Explain the Hardness of Stainless Steel  & Hardness Chart

As an important indicator of material ability, hardness is crucial for the performance evaluation and application selection of stainless steel. We explain in detail the concept, measurement method, influencing factors, significance and methods of improving the hardness of stainless steel, and compare it with carbon steel so that you can better understand stainless steel. Finally, a stainless steel hardness table is attached for reference.

What is the Hardness of Stainless Steel?

Hardness is the ability of a material to resist local pressure deformation or scratching. It is not inherent in the material and is affected by the test method and conditions. Measuring hardness is crucial to evaluating the wear resistance, processing performance and life of the material. For stainless steel, hardness is directly related to its application breadth and durability.

What Is the Standard Hardness of Stainless Steel?

The standard hardness of stainless steel varies by grade:

• Austenitic stainless steels (such as 304 and 316) are typically 70 to 90 HRB (Rockwell B).
• Martensitic stainless steels (such as 410 and 420) can reach 40 to 60 HRC (Rockwell C) after heat treatment, and may be harder.
• Ferritic stainless steels (such as 430) are typically 60 to 90 HRB.

These values ​​can vary depending on the specific alloy composition and processing methods.

Stainless Steel Hardness Test Method

Brinell hardness

The Brinell hardness test is a commonly used hardness assessment method suitable for softer materials. It calculates the hardness by the size of the indentation left by a steel ball when it is pressed into the material. It is expressed in HB, and the larger the value, the harder the material. However, due to its large indentation, it is not suitable for measuring thin plates or small parts.

Rockwell Hardness

Rockwell hardness test is widely used for a variety of materials. The diamond cone indenter is used to lightly press the surface of the material, and the depth of the indentation is measured to obtain the hardness. There are HRA, HRB, HRC and other scales. The HRC scale is commonly used for stainless steel. The larger the HRC value, the harder the material.

Vickers Hardness

Vickers hardness (HV) is a common technique for evaluating the hardness of metals (such as stainless steel) and non-metallic materials. A diamond square cone indenter is used to apply a load to the material, and the hardness is quantified by measuring the diagonal length of the tiny indentation. The smaller the indentation, the harder the material. This technique is known for its high precision, small indentation and good repeatability, but it is necessary to ensure that the sample is flat and the test conditions are stable to ensure accurate results.

Mohs hardness

Mohs hardness is a relative hardness test method that compares the material’s ability to resist scratching. It is divided into ten levels, with level 1 being the softest, such as talc, and level 10 being the hardest, such as diamond. This test is simple but highly subjective and is not suitable for accurately measuring the hardness of metals such as stainless steel.

What Affects the Hardness of Stainless Steel?

The hardness of stainless steel is affected by many factors, mainly including chemical composition, heat treatment process, degree of cold working and microstructure.

Chemical composition

In stainless steel, the chromium, nickel and molybdenum content affects its hardness and corrosion resistance. More carbon increases the hardness, but decreases the corrosion resistance.

Heat treatment process

The microstructure of stainless steel can be changed by heat treatment methods such as quenching and tempering, thereby affecting its hardness. Quenching can significantly increase the hardness of stainless steel, but it is easy to increase brittleness; tempering can improve the toughness of the material while maintaining a certain hardness.

Cold working degree

Cold working such as cold rolling and cold drawing will cause stainless steel to produce work hardening, that is, as the amount of deformation increases, the hardness gradually increases. However, excessive cold working may result in the material becoming brittle and impacting its properties.

Microstructure

The microstructure of stainless steel, such as grain size and phase composition, has a significant effect on its hardness. Refining grains and optimizing phase composition are effective ways to improve the hardness of stainless steel.

The Significance of Stainless Steel Hardness

The hardness of stainless steel has an important influence on its performance in practical applications. Materials with high hardness usually have better wear resistance and scratch resistance, and are suitable for occasions requiring high wear resistance, such as tools, bearings, molds, etc. Stainless steel with lower hardness has better ductility and machinability, and is suitable for occasions requiring forming processing, such as pipes, containers, etc.

Hardness also affects the cutting performance of the material. High-hardness materials are prone to wear of the tool during cutting, but the quality of the machined surface is better. For parts that require higher processing accuracy, appropriate hardness is necessary.

How to Improve the Hardness of Stainless Steel?

There are many ways to improve the hardness of stainless steel, mainly including adjusting the chemical composition, optimizing the heat treatment process, increasing the degree of cold processing, and using surface treatment technology.

Adjusting the chemical composition

The hardness of stainless steel can be improved by increasing the carbon content, adding alloying elements (such as molybdenum, vanadium, etc.) or using special alloying technology. However, attention should be paid to the fact that increasing the carbon content may reduce the corrosion resistance of the material.

Optimizing the heat treatment process

By accurately controlling parameters such as quenching temperature, holding time and cooling rate, the ideal microstructure and hardness can be obtained. At the same time, a reasonable tempering treatment can maintain a certain hardness while increasing the toughness of the material.

Increasing the degree of cold processing

Through cold processing methods such as cold rolling and cold drawing, stainless steel is hardened, thereby increasing its hardness. However, it is necessary to control the processing volume to avoid excessive processing that causes the material to become brittle.

Using surface treatment technology

Such as carburizing, nitriding, surface hardening treatment, etc., can significantly improve the hardness and wear resistance of the material surface without changing the performance of the stainless steel matrix.

Is Stainless Steel Hard Steel?

Stainless steel is not always hard steel. Although some types of stainless steel, such as martensitic stainless steel, can reach very high hardness with proper heat treatment, most stainless steel, such as austenitic stainless steel, are usually lower in hardness and more focused on corrosion resistance. Hard steel usually refers to high carbon steel or alloy tool steel, which has much higher hardness and strength than most stainless steel.

Stainless Steel Hardness Chart

The following are the typical hardness values ​​of some common stainless steel types. Please note that the specific hardness values ​​may vary due to different material processing and heat treatment processes. They are for reference only. In actual applications, it is recommended to determine them based on the test results of specific materials.

Hardness of Stainless Steel vs Carbon Steel

Stainless steel and carbon steel have certain differences in hardness, which mainly stem from their different chemical composition and microstructure.

Chemical composition: Carbon steel consists mainly of iron and carbon and may contain a few alloying elements to improve properties. In addition to iron and carbon, stainless steel also adds alloying elements such as chromium and nickel, which have an important influence on the corrosion resistance and hardness of stainless steel.

Hardness range: Carbon steels have a wide range of hardness, from low to high. Stainless steels have varying hardnesses, from low for austenite to high for martensite and precipitation hardening.

Application field: Due to its excellent corrosion resistance and good mechanical properties, stainless steel has been widely used in occasions where corrosion resistance and hardness need to be considered at the same time (such as chemical equipment, food processing machinery, etc.). Carbon steel is more common in situations where corrosion resistance is not a particular concern (such as building structures, bridges, etc.) because of its low cost and good processing performance.

Hardness of Stainless Steel vs Aluminum

Aluminum: Typically softer than stainless steel, with hardness values depending on the alloy. For example, common alloys like 6061 have a hardness of about 60 to 70 HRB, while harder alloys like 7075 can reach around 90 HRB.

Stainless Steel: Generally has a higher hardness compared to aluminum. Common grades like 304 and 316 typically range from 70 to 90 HRB (Rockwell B) in their annealed condition, while martensitic grades like 420 and 440C can achieve 50 to 65 HRC (Rockwell C) after heat treatment.

What Is the Hardness of 316 Stainless Steel?

The hardness of 316 stainless steel typically ranges from 70 to 90 HRB (Rockwell B) in its annealed condition. When subjected to cold working or other processes, its hardness can increase, reaching about 30 to 40 HRC (Rockwell C). The exact hardness can vary based on specific processing methods and the material’s condition.

What Is the Hardness of 304 Stainless Steel?

The hardness of 304 stainless steel typically ranges from 70 to 90 HRB (Rockwell B) in its annealed condition. Similar to 316 stainless steel, if 304 stainless steel undergoes cold working or other processes, its hardness can increase, potentially reaching about 30 to 40 HRC (Rockwell C). The exact hardness can vary based on specific processing methods and conditions.

What Is the Hardness of 18-8 Stainless Steel?

The hardness of 304 stainless steel, also known as 18-8 stainless steel due to its composition of approximately 18% chromium and 8% nickel, typically ranges from 70 to 90 HRB (Rockwell B) in its annealed condition. If cold worked, the hardness can increase to about 30 to 40 HRC (Rockwell C). The specific hardness can vary based on processing methods and the condition of the material.

What Is the Hardness of 420 Stainless Steel?

The hardness of 420 stainless steel typically ranges from 50 to 60 HRC (Rockwell C) after heat treatment. In its annealed condition, it generally has a hardness of around 30 to 40 HRC. The exact hardness can vary based on specific processing and heat treatment methods.

What Is the Hardest Grade of Stainless Steel?

The hardest grade of stainless steel is often considered to be 440C, a martensitic stainless steel. It can achieve a hardness of around 58 to 62 HRC (Rockwell C) after proper heat treatment. Other hard stainless steel grades include 420 and AISI 630, but 440C is typically recognized for its superior hardness and wear resistance, making it suitable for applications like knives and other cutting tools.

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