Heat treatment method of A387Gr11Cl2 steel plate for steel pipe with low surface hardness and high impact toughness

The invention discloses a heat treatment method of an A387Gr11Cl2 steel plate for a steel pipe with low surface hardness and high impact toughness, which comprises the following steps: S1, carrying out shot blasting on a steel billet, setting the furnace temperature to be AC3 plus 0-10 DEG C, entering a furnace, carrying out complete austenitizing, and carrying out heat preservation for 10-20 minutes; s2, after normalizing, accelerated cooling is conducted, the quenching roller speed is 0.3-0.5 m/s, the quenching roller gap is set to be the sum of the thickness of the steel plate and 0.5-1 mm, the water ratio is set to be 1.3, the water amount of a slit nozzle in the width direction of the steel plate is larger than or equal to 156 m < 3 >/h per meter, and the flatness of the plate shape after water cooling is smaller than or equal to 3 mm/2 m; s3, when the steel plate is taken out of the quenching machine, the temperature is 350 +/-50 DEG C, and a lower bainite structure is obtained; s4, a tempering procedur