Thick-walled high-toughness high-tensile steel plate excellent in material uniformity and manufacturing method thereof

Abstract

A high tensile strength thick steel plate with excellent material homogeneity and excellent strength, elongation, and toughness in a mid-thickness part is provided by heating a continuously-cast slab adjusted to a specific chemical composition to at least 1200 °C and no higher than 1350 °C, hot forging the continuously-cast slab under conditions of a temperature of 1000 °C or higher, a strain rate of 3 / s or less, and a cumulative working reduction of 15 % or more using opposing dies having respective short sides differing such that when a short side length of a die having a shorter one of the short sides is taken to be 1, a short side length of a die having a longer one of the short sides is 1.1 to 3.0, allowing cooling to obtain a steel raw material, reheating the steel raw material to at least the Ac 3 temperature and no higher than 1250 °C, performing hot rolling of the steel raw material including at least two passes carried out with a rolling reduction of 4 % or more per pass, allowing cooling to obtain a thick steel plate, reheating the thick steel plate to at least the Ac 3 temperature and no higher than 1050 °C, rapidly cooling the thick steel plate to 350 °C or lower, and tempering the thick steel plate at at least 550 °C and no higher than 700 °C.

Description

technical field [0001] The present invention relates to a thick steel plate suitable for steel structures such as buildings, bridges, shipbuilding, marine structures, construction machinery, tanks, and pressure water pipes, which is excellent in strength, elongation, toughness, and material uniformity in the thickness direction and methods of manufacture thereof. [0002] In particular, the present invention relates to a thick-walled, high-toughness, high-tensile steel sheet having a thickness of 100 mm or more, having a yield strength of 500 MPa or more in the central portion of the thickness, and a reduction in area caused by tension in the thickness direction of the central portion of the thickness being 40% or more, and the low-temperature toughness at -60°C at the central part of the plate thickness is 70J or more. [0003] In the present invention, excellent material uniformity means that the hardness difference in the plate thickness direction is small. Background te...

AI Technical Summary

Problems solved by technology

However, in this ingot-slab casting process, the concentrated segregation part at the riser and the negative segregation part at the bottom of the ingot must be cut off, so there is a problem that the yield is not improved, but the manufacturing cost is increased and the construction period is lengthened.

[0006] On the other hand, when a thick-walled steel plate having a thickness of 100 mm or more is produced by a process using a continuous casting slab as a raw material, there is no concern as described above, but since the thickness ratio of the continuous casting slab is used The thickness of the slab produced by the ingot method is small, so there is a problem that the amount of reduction to the product thickness is small

In addition, in recent years, there is a general tendency to demand higher strength and thicker steel materials, and the amount of alloying elements added to ensure the required properties has increased. As a result, center porosity due to center segregation has occurred. Deterioration of internal quality due to upsizing is a new issue

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