| 摘要 |
PROBLEM TO BE SOLVED: To provide a method of surely manufacturing a high carbon steel sheet capable of meeting the recent demand of users for simplification of a forming process and lowering in heat treatment temperature and shortening in time of heat treatment and excellent in formability and hardenability. SOLUTION: In the method of manufacturing a high carbon steel sheet having a component system specified by a carbon steel for machine structural use or a carbon tool steel stock or a cold rolled steel strip for spring, a steel is hot-rough-rolled and subjected to heating treatment at a temperature of >=Ar3, and the resultant slab is hot-rolled at a temp. of >=Ar3. The resultant hot-rolled steel plate is cooled at a cooling rate of >=5 deg.C/sec, held at a temp. of 560 to 650 deg.C for 2 to 10 sec to undergo short-time heat treatment, and cooled again at a cooling rate of >=7 deg.C/sec. Then, the steel plate after cooling is coiled at a temp. of <=600 deg.C, cold-rolled at a draft of >=30%, and annealed at a temperature between 580 deg.C and the Ac1 transformation point, thereby, cementite grains of <=1.1μm average grain size and <=1.5 average aspect ratio and ferrite grains of >=2μm average grain size can be formed.
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