NON-HEAT-TREATED STEEL SHEET HAVING HIGH YIELD STRENGTH IN WHICH HARDNESS OF A WELDING-HEAT-AFFECTED ZONE AND DEGRADATION OF LOW-TEMPERATURE TOUGHNESS OF THE WELDING-HEAT-AFFECTED ZONE ARE SUPPRESSED

WIPO Patent Application WO/2017/094593

A1

Provided is a non-heat-treated steel sheet having high yield strength in which hardness of a welding-heat-affected zone and degradation of low-temperature toughness of the welding-heat-affected zone are suppressed. A non-heat-treated steel sheet having high yield strength in which hardness of a welding-heat-affected zone and degradation of low-temperature toughness of the welding-heat-affected zone are suppressed, the non-heat-treated steel sheet characterized by including predetermined components in the steel, the Ceq specified by expression (1) is less than 0.44, the A value specified by expression (2) is 2.5 or greater, the B value specified by expression (3) is 2.37 or greater, the area ratios of the metallographic structure below at a position 1/4 of the thickness of the steel sheet satisfy the values of 80% or more of bainite and 0% to 0.26% of island martensite, and the maximum hardness of the bainite is 270 HV or greater. (1): Ceq = C + Mn/6 + (Cu + Ni)/15 + (Cr + Mo + V)/5. (2): A value = 1.15 × Mn + 2.20 × Mo + 6.50 × Nb. (3): B value = 1.20 × Mn + 0.50 × Ni + 4.25 × Nb.

KURATA KOJI
KAWANO HARUYA
TASHIRO KIICHIRO
KAKIZAKI MOTOKI

PCT/JP2016/084857

June 08, 2017

November 24, 2016

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KK KOBE SEIKO SHO(KOBE STEEL LTD ) (JP)

C22C38/00; C22C38/58; C21D8/02

JP2006169591A	2006-06-29
JP2003160833A	2003-06-06
JP2011006772A	2011-01-13
JP2012193411A	2012-10-11
JP2010209433A	2010-09-24
JP2009149917A	2009-07-09
JP2013237101A	2013-11-28

See also references of EP 3385399A4

UEKI, Kyuichi et al. (JP)

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