| 摘要 |
PURPOSE:To make the production of a two-phase steel strip of ferrite-martensite possible by regulating the cooling rate of the steel strip in the stage of transforming austenite to martensite by the heat treatment of the two-phase steel strip of ferrite-austenite. CONSTITUTION:After a steel strip is heated to a two-phase region of ferrite- austenite in a continuous annealing device, it is quickly cooled to transform austenite to martensite, whereby the steel strip which is superior in both strength and ductility is produced. In the stage of cooling a steel strip 8 heated to a two phase region of ferrite-austenite quickly with gaseous jets 54 in a quick cooling zone 28 of the continuous annealing device, a measuring device 50 for the amt. of austenite is provided in the temp. region where the temp. of the steel strip is higher than a martensite transformation initiation temp. Ms, and the cooling rate CR1 down to the measurement point and the cooling rate CR2 from the measurement point down to the temp. Ms are so controlled that the amt. of martensite in the steel attains 3-20%, whereby the steel strip which is superior in both strength and ductility is produced. |
