Method of heat treatment

Claim 1

IN THE HEAT TREATING OF STACKS OF LAMINATIONS COMPOSED OF ALUMINUM-IRON ALLOYS AND IRON OXIDE IN THE FORM OF MILL SCALE TO PRODUCE DESIRABLE MAGNETIC PROPERTIES, INCLUDING HEATING SAID STACKS UNDER AN AXIAL LOAD IN A SUBSTANTIALLY DRY HYDROGEN ATMOSPHERE AT TEMPERATURES IN EXCESS OF 1812*F., THE IMPROVEMENT WHICH COMPRISES A METHOD OF PRODUCING AN INSULATING FILM OF ALUMINUM OXIDE ON THE SURFACES OF SAID LAMINATIONS TO PREVENT INTERLAMINATION WELDING, SAID METHOD INCLUDING: (1) SIMULTANEOUSLY REDUCING THE IRON OXIDES AND OXIDIZING THE ALUMINUM IN SAID LAMINATIONS BY HEATING IN AN ESSENTIALLY DRY HYROGEN ATMOSPHERE HAVING A DEW POINT OF NOT GREATER THAN APPROXIMATELY -35* F. UNTIL A TEMPERATURE OF APPROXIMATELY 1400*F. IS REACHED; (2) RAISING THE MOISTURE CONTENT OF SAID HYDROGEN ATMOSPHERE TO THE EQUIVALENT OF A DEW POINT OF GREATER THAN APPROXIMATELY +55*F. AND CONTINUING SAID HEATING AT 1400*F. FOR APPROXIMATELY ONE HOUR TO PRODUCE A FILM OF ALUMINIUM OXIDE CONTIGUOUS WITH THE SURFACES OF SAID LAMINATIONS; AND (3) REDUCING THE MOISTURE CONTENT OF SAID HYDROGEN ATMOSPHERE AND ALLOWING SAID LAMINATIONS TO COOL TO BELOW APPROXIMATELY 300*F.