A Complete Guide To Stainless Steel AISI 420

Although austenitic steel is more widely used compared to martensitic steel, this does not mean that martensitic steel like the AISI 420 is not worth considering. It has its pros and cons and specific functions that austenitic steel is not capable of withstanding or performing and vice versa.

Nonetheless, these two types of steel are great and are at the top tier of what they are designed to function.

To better understand the abilities and characteristics of the stainless steel 420, YAOYI provided you with this detailed article to help you make the right purchase decision.

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Table of Contents

What does AISI Stand For?

The meaning of AISI was found back in 1908, and it stands for American Iron and Steel Institute. AISI was one of the companies that contributed a lot of effort together with the Society of Automotive Engineering (SAE) in standardizing the numbering system for steel we have today.

  • We can provide 420 stainless steel with more than semi-hard strength.
  • It can be used in Dental, Shear Blades and other fields.
  • Thickness: 0.1mm~0.76mm

What is Martensitic Steel?

“Martensitic” refers to a solid crystalline structure. In an industrial aspect, martensitic steel is one of the types of stainless steel that is corrosion-resistant. 

But what makes it special? AISI 304AISI 316AISI 321, and other grades are also corrosion-resistant.

For martensitic steel like the stainless steel 420, this stainless can both have a  low or high percentage of Carbon. Martensitic steel also contains a solid solution of iron, which contributes to its toughness in tensile strength.

Learn more about Why Do Customers Choose Yaoyi to Test The 304 Stainless Steel Yield Strength?  

What is Austenitic Steel?

The AISI steels mentioned above (except the sus 420) are all austenitic stainless steel. They are more used in industrial applications than martensitic steel. 

The chemical components of austenitic steel are primarily composed of high chromium content and nickel. These elements give austenitic steel a stronger protective layer against corrosion.

Read on 316L Stainless Steel Properties

The Difference between Austenitic and Martensitic stainless steel

The main differences between Austenitic steel and martensitic steel are their mechanical properties, chemical compositions, and heating treatment.

Martensitic steel can be heat-treated and hardened, but in terms of protective resistance, austenitic stainless steels are the superior choice.

Martensitic steels are used when hardness is critical. 

The perfect examples of this are knives. Have you noticed its surface hardness creates a sharper edge or blade? That is because of that very reason.

Try for free The application’s Guide to 301 Stainless Steel Strip  

What is AISI 420?

AISI 420 is a stainless steel that has excellent hardenability and strength with great corrosion resistance properties that hold out against acidic and alkaline substances.

AISI 420 is great for projects and applications that require good hardenability attributes. sus 420 has a similar resistance to the AISI 410 but the stainless steel 420 is much stronger in terms of hardness.

Get A complete guide to A Complete Guide to 316 Stainless Steel Plate sheets  

How do you Use AISI 420?

AISI 420 offers outstanding ductility in its annealed condition. Moreover, it provides superb corrosion resistance as well when the metal is polished whether it is surface grounded or hardened. The AISI 420 has the highest hardness of 50 HRC (Rockwell C Scale) which is much more than other stainless steel grades with 12% of Chromium.

Common Uses for AISI 420:

AISI 420 is commonly used for cutting instruments or cutlery but of course, it is not only limited to that as it can also be used for other important matters such as:

Surgical Materials

AISI 420 is great for surgical materials because of its hardenability and corrosion resistance. Ideal for cutting hard structures such as bones during critical operations.

It does not also rust, which means that it does not deteriorate which is good for the longevity of the material.

Dental Equipment

The same goes for dental equipment. Sharp mediums for extracting teeth and modifications are necessary, which is why AISI 420 is the right type of steel for the job.

They are very durable and their hardness easily handles dental procedures, and it is also worth mentioning that AISI 420 has great wear resistance of carbon steel.

Shear Blades

Shear blades commonly use stainless steel 420 because this steel grade is very easy to sharpen, and it also has properties that keeps the blade from corroding. YAOYI provides budget-friendly quotes for your cutlery needs for your business.

Diesel Engine Pumps

Since the chemical composition of the AISI 420 contains formidable corrosion resistant properties, it is no surprise that they can be used for diesel engine pumps even in highly aggressive, non-chlorinated environments that can easily harm other steel grades.

Needle Valves

It is not rare for AISI 420 to be used in needle valves since this grade is best suited for this application. Needle valves also need to be durable, which is why AISI 420 and other steel grades that have a high HRC, are perfect for needle valves.

AISI 420 Mechanical Properties

Below are the mechanical properties of sus 420. In this section, you will learn the technical aspects of AISI 420, which will give you a better understanding of why its durability is supreme.

For comparison of other steel grades, you may check YAOYI’s mechanical properties table.

Steel Grade

If you did not know what steel grade means, here is the definition.

The definition of steel grade is to classify different types of steel by looking into its mechanical properties and chemical composition. Each type of steel grade is different from one another as it has its own unique elements and purposes.

For AISI 420, it is capable of having both high or low carbon content, and it has martensitic components. 

Tensile Strength

Tensile strength is the resistance of steel to breaking under tension. Tensile strength plays a vital role in the flexibility or formability of the steel. For sus 420 Stainless steel, it has a tensile strength of 665 PSI (Per square inch) in its annealed condition.

If you are not sure what tensile strength you should use for your projects, you can contact us by clicking/tapping here. YAOYI will guide you to what tensile strength is appropriate for your projects since the wrong tensile strength risks your project from breaking.

Yield Strength

Yield strength is when a steel is stressed by an amount that is less than it yields. This is also an important factor to determine a steel’s durability. Any steel that breaks easily under moderate tension is considered low steel grades that are not suited for big projects such as infrastructures.

In this case, the Yield Strength Minimum 0.2% offset (psi) of AISI 420 is 345, which means that it is capable of going under a large amount of stress without showing any signs of breaking or damage.


Some steels are capable of long stretches and this is important for its formability to be versatile. Steel elongation is the rate or percentage of how much the steel can stretch from its original length. AISI 420 has 11% Elongation in 50mm which is excellent for forming the steel into various shapes without breaking.

AISI 420 Chemical Compositions

The sus 420 has a lot of elements in its chemical composition with Chromium (12%-14%) and Carbon (0.16%-0.25%) having the highest content.

Below are the other elements that AISI 420 contains.

Manganese – 1.5%

Silicon – 1%

Molybdenum – 0.3%

Nickel – 0.1%

Phosphorus – 0.04%

Sulfur – 0.03%

Each of these elements contributes an attribute to the AISI 420. However, it does not outperform the effects of chromium and carbon.

AISI 420 Thermal Properties

The AISI 420 is capable of withstanding extreme temperatures, which is why outdoor exposure to different weather conditions is no problem for the AISI 420.

This is because of its thermal properties. The properties are indicated below. 

Thermal Conductivity

Its test method is ASTM 1461-13 with an as-built of 30 W/m°C which gives it incredible endurance to high temperatures.

Heat Capacity

For its specific heat capacity, with the same method of ASTM 1461-13 it has an as-built of 460 J/kg°C


Questions frequently asked about AISI 420:


Here are commonly asked from consumers who are interested in using AISI 420 for their projects.


Try for free information about the A Complete Guide to Stainless Steel Price  

Is AISI 420 a Food Grade?

In the stainless steel 420-range, many grades meet the minimum chromium requirements for those to be considered a food grade. AISI 420 and AISI 440 are both considered food-grade steels. This is the reason why sus 420 can be used as kitchenware and knives.

Read more about A Complete Guide to Steel Coil Manufacturers 

What is the Primary Composition of AISI 420?

AISI 420 has exceptional hardenability. In fact, it is the upgraded version of the already-tough steel AISI 410. Similar to the AISI 410, the AISI 420 also contains 12% chromium, which is just the right amount to obtain corrosion resistant properties.

Is AISI 420 the Highest Grade of Steel?

No, the highest grade of steel is the AISI 304, this type of steel has an incredibly high tensile strength of 621 MPa (90 ksi) with operating temperatures reaching up to about 870˚C.


In fact, AISI 304 is one of YAOYI’s best selling stainless steel. It has superb corrosion resistance, and it can handle extreme temperatures. 

However, when it comes to hardenability, the sus 420 is the better option.


Keep reading: A Complete Guide to Steel Coil Suppliers

Is AISI 420 Magnetic?

Stainless steel420 is a martensitic type of steel that is capable of providing durability due to its high amount of hardenability properties similar to the AISI 410.


Although it has moderate corrosion resistance, it does have properties that make it magnetic in both its annealed and hardened state.


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Is AISI 420 Reliable?

AISI 420 is safe and reliable when it comes to food applications. This is because AISI 420 is considered as a food-grade type of steel or “cutlery grade”. This alloy can be broken down in the process of sharpening with having their corrosion-resistance remain.


However, for extra corrosion resistance and high moisture uses, surgical steel is the best choice.


Advantages and Disadvantages


Below are the advantages and disadvantages of AISI 420. This section will help you make your purchase decision and give you the final verdict.


In case you are still confused after reading the article,YAOYI’s service team is one call away for the professional help you need.




Here are the key advantages the AISI 420 offers:


Can Withstand Extreme Heat 


The sus 420 has no problems whatsoever with scaling resistance at temperatures ranging up to 650°C. However, any further than that could damage the steel.


Corrosion Resistance


When it comes to corrosion resistance, the stainless steel 420 may not have the strongest resistance compared to common austenitic steels, but they are capable of protecting themselves with corrosion attacks.

In a hardened state, stainless steel 420 stainless steel is resistant to fresh water, acid, air, food, and alkalis. AISI 420 is designed to endure such elements for the best performance. However, the corrosion resistance will fall when it is in its annealed condition.


In fact, its corrosion resistance is lower than SUS 420, with a Chromium content of 17%


AISI 420 is great for various types of knives including carving knives, table knives, and so on. AISI 420 has a moderate corrosion resistance against food, but continuous exposure could lead to pitting corrosion which is something you should consider.


Can Be Heat-Treated


In its annealing stage, SUS 420 can be heated at temperatures ranging from 840°C to 900°C with a slow furnace burning  at 600°C

For process annealing, SUS 420 can be annealed at 735°C to 785°C followed by air-cooling.

In terms of hardening, this process involves heating between temperatures 980°C to 1035°C, and once again followed by air cooling. It is important to keep this in mind that stainless steel 420 should not  be tempered at temperatures between 425°C to 600°C.

Easy to Weld

AISI 420 is surprisingly easy to weld. They are welded using welding rods coated with AISI 420 metals to gain strong joints. They are also pre-heated and post-heated during the process of this stage.

Easy to Machine

In its annealed state, stainless steel 420 is easy to machine. But when its hardness reaches 30 HRC, then that is a different story. It will be difficult to machine since 30 HRC is already hard.


AISI has its cons as well, but depending on what your purpose is, if what you expect matches the capabilities of AISI 420, then it will be a good choice for you.

Here are the main disadvantages of AISI 420.

Weaker Corrosion Resistance

As aforementioned, its corrosion resistance is not as strong as other steel grades. This is because it differs in the elements it is composed of. However, rating its corrosion resistance, it does the job well in environments that are not exposed to high moisture.

Cannot be used in High Chloride Environments

However, in high chloride environments, there is a high probability that  pitting, and rust will occur. This is something you should consider as well.

Hard to Cut
Due to its hardness, they are very hard to cut. This is to compensate for its superb hardenability.

Keep on reading:301 Stainless Steel Foil: Production, Application, and Packaging

Chemical Composition of 4140 Low Alloy Steel

The chemical composition of 4140 Low Alloy Steel plays a crucial role in determining its physical and mechanical properties. Below is an overview of the key elements present in AISI 4140:

  • Chromium (Cr): 0.80% – 1.10%
  • Carbon (C): 0.380% – 0.480%
  • Manganese (Mn): 0.80% – 1.10%
  • Silicon (Si): 0.15% – 0.30%
  • Sulfur (S): 0.040% (maximum)
  • Phosphorus (P): 0.035% (maximum)
  • Iron (Fe): Balanced

The significant amounts of chromium and carbon give 4140 Low Alloy Steel its remarkable strength and hardness. The addition of manganese and silicon provides improved hardenability and enhanced mechanical properties. It is worth noting that the balanced iron content forms the base of this alloy and imparts its overall structural integrity.

Mechanical Properties of 4140 Low Alloy Steel

The mechanical properties of 4140 Low Alloy Steel make it highly desirable for a wide range of applications. The following are the key mechanical properties of AISI 4140:

  • Tensile Strength: 95,000 pounds per square inch (PSI)
  • Yield Strength: 60,200 PSI
  • Elongation: 25.70%

The high tensile strength of 4140 Low Alloy Steel enables it to withstand significant stress and pressure without deforming or breaking. The yield strength represents the stress level at which the material permanently deforms, making it an essential parameter for design considerations. The elongation value indicates the steel's ability to stretch without fracturing, conferring excellent formability.

It is important to note that the mechanical properties of 4140 Low Alloy Steel can be further enhanced through heat treatment processes such as oil-hardening. This aspect makes it a sought-after option for applications requiring superior hardness and strength.

Uses and Applications of 4140 Low Alloy Steel

Thanks to its exceptional properties, 4140 Low Alloy Steel finds diverse applications across several industries. Some common uses include:

  • Aerospace components: AISI 4140 is frequently employed in the manufacture of aircraft parts, including gears, pinions, and shafts, due to its high strength and fatigue resistance.
  • Automotive components: This steel grade is utilized in the production of automotive parts like axles, crankshafts, and connecting rods, where its durability and impact resistance are invaluable.
  • Machinery manufacturing: 4140 Low Alloy Steel is extensively used in the production of machine plates, gears, sprockets, screws, and other machine components that require high strength and resistance to abrasion.
  • Tooling and equipment: With its excellent hardness and toughness, AISI 4140 is a popular choice for tool and die making, as well as in the manufacture of industrial equipment, such as shafts, bolts, and nuts.
  • Oil and gas industry: This steel grade finds application in critical components within the oil and gas sector, including drill collars, stabilizers, and valve bodies, owing to its resistance to high-pressure environments and corrosion.

These are just a few examples of how 4140 Low Alloy Steel contributes to various industries. Its versatility and reliability make it a top choice for manufacturers seeking high-performance materials.

Comparing 4140 Low Alloy Steel with Other Steel Grades

When selecting a steel grade for a specific application, it is important to consider the alternatives available. Here is a comparison between 4140 Low Alloy Steel and other commonly used steel grades:

  • 4140 Low Alloy Steel vs. 4130 Low Alloy Steel: Both AISI 4140 and 4130 low alloy steels offer similar mechanical properties and are often used interchangeably. However, the key difference lies in the carbon content, with 4130 containing less carbon, making it easier to weld.

  • 4140 Low Alloy Steel vs. 4340 Low Alloy Steel: While both steels exhibit excellent strength and hardenability, 4340 low alloy steel offers higher toughness and is ideal for applications requiring impact resistance.

  • 4140 Low Alloy Steel vs. Stainless Steel: Unlike stainless steel, which predominantly contains chromium and nickel, 4140 Low Alloy Steel possesses chromium and molybdenum as its primary alloying elements. This grants it superior strength and hardness, making it preferable for high-stress applications.


In conclusion, 4140 Low Alloy Steel is a remarkable material renowned for its exceptional strength, durability, and versatility. With its unique chemical composition and impressive mechanical properties, it finds diverse applications across various industries. Whether in aerospace, automotive, or machinery manufacturing, AISI 4140 proves to be a reliable and high-performance steel grade.

What is the equivalent of AISI 4140?

A: AISI 4140 is often considered to be equivalent to other steel grades such as SAE 4140, ASTM A519 4140, and DIN 1.7225. These steel grades have similar chemical compositions and mechanical properties, making them interchangeable in many applications.

What is the difference between 4140 steel bar and 4140 steel plate?

A: The main difference between 4140 steel bar and 4140 steel plate lies in their forms and uses. 4140 steel bar is typically a solid cylindrical bar that is used in applications where high tensile strength and toughness are required, such as in the production of shafts and bolts. On the other hand, 4140 steel plate refers to a flat sheet of 4140 steel, often used in the fabrication of machinery parts, tooling, and structural components.

What are the mechanical properties of AISI 4140?

A: The mechanical properties of AISI 4140 include a tensile strength of 95,000 pounds per square inch (PSI), a yield strength of 60,200 PSI, and an elongation of 25.70%. These properties make AISI 4140 a strong and ductile steel grade, capable of withstanding high stress and exhibiting excellent formability.

What are the uses and applications of 4140 Low Alloy Steel?

A: 4140 Low Alloy Steel finds application in a wide range of industries. Its exceptional mechanical properties and versatility make it suitable for uses such as aircraft parts, gears, pinions, shafts, bolts, nuts, machine plates, and more. Additionally, it is commonly utilized in the automotive, oil and gas, and machinery manufacturing sectors due to its strength and durability.

What is the composition of 4140 steel?

A: The chemical composition of 4140 Low Alloy Steel includes 0.80% – 1.10% chromium, 0.380% – 0.480% carbon, 0.80% – 1.10% manganese, 0.15% – 0.30% silicon, with maximum limits of 0.040% sulfur and 0.035% phosphorus. Iron forms the balance of the composition.

What is the hardness of AISI 4140?

A: AISI 4140 has a hardness of approximately 28-32 HRC (Rockwell C hardness scale) when it is in the annealed state. However, this hardness can be further increased through various heat treatment processes such as quenching and tempering.

Can AISI 4140 be welded?

A: Yes, AISI 4140 can be welded using conventional welding methods. However, it is important to note that preheating the steel and using suitable welding techniques can help prevent cracking and ensure a sound weld. Consultation with a welding professional is recommended to achieve optimal results.

How does AISI 4140 compare to stainless steel?

A: AISI 4140 is a low alloy steel, while stainless steel predominantly contains chromium and nickel. The key difference lies in their composition and properties. AISI 4140 offers exceptional strength, hardness, and wear resistance, making it suitable for high-stress applications. Stainless steel, on the other hand, provides superior corrosion resistance and high aesthetic appeal, making it ideal for applications where hygiene and appearance are paramount.

Can AISI 4140 be heat treated?

A: Yes, AISI 4140 can be heat treated to enhance its mechanical properties. Common heat treatment processes include quenching and tempering, which can significantly increase the hardness and strength of the steel. Proper heat treatment can help optimize the performance of AISI 4140 for specific applications.

Where can I find reliable suppliers of AISI 4140 Low Alloy Steel?

A: If you are looking for high-quality AISI 4140 Low Alloy Steel, YAOYI, China’s leading steel manufacturing company, is a trusted supplier. Their team of professionals offers excellent service and expertise to accommodate your steel needs efficiently.

We hope these FAQs have provided valuable insights into 4140 Low Alloy Steel, its properties, and uses. If you have any further questions or need more information, feel free to reach out to YAOYI, your trusted steel partner.

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