We are heat treating 4350 material using endothermic gas as a protective atmosphere. The parts are failing at the site of large aluminum inclusionslocated approximately one eight of an inch below the surface. The mill that produced the material claims we induced hydrogen into the material during our heat treating, and the hydrogen migrated to the inclusion, which caused internal cracking. I have never heard of this happening in our operation. The parts are heated to 1550 F for two and one half hours, quenched in oil, then double tempered. I have heard that only atomic hydrogen can diffuse into material and cause this type of damage. At what temperature does molecular hydrogen become atomic hydrogen, and has anyone else ever had this problem. Thanks in advance.