| 主权项 |
1. A method for strengthening a steel plate member employing a hearing and quenching treatment, the method comprising; a first heating step, a partial cooling step, a second heating step and an entire cooling step; wherein
each step is conducted in a written order;
in the first heating step, an entire of a steel plate is heated to a non-quenching temperature (NQT) set at lower than a transformation start temperature (AC1), then a heating is once suspended;in the partial cooling step, a non-strengthened part of the steel plate is cooled while the heating is suspended to generate a temperature difference between a strengthened part and the non-strengthened part with reference to a temperature difference (ΔT) determined by subtracting the non-quenching temperature (NQT) from a quenching temperature (QT) set at higher than or equal to a transformation end temperature (AC3);in the second heating step, the entire of the steel plate is again heated until the strengthened part of the steel plate reaches the quenching temperature (QT) while the non-strengthened part remains at lower than the transformation start temperature (AC1), and stopping the heating, followed by the entire cooling step; andin the entire cooling step, the entire of the steel plate is rapidly cooled while heating is stopped, to thereby hardening the strengthened part but not hardening the non-strengthened part. |
