To reduce energy cost and to execute sufficient spheroidize-annealing treatment by an inexpensive heat treatment by applying a steel cong. a specified ratio of C with the magnetic field in a specified temp. range in succession to hot rolling and furthermore executing cooling at a specified cooling rate.
In the steel to be produced, the content of C is regulated to 0.01 to 0.8 mass%. This steel is applied with the magnetic field in the temp. range of 800 to 500°C at the time of cooling in succession to hot rolling, and the cooling rate in the temp. range is regulated to ≤10°C/sec. In this way, before austenite is transformed into a ferritic/pearlitic structure, the precipitation of cementite in pearlite is suppressed, and the lamellar intervals in cementite is shortened, by which a fine ferritic/pearlitic structure an be obtd. Preferably, the intensity of the magnetic field to be applied is regulated 2 to 30 T, and the size of the magnetic field gradient is regulated to 0.1 to 10 T/cm by absolute value.
HASE KAZUKUNI
ATSUMI TAKUYA
HOSHINO TOSHIYUKI
AMANO KENICHI
SHIMOTOMAI MICHIO
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