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HSK levels

    回火

    huíhuǒ

    1. to temper (iron)
    2. to flare back; flareback (in a gas burner); (of an engine) to backfire

    铁匠将烧红的刀片放入冷水中回火,使其变得更加坚硬。 tiějiàng jiāng shāohóng de dāopiàn fàngru lěngshuǐ zhōng huíhuǒ, shǐ qī biàn de gèngjiā jiānruò.