Heat Treatment

Frequently people ask if there is a metal or material better than steel. If you are one of those, and if your prior exposure to swords have been poorly made-swords from third world countries, then you're in for a surprise. The Holy Grail of steel is, still, steel. There are still many metallurgical mysteries awaiting to be unlocked, despite mankind's advanced knowledge in steel. Much is revealed through the process of heat treating in the crafting of a high performance sword blade.

Simply put, heat treatment is the process of submitting a blade to certain temperatures and then quenching the blade in order to obtain certain desired crystaline structures. A sword's overall performance is partly based on the hardness level(s) achieved as a result of the crystaline structures that form once the sword blade is quenched, as different crystaline states of steel yield different physical properties. The purpose of heat treating is to achieve the best balance between hard and soft in pursuit of qualities such as edge-retention (a function of hardness) and impact tolerance (a function of softness). Advanced and skillful heat treating (usually found only at the custom sword maker's level) will yield various properties in the same steel (e.g. Japanese swords with a hard edge and softer body).

A well-made blade will also be a product of good design (distal taper, profile taper, weight distribution, cross sectional geometry, center of gravity, etc.) and good heat treating - the result of which is a sword with the handling characteristics of yesteryear's weapons such that the sword can truly feel alive in one's hands and perform admirably for decades to come.

Simply put, no matter how a sword is advertised, be it "functioning like a single crystal" or "emmanating an electromagnetic signature" or "magical", if steel is not heat-treated properly, it will yield poor performance. If heat treated too hard, the sword can become brittle and fracture easily. If heat treated too softly, the sword can bend just by waving it in the air!

Thus, inferior heat treating to "superior" steel will yield an inferior sword.

Crystaline Formations and their Properties

There are various crystaline structures of steel. Many of them are applicable in the knife industry. Swords, on the other hand, are not elongated knives; they have physical handling and performance characteristics that are far different than knives. Thus, the following are just a few highlights:

• Ferrite - The iron portion of steel. (Steel is a product of Iron and Carbon)
• Cementite - The carbon portion of steel.
• Austenite - A mixture of cementite (Carbon) and Ferrite (Iron) at approximately 1400^oF (varies depending on steel metallurgy). The temperature at which austenite forms is known as austenizing temperature.
• Martensite - Hard crystaline form of steel, common in edges of Chinese and Japanese swords that are differentially heat treated.
• Pearlite - Soft form of steel, good for impact absorption and shock tolerance. Named pearlite because it looks like mother of pearl under a microscope.
• Bainite - Steel in its springiest form. Do not confuse with the term "spring steel" as this term is designated for steels that will serve as automobile springs.

Hardness of steel is generally measured by units known as Rockwells on a scale known as the Rockwell "C" scale. The following will give you an idea of what Rockwell levels are pertinent to swords:

• 20-25 HRc - Mild Steel. At this level, steel bars can flex a few inches and return true, but do not let this factor be a marketing/selling point in your purchase consideration. Anything heat treated harder than mild steel can cut into mild steel. Many of the fake Highlander swords are not heat treated and are at this level. Edge-retention is poor.
• 30-40 HRc - The minimum softness that you should allow a sword. Some of the cheap swords from third world countries might be at 40. Against other swords at 40 HRc they will do fine, and swords recklessly exposed to incorrect edge-on-edge fighting will dent but not chip and can be hammered back straight. However, this is sub-optimal.
• 40-45 HRc - A good range for the backs/spines/bodies of differentially heat-treated swords (e.g. Chinese, Japanese, etc.) This hardness level will have some spring qualities.
• 50-52 HRc - This is typically the ideal for European-style medieval swords, being a good balance between toughness (slightly soft enough for shock tolerance) and hardness (for edge holding). Del Tin swords, for example, rate at 50 HRc.
• 58-60 HRc - Ideal hardness for the edge of differentially heat treated swords (e.g. Chinese, Japanese). An edge of this hardness can cut into most materials that are comparably softer (flesh, bone, etc.) with little problems and, if stress-relieved through heat treating, should be able to perform without chipping or cracking. However, do not use swords, ever, for edge-on-edge fighting, as this is improper use of a sword.

A typical decorative sword from Spain rates at 48-52 HRc. A typical taiwanese fake sword rates at 56-58 HRc.

The Blade Forging Process

The forging process starts out by heating steel to austenizing temperature (approximately 1400-degrees F depending on the metallurgy of the steel, as mentioned before). Once the steel has assumed its proper shape, it is important to ensure that the steel is in a consistent soft state throughout, in preparation for the final heat treatment.

The process of achieving this consistency is called annealing. This involves heating the steel up to critical (austenizing) temperature and then allowing it to cool very slowly so that the steel is in its softest state. This is sometimes also called normalizing though the normalization process actually comes later.

Annealing may be done two or three times depending on the custom smith. Certain steels (e.g. AISI 1050) are flexible enough (no pun intended) to not need to be cooled so slowly and can thus be allowed to air-cooled.

Once the steel is adequately prepared it is subjected to heat to critical temperature, at which point the steel will take on a deep red-orange glow. The custom smith ensures the color is consistent throughout the length of the blade and will quench the steel in water or oil (depending on what the steel being used requires.)

Afterwards, the custom smith may choose to stress-relieve the blade by submitting it to temperatures far below austenizing temperature (e.g. 325-400 F).

Additional Reading

• Article: "Metallurgical Terms Made Simple" - Navigating us through a sea of confusing terms, ABS Master Bladesmith Kevin Cashen simplifies the complexities of metallurgical activities. Sword Forum Magazine Online, March 1999 Edition (accessible via Main Menu.)
• Article: "Differential Heat Treating on Broadswords" - Marrying the strengths of hard and soft steel for cutting power and shock absorbance for Western-style broadswords. Sword Forum Magazine Online, January 1999 Edition (accessible via Main Menu.)
• Article: "The Annealing/Normalization Process" - Lesser-known thermal treatments and their role in the creation of quality blades. Sword Forum Magazine Online, January 1999 Edition (accessible via Main Menu.)
• Article: "Titanium - Miracle Metal?" - Sword Forum Magazine Online, January 1999 Edition (accessible via Main Menu.)
• Article: "Is My Sword Real?" - Sword Forum Magazine Online, January 1999 Edition (accessible via Main Menu.)