Title:
THICK STEEL SHEET HAVING EXCELLENT FATIGUE PROPERTIES, AND METHOD FOR PRODUCING SAME
Document Type and Number:
WIPO Patent Application WO/2015/029873
Kind Code:
A1
Abstract:
A thick steel sheet according to the present invention satisfies a predetermined chemical composition, wherein the metallic structure meets requirements (a) to (d) as mentioned below when determined at an observation point that is located at the depth of 3 mm from the surface of the steel sheet on the vertical cross-sectional view that is taken in a direction parallel to the rolling direction, and wherein precipitates meet requirement (A) as mentioned below: (a) the metallic structure is composed of a bainite structure and a remainder structure that is harder than the bainite, wherein the bainite fraction in the whole structure is 80% by area or more; (b) the average length of a crystal grain of bainite is 7 μm or less as observed in the direction of the thickness of the crystal grain when the crystal grain of bainite is determined on the basis of the high-angle grain boundary having an orientation difference between adjacent crystals of 15° or more; (c) the harder remainder structure has an equivalent circle diameter of 3 μm or less; (d) the difference between the hardness of the bainite and the hardness of the harder remainder structure (i.e., [the hardness of the harder remainder structure] - [the hardness of the bainite]) is Hv 100 or more; and (A) the number of precipitates each containing at least one of Nb, Ti and V and each having an equivalent circle diameter of 20 nm or less is 100/μm2 or more.
Inventors:
SANDAIJI YUSUKE
KINEFUCHI MASAO
KAWANO HARUYA
KANEKO MASAHITO
KINEFUCHI MASAO
KAWANO HARUYA
KANEKO MASAHITO
Application Number:
PCT/JP2014/071894
Publication Date:
March 05, 2015
Filing Date:
August 21, 2014
Export Citation:
Assignee:
KOBE STEEL LTD (JP)
International Classes:
C22C38/00; B21B1/38; C21D8/02; C22C38/58
Foreign References:
| JP2002241891A | 2002-08-28 | |||
| JP2003239036A | 2003-08-27 | |||
| JP2007162076A | 2007-06-28 | |||
| JP2010209433A | 2010-09-24 | |||
| JPH1060575A | 1998-03-03 | |||
| JP2011195944A | 2011-10-06 | |||
| JP2009084643A | 2009-04-23 |
Other References:
ABE ET AL., IRON AND STEEL, 1984, pages 1459 - 1466
Attorney, Agent or Firm:
HAMADA Yuriko et al. (JP)
Yuriko Hamada (JP)
Yuriko Hamada (JP)
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