| 摘要 |
PURPOSE:To obtain a cold rolled steel sheet for drawing having excellent dent resisting property by performing a water hardening on a steel strip after rapidly heating primarily them just before their cooling process terminates, and then, by applying an over aging treatment on them, in the course of continuous treatments of steel strips, and forming a hardened layer of a two-phase structure. CONSTITUTION:A steel strip is gradually cooled to a temperature from which the quenching starts in a primary cooling zone 6 of a continuous anealing furnace after passing through a heating zone 4 and a soaking zone 5. At the outlet side of the primary cooling zone 6, a rapid heating device 11 is installed, and only the surface layer of the strip is heated to a temperature higher than the A1 transformation point just before the cooling process terminates. Then, a water hardening is performed on the strip with a water hardening device 7, and a hardened layer of two-phase structure of martensite and ferrite is formed in the surface layer of the strip. The strip is then coiled by a real 10 after passing through an over aging treatment zone 8 and a final cooling zone 9. When this method is applied, cold rolled steel sheets for drawing having a high yielding point and an excellent dent resisting property are obtained. |
