Answered by Shaykh Faraz Rabbani
According to the Hanafi Fiqh is loud recitation by the Imam in the Fajr, Maghrib or Isha prayers a rukn of the prayers, or is it wajib? What if an Imam forgets to recite loudly? And what if an Imam recites in the Zhor and Asr prayers loudly? Though extraordinary such situations arise amongst those newly practicing.
Reciting out loud in loud prayers and quietly in quiet prayers is wajib for the imam. It would be obligatory to repeat such prayers. There are quite a few posts on reciting in prayer in the Hanafi list archives.