Selection of Stainless Steel Suitable for Environment

Stainless steel is short for stainless steel and acid-resistant steel. Weak corrosive medium such as air, steam, water or the steel with antirust property.

Every kind of stainless steel has good performance in its specific application field. The key to success is to define the usage first, and then determine the correct steel grade.

Let's analyze how to choose stainless steel suitable for usage environment.

1. What is stainless steel?

2. How many kinds of stainless steel?

3. How to choose suitable stainless steel?

1. What is stainless steel?

Stainless steel is an iron alloy containing at least 10.5% Chromium. Chromium produces a thin oxide layer on the steel surface, which is called passivation layer. Increasing the content of chromium can improve the corrosion resistance, which can prevent the surface from further corrosion.

Stainless steel also contains different amounts of carbon, silicon and manganese. Other elements,such as nickel and molybdenum may also be added to impart other useful properties, such as enhanced formability and corrosion resistance.

The corrosion resistance of stainless steel decreases with the increase of carbon content. Therefore, the carbon content of most stainless steels is low, the maximum carbon content of mas is 1.2%, and the carbon content of some steels is even lower than 0.03% (such as 00Cr12). The main alloying element in stainless steel is chromium. Only when the content of chromium reaches a certain value can the steel have corrosion resistance.  Therefore, the general content of Cr (chromium) in stainless steel is at least 10.5%. The stainless steel also contains Ni, Ti, Mn, N, Nb, Mo, Si, Cu and other elements.

Due to the different uses of products, the processing technology and quality requirements of raw materials are also different.

2. How many kinds of stainless steel?

Stainless steel is usually divided into martensitic steel, ferritic steel, austenitic steel, austenitic-ferritic (duplex) stainless steel and precipitation hardening stainless steel.

According to the composition, it can be divided into chromium stainless steel, chromium-nickel stainless steel and chromium-manganese-nitrogen stainless steel. There are also stainless steels specially used for pressure vessels.

3. How to select suitable stainless steel?

By understanding the corrosion mode, it can also be used as a reference for selecting stainless steel types.

General Corrosion - Stainless steel will not corrode as uniformly as ordinary carbon steel and alloy steel. However, for some certain chemicals, especially acids, the passivation layer may be uniformly corroded due to different concentrations and temperatures. Certain high concentrations of hydrochloric acid and sulphuric acid are particularly corrosive to stainless steel.

Pitting Corrosion - The passivation layer on stainless steel will be corroded by some chemicals. In daily materials such as salts and bleaching agents, pitting corrosion can be avoided by ensuring that stainless steel is not exposed to harmful chemicals for a long time or selecting a more corrosion-resistant steel grade.

Crevice Corrosion - stainless steel is supplied with oxygen, and passivation layer can be formed on its surface. In a narrow gap, oxygen cannot always contact the surface of stainless steel, which makes stainless steel vulnerable to erosion.  In order to avoid crevice corrosion, a more corrosion-resistant grade is required.

Stress Corrosion Cracking (SCC) - This is a relatively rare form of corrosion that requires a special combination of tensile stress, temperature and corrosive substances (usually chloride ions). The environment that often occurs is hot water tanks and swimming pools. Another form is called sulfide stress corrosion cracking (SSCC), which is related to hydrogen sulfide in oil and gas exploration and production.

Intergranular Corrosion - This is a very rare form of corrosion. If the carbon content in steel is too high, chromium can combine with carbon to form chromium carbide. This happens when the welding process is between 450 and 850 degrees Celsius. This can be avoided by choosing low carbon grade (so-called "L" grades) or using titanium or niobium steel (preferred carbon bonding).

Galvanic Corrosion - If two different metals come into contact with each other or electrolyte (such as water or other solutions), corrosion occurs. It can be avoided by separating metals with non-metallic insulators such as rubber.

Stainless steel is widely used for its durability and almost maintenance-free surface properties. Stainless steel can be used in furniture, transportation, chemistry, medical treatment, construction and so on. D and D Hardware sells high-quality stainless steel hinge, mortise lock, door handle, door bolt and other door hardware products, which are widely used in hotel, hospital, educational institutions, etc. We also provide complete product support solutions to solve customers' questions.

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