In this article, you will learn the complete overview of stainless steel such as its definition, types, properties, uses, as well as grades of stainless steel, advantages and disadvantages, and many more.
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.
Properties Of Stainless Steel
- It has high ductility and formability.
- Good Mechanical Properties at high and low temperatures.
- It has high resistance to scaling and oxidation at elevated temperatures.
- Good Weldability.
- Good Machinability
- Good Creep resistance.
- Excellent surface finish and appearance.
- Antibacterial properties and It can be steam cleaned and sterilized.
- Doesn't need paint or other surface finishes.
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Types of Stainless Steel
Stainless steel can be classified into the following types:
- Austenitic Stainless Steels
- Ferritic Stainless Steels
- Martensitic Stainless Steels
- Precipitation Hardening Stainless Steels
- Duplex Stainless Steels
Austenitic Stainless Steels
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 AISI 202, 302, 304, 316, 321, etc.
Properties of Austenitic Stainless Steels
- 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 Steels
These steels are used for food and chemical plants, tubular exchangers, sanitary fittings, aircraft heaters, domestic and industrial utensils, etc.
Ferritic Stainless Steels
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 Steels
- 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 Steels
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 Steels
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 Steels
- 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 Steels
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 Steels
- 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 Steels
These steels are used for bulkheads, nibs, skins, and other structural parts.
Duplex Stainless Steels
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 Steels
- 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.
Grades of Stainless Steel
There are more than 150 grades of stainless steel found here we have discussed only some of the commonly used stainless steel grades which are:
- Grade 100 Series
- Grade 200 Series
- Grade 300 Series
- Grade 400 Series
- Grade 500 Series
- Grade 600 Series
- Grade 2205
- Grade 2304
- Grade 2507
- Grade 17-4
- Grade 15-5
- Grade 904L
Grade 100 Series
It is an austenitic type of stainless mainly used in furniture making.
Grade 200 Series
Grade 200 series is austenitic type stainless steel which contains chromium, nickel, and manganese alloy which is used for general purposes such as metalwork.
In this 200 series the most popular two types of stainless steel grades are used:
- Grade 201
- Grade 202
Grade 201
Grade 201 stainless steel is an austenitic stainless steel containing 16 to 18% chromium and 3.5 to 5.5% nickel.
Due to its low nickel content, it provides average protection against corrosion.
However, it is cheaper than other stainless steels, and the concentration of manganese and nitrogen can be increased to improve its yield strength.
The versatility of grade 201 is due to its good formability and weldability.
Grade 202
Grade 202 stainless steel is an austenitic stainless steel containing 17 to 19% chromium, 4 to 6% nickel, and 7.5 to 10% manganese.
This type of grade is mostly used for precipitation hardening and it also has good corrosion resistance, high hardenability, strength, toughness, and weldability.
Grade 300
300 Series is also an austenitic type of stainless steel that contains chromium, and nickel alloy.
This series of grades is used for food utensils, surgical scrub sinks, instruments, etc.
In this 300 series the most popular types of stainless steel grades are used which are:
- Grade 301
- Grade 301L
- Grade 301LN
- Grade 302
- Grade 304
- Grade 304L
- Grade 305
- Grade 309
- Grade 316
- Grade 316L
- Grade 316H
- Grade 321
- Grade 321H
- Grade 347
Grade 301
Grade 301 is an austenitic type of stainless steel that contains lower than 16 to 18% chromium due to this corrosion resistance low.
Grade 301 has high strength and is also available in annealed and cold-worked conditions.
Grade 301L
Grade 301L is a variant of Grade 301 with an improved version of ductility and weldability.
It requires no annealing for maximum corrosion resistance.
Grade 301LN
This is also another variant of 301 which contains higher nitrogen and has a higher work hardening rate.
There is also no need for annealing.
Grade 302
Grade 302 is an austenitic type of stainless steel that contains up to 18% chromium and 8% nickel.
This type of grade has high toughness, tensile strength, yield strength, and also corrosion resistance.
It can be processed at low speeds and also high feed volumes to overcome their work-hardening tendencies.
In this grade, post-weld annealing must be performed.
Grade 304
Grade 304 is the most popular austenitic stainless steel which contains up to 18% chromium and 8% nickel.
So grade 304 is also known as grade 18/8.
It has high corrosion resistance in a wide range of temperatures.
But, it becomes susceptible to pitting corrosion and stress corrosion cracking when exposed to chlorides.
Grade 304L
It is a variant of grade 304 which has a lower carbon percentage than grade 304, thus giving it a higher corrosion resistance.
Grade 305
It is an austenitic type of stainless steel that contains up to 18% chromium, and 10% nickel.
It has high corrosion resistance and strength.
It can be welded with resistance and fusion techniques.
Grade 309
It is a type of austenitic stainless steel that contains up to 22% chromium, 12% nickel, and some amount of carbon.
It possesses excellent corrosion as well as oxidation resistance, and high tensile and creep strengths.
It can also withstand saline environments.
It can be rolled, formed, and deep drawn.
Grade 316
This is the most popular and widely used next to grade 304.
Grade 316 contains elevated amounts of molybdenum and high amounts of silicon, manganese, carbon, chromium, and nickel.
High molybdenum concentration makes it more resistant to pitting and crevice corrosion as compared to grade 304 in saline environments.
It has good forming and welding characteristics.
In this type of grade, there is no need for annealing after welding thin sections.
Grade 316L
Grade 316L is the variant of Grade 316 which contains a minimum amount of carbon and is insusceptible to chromium carbide precipitation.
That's why this grade is preferred where heavy welding requires.
Grade 316H
Grade 316H is also a variant of Grade 316 that contains a higher amount of carbon which makes it have higher tensile and yield strength and is more suitable for high-temperature applications.
Grade 321
Grade 321 is a titanium-stabilized austenitic stainless steel.
when exposed to high temperatures it has excellent resistance to chromium carbide precipitation.
As compared to grade 304 it has high creep and stress rupture properties.
Grade 321H
It is a variant of grade 321 that contains high carbon content which makes its strength at higher temperatures.
Grade 347
It is a niobium-stabilized austenitic stainless steel.
As compared to grade 304 It has higher creep and stress rupture properties.
It has better corrosion resistance and oxidation resistance than grade 321.
Grade 400 Series
It is a ferritic and martensitic chromium alloy series that contains some amount of stainless steel.
This grade is mostly used for car exhausts, cutlery steel, knives, etc.
In this 400 series the most popular types of stainless steel grades are used which are:
- Grade 409
- Grade 410
- Grade 420
- Grade 420HC
- Grade 420J2
- Grade 430
- Grade 434
- Grade 440
Grade 409
Grade 409 is a ferritic type of stainless steel that has the presence of titanium and niobium.
It has good corrosion resistance that is maintained at high temperatures.
It also has good formability and welding characteristics.
This type of grade can be welded by various methods such as arc, resistance spot, and seam welding.
Grade 410
Grade 410 is a type of martensitic stainless steel that contains up to 11.5% chromium.
This type of grade is compatible with water, air, hot gases, food products, as well as most chemicals such as mild acids, nitric acid, concentrated sulfuric acid, etc.
Grade 420
Grade 420 is a type of martensitic stainless steel that contains 0.15 to 0.45% carbon and up to 12% chromium.
It has much lower corrosion resistance than austenitic and ferritic stainless steels but is sufficient to withstand mild acids, alkalis, freshwater, normal atmospheric conditions, etc.
It can be machined easily, but machinability decreases when increasing hardness.
Grade 420HC
Grade 420HC is a variant of grade 420 which contains a higher carbon content.
Due to its higher carbon content gives higher hardness than grade 420.
It has a lower corrosion resistance as compared to grade 420.
Grade 420J2
Grade 420J2 is also a variant of grade 420.
It can be annealed and is used to manufacture surgical instruments, daggers, swords, budget knives, etc.
Grade 430
Grade 430 is ferritic-type stainless steel which contains chromium iron, nickel, and some other alloying elements.
It has good corrosion resistance.
It has good machinability and formability characteristics as well as a low work hardening rate.
Grade 434
This is the most common type of ferritic stainless steel, which contains high molybdenum which increases its corrosion and heat resistance.
Grade 440
It is a ferritic type of stainless steel that contains high carbon.
Due to the high carbon content, it has a higher hardness which makes it suitable for valve components and ball bearings.
Grade 500 Series
It is a heat-resistant chromium alloy series.
Grade 600 Series
It is a martensitic alloy series that is formed by precipitation hardening.
Grade 2205
It is a duplex type of stainless steel that has excellent strength and corrosion resistance.
Grade 2304
It is a duplex type of stainless steel that is almost similar to grade 2205.
Grade 2507
It is a duplex type of stainless steel that has high thermal conductivity, strong chloride stress corrosion resistance, and also has a low coefficient of thermal expansion.
It has excellent corrosion resistance and strong tensile strength.
Grade 17-4
It is a type of precipitation-hardening stainless steel that has both high strength and corrosion resistance.
Its degree of strength can be manipulated through heat treatment.
Grade 15-5
It is a type of precipitation-hardening stainless steel that has high strength and corrosion resistance.
This type of grade is only suitable for hot working.
Grade 904L
It contains 0.02% C, 19 to 23% Cr, 23 to 28% Ni and 4 to 5% Mo.
Advantages of Stainless Steel
- Due to its non-corrosiveness, It is widely used in the surgical, food industry, and 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 stainless steel.
If you have any doubts then you are free to ask me by mail or on the contact us page.
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