship between test medium and actual medium. And acceleration factors relating accelerated testing to real service are generally hard to establish precisely. Morphological observation deserves to be a standing item: the same mass loss from uniform corrosion and from pitting carries entirely different practical risk, and mass loss data alone cannot distinguish them.

How we handle it. For corrosion assessment of metal components we choose methods from the actual service environment and the corrosion type of concern: simulated body fluid for body contact, actual disinfectants for disinfection exposure, and electrochemical measurement where pitting is the concern. Morphological observation is a standing item for us, since the type of corrosion says more than its quantity and type can only be established by observation. For welded products we attend particularly to the weld region, since heat-affected zone corrosion resistance is often below that of the parent material.

Send us the material, surface treatment and service environment and we will discuss the method. Phone or WeChat: +86 132 4819 8029.