回火 [－－]

Jyutping wui4 fo2
Pinyin huí huǒ

Definitions (CC-CEDICT)
  1. to temper (iron)
  2. to flare back
  3. flareback (in a gas burner)
  4. (of an engine) to backfire
Definitions (粵典–words.hk)
  1. 名詞
    鋼料​熱處​理​嘅​一​個​環​節​，​用​嚟​增加​鋼​料​嘅​韌​性
    tempering
Definitions (Wiktionary)
  1. verb
    to temper (iron); to flare back; to backfire