Differential Heat Treating on Broadswords

Article by WarAngel. Special thanks to Randal Graham.

While maintaining the traditional shape of the Katana, the ancient Japanese smiths had for centuries employed various means to marry the strengths of hard and soft steel within a singleblade by essentially creating a harder edge for cutting and edge-holding, and a softer body for shock-tolerance in combat.

Traditionally, European swords do not benefit from techniques such as the Japanese smiths' use of clay to allow for differential heat treating (during the water quench, the clay allows the covered body to cool at a different rate than the exposed edge, causing the harder martensitic form of steel of the edge to "freeze" its crystaline state when quenched, and allowing the covered body to achieve a softer pearlitic form of steel.) Interestingly, however, some swords have exhibited properties of having been edge-hardened.

Today, the differential heat treating - and, especially, clay treatment - of broadsword blades have been the subject of discussion and experimentation. Though unconventional, modern-day smiths such as Randal Graham take on an approach that North American blademsmiths are not constrained by the bounaries of tradition, and thus can take the best from all cultures and fuse them to make a better blade.

Randal Graham relates from his experience two ways of achieving a differential heat treat:

The first way is to bring the whole blade up to temperature, and to quench it for 1 to 1.5 seconds - and then interrupt the quench by lifting it out and holding it in the air for 2 seconds, then finishing the quench. This, in fact, is how many combat blades were treated historically. There is yet a different approach to this, but it is harder to control and is not as ideal. The blade would be brought up to temperature very quickly and then quenched quickly. The idea is that the edges reach hardening temperature before the center does.

The second way - and perhaps the better way - is the use of clay. While some smiths may have experienced problems keeping the clay on their broadsword blades, Randal shares: "I've not had any problems keeping the clay on, but I heat-treat my blades in a draw-filed condition, so there's lots for the clay to hold onto."

Though refractory cements have been used by some, Randal Graham prefers a simple mix of powdered pottery clay, charcoal, and some ground--up fire bricks. "I don't use refractory cement for the clay," relates Randal. "It shrinks too much during the heat-up, and is what causes it to be less than reliable, sometimes."

Randal Graham grew up in a family that was very dedicated in their collection of antiques and artifacts and thus had the opportunity to examine and work on old blades as of a young age. "One of the biggest shocks I had is when I had the chance to examine a Scottish broadsword from about 600-700 A.D. It was most definitely differentially hardened, and was very rough, obviously a weapon for use. That got me started in the area of research, as this finding went against everything I was being told in the books and by some other smiths." Randal had found - of the various sword he had come across, from bronze leaf swords to 16th century "longswords" - that blades which showed the signs of battle almost always were edge-hardened, and those blades had very little flex - perhaps just enough to survive impact.

While western swords of old were differentially hardened by different means than that of traditional Japanese swords, the goal was possibly the same - which is to combine maximum durability with cutting ability.

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