| 摘要 |
Provided is a low yield ratio, high strength and high toughness steel plate having excellent strain ageing resistance equivalent to API 5L X70 Grade or lower and a method for manufacturing the same. The steel plate has a metallographic microstructure that is a three-phase microstructure consisting of bainite, M-A constituent, and quasi-polygonal ferrite, the area fraction of the bainite being 5% to 70%, the area fraction of the M-A constituent being 3% to 20%, the remainder being the quasi-polygonal ferrite, the equivalent circle diameter of the M-A constituent being 3.0μm or less. The steel plate has a yield ratio of 85% or less and a Charpy impact test absorbed energy of 200 J or more at−30° C. before or after being subjected to strain ageing treatment at a temperature of 250° C. or lower for 30 minutes or less.
|
