H section and method for manufacturing same

Abstract

This H section includes, as a chemical composition, C, Si, Mn, Nb, V, Ti, and N; in which the H section includes, as a metallographic structure, ferrite of 60 area % to less than 100 area %, an average grain size of this ferrite is 1 μm to 30 μm, a thickness of a flange is 20 mm to 140 mm, tensile yield stress is 385 MPa to 530 MPa, and Charpy absorbed energy at −20° C. is 100 J or more.

Description

TECHNICAL FIELD OF THE INVENTION[0001]The present invention relates to a thick H section, which has excellent strength and low temperature toughness, and a method for manufacturing the same. Priority is claimed on Japanese Patent Application No. 2016-248181, filed on Dec. 21, 2016, the content of which is incorporated herein by reference.RELATED ART[0002]Recently, buildings such as high-rise buildings are becoming large and high, and thick steels have been utilized as strength members required for the structure. However, generally, in ferrous materials, as the thickness of a product increases, it becomes difficult to ensure the strength, and it is also difficult to ensure the toughness.[0003]In regard to such a problem, in Patent Document 1, a technology of ensuring the toughness by utilizing an effect of refining prior austenite grains due to a Ca—Al-based oxide and obtaining a steel, in which high strength is ensured by applying accelerated cooling, is proposed.[0004]In addition, ...

AI Technical Summary

Benefits of technology

The present invention provides a way to make a strong and low-temperature toughness H section, and a method for making it.

Problems solved by technology

However, generally, in ferrous materials, as the thickness of a product increases, it becomes difficult to ensure the strength, and it is also difficult to ensure the toughness.

However, when a thick steel plate is manufactured, if accelerated cooling is applied after hot rolling, the cooling rate becomes slow inside the steel plate compared to its surface, so that a significant difference is caused between the surface and the inside in the temperature history during cooling, and a difference is caused in mechanical properties such as strength, ductility, toughness, depending on a portion of a steel.

However, rolling conditions (temperature and rolling reduction) are limited in universal rolling.

Therefore, in a case where an H section is manufactured, particularly in a case where a thick H section having a thickness of a flange of 20 mm or more is manufactured, it is not easy to control mechanical properties compared to general thick steel plates (thick steel plates).

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