Double-stepped annealing for improvement of super-deep drawing property of steel sheet

Claim 1

A METHOD OF ANNEALING STEEL IN TWO STAGES TO MAKE IT HIGH-DEEP DRAWABLE, WHICH COMPRISES COLD ROLLING LOW CARBON STEEL SHEET INTENDED TO BE USED FOR DEEP DRAWING AT A REDUCTION RATE RANGING FROM 40 TO 90%, ANNEALING THE COLD-ROLLED STEEL SHEET IN AN ATMOSPHERE OF AN INERT GAS AT A TEMPERATURE BELOW COMPLETE RECRYSTALLIZATION TEMPERATURE WITHIN THE RANGE FROM 470 TO 570*C. FOR MORE THAN 30 MINUTES, WHEREBY THE ORIENTATION WHICH THE CRYSTALS WILL TAKE IN DEEP DRAWING WILL BE WITH THE GREATEST DRAWABILITY PARALLEL TO THE ROLLING PLANE OF SAID STEEL SHEET IN PREFERENCE TO OTHER ORIENTATIONS, THEN ANNEALING THE LOW TEMPERATURE ANNEALED STEEL SHEET AT TEMPERATURE ABOVE THE COMPLETE RECRYSTALLIZATION TEMPERATURE FOR SOFTENING IT, SAID LAST MENTIONED ANNEALING BEING AT A TEMPERATURE ABOVE 600*C. AND BELOW THE A3 TRANSFORMATION POINT IN AN ATMOSPHERE OF A DECARBONIZING AND DENITRIDING GAS, THEREBY ACCELERATING THE GROWTH OF SAID ORIENTED CRYSTALS IN THE DIRECTION OF SAID ORIENTATION IN PREFERENCE TO OTHER ORIENTATIONS AND GIVING A STRONG PLASTIC ANISOTROPY TO SAID STEEL SHEET.