Method of heat treating cast iron

Claim 1

A PROCESS FOR THE TREATMENT OF WHITE CAST IRON SUITABLE FOR FORMATION OF PEARLITIC MALLEABLE IRON WHICH COMPRISES SUBJECTING A CASTING OF SAID WHITE CAST IRON AFTER COOLING TO A SEQUENCE OF STEPS WHICH INCLUDES EFFECTING MATERNISTIC HARDENING OF THE CASTING BY AUSTENZATION WITH HEAT AT A TEMPERATURE SLIGHTLY ABOVE THAT AT THE END OF THE ENTACTED TRANSFORMATION FOLLOWED BY PROGRESSIVE COOLING INCLUDING QUENCHING IN A SALT BATH MAINTAINED BETWEEN 150-250*C. MAINTAINING THE CASTING IN THE SALT BATH FOR A PERIOD OF TIME BETWEEN 30 SECONDS AND 6 MINUTES, AND THEN COOLING TO ROOM TEMPERATURE TO PRODUCE THE MARTENSITIC TRANSFORMATION, TEMPERING THE THUS PRODUCED MARTENSITIC BY HEATING AT A TEMPERATURE OF 450 TO 500*C. FOR A PROLONGED PERIOD OF TIME OF 3 TO 48 HOURS FURTHER HEATING THE THUS TREATED IRON AT A TEMPERATURE OF ABOUT 900*C. TO EFECT GRAPHITIZATION OF THE IRON, AND COOLING TO ROOM TEMPERATURE.