In this article, you will know the different types of stainless steel as well as their properties and uses.
In our previous article, we learned about the different types of metals and their uses.
Metal can be classified into three categories which are: Ferrous Metal, Non-Ferrous Metal, and Alloys.
Stainless steel is a type of ferrous metal that comes under alloy steel which is a type of steel.
So without wasting time let's get started.
What is Stainless Steel?
Stainless Steel is an alloy of iron, carbon, chromium, nickel, silicon, copper, etc.
If any steel has more than 10.5% of chromium then it is considered stainless steel.
Chromium forms as a thin layer of oxide on the surface of the steel
Due to its chromium content, it has excellent resistance to corrosion.
Increasing the amount of Chromium increases the corrosion resistance.
Elements Present in Stainless Steel
The following elements are present in stainless steel:
- Carbon
- Chromium
- Nickel
- Molybdenum
Carbon
Carbon provides strength but forms precipitates i.e harmful to corrosion resistance.
Chromium
Forms a surface film of chromium oxide to make it corrosion-resistant.
Nickel
Enhance ductile property.
Molybdenum
Increase corrosion resistance, and strength at the higher temperature.
Types of Stainless Steel
Stainless steel can be classified into the following types:
- Austenitic Stainless Steel
- Ferritic Stainless Steels
- Martensitic Stainless Steel
- Precipitation Hardening Stainless Steel
- Duplex Stainless Steel
Austenitic Stainless Steel
These stainless steels make up over 70% of total stainless steel production.
These steels are non-magnetic in annealed conditions.
They cannot be hardened by heat treatment. They can be hot-worked or cold-worked.
They contain a maximum of 0.15% carbon, a minimum of 16% chromium, and sufficient nickel and manganese to retain an austenitic structure at all temperatures from the cryogenic region to the melting point of the alloy.
These steels are specified as different grades of stainless steel such as AISI 202, 302, 304, 316, 321, etc.
Properties of Austenitic Stainless Steel
- They are non-magnetic, soft, ductile malleable in character.
- The corrosion resistance of this group of steels is superior to ferritic and martensitic stainless steels.
- In this type of steel heat treatment is not possible.
- Cold working can be performed.
- A forging operation can be done on it.
- It can be used in low and high-temperature applications.
- For non-destructive testing, Penetrant Method is used.
- These stainless steels are found in the FCC structure.
Uses of Austenitic Stainless Steel
These steels are used for food and chemical plants, tubular exchangers, sanitary fittings, aircraft heaters, domestic and industrial utensils, etc.
Ferritic Stainless Steel
These are plain chromium stainless steels with varying chromium content between 11% and 18%, but with low carbon 0.08 to 0.2% content.
They have moderate to good corrosion resistance.
These steels are not hardened by heat treatment by martensitic transformation due to the absence of the austenite phase at any temperature.
The only annealing heat treatment is suitable for ferritic stainless steel.
These steels can be moderately hardened by cold working.
These steels are specified as AISI 405, 430, and 446.
Properties of Ferritic Stainless Steel
- They are magnetic, soft, ductile malleable in character.
- Magnetic below 768°C.
- Cheapest as compared to other types of Stainless Steel.
- As they have BCC structure hence difficult to shape by cold working.
- Good weldability.
Uses of Ferritic Stainless Steel
These steels are widely used for furnace parts, food industries, pressure vessels, heaters, juice-carrying pipes in sugar industries, pots and pans, etc.
Martensitic Stainless Steel
These are commercially developed for cutlery purposes.
They are plain chromium steels containing between 12 to 18% chromium, and a high carbon content of 0.1 to 1.2% compared to other grades of stainless steel.
The stainless steel is of moderate corrosion resistance which can be hardened by heat treatment resulting in high strength and hardness.
These steels are specified as AISI 403, 410, 416, 420, 501, and 502.
Properties of Martensitic Stainless Steel
- It has poor weldability.
- It is magnetic in nature.
- It can sustain impacts and loads.
- Heat treatment is possible.
- Poor corrosion resistance.
Application of Martensitic Stainless Steel
It is commonly used for knife blades, surgical instruments, shafts, turbine blades, paper machinery parts, spindles, pins, etc.
Precipitation Hardening Stainless Steel
The precipitation-hardening stainless steels are iron-nickel-chromium alloys containing one or more precipitation-hardening elements such as aluminum, titanium, copper, niobium, and molybdenum.
The precipitation hardening is achieved by a relatively simple aging treatment of the fabricated part.
The two main characteristics of all precipitation-hardening stainless steels are high strength and high corrosion resistance.
High strength is achieved at the expense of toughness.
Properties of Precipitation Hardening Stainless Steel
- It has elevated strength.
- Good corrosion resistance.
- Good ductility.
- Good tenacity.
- It can be welded.
- Crystal structure of precipitates formed in ferritic and austenitic precipitation strengthened steels.
Applications of Precipitation Hardening Stainless Steel
These steels are used for bulkheads, nibs, skins, and other structural parts.
Duplex Stainless Steel
These steels contain relatively high chromium up to 18 to 28% and moderate amounts of nickel up to 4.5 to 8%.
The nickel content is insufficient to generate a fully austenitic structure and the resulting combination of ferritic and austenitic structures is called duplex.
Most duplex steels contain molybdenum in a range of 2.5 to 4%.
Properties of Duplex Stainless Steel
- These have a high resistance to stress corrosion, cracking, and chloride ion attacks.
- They have a higher tensile and yield strength than austenitic or ferritic steels.
- High toughness and ductility.
- Good weldability.
- Good formability.
Application of Duplex Stainless Steel
They are commonly used in marine applications, desalination plants, heat exchangers, and petrochemical plants.
Advantages of Stainless Steel
- Due to its non-corrosiveness, It is widely used in the surgical, food industry, pharma industries, etc.
- It is ideal for making kitchen appliances.
- High resistance to chemicals, heat, and oxidation.
- It is non-porous, so it has a more hygienic surface than wood and plastic.
Disadvantages of Stainless Steel
- Its cost is high compared to other steels.
- If it is exposed to gases like CO, CO2 carbon will pick up which causes embrittlement of stainless steel.
So here you have to know all aspects related to types of stainless steel.
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