maintained at this temperature soaked for a period of at least about 4 hours up to about 12 hours the ingot is then subjected to a series of roll milling operations to transform it into a sheet material having the desired thickness the first operation is a hot rolling operation carried out at a metal temperature within the range of about 460 u00b0 to about 550 u00b0 c during this operation the thickness of the ingot is reduced considerably next the sheet is subjected to a hot strip milling process at a temperature in the range of about 300 u00b0 to 330 u00b0 c and rolled to produce a sheet or strip thickness within the range of about 2 5 to about 3 5 millimeters the resulting sheet is then cooled to room temperature below about 30 u00b0 c and subjected to a cold rolling process to yield a final sheet thickness in the range of about 0 5 to about 1 millimeter optionally the cold rolling process may be interrupted and the sheet may be annealed prior to further cold rolling the annealing process involves reheating the metal to a temperature in the range of about 320 u00b0 to 380 u00b0 c and holding it at that temperature for a period.