Through-Tempered vs. Differentially Hardened Katana Blades

As you shop for a new katana sword, the different options and terminology can be confusing for those new to the sword world as well as those with a few already in their collection. Here we will dive in and take a closer look at through-tempered vs. differentially hardened katana blades and what each process means to the strength and sharpness of the blade. Deciding which blade is best for you depends on whether you are looking for an authentic katana, one for learning cutting techniques, or one for an experienced cutter. It also depends a lot on personal preference. Our goal is to help you better understand the difference between through-tempered and differentially hardened processes so you can make a more informed decision when purchasing your katana. 

Differential Hardening

Differential hardening is the authentic process for blades like the katana and swordsmiths used this process to adjust the hardness of the metals, as well as create the signature curve of the blade. When a traditional katana blade with laminated construction is forged, high-carbon steel formed the outer shell and blade, while lower carbon steel created the body and core of the blade. Once forged together, the swordsmith coats the blade with a clay mixture. They apply the clay with a thicker coat along the sides and dull edge, while the blade has minimal to no clay coating. The swordsmith then heats the blade and quenches it. 

The clay on the blade creates an insulation of sorts. So, when the blade cools, the area of the blade covered in clay cools slower, resulting in a much softer steel. In contrast, the area without clay, cools much faster, resulting in a hard edge that helps retain sharpness. This method is also what creates the signature wavy hamon markings on the blade that indicate the line between the softer and harder metals. 

In addition to affecting the hardness of the metal, differential hardening is also responsible for the signature curve found in the katana. When forged, the metal billet is straight. Once heated and quenched, the clay-covered steel cools at different rates, causing different shrinking rates that produce the signature curve in the blade. 

If we look at the Hardness Rockwell Cone (HRC), a differentially hardened katana blade has an average HRC of 58-62 edge hardness and 38-45 on the spine.

So, what does all this mean in terms of pros and cons for differential hardening? Let’s take a closer look below.

Pros of Differentially Hardened Katana Blades

A differentially hardened blade is the way to go for those looking for an authentic katana blade. Other benefits of this method include:

• Blade can be sharpened more than a softer edge
• Blade will retain sharpness for longer
• Softer spine provides extra shock absorption
• Provides a noticeable hamon 
• Provides superior cutting, even when not particularly sharp, on soft targets

Cons of Differentially Hardened Katana Blades

As with anything, there are downsides to the differential hardening process. These can include:

• Blade loses the springy characteristics that can be obtained from a monotempered blade
• A poorly aligned cut can cause the blade to bend and twist and remain bent and twisted (this can be straightened out without serious issues to blade quality but skill and experience here is needed for good results)
• The harder edge is more prone to chipping or cracking when you hit a hard target
• Increased price – Differential hardening has a high failure rate, which plays a role in its higher pricing. The bladesmiths who can make these swords reliably are more experienced and skillful and their work will command a higher price.

Through-Tempered Katana Blades

Through-tempered blades typically have one type of steel, and the curved katana shape is created during the forging process, as heating and quenching is uniform. The swordsmith heats the blade and quenches with no additional material, meaning there is uniform harness throughout. If we look at the Hardness Rockwell C scale on a through-tempered, or monotempered, blade, the average HRC is in the low 50s throughout the length of the blade, from the edge to the spine. 

In addition, a monotempered blade does not produce the characteristic hamon. However, a false hamon can be added in a variety of different ways, such as wire brushing or chemical etching, in order to replicate the authentic hamon look.

So, what does a blade with consistent hardness mean?

Pros of Through-Tempered Katana Blades

For those looking for a more forgiving blade, the monotempered katana may be the right choice. Pros include:

• Most monotempered production blades have a spring steel characteristic, meaning they will spring back into a straight form even if you make a bad cut.
• Resistant to edge chipping
• Much Easier to polish scuffs and scratches out without requiring high levels of skill in polishing and blade finishing.
• Durable blade that is good for beginners
• Lower price than a differential blade

Cons of Through-Tempered Katana Blades

There are some cons to the monotempered blade, especially for those looking more a more authentic-looking Kanata.

• Will not retain sharpness as long as a differential blade
• Will not have a hamon, or will have a fake hamon added

At Kult of Athena, we strive to bring you a wide selection of high-quality katana swords based on and inspired by traditional swordsmith techniques. We work to offer both swords that meet artistic value as well as practical and functional value. Browse our selection today to discover the perfect katana to meet your needs.