Yaki ga Mawaru (焼きが回る - Becoming Dull)

Yaki ga Mawaru

To become dull or to decline ability is expressed as 'yaki ga mawaru' (焼きが回る) in Japanese.

'Yaki' (焼き) means "burnt" and 'mawaru' (回る) means "to go around" or "to spread," so the literal meaning of 'yaki ga mawaru' is "the burnt area spreads."

When making a blade or edged tool, it is burned then cooled to improve the edge.

However, if you overheat it, the blade will be fragile, and the edge will become dull.

That is to say, the expression 'yaki ga mawaru' compares the sharpness of a blade with human ability.

焼きが回る

年をとるなどして思考力や能力が鈍くなることを、「焼きが回る」と言います。

「焼き」は ""、「回る」は "" を意味するので、「焼きが回る」の文字どおりの意味は "" です。

刃物を作る際、切れ味を良くするために高温に熱してから冷やす工程があります。

ここで、熱を加えすぎてしまうと、かえって刃がもろく切れ味が悪くなってしまいます。

すなわち「焼きが回る」という表現は、刃物の切れ味を人間の能力に例えているというわけです。

• To become dull or to decline ability is expressed as 'yaki ga mawaru' (焼きが回る) in Japanese.
• To become dull or to have a decline in ability is expressed as 'yaki ga mawaru' (焼きが回る) in Japanese.

• 'Yaki' (焼き) means "burnt" and 'mawaru' (回る) means "to go around" or "to spread," so the literal meaning of 'yaki ga mawaru' is "the burnt area spreads."
• This sentence is perfect! No correction needed!

• When making a blade or edged tool, it is burned then cooled to improve the edge.
• When making a blade or edged tool, a process of burning and cooling is utilized to forge and sharpen the blade.

• However, if you overheat it, the blade will be fragile, and the edge will become dull.
• However, if you overheat it, the blade will become fragile, and the edge (will become) dull.

  (will become) is optional:
  
  ... the blade will become fragile, and the edge dull.

• That is to say, the expression 'yaki ga mawaru' compares the sharpness of a blade with human ability.
• This sentence is perfect! No correction needed!

Good!
Keep sharpening those English skills! :)