1、 Corrosion under scale

正好在沉淀物下面或缝隙内，溶液中的氧含量是低的，在缝隙的外面大量溶液中的氧含量很高，这就建立了一个电池，其沉淀物下或缝隙中是阳极而其外面是阴极。含氯化物介质的缝隙的内部，pH值下降而氯化物浓集。这种酸性氯化物条件导致腐蚀加快并且是自动起媒介作用的。

Just under the sediment or in the crevice, the oxygen content in the solution is low, and outside the crevice, the oxygen content in a large number of solutions is very high, which establishes a battery. Under the sediment or in the crevice is the anode, and outside it is the cathode. In the crevice of chloride containing medium, pH value decreases and chloride concentrates. This acidic chloride condition results in accelerated corrosion and acts as an automatic mediator.

接着便发生了严重的局部腐蚀。这种腐蚀形式的例子：当一个不锈钢紧固件放置在一块不锈钢钢板上并暴露于含氯化物的水中时产生。缝隙腐蚀可以在螺栓头或垫圈作为阳极区时发生。防止沉淀物和结垢生成或使用高合金含量的材料将有助于减少缝隙腐蚀。

Then severe localized corrosion occurred. An example of this form of corrosion: occurs when a stainless steel fastener is placed on a stainless steel plate and exposed to chloride containing water. Crevice corrosion can occur when the bolt head or gasket is used as the anode area. Preventing the formation of deposits and scales or using materials with high alloy content will help to reduce crevice corrosion.

二、剥落腐蚀

2、 Exfoliation corrosion

在此情况下，金属表面上形成疏松、片状的腐蚀层。即使低速流动也会将腐蚀物的疏松层很容易地除去。于是，新的未腐蚀的金属又被暴露出来，从而将形成许多另外的片状层。再一次重复，这些片状层被很容易地除去并且过程在继续进行着。使用不易起化学反应的合金可以避免剥落腐蚀。

In this case, a loose and flaky corrosion layer is formed on the metal surface. Even if the flow rate is low, the loose layer of corrosives can be easily removed. As a result, new uncorrosive metal is exposed, and many other lamellar layers are formed. Again, these flakes are easily removed and the process continues. Exfoliation corrosion can be avoided by using alloy which is not easy to react.

三、晶间腐蚀

3、 Intergranular corrosion

出现于某些特殊的合金中，通常当它们在焊接或热处理期间加热到其敏感温度区时即可能会发生晶间腐蚀。当诸如某些不锈钢合金加热到425～870℃时，铬的碳化物即会在晶粒边界析出。

Intergranular corrosion occurs in some special alloys when they are heated to their sensitive temperature zone during welding or heat treatment. When some stainless steel alloys are heated to 425-870 ℃, chromium carbides will precipitate at grain boundaries.

导致碳化物附近出现贫铬区同时影响晶界区的钝化性。在特殊介质中，如硝酸或高温水中，可能出现低铬区的溶蚀现象。晶粒是以一种砂糖似的表面出现的，当用一取样器擦过时，它们很容易被擦掉。不锈钢和镍合金的晶间腐蚀可以通过采用低碳合金、加入碳化物形成元素如钛或铌，或利用稳定化退火来使之避免。

The results show that the chromium poor zone appears near the carbide and the passivation of the grain boundary zone is affected. In special media, such as nitric acid or high temperature water, the corrosion of low chromium zone may occur. Grains appear as a sugar like surface, which can be easily wiped off by a sampler. Intergranular corrosion of stainless steel and nickel alloy can be avoided by using low carbon alloy, adding carbide forming elements such as titanium or niobium, or stabilizing annealing.