Hardening is the process of heating a piece of steel to a temperature within or above its critical range and then cooling it rapidly.
淬火就是把钢件加热到或超过它的临界温度范围，然后使其快速冷却的过程。
Steel is tempered by heating and then cooling it.
钢是通过先加热后冷却来回火的。
Steel is tempered by heating and then cooling it.
钢是通过先加热后冷却来回火的。
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