All You Ever Needed to Know About Japanese Steel, Tools, and Knives

When you’re looking for a quality Japanese tool or chef’s knife, the first thing you’re probably going to consider is what it’s made out of. Especially when it comes to bladed tools like chisels, planes and knives, the one question that keeps coming up again and again is: Which steel is best?

There are so many different things to consider when choosing a tool based on its steel. Do you want carbon steel or stainless steel (and which one is best for the job?). Do you want a hard steel, or a soft steel? Do you want Japanese steel, or German steel? How pure is the steel? How expensive is the steel? The list goes on.

This article aims to be a one-stop-shop for all of your questions about steel composition, steel quality, and the best Japanese steel for knives and tools. If you have questions about steel, you’ve come to the right place.

Properties Of Steel

When you’re choosing a tool based on its steel, there are a few properties to understand. Steels can be made up of various different elements, and each element lends different properties to the finished product. The most important properties to consider are toughness, hardness, tensile strength, ductility, and corrosion resistance.

Hardness and Toughness

Toughness refers to how much stress, impact and force a steel can take before breaking. Steel with high toughness is more likely to bend or warp than crack or chip. Chromium, molybdenum and tungsten all increase the toughness of a steel to varying degrees, while carbon can significantly reduce it. 

Hardness is more straightforward, and can be measured on a standardized scale, like the Rockwell scale. Steel with more hardness is less likely to warp or wear, so it makes for great blades, as it will keep the edge much longer than a softer steel. However, the harder a steel is, the more likely it is to crack and chip. Carbon is the element most responsible for increasing the hardness of a steel, though chromium, cobalt, manganese, nickel, phosphorus, tungsten, vanadium and silicon can also help.

Tensile Strength and Ductility

Tensile strength and ductility are similar properties, in that they essentially measure the way a material behaves when stretched. But they do have some key differences, so it’s important not to put them completely into the same basket.

Ductility refers to how well a steel can be shaped by force: its malleability. Can it be stretched to become longer and thinner? Can it be hammered flat? Can it be twisted? Whereas tensile strength refers to how much stretching a steel can take before fracturing or breaking.

Carbon, chromium, manganese, and silicon all increase a steel's tensile strength, and carbon and sulfur lower its ductility.

Corrosion Resistance

The corrosion rate of steel is directly affected by how much chromium is in the mix. To be considered a “Stainless Steel”, the steel must have at least 10.5% chromium. Neither corrosion resistance nor corrosion rate have standardized systems of measuring, like hardness does, so we can’t compare the corrosion of all the types of steel on the market. However, there has been some research about how chromium levels affect corrosion.

One study established a baseline corrosion rate in steel with 0% chromium, by measuring how much the steel corroded over a set period of time. They then repeated this measurement on steels with varying levels of chromium.

Steel with 2% chromium:

• Corrosion rate reduced approx. 65% from baseline.

Steel with 4% chromium:

• Corrosion rate reduced approx. 75% from baseline.

Steel with 6% chromium:

• Corrosion rate reduced approx. 85% from baseline.

Steel with 8%+ chromium:

• Corrosion rate reduced approx. 90% from baseline.

So the effect of chromium on corrosion rate is significant, even at low percentages. If rust is something that you just don’t want to deal with when it comes to your tools, be sure to check the composition of the steel used to find out how much chromium is in the mix.

Now that we understand the basic elements and properties of steel, we can take a look at the different types of Japanese steel and what makes them unique.

What Is JIS SK Steel?

SK steel is a simple carbon tool steel often used in woodworking saws, axes, drill bits, and circular saw blades. It’s not the type of steel that you’d make a fancy kitchen knife or good pair of pruning shears out of, but for most tools it does the job well.

A simple steel is one that has undergone relatively limited refining. To make steel, the first step is to remove or reduce a number of impurities from iron - impurities like nitrogen, silicon, phosphorus, excess carbon and sulfur. Finally, an alloying element such as manganese, nickel, chromium, carbon, or vanadium should be added.

Being a simple steel, SK steel still has relatively high levels of various impurities. There are five main varieties of JIS SK steel commonly used to make tools, and they all have slightly different properties.

Composition of JIS SK Steel

	Carbon	Silicon	Manganese	Phosphorus	Sulfur
SK1	~1.5%	~0.35%	~0.5%	< 0.03%	< 0.03%
SK2	~1.25%	〃	〃	〃	〃
SK3	~1.1%	〃	〃	〃	〃
SK4	~1%	〃	〃	〃	〃
SK5	~0.9%	〃	〃	〃	〃

As you can see, the only real difference between the types of SK steel is the carbon content, and as we’ve learned, the higher the carbon, the higher the hardness. So a low-carbon SK steel like SK5 is tougher, and less likely to fracture, while a high-carbon option like SK1 is more wear-resistant.

Japanese Carbon Steel

While there are many Japanese carbon steels in production, there’s one series that stands out well above the competition, so much so that it has become the only Japanese carbon steel worth considering for chef knives, nata hatchets, and kiridashi marking knives.

These are the “paper” steels produced by Hitachi. Each variety is named after the color of the paper the steel comes wrapped in. The main varieties are kigami (yellow paper steel), shirogami (white paper steel, or white steel), and aogami (blue paper steel, or blue steel).

Hitachi’s paper steels are made by taking JIS SK steel and decreasing the impurities, as well as adding some other elements that can lend various additional properties to the steel.

As you can see in the flowchart above there is a linear progression from JIS SK steel through kigami, shirogami, and aogami, all the way to aogami super (or blue super). The quality (and price) of the steel significantly increases along this progression, but that doesn’t mean that aogami super is always the right choice.

If you want a tougher, softer steel (think impact tools, axes, hatchets etc.) then kigami #3 would be a much better choice than aogami super. If you want a very sharp blade, but still want it to be relatively easy to sharpen, then shirogami #3 would work wonders. If you want the sharpest blade you can get, with excellent wear resistance, then aogami super is a fantastic choice - though it may be weak against impacts.

We sell a variety of Japanese tools made out of various types of Hitachi carbon steel, like this shirogami #3 mountain hatchet, these aogami pruning shears, or this aogami pocket knife.

Composition of Hitachi Paper Steel

	Carbon	Silicon	Manganese	Phosphorus	Sulfur	Chromium	Tungsten
Kigami #3	~0.9%	~0.2%	~0.3%	< 0.03%	< 0.006%
Kigami #2	~1.15%	〃	〃	〃	〃
Shirogami #3	~0.9%	〃	〃	< 0.025%	< 0.004%
Shirogami #2	~1%	〃	〃	〃	〃
Shirogami #1	~1.35%	〃	〃	〃	〃
Aogami #2	~1.15%	〃	〃	〃	〃	~0.5%	~1.5%
Aogami #1	~1.35%	〃	〃	〃	〃	〃	~2%
Aogami Super	~1.5%	〃	〃	〃	〃	〃	~2.5%

Japanese Stainless Steel

Carbon steel rusts, and it rusts fast. If you leave your carbon steel tool or knife in water for more than a few minutes, rust spots will start to appear. For people who don’t want to deal with the hassle of cleaning and drying their tools immediately after use, and removing rust as it crops up, stainless steel could be a better choice.

Stainless steel developed a reputation in the mid-1900s of being low quality and too soft. Especially when it came to bladed tools like knives, planes, chisels, and axes, carbon steel was always the obvious choice.

However, the difference between stainless steel of the 1970s and stainless steel today is night and day. Modern forging technology has progressed leaps and bounds in such a short period of time.

Typically, the downside of stainless steel is that to add so much chromium for corrosion resistance, you’re forced to reduce the amount of carbon, which reduces its hardness. But these days makers of stainless steel are finding new ways to increase the chromium content without sacrificing carbon.

Most of Japan’s best stainless steels are produced by Takefu Steel in Echizen, and their most popular steels for tools and cutlery are of the VG and SG series’.

Composition of Takefu Steel

	Carbon	Chromium	Molybdenum	Vanadium	Tungsten	Cobalt
VG1	1%	14%	0.3%
VG5	0.75%	〃	〃	0.15%
VG10	1%	15%	1%	0.25%		1.55%
SG2	1.4%	〃	2.8%	2%

As you can see SG2 has an estimated 1.4% carbon, which is an enormous amount for a stainless steel, more than any of the Hitachi carbon steels except for aogami super. This is because SG2 is a powdered steel, also called a high speed stainless steel. Powder metallurgy is a relatively modern technique which allows manufacturers to make steel out of metal powders, affording them greater control over the composition of the finished product.

This means that SG2 steel has a rating of 64 HRC (Rockwell hardness), about the same as aogami super (61-65 HRC) while having the clear advantage of near total corrosion resistance thanks to its 15% chromium content.

This has made SG2 stainless steel the steel of choice for many of the world’s knifemakers, as they hail it the “blade steel of the future”. Unfortunately, as a steel from the future, it’s also priced for the future. So for a more affordable stainless steel, with a relatively high hardness, VG10 is another great choice. We sell a variety of Japanese folding knives made out of VG10 steel, like this modern outdoor/edc knife from G. Sakai, or these handmade wooden-handled pocket knives from Kanekoma.

But while SG2 may be the perfect steel for a precise cutting tool, like a kitchen knife, a chisel, a hand plane, or a kiridashi - it’s too hard (therefore, too brittle) to be used in impact tools like axes, hatchets and hammers, and doesn’t have enough ductility to be used in tools that undergo twisting pressure like drill bits and screwdrivers.

So if you’re looking for a tool made of a softer stainless steel, with greater ductility, VG1 and VG5 both have hardness around 58 HRC and are therefore less prone to cracking or breaking.

Is German Steel Better Than Japanese Steel?

When we talk about German steel, we’re almost always talking about knives. Germany, and Solingen in particular, is teeming with renowned knife makers like Wusthof, Zwilling, Messermeister and F. Dick.

So to compare German and Japanese steels, it's best to compare them in terms of the properties most relevant to knives and other bladed tools.

The fact is, German and Japanese steels aren’t actually that different. Most steels aren’t proprietary, so there’s nothing stopping another company from making a steel with the same composition. You can find German steels with similar elemental compositions to most of the Japanese steels mentioned here.

X50CRMOV15 stainless steel is one of the most common steels used in German cutlery, so much so that it’s colloquially referred to simply as German steel. Wustof uses X50CRMOV15 steel for most of their blades, and Zwilling's proprietary German steel is thought to be an equivalent.

When you compare it with VG10 you can see the similarities immediately.

	Carbon	Silicon	Manganese	Phosphorus	Sulfur	Chromium	Molybdenum	Vanadium
X50CRMOV15	0.55	1	1	0.04	0.015	15	0.8	0.2
VG10	1	0.5	0.5	0.03	0.03	〃	1	0.25

When it comes to carbon steel the similarities are even more apparent. K460 is a popular German carbon tool steel from Bohler, which is used in axes, drill bits, saw blades and punching tools. When you compare this with a Japanese carbon steel, the differences are really negligible:

	Carbon	Silicon	Manganese	Phosphorus	Sulfur	Chromium	Tungsten
K460	1.1%	0.35%	0.5%	0.03%	0.03%	0.5%	1.2%
Aogami #2	1.15%	0.2%	0.3%	0.025%	0.004%	〃	1.5%

So it’s difficult to compare one country’s steel against the other’s. What we can compare, however, is what the market, and therefore the manufacturers, prefer. While you can find carbon steels similar to aogami in Germany, it’s not typically favored by blade makers, as the German knife market prefers stainless. 

A blade from Solingen, Germany is more likely to be stainless steel, so it will be less likely to rust and less likely to chip than a typical knife from Sakai, Japan. Conversely, a knife from Sakai is more likely to be carbon steel, so it will likely be sharper, and will hold its edge for longer.

Though, if we had to choose, there is one point that gives a major advantage to Japanese steel, and that’s that Zwilling, one of Solingen’s most well-known knifemakers, makes many of their premium chef knives out of Takefu steel from Echizen, Japan.

While none of these are hard and fast rules, if you’re looking at a German or a Japanese tool and are unable to identify exactly which steel has been used, there are a few common points that may help you make your decision:

• German blades are more likely to be stainless steel:
• Focus on durability and toughness
• Rust resistant
• Softer and not as sharp
• Easy to dull, but quick to sharpen

• Japanese blades are more likely to be carbon steel:
• Focus on hardness and sharpness
• Prone to rust
• Harder and sharper
• Difficult to dull, but slow to sharpen

• German blacksmiths prefer hot forging methods:
• Larger grain structure
• Reduced tensile strength
• Increased ductility

• Japanese blacksmiths tend to use a combination of both hot and cold forging:
• More uniform fine grain structure
• Increased tensile strength

• Japanese blacksmiths use other methods to protect from rust:
• Warikomi (laminated steel)
• Scorched/blackened steel

• Japanese steel tools are more likely to be handmade, or hand finished.

Now that you know more than you ever wanted to know about steel, there’s one more important thing to learn. When you’re choosing a tool, or a knife, the type of steel used should never be your first consideration – aside from your preference over carbon or stainless.

Respectable toolmakers and blacksmiths will always choose the best steel for the intended application, and how a blacksmith heat-treats, molds, and constructs the tool or knife will have a much bigger impact than whether it uses aogami or shirogami. 

You should first choose whether you’re going carbon or stainless, then find a respected blacksmith, preferably one that still makes their tools by hand, then choose the right size and weight for your needs, finally, if there are still options (VG5 vs. VG10, shirogami vs. aogami etc.) pick the best quality for your budget.

Do you have a favorite steel tool or knife from Japan? Share it in the comments below.