Steel types

Understanding Steel Hardness and Toughness in Kitchen Knives

When buying a kitchen knife, the hardness of the steel is just one factor to consider. Extremely hard steel without the necessary toughening agents can be impractical, as it may chip easily. The ideal blade combines high hardness with durability, creating a knife that retains sharpness without compromising strength. In our opinion, Aogami Blue Steel and ZDP-189 are excellent steel choices for kitchen knives due to their balance of these properties.

What is Rockwell Hardness?

The Rockwell hardness scale measures the hardness of materials using a standardized test, which gauges “hardness” as “resistance to localized penetration.” During this test, a “penetrator” applies force to the material, measuring the net depth of penetration after applying a standardized load.

Hardness and Toughness

Rockwell hardness is expressed as a numerical value (without a unit) on various scales, depending on material type and test conditions. For instance, the Rockwell C scale is commonly used for hard steels, while scales R and M are used for other materials. Generally, a higher number on a specific scale indicates a harder material, with a rating written as, for example, 61 HRC (meaning 61 on the Hardness Rockwell C scale).

In practice, for every two additional Rockwell points, a knife’s sharpness retention approximately doubles. For example, a knife rated at 52 HRC may stay sharp for about a week with regular use, while a knife at 62 HRC may remain sharp for nearly 12 months under the same conditions.

Comparing European and Japanese Knives

European knives (such as Sabatier, Gude, Zwilling, Henckels, and Wusthof) generally use softer steels with lower carbon content but higher toughness. These knives typically fall between 54 and 58 HRC, making them easy to hone with a steel rod. In Western professional kitchens, it’s common to hone these knives daily or even several times a day. Cheaper Chinese knives, often found in kitchen knife blocks, usually have a hardness of around 52 HRC, meaning they hold an edge for a shorter time and require more frequent sharpening compared to Japanese knives made from harder steels.

For instance, Global, one of the most well-known Japanese kitchen knife manufacturers, uses Cromova steel with a hardness of 58 HRC, which is softer than the steels used by other Japanese brands. Significant differences exist even within Japanese knives, and the brands we select at JapaneseKnives.com offer a particularly good value for quality. Comparing these to European knives with lower-quality steels (<56 HRC) isn’t relevant due to the superior quality of Japanese steels.

Some Henckels knives (like those in the Miyabi series) reach hardness levels of 61 or even 66 HRC. These are produced in Japan for Henckels, as are knives from brands like Cold Steel, Fällkniven, and Spyderco (mostly pocket knife producers) who rely on Japanese manufacturing for their premium lines.

Chinese-Made Knives with Japanese Steel

Today, many companies manufacture knives in China, using Japanese steel (often layered steel with a VG-10 core) assembled by inexpensive Chinese labor. These knives are attractively priced, but finishing, polishing, and handle quality often fall short, resulting in inconsistent quality. Due to limited knowledge of traditional forging, these knives are frequently not properly hardened and are sometimes sharpened on non-water-cooled grinding stones, which can overheat the steel and reduce the Rockwell hardness. While Japanese VG-10 steel knives are typically rated between 60 and 61 HRC, these Chinese-made knives often measure much lower, rendering them no harder than basic knives at half the price.

Types of Knife Steels

Steel comes in many compositions. Technically, “stainless steel” is a misnomer, as all steels can rust without proper care. A better term is “stain-resistant.” Generally, chromium is the key to corrosion resistance, and knives with at least 11% chromium are highly stain-resistant. In this document and elsewhere on this site, the term “stainless” should be understood as “stain-resistant.” There’s a significant relationship between hardness (measured on the Rockwell C scale, or HRC) and toughness, and steel producers continually seek an optimal balance. Complex alloys and exotic elements are primarily added to enhance steel toughness.

It’s also important to understand that forging and tempering methods influence hardness, so variations exist in hardness levels even among different knife makers. For example, Shirogami White Steel #1, a traditional, highly pure Japanese steel, is not particularly tough but can be tempered to extreme hardness. Thus, it commonly varies from 60 to 65 HRC.

Many manufacturers produce steel for Japanese kitchen knives. While VG-10 remains a popular choice in higher-end knives, steel from the following makers is also frequently used:

Takefu Special steel (Japan)

• VG-10 (60-61 HRC) - Stainless -
• VG-5 (60 HRC) - Stainless -
• VG-2 (59-60 HRC) - Stainless -
• VG-1 (59-60 HRC) - Stainless - (identiek aan VG-10 maar dan zonder Vanadium en Kobalt)
• V2 (58-61 HRC) - non-Stainless -
• V1 (58-59 HRC) - semi-stainless -
• SG-2 of R2 (62-63 HRC) - Stainless -

Hitachi Steel Ltd (Japan) (“Yasuki Hagane” YSS (Yasuki Speciality Steel))

Non Stainless:

• Aogami Super (63-65 HRC)
• Aogami Blue #1 (Ao ko of Ao ichi ko) (62-64 HRC)
• Aogami Blue #2 (Ao ni ko) (61-63 HRC)
• Shirogami White #1 (Shiro-Ko 1 of Shiro ichi ko) (60-64 HRC)
• Shirogami White #2 (Shiro-Ko 2 of Shiro ni ko) (60-63 HRC)
• Shirogami White #3 (58-62 HRC)
• Kigami Yellow #1 (60-62 HRC)
• Kigami Yellow #2 (60-62 HRC)
• Kigami Yellow #3 (59-60 HRC)

Stainless:

• ZDP-189 (64-67 HRC), 3% carbon en 20% chromium (comparable to Cowry X and also known as MC66)
• SLD-Magic (60-62 HRC)
• SLD of SKD11 (60-64 HRC)
• Gingami #1 up to #5 (also GIN-1 of G1 ) (58-61 HRC)
• AUS-8
• AUS-10
• SRS-15
• SRS-13
• SK-5

Generally, Shirogami steel (White Paper steel) can achieve a sharper edge, while Aogami steel (Blue Paper steel) maintains sharpness for longer. For traditional Japanese knives like Yanagiba and Deba, Shirogami White #1 is often recommended due to its exceptional sharpness. Aogami, however, is a better choice for more versatile, everyday use as it combines hardness with improved edge retention. Aogami steel is typically more expensive than Shirogami. Essentially, Aogami is Shirogami with added elements like tungsten and chromium, making it tougher and more durable.

Types of Shirogami and Aogami:

1. Shirogami (White Paper Steel)  
   Shirogami steel, or White Paper steel, is revered for its purity and ability to take on an extremely sharp edge. Due to its high carbon content and minimal impurities, Shirogami White #1 and #2 are highly sought after in Japanese knife making, especially for precision tasks like slicing sushi or cutting delicate fish fillets. The edge sharpens finely but can be somewhat brittle if not handled carefully.

2. Aogami (Blue Paper Steel)  
   Aogami steel adds elements like tungsten and chromium to Shirogami’s base formula, enhancing its toughness and making it more resistant to wear. It also tends to maintain its edge longer than Shirogami, although it is known to be prone to rust and staining. Regular cleaning and drying are essential to prevent corrosion, making it a great choice for professional use where knives are well-maintained. Aogami Super, a variant of Aogami, also includes molybdenum and vanadium, making it one of the hardest and most resilient steels available. For these reasons, Aogami Super is highly prized among Japanese knife enthusiasts, alongside ZDP-189, as one of the best steels for kitchen knives.

3. Kigami (Yellow Paper Steel)  
   Kigami steel is a more affordable option compared to Shirogami and Aogami, commonly used in less expensive kitchen knives. Kigami #2, with its relatively higher carbon content, is suitable for budget-friendly kitchen knives that can still hold a sharp edge, although it does not offer the same sharpness or edge retention as Shirogami or Aogami.

The color terminology (White, Blue, and Yellow) does not refer to the color of the steel itself but rather to the colored paper Hitachi used to wrap the steel bars when delivering them to Japanese forges. Thus, the term “Blue Paper Steel” simply means “steel wrapped in blue paper,” and likewise for White and Yellow paper steel.

Some Japanese knife blades are marked with the type of steel used. This information can help you understand the unique properties of your knife and care for it properly. By checking the engravings or stamps on the blade, you can identify which type of steel has been used in your knife, allowing you to choose the appropriate maintenance routine.

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AUS8 steel, also referred to as 8A or informally as “Molybdenum Steel,” is widely popular for its affordability and versatility in household knives. This stainless steel is corrosion-resistant, easy to sharpen, and, most importantly, offers impressive sharpness. Here, we’ll dive deeper into the unique qualities of AUS8 stainless steel to help you determine if it’s the right fit for your kitchen needs.

What is AUS8 Stainless Steel?

AUS8 stainless steel is highly valued by both professionals and home cooks for its balanced characteristics: it resists rust, holds an edge reasonably well, and can be sharpened easily. Often marketed as “Molybdenum Steel,” “Molybdenum-Vanadium Steel,” or even “INOX Steel,” AUS8 contains specific elements like molybdenum and vanadium that set it apart from more basic stainless steels. However, it’s important to note that there is no formal “Molybdenum Steel.” These labels are applied to various types of stainless steel, including AUS8, and are generally used as a simple way to communicate the steel’s qualities.

Why the Different Names?

Manufacturers sometimes use names like “Molybdenum Steel” instead of AUS8 to avoid overly specific comparisons between AUS8 knives across different brands, as the steel composition is only part of the equation. The quality of a knife also depends heavily on how the steel is processed and manufactured. In fact, any steel containing molybdenum could be called “Molybdenum Steel,” and some brands choose names based on other elements or specific manufacturing processes, especially when higher-end or rare elements are added.

The Role of Molybdenum in Knife Steel

About 30-40 years ago, stainless steel knives often had lower carbon content—around 0.6%—and included steels like AUS6 and 420J2. These steels had limited edge retention and hardness, and were typically free from added elements like molybdenum or vanadium. At the time, many perceived stainless steel as inferior to carbon steel in terms of sharpness and longevity, leading to the idea that “stainless steel knives are dull and hard to sharpen.”

The introduction of molybdenum and vanadium was a game-changer. These elements enhanced the durability, edge retention, and overall performance of stainless steels, shifting public perception and making stainless knives a much more appealing option. The addition of molybdenum, especially when combined with about 13% chromium, improved rust resistance, sharpness, and durability. Manufacturers took advantage of these qualities and began to market their knives as “Molybdenum Steel” or “INOX Steel,” highlighting the advanced rust resistance and sharper edges.

Why Choose AUS8 Steel for Your Kitchen?

AUS8 steel is ideal for everyday kitchen knives because it balances affordability with performance. Its unique blend of molybdenum and vanadium gives it the strength and edge retention needed for regular kitchen tasks, while also ensuring the steel resists rusting and staining. Because it’s easy to sharpen, AUS8 knives are a great choice for home cooks and professionals alike who want a reliable, low-maintenance knife that stays sharp with minimal upkeep.

In summary, AUS8 stainless steel has come to be a highly accessible and reliable option for anyone looking for a durable, rust-resistant knife that’s both sharp and easy to maintain—an ideal choice for practical, everyday kitchen use.

High-Speed Powdered Stainless Steel (R2, SG2, SRS13, SRS15, ZDP-189)

This category includes steels like SRS13, SRS15, R2, and SG2, all powdered stainless steels with a Rockwell hardness of 62–63. Known for their exceptional hardness and edge retention, these steels share similar characteristics, so they’re grouped together here.

While VG10 has become a staple in knife making today, Powdered Steel is often regarded as the future of high-performance knife steel. Also known as High-Speed Steel, Tool Steel, or Die Steel, it is valued for its toughness and durability. Powdered steels are often used in hard-wearing tools, such as dental drills and metal-cutting tools, where extreme durability and sharpness are critical. When applied to knives, Powder Steel allows for blades with an unparalleled cutting edge that stays sharp through heavy use.

Powder Steel knives are precision tools and require careful handling, especially because of their high hardness, which can make the blade somewhat brittle if not treated well. Thin-edged Powder Steel knives, in particular, may occasionally chip, a minor trade-off for their outstanding performance and razor-sharp edge.

Another powdered stainless steel in this category is the "King of Modern Steels" ZDP-189, is even harder than R2 and SG2, making it one of the toughest high-speed powdered steels available for kitchen knives.

Additional Insights: Japanese Steel in Kitchen Knives

1. Patina Formation on Carbon Steel  
   High-carbon steels like Shirogami and Aogami will naturally develop a patina over time, a protective layer that can help reduce corrosion. Many chefs and knife enthusiasts see patina as a sign of a well-used and well-cared-for knife, adding a unique look that reflects the knife’s history in the kitchen.

2. Care Tips for High-Carbon Steels  
   Given the tendency of Aogami and Shirogami steels to rust, it’s essential to dry knives thoroughly after each use. Many knife users apply a thin layer of camellia oil or another food-safe oil to protect the blade, especially when storing knives for extended periods. This step helps preserve the steel and prevent rust, enhancing the knife’s longevity.

3. Cost and Performance Balance  
   While high-end Japanese steels like Aogami Super and ZDP-189 are highly prized for their sharpness and durability, they come with a higher price tag and often require more maintenance. Knives made from these steels are ideal for those who prioritize performance and are willing to invest time in care. For those seeking a balance of affordability and quality, Kigami and standard Shirogami knives provide an accessible entry point into high-carbon Japanese steel knives.

These elements reflect the rich craftsmanship and tradition behind Japanese knife making, where steel selection, blade design, and forging technique come together to create knives that are both functional tools and works of art.

Overview of some knife Steels used in kitchen knives: Pros and Cons for Kitchen Knives

When choosing a kitchen knife, the type of steel used is crucial as it affects the durability, sharpness, and ease of maintenance. Below is an overview of commonly used steels, their characteristics, and how they perform in the kitchen.

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• Surgical Steel

Often referred to as “surgical steel” or “stainless surgical steel,” there’s no official “surgical steel” in the knife industry. This term is usually applied to softer, less durable steels, such as 17-4, 17-4 PH, and 455 stainless steel. Although very rust-resistant, these steels are too soft for quality kitchen knives. Marketers frequently use the term “surgical steel” to give products a premium image, but in reality, knives made from this steel (like 420 steel) are often low-quality and cheaply made.

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• 420 Series

420 steel has very low hardness and a carbon content between 0.3% and 0.5%. It is extremely rust-resistant, making it suitable for dive knives but not ideal for kitchen knives as it quickly dulls. Many budget knives use this steel.

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• 440A and 440B

Common in low-cost kitchen knives, these steels are suitable for basic tasks but lack the durability and edge retention needed for quality kitchen knives. They offer a step up from 420 but still fall short for intensive kitchen work.

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• 440C

Once considered a good knife steel (30 years ago), 440C offers decent wear resistance and rust resistance. Though now somewhat outdated, some manufacturers still use 440C, as it can be effective in kitchen knives if properly heat-treated.

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• Sandvik 12C27 

This Swedish steel, known for being used in razors, has good sharpness retention. Although not exceptional among kitchen knives, it can be honed to a fine edge and resists rust, making it a solid choice for entry-level knives.

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• Sandvik 19C27

Similar to 12C27 but with higher carbon and manganese, allowing it to achieve a higher hardness (up to 60-62 HRC). Many Japanese and Western brands, like Kagemitsu, use this steel for its excellent edge retention.

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• Sandvik 13C26

Similar to 12C27 but with less chromium and more carbon, making it slightly harder and more wear-resistant. Comparable to AEB-L steel, which is highly regarded by knifemakers for its fine grain structure.

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• 1.4116 (X50CrMoV15)

Also known as X50CrMoV15, this German stainless steel is popular in brands like Wüsthof and Victorinox. It balances toughness with corrosion resistance but has average edge retention, requiring frequent sharpening.

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• Aogami (Blue Paper Steel)

A traditional Japanese steel known for its high hardness (60-65 HRC) and toughness, Aogami requires care due to its vulnerability to rust. The “Super” variant includes molybdenum and vanadium, enhancing toughness and making it a top choice for premium kitchen knives.

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• AUS-8

This Japanese stainless steel is corrosion-resistant and tough, with a hardness of 57-59 HRC. It’s comparable to the steel used in high-quality German knives and is valued for its balance of sharpness and affordability. These blades are comparable to VG-10 but is less prone to chipping and is excellent for use in professional kitchens

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• CROMOVA 18

Used by Global, this steel contains 18% chromium, making it very rust-resistant and easy to sharpen due to its relatively low hardness (58 HRC). This steel is very easy to dull and is not very suitable for professional use.

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• VG-10

One of the most produced Japanese steels for kitchen knives, VG-10 is known for its high edge retention, hardness, and toughness. Commonly hardened to 60-62 HRC, it offers excellent sharpness and durability. VG-10 is rust-resistant and popular among mid-range brands like Shun, MCUSTA and Tojiro.

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• X30CrMoNi1-5-1 (Cronidur 30)

Used by Henckels in their high-end knives, this steel is highly rust-resistant and durable. It is expensive due to its unique combination of toughness and wear resistance.

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• ZDP-189

This Japanese powder steel from Hitachi is the best knife steel that you can buy. It has an extremely high carbon and chromium content, making it exceptionally hard and wear-resistant. However, it is challenging to sharpen and can be prone to chipping due to its high hardness. Often hardened to 65 HRC, brands like Kagemitsu and Katsumoto use it for premium knives.

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Choosing the right steel can significantly improve the longevity and performance of your knives. Good knives strike a balance between hardness, sharpness, and toughness, tailored to their intended use and maintenance needs.