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After shaping, the blade required heat treatment—controlled heating and cooling that transformed steel’s internal structure, creating desired combination of hardness and toughness.
The Differential Hardening:
For blades with steel edges on iron core, only edges needed hardening—heating edge to critical temperature, quenching rapidly to create hard martensitic structure, while core remained relatively soft and flexible. This differential hardening required skill—heating edges without overheating core, quenching with proper technique and speed.
The quenchant varied—water for maximum hardness (but higher risk of cracking), oil for slower cooling (less hard but more reliable), brine for intermediate effect. The choice depended on steel’s carbon content, blade’s geometry, smith’s assessment of risks and requirements.
The Tempering:
After hardening made blade dangerously brittle, tempering reduced brittleness while retaining most hardness. The blade was reheated to moderate temperature—judged by color change, blue-purple indicating proper temperature—then cooled slowly. The tempering relieved internal stresses, transformed some brittle martensite into tougher structure, created final balance between hardness and toughness.
The tempering temperature was critical—too low left blade brittle, too high sacrificed too much hardness. The smith’s skill in judging proper temperature, developed through experience and many failures, distinguished master from apprentice.
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