Originally Posted by Rugger_can
Originally Posted by Combine
I thought it was to make it easier to cut limbs off, usually the arabs had curved blades ( simitars ) and cut off peoples heads and such
Scimitars and other curved cast blades of that nature are made in a curved shape as a point of style.
A Katana's curve is a result from the cooling of the blade. Traditional Katana's (and most Japaniese Fighting Swords) are formed from Folded steel, When this steel cools in its shaped form it actually contracts. This causes the blade to curve. The degree of curve on a sword can be an indication of its level of craftmenship.
This is also the reason why longer blades (like a No-Dachi and a Katana) have more of a curve then shorter blades (like a tanto or Washaki)
A common misconception, Katanas are curved from the forging process not the tempering process. the curve is already there before they are differentialy tempered.
Although the curve is certainly "set" by the cooling process.
Traditionally forged Katanas are composed of layered, forge welded compositions of iron and steel.. before the tempering the crystaline structure throughout the blade is homologous. the differential tempering process is what creates the composite character of the blade, The edge is tempered to a greater hardness than the back of the blade creating a weapon that has both a hard edge but a durable spine.
A very fine grade of clay is used to insulate the spine of the blade while the blade is heated to tempering temperature... if the blade changed shape significantly at this point , the heating or the quenching, this clay would crack off spoiling the temper.
Longer blades are curved more because the edge is longer, eventually of you had a long enough blade or forged the edge out thin enough it would form a circle.
You can test this out with a piece of plasticine.. and a hammer.. form a bar of plasticine.. and hammer ( lightly) down one edge from one end to the other.. the bar will curve, this is why one edged knives that are forged (not ground from barstock) typically have curved or "bellied" blades.
( I have some very good friends of nearly 20 years that are professional blacksmiths/ bladesmiths I'm not pullin this info out of my butt)