Method of producing non-ageing special low carbon iron sheets

Claim 1

IN A METHOD FOR PRODUCING NON-AGEING LOW CARBON STEEL SHEET WHICH IS SUPERIOR TO COLD-WORKABILITY AND ENAMELABILITY AND WHICH CONTAINS QUANTITIES OF ALUMINUM, BORON, VANADIUM AND MANGANESE, THE IMPROVEMENT COMPRISING (1) FORMING STEEL INGOTS CONTAINING ACID-SOLUBLE AL OF FROM 0.020 TO 0.080%, ACID-SOLUBLE BORON OF FROM 0.003 TO 0.020% AND ACID-SOLUBLE VANADIUM OF FROM 0.020 TO 0.050% AS NITRIDE-PRODUCING ELEMENTS, AND FURTHER CONTAINING CARBON OF FROM 0.040 TO 0.070% AND MANGANESE OF BELOW 0.20%, (2) SUBJECTING SAID INGOT TO SLABBING, (3) HOT-ROLLING THE RESILIENT SLAB AT A TEMPERATURE ABOVE 1050*C. TO A SHEET OF FROM 2.0 TO 4.5 MM. IN THICKNESS (4) COLD-ROLLING SAID SHEET AT THE REDUCTION RATE ABOVE 30%, AND (5) SUBJECTING SAID COLD-ROLLED SHEET TO A DECARBURIZING ANNEALING AT A TEMPERATURE OF FROM 620* TO 900*C. IN AN ATMOSPHERE CONTAINING WATER VAPOR LESS THAN 30% BY VOLUME, THEREBY REDUCING THE CARBON CONTENT TO LESS THAN 0.020% AND REDUCING SOLID-SOLUBLE NITROGEN CONTENT TO LESS THAN 0.0002%.