PURPOSE: To control material quality such as strength of rolled stock to the aimed value, by assuming volume ratios of ferrite, pearlite, bainite from assumption formula of isothermal transformation ratios of ferrite and pearlite, in manufacturing thick plate stock or hot strip from slab by hot rolling.
CONSTITUTION: In manufacturing thick plate, hot strip, etc. by heating carbon steel to temp. of Ar3 point or above, hot rolling it, strength of these worked product depends on vol. ratios of ferrite, pearlite, bainite in structure. Consequently, addition rule of transformation ratio is applied to assumption formula of isothermal transformation ratios of ferrite and pearlite, to assume vol. ratios thereof by calculation relating to arbitrary cooling curve. Total value of the assumed volume ratios is subtracted from (1) to obtain vol. ratio of bainite. Conditions of hot rolling and cooling are set so that vol. ratios of said three structures are regulated to the aimed value, and working and heat treatment are carried out to manufacture rolled stock having the aimed material quality.
KONO OSAMU
TAKAHASHI MANABU
EZAKA KAZUAKI
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