Thick steel sheet and production method therefor

Abstract

A thick steel sheet: which contains C: 0.04-0.06 mass%, Si: 0.35-0.45 mass%, Mn: 1.49-1.59 mass%, P: greater than 0 mass% to 0.01 mass%, S: greater than 0 mass% to 0.002 mass%, Cu: 0.23-0.33 mass%, Al: 0.02-0.06 mass%, Ni: 0.24-0.34 mass%, Nb: 0.015-0.021 mass%, Ti: 0.012-0.018 mass%, B: 0.0007-0.0013 mass%, Ca: 0.0010-0.0030 mass%, and N: 0.0040-0.0060 mass%, the balance being made of iron and unavoidable impurities; and in which the metal structure comprises a first phase and a hard second phase that is harder than the first phase, said hard phase being a phase made of pearlite, and the hardness of the second phase being 260 HV or less.

Description

technical field [0001] The present invention relates to a thick steel plate and its manufacturing method. Background technique [0002] In large-scale structures such as ships, buildings, bridges, and construction machinery, the size of the structure is advancing, and on the other hand, higher reliability is required for its structural members due to the magnitude of damage when damage occurs. Accordingly, high strength is required for the steel plates constituting the structures. On the other hand, as the strength of the steel sheet tends to be high, the workability represented by the uniform elongation tends to decrease, and a steel sheet having both of them is required. [0003] For example, in Patent Document 1, a technique of producing a steel with good uniform elongation and strength by obtaining a fine metal structure mainly composed of an α phase and then achieving precipitation strengthening has been studied. [0004] As a method of obtaining the above-mentioned m...

AI Technical Summary

Problems solved by technology

[0014] Both Patent Documents 1 and 2 achieve a fine structure by precisely controlling the cooling rate by accelerated cooling after rolling, but in the actual manufacturing process, it is difficult to strictly manage long and large thick steel plates from the beginning to the end. Depending on the position of the steel plate, the characteristics may vary, reducing productivity

[0015] In addition, in the production method of Patent Document 3, in order to allow retained austenite contributing to uniform elongation to remain at room temperature, it is necessary to perform the above-mentioned reheating process, which leads to a large number of production steps and a decrease in productivity. question

[0016] In Patent Documents 1 to 3, as described above, various studies have been conducted from the viewpoints of uniform elongation, strength, toughness, etc., but when paying particular attention to uniform elongation, the current situation is that it cannot be achieved from the viewpoint of productivity. Not to mention there are still problems

Images