Manufacturing method of steel plate for high heat input welding

Abstract

Provided is a method of manufacturing a medium-thick non-tempered high-tensile strength steel sheet that has excellent joint properties such as toughness even under high-energy-input welding and has a yield strength of 460 MPa or more, that is, a steel sheet for high-energy-input welding. The following steel materials are heated to 1050°C to 1200°C, and the temperature at the end of rolling is Ar 3 Hot rolling is carried out at a temperature above the transformation point, and water cooling is carried out at 5°C / sec or above until the surface temperature becomes (-t×1.5)+400°C or more and (-t×1.5)+620°C or less, in mass %, Steel contains: C: 0.03-0.1%, Si: 0.01-0.1%, Mn: 0.8-2%, P: less than 0.02%, S: 0.0005-0.005%, Al: 0.005-0.1%, Nb: 0.003-0.03% , Ti: 0.005-0.05%, Cu: 0.1-0.5%, Ni: 0.3-2%, N: 0.003-0.01%, B: 0.0003-0.0025%, Ca: 0.0005-0.003%, O: less than 0.004%, and Satisfy C eq : 0.38~0.43, ACR: 0~1.

Description

technical field [0001] The present invention relates to non-quenched and tempered high-tensile-strength steel with a yield stress of 460 MPa or more and a plate thickness of 25 mm or more and 50 mm or less, which is used in various steel structures in the fields of ships, construction, and civil engineering. A method of manufacturing a steel plate for high heat input welding that has excellent joint properties even when high heat input welding is performed with a heat input amount exceeding 200 kJ / cm. Background technique [0002] Steel materials used in various steel structures in the fields of ships, construction and civil engineering are increasing in strength and thickness. With the increase in strength and thickness of such steel materials, there are more and more opportunities to use high-energy input welding with excellent productivity, such as submerged arc welding, electric welding, and electroslag welding, when welding steel materials. [0003] For various steel s...

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Problems solved by technology

[0007] However, with regard to the techniques described in Patent Documents 1 to 4, it is difficult to sufficiently suppress the grain growth of austenite in the HAZ and prevent the toughness of the HAZ from decreasing for large heat input welding with a heat input of more than 200 kJ / cm. of

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