The chemical composition of stainless steel forms the basis for classifying this metallurgical material as Ferritic, Austenitic, Martensitic, Duplex, or Precipitation Hardness.
In this guide, you are going to learn two critical aspects of stainless steel:
One is the various stainless steel composition percentage of every chemical element.
Then two, how the chemical composition of steel affects its properties and applications.
Let’s dive right in:
Stainless Steel Chemical Composition
Even before exploring the different stainless steel grades’ chemical composition, it is important to note that iron and chromium are the main alloying elements.
Therefore, maybe we can have the “stainless steel formula” as:
So, depending on the stainless steel properties you can vary the above chemical composition as you will see shortly. Furthermore, the variation in the chemical composition will also determine stainless steel uses.
But first, let’s look at the effects of alloying elements in stainless steel.
It is important to note that iron is the main element in stainless steel material. Ideally, iron is popular for:
- Lustrous nature
- Easily dissolve in dilute acids
- It is chemically active
Most metals are never useful in their pure form. A reason you should mix iron with other elements to form stainless steel with superior properties.
Other elements in stainless steel include:
|Stainless Steel Alloying Element||Function and Properties in Stainless Steel|
|Carbon||· When you alloy carbon and iron, you will get steel
· Most stainless steel grades have low carbon content save for martensitic stainless steel
· High carbon composition in stainless steel implies high hardness and strength
· Usually, it becomes detrimental when carbon forms chrome carbides. It reduces corrosion resistance properties.
· Austenitic and Ferritic have low carbon content.
|Nickel||· When nickel content is more than 8% it produces stainless steel with excellent resistance to corrosion and heat
· Contributes to excellent impact on strength and toughness.
· Improves stainless steel resistance to both oxidation and corrosion
· Help stainless steel maintain excellent toughness, strength, and ductility at cryogenic temperatures
· Makes stainless steel magnetic
|Chromium||· Most stainless steels have at least 10.5% chromium. More chromium implies better corrosion resistance
· Chromium makes stainless steel have a passive and self-repairing property
|Manganese||· It improves hardenability and strength
· Boosts toughness
· Helps in de-oxidation
· 4 to 15%, manganese stabilizes austenitic SS
· In some instances, it replaces the nickel
· Prevents hot cracking since iron sulfide will not form
|Nitrogen||· Increases austenitic stainless steel stability
· It enhances stainless steel yield strength
· Excellent pitting corrosion resistance
|Titanium||· Helps to stabilize carbide. It is critical when welding stainless steel
· Titanium carbide prevents inter-granular corrosion
· Low-carbon stainless steels are easily weldable without the need for stabilization.
|Copper||· It mainly exists as a residual element
· Improves the precipitation hardness properties of stainless steel
· Perfect for stainless steel being used in seawater or an environment with sulphuric acid. Copper improves corrosion resistance in such environments.
|Molybdenum||· Improves austenitic stainless steel resistance to pitting and crevice corrosion. It is an important stainless steel alloying element, especially for applications where chlorides and sulphur are involved.|
|Phosphorus||· Adding phosphorus alongside sulphur improves stainless steel machining properties
· In austenitic stainless steel, phosphorus improves material strength.
· However, it may affect stainless steel corrosion resistance. During welding, stainless may break.
|Selenium||· Initially, manufacturers could add selenium to improve stainless steel machinability properties|
|Silicon||· When melting steel, you will use silicon as a deoxidizing agent
· Exists in small quantities
|Calcium||· Exists in a small amount
· Improves stainless steel machinability properties
|Cobalt||· For stainless steel in nuclear reactor plants, the allowable quantity is 0.2% maximum|
|Niobium or colombium||· It stabilizes carbon
· Boost stainless strength hence not affected in high-temperature environments
|Sulphur||· Exists only in small quantity
· Improves stainless steel machinability properties.
· It may reduce the SS weldability and corrosion resistance
As you can see from the above stainless steel composition table, each element plays a significant as an alloying element. However, in some instances, the alloying element quantity must have certain limits.
You can use the information above when evaluating stainless steel grades. This will help you determine the correct stainless steel uses or applications.
Let’s move a step further to evaluate the stainless steel composition percentages in different grades.
But first, it is important to note the following symbols for various stainless steel alloying elements:
- Carbon – C
- Silicon – Si
- Nickel – Ni
- Manganese – Mn
- Phosphorus – P
- Iron – Fe
- Sulfur – S
- Chromium – Cr
- Titanium – Ti
- Nitrogen – N
- Niobium – Nb
- Molybdenum – Mo
Ferritic Stainless Steel Grade
Generally, Ferritic stainless steels are unique due to their chemical composition and grain structure. Their grain structure features a unique microstructure called ferrite.
That is, they have a body-centered cubic grain.
For the scope of this guide, let’s focus on the chemical composition of Ferritic stainless steel grades.
The most basic grade of Ferritic stainless steel is the 430. Below is a table with the chemical composition:
|430||Remaining %||0.12%||17.0%||0.5%||< 0.04%||< 1%|
At times, this chemical composition of 430 stainless steel may vary depending on the manufacturer. In general, ferric stainless steel’s chemical composition may be:
|409||Remaining||0.03%||1%||1%||[6 x (C+N)] to max 0.65%||0.04%||10.5% to 12.5%||0.015%|
|434||Remaining||0.08%||1%||1%||0.04%||16.0% to 18.0%||0.015%|
|439||Remaining||0.05%||1%||(3 x C + 0.3) to max 1%||1%||[4x (C+N) + 0.15] to max 0.8%||0.04%||16.0% to 18.0%||0.015%|
|4509||Remaining||0.03%||1%||1%||0.1% to 0.6%||0.04%||17.5% to 18.5%||0.015%|
|436||Remaining||0.02%||0.025%||0.8 to 1.4 %||1%||1%||[4x(C+N)+0.15] to 0.8% max||0.04%||16.0% to 18.0%||0.015%|
Note: The values may vary slightly depending on the stainless steel manufacturer.
The chemical composition of Ferritic stainless steel contributes to its unique properties such as:
- Low corrosion resistance and melting point than austenitic SS
- Not suitable for heat hardening
- Magnetic properties
- Easy to weld applications
Austenitic Stainless Steel Grade
The basic austenitic stainless steel is 304 or 18/8 with at least 6% nickel by weight and 16% chromium by weight.
At the same time, there are super austenitics such as the stainless steel 904L. This stainless steel composition has 6% molybdenum.
Depending on the stainless steel grade, they may have titanium, copper, or any other additional alloying element.
|301||Rem. %||0.05% to 0.15%||0.1%||2%||6% to 9.5%||2%||0.8%||0.045%||16% to 19%||0.015%|
|304||Rem. %||0.07%||0.1%||1%||8% to 10.5%||2%||0.045%||17.5% to 19.5%||0.015%|
|304L||Rem. %||0.03%||0.1%||1%||8% to 10.5%||2%||0.045%||17.5% to 19.5%||0.015%|
|201||Rem. %||0.15%||0.05% to 0.25%||1%||3.5% to 5.5%||5.5% to 7.5%||0.045%||16% to 18%||0.015%|
|316||Rem. %||0.07%||0.1%||1%||10% to 13%||2%||2% to 2.5%||0.045%||16.5% to 18.5%||0.015%|
|316L||Rem. %||0.03%||0.1%||1%||10% to 13%||2%||2% to 2.5%||0.045%||16.5% to 18.5%||0.015%|
Again, it is important to note that this % by weight may vary, depending on the stainless steel manufacturer.
The chemical composition of stainless steel gives them:
- Face-centered cubic structure
- Excellent corrosion resistance
- Non-magnetic property
- Heat treatment
- Best for cryogenic applications
Martensitic Stainless Steel Grade
Martensitic stainless steel chemical composition has:
- 2% carbon content
- Chromium ranges between 5% and 18%
- Suitable for heat treatment
- Magnetic properties
|410||Rem. %||0.08% to 0.15%||–||1%||0.75%||1.5%||11.5% to 13.5%||0.04%||0.015%|
|420||Rem. %||0.16% to 0.25%||–||1%||–||1.5%||12% to 14%||0.04%||0.015%|
Duplex Stainless Steel Grade
Duplex stainless is a unique material whose chemical composition combines Ferritic stainless steel and Austenitic stainless steel.
They are known for superior resistance to corrosion cracking and high strength.
The stainless composition is mainly:
- 2205 – known for 22% chromium content and 5% nickel composition by weight
- 2304 – 23% chromium and 4% nickel by weight
Of course, we have other duplex stainless steel grades.
The UR52N is known as super duplex stainless steel grade. It has exceptional corrosion resistance and high strength. Additionally, it has superior resistance to hot chlorides. This also includes sulphuric acids.
Ideally, these stainless steel compositions of both chromium and nickel determine the naming or designations. Of course, they may have other stainless steel alloying elements such as:
|2205||0% to 0.03%||2%||1%||0% to 0.03%||0% to 0.02%||21% to 23%||2.5% to 3.5%||4.5% to 6.5%||0.08% to 0.2%||–|
|UR52N+||0.03% Max||1.5%||0.8%||0.035%||0.02%||24% to 26%||3% to 5%||5.5% to 8%||0.2% to 0.35%||0.5% to 3.0%|
Although Duplex SS has good welding properties, machining can be difficult for high-tensile strength options.
Note: The % by weight may vary depending on the stainless steel manufacturer.
Precipitation Hardening Stainless Steel Grade
Precipitation hardening SS is known for:
- Exception strength – both high tensile strength and yield strength
- Good properties for hardening
The popular grades include 17-4 PH and 15-5 PH. In 15-5 PH, you find 5% nickel by weight and 15% chromium by weight.
On the other hand, the 17-4PH has about 3% to 5% nickel content by weight and 15% to 17% chromium by weight. Of course, these are alongside other elements as you will see in the stainless steel composition chart below for the PH:
|17-4 PH||0% to 0.07%||0% to 1.5%||0% to 0.7%||0% to0.04%||0% to 0.02%||15% to 17%||3% to 5%||3% to 5%||3% to 5%||0% to 0.45%||0% to 0.6%||Rem. %|
From the above information, it’s quite clear that the chemical composition of stainless steel varies depending on the % by weight. These variations affect the properties and ultimately the applications.
Depending on your applications, we will help you choose suitable alloying elements for stainless steel composition.
If you need a complete list of all stainless steels by composition contact Tuolian Metal now.
Stainless Steel Alloying Elements – Source: AZO Materials
Ferritic Stainless Steel – Source: Tuolian Metal
Classes of Stainless Steel – Source: Metal Supermarket
Stainless Steel Grades – Source: Tuolian Metal
What is Stainless Steel – Source: Aperam
Duplex Stainless Steel – Source: Tuolian Metal
Stainless Steel – Source: Britannica
Martensitic Stainless Steel – Source: Tuolian Metal
Stainless Steel(Role of Nickel) – Source: Nickel Institute
PH Stainless Steel – Source: Tuolian Metal