The present application is a U.S. National Phase application based upon PCT Application Serial No. PCT/CN2016/102350 filed on Oct. 18, 2016 which titled “TOOTHED RACK STEEL PLATE HAVING THICKNESS OF 177.8 MM AND MANUFACTURED BY CONTINUOUS CASTING BILLET AND MANUFACTURING METHOD THEREFOR”, the entire disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The present application relates to a field of manufacturing a rack steel plate, specially relates to a rack steel plate with a thickness up to 177.8 mm by a continuous casting slab and manufacturing method thereof.

BACKGROUND ART

The rack steel plate for self-elevating marine platform requires high strength, good plasticity, high toughness and large thickness, and requires a uniform performance along the steel plate thickness direction, for example, the steel rack plate with a thickness of 177.8 mm for self-elevating marine platform requires: yield strength is ≥690 MPa, tensile strength is 770˜940 MPa, elongation is ≥14%, and at low temperature (normally, at ¼ thickness of the steel plate at −40°, at the center of the steel plate, i.e. at ½ thickness of the steel plate at −30° C.) Charpy impact energy is ≥69 J. Hence, industry always devotes to developing a rack steel plate of large thickness that meets this requirement, and has developed using a moulded casting ingot to manufacture the rack steel plate of large thickness and the manufacturing method thereof. For example, the invention patent of publication number CN102345045A disclosed a rack steel plate with a thickness of 120˜150 mm by the moulded casting ingot for marine platform and manufacturing method thereof. With regards to the rack steel plate manufactured by the moulded casting ingot, not only the production technology is complicated but also the yield ratio is low, so that the manufacturing cost dramatically increases.

