Corrosion resistant metals are favored in many applications because of their ability to resist the corrosion process. In general, these corrosion resistant metals possess superior oxidation-corrosion resistance. They also exhibit excellent mechanical strength and can resist thermal deformation and oxidation. Here are the three main types of corrosion resistant metals: ferritic, wrought iron, and duplex stainless steel.
The Different Corrosion Resistant Metals
Besides stainless steel, copper alloys are also a corrosion resistant matal, for example, forms an oxide layer when exposed to oxygen, protecting the base material from oxidation. Brass, bronze, and copper alloys are widely used in electrical equipment, plumbing supplies, and carrying liquids. In addition to those, they’re also used in artwork, industrial products, and structures.
Stainless Steel
Stainless steel is one of the many corrosion resistant metals available today. Its resistance to rust, corrosion, and a wide variety of other reactions makes it ideal for use in various applications. Stainless steel parts can be CNC machined, sheet metal fabrications, 3D-printed, and more. The various post-processing options help to further enhance their corrosion-resistant qualities. Stainless steel is one of more than 200 different alloys, each containing high levels of chromium (up to 10.5%), which creates a passive oxidation layer.
Stainless steel is susceptible to pitting corrosion, a process whereby localized spots of metal become exposed to oxygen. Generally, this process occurs in the presence of chloride ions. The concentration of chloride ions can become uneven in some areas of the surface, causing pitting. Moreover, other conditions such as evaporation and condensation and the presence of oxidizing species increase susceptibility.
Aluminium
The surface of aluminium forms an oxide film that is a result of chemical reactions with water and oxygen. This oxide layer is about five to ten nanometers thick. This protective layer prevents the metal from rusting in water, preventing corrosive reactions. The corrosion rate of aluminum alloys is considerably lower than that of steel and iron in most environments, and it also varies depending on the pH level of the water.
Commercially pure aluminum has a tensile strength of approximately 90 MPa, which limits its use in structural applications. Cold rolling or alloying is one way to increase the strength of aluminium, adding manganese or silicon. Copper, magnesium, zinc, or manganese are common additions to aluminum alloys. Some alloys are further strengthened through heat treatments and cold working. If strength is an important aspect for your application, aluminum may be the best choice.
Copper & Brass
These two metals are commonly used in construction, marine equipment, and appliances. Copper and brass have similar characteristics and are highly resistant to corrosion and rust. Brass is also a good choice for marine equipment because of its high electrical conductivity, moderate strength, and good machinability. Brass and copper are often alloyed to form other materials such as bronze, which is highly corrosion-resistant. They are commonly used in mechanical products, pumps, valves, and fasteners.
Compared to pure copper, brass is the strongest and most ductile of all the metals. It also resists corrosion to a much greater degree than bronze and copper. This makes it a great choice for outdoor furniture, boats, and even cars. Brass alloys are also corrosion-resistant due to their zinc content, which makes them good choices for marine equipment. And because they have lower melting points than bronze and copper, they are also a good choice for marine applications.
Galvanized Steel
The main benefits of galvanized steel include its strength and durability. Because it is coated with zinc, this metal resists corrosion. Galvanized steel is commonly used in fasteners and stands up well to exposure to saltwater and water. It also resists rusting. It is the most cost-effective method of protecting steel from corrosion. It also has the advantage of being ready to use out of the factory.
There are several methods of galvanizing steel. The most common method involves hot-dipping, which entails dipping standard steel in zinc molten. This process bonds the zinc to the steel surface. More complex parts are galvanized using electro-dipping or thermal diffusion. The zinc layer serves the same purpose as the passive chromium oxide layer on stainless steel, preventing the metal from rusting and corroding under mild conditions. However, hot-dip processes result in a layered metal, not a fully alloyed product like stainless steel.
Why Is Stainless Steel The Most Corrosion Resistant Metal?
Stainless steel sheets are widely used in various applications, such as architectural metal work, electronic appliances, kitchen design, chemical containers, medical equipment, marine, etc. It’s a complex material, but the benefits far outweigh the cons. Learn how stainless steel is made and why it is the metal of choice for many applications. This part will explore some of the reasons why stainless steel is the most corrosion resistant metal. Hopefully you’ll find it useful.
- Stainless steel is an alloy of carbon steels. Its resistance to rust results from the reaction of chemical elements in air and water with the steel's surface. This reaction produces a thin, stable film, preventing additional corrosion and limiting oxygen's access to the metal surface. It also gives steel a "stainless" appearance. Its strength, tensile strength, and resistance to oxidation are what making stainless steel the most corrosion resistant metal.
- Stainless steel has been classified into five main groups: austenitic, ferritic, and martensitic. Austenitic stainless steels have higher chromium content and lower carbon content. This means that it is resistant to more acids and corrosive elements than other types of steel. Stainless steel is extremely durable, so it can be used in a wide range of applications.
- Stainless steel's corrosion resistance is largely due to the content of chromium. It contains at least 10.5% chromium, which acts as a protective barrier. Its higher content of chromium reduces the chances of rusting, but it can still corrode in certain conditions. Despite its chromium content, stainless steel is still susceptible to a few types of corrosion.
- Stainless steel is a common name for corrosion resistant metals, but the specific corrosion resistance varies by alloy. Alloys containing more chromium improve corrosion resistance by forming a protective passive layer. This passive layer is not enough to protect stainless steel from corrosive environments. Although stainless steel is highly resistant to many types of acid and alkali environments, it is still vulnerable to corrosion.
- Stainless steel alloys can suffer from scaling when exposed to high temperatures. Scales on hot metal can cause bimetallic corrosion. Bimetallic corrosion occurs when the scales are different in composition from the base metal. Temperature extremes can also cause the metal to lose its protective oxide layer, which increases the risk of corrosion. So, if you want a stainless steel instrumentation valve, it's best to get a piece made with more nickel than the minimum ASTM specifications.
- There are numerous applications where corrosion is a major concern. Offshore drilling sites, for example, are exposed to corrosive water conditions. Other applications that require shielding from saltwater include cables and sensors in marine environments. Choosing a corrosion resistant metal that can resist these extreme conditions is critical. So, why is stainless steel the most corrosion resistant metal? A lot of it comes down to trace amounts.
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