Thick, tough, high tensile strength steel plate and production method therefor

Abstract

The invention provides thick high-toughness high-strength steel plates having excellent strength and toughness in the central area through the plate thickness, and methods for manufacturing such steel plates. The thick steel plate has a specific chemical composition and includes a microstructure having, throughout an entire region in the plate thickness direction, an average prior austenite grain size of not more than 50 µm and a martensite and / or bainite phase area fraction of not less than 80%. A continuously cast slab having the specific chemical composition is heated to 1200°C to 1350°C, hot worked with a strain rate of not more than 3 / s and a cumulative working reduction of not less than 15%, and thereafter hot rolled and heat treated.

Description

technical field [0001] The present invention relates to a thick-walled, high-toughness, high-tensile steel plate with excellent strength, toughness, and weldability that can be used in steel structures such as buildings, bridges, shipbuilding, marine structures, construction and industrial machinery, tanks, and gates, and a manufacturing method thereof. Preferably, it is a steel plate having a plate thickness of 100 mm or more and a yield strength of 620 MPa or more. Background technique [0002] In recent years, the increase in size of steel structures has been remarkably advanced, and the high-strength and thick-walled steel materials used have also been remarkably advanced. Generally, a large steel ingot produced by an ingot casting method is rough-rolled, and the obtained bloom slab is then hot-rolled to manufacture a thick steel plate having a plate thickness of 100 mm or more. However, the thick segregation portion at the hot top and the negative segregation portion a...

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Problems solved by technology

However, the thick segregation part at the hot top and the negative segregation part at the bottom of the ingot must be cut off and discarded in this ingot-blooming process, so the yield is reduced, the manufacturing cost is increased, and the construction period is extended.

[0003] On the other hand, in the process of using continuous casting slabs as raw materials, although there is no such concern, since the thickness of continuous casting slabs is smaller than that of ingot casting slabs, the reduction rate until the thickness of the product is small, and it is necessary to increase the strength and thickness of steel materials. In the case of walling, the amount of alloying elements added to ensure the necessary properties increases, causing problems such as center porosity due to center segregation, and internal quality deterioration due to enlargement.

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