| 摘要 |
PURPOSE:To make the economization of blank material alloys possible without reheating and to cool a steel strip with good shapes by incorporating a cooling method by immersion in static hot water and a cooling method by hot water jets under water in the post stage to a primary cooling method after soaking. CONSTITUTION:In a primary cooling stage of titled treatment consisting of heating, soaking, primary cooling and post-treatment stages, the steel strip S after holding at temp. Ac1-Ac3 is immersed in static hot water W kept at >=90 deg.C, and is cooled down to 710-550 deg.C at 20-90 deg.C/sec cooling rate. As the 2nd stage, the steel strip is cooled by the hot water jets from underwater headers 23 immediately down to the Ms point lower than 200 deg.C at 50-400 deg.C/sec cooling rate in the hot water W' kept at >=90 deg.C. Since the steel strip can be cooled without cutting the nose of CCT curves by the 2nd stage of the quick cooling, the blank material alloys can be economized. The shape of the steel strip is assured by the above-mentioned selection of the inflection point of the two-stage cooling. If the steel strip after soaking is slowly cooled with gaseous jets down to about 800-600 deg.C in the fore stage of the primary cooling, the shape of the steel strip is assured and the easy tendency to cutting of the nose of the CCT curves is prevented. |
