Stainless steel is very well-known for its anti-corrosion capable from the effects that cause common steel and iron (and other materials) to rust. However, many people do not know why stainless steel is “stainless” and why it is the preferred material for countless manufacturing applications such as household appliances, medical equipment, architectural works… So does stainless steel get rusty? Can elements cause corrosion or rust to stainless steel?
Of course, it’s important to know that stainless steel is not completely free from corrosion. Under certain circumstances, stainless steel alloys can corrode, show signs of rust or other problems. This often leads to the question: “What corrodes stainless steel?” In this article, we’ll look at what makes stainless steel different from regular steel and what elements can actually cause it to corrode.
Why is it called stainless steel?
According to the experiments, the chemical elements in stainless steel react with oxygen from water and air to form a very thin, stable film… The presence of this stabilizing film prevents additional corrosion by acting as a barrier which limiting the access of oxygen and water to the layer below the metal surface.
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5 Elements can cause stainless steel to corrode
There are several reasons why a piece of stainless steel may begin to rust. However, there are hundreds of different stainless steel alloys so what can cause a corrosive stainless steel alloy may not affect other alloys. Here are five elements that can cause corrosive stainless steel.
1: Strong chloride can cause corrosion pitting on stainless steel
Many types of stainless steel alloys will be extremely corrosive when exposed to chloride-rich environments (such as salt). For example, stainless steel grade 304 when used in naval applications, over time can start corrosion pitting due to contact with seawater (very rich in salt) or sea breeze which is also rich in salt.
To avoid corrosion pitting, the most important point is to use stainless steel type which has the special strong resistance to chloride – such as stainless steel grade 316. In addition, a special dedicated coating can prevent stainless steel surface contact directly with chloride in the environment.
2: Bipolar Electrochemistry/electroplate corrosion due to welding different stainless steel alloys
A basic mistake that some manufacturers may suffer when creating a form of custom stainless steel wire or sheet is that they can weld two different types of steel together.
Why is this a problem?
When two different types of steel are connected through a common electrolyte material (such as water or welding material), there may be an electric current from one material to the other. This will make it easier for steel to receive new electrons, become an “anode” and start to corrode faster.
The speed of this corrosion will vary depending on a number of elements such as the specific type of stainless steel, type of welding material used, temperature and surrounding humidity; and the area of surface of the steel connected with each other.
Precautions
The best preventive method for bipolar electrochemistry corrosion is to avoid permanent connection with two different types of steel from the beginning. The second method is to seal them with a coating to prevent electrons moving from the negative to the anode.
It should also be noted that the usage of welded fillers totally different from the connected steels can also lead to electrical corrosion at the welding position.
3: Embed iron or steel on stainless steel
In some applications, granules from steel or iron can be transferred to the surface of a stainless steel part. These iron or steel granules can break the protective oxide layer of stainless steel billet – damaging its corrosion resistance causing it start to rust.
The difference between this issue and the bipolar electrochemistry corrosion problem listed above is the contact between totally different metals. A common reason for normal iron or steel is embedded into a part or stainless steel billet that the device is used to handle this material can be used for the other material without properly cleaned.
To prevent embedding normal steel or iron (or any other metals) to stainless steel billet, it is important to carefully clean and prepare equipment when switching to new materials. Some devices, such as steel brushes, are never used the same one for different types of metal.
4: Apply extremely high temperature for stainless steel
Stainless steel alloys usually have very high melting point (common temperature is 1400-1450°C). However, while metal does not melt at high temperatures, it can undergo other changes that affect its anti-corrosion.
For example, elasticity is a common problem with stainless steel alloys when they are exposed to extreme temperature (such as the temperature used in many heat treatment/composting processes). When the scales forming on hot metals, the remaining flaking material can cause bipolar electrochemistry corrosion because the scales element are different from the basic metal elements.
In addition, too high temperature can cause stainless steel alloys to lose the protective oxide layer, increasing the risk of corrosion until the oxide layer can be formed again.
To prevent corrosion caused by elasticity or other issues caused by extremely high temperature, it is important to check the proposed operating temperature for any specific stainless steel to make sure the heat level used in your production process do not exceed those limits.
5: Unpredictable environmental elements
There are many cases where manufacturers can create a perfectly customized stainless steel product according to specifications, only to be corroded due to some unpredictable environmental elements. The presence of salt and moisture in the air due to the factory’s coastal location is an example of environmental elements that may be missed in the design document.
When using stainless steel to produce any product, it is important to consider as many environmental elements as possible. This helps ensure that products for different uses or stainless steel parts will resist corrosion as long as possible, instead of being rusted immediately.
Thank you for your interest in the article: “Elements can cause corrosion or rust to stainless steel” of OSS Dai Duong. Hopefully our article will help you to understand more about stainless steel products and how to protect and keep it longer.
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