STEEL FOR HIGH-STRENGTH BOLTS AND PROCESS FOR PRODUCTION OF HIGH-STRENGTH BOLTS

WIPO Patent Application WO/2011/048971

A1

Provided are: a steel for high-strength bolts which has excellent workability and good delayed fracture resistance and which can attain a tensile strength of 1550MPa or more; and a process for the production of high-strength bolts using the steel. A high-strength bolt that exhibits a tensile strength of 1550MPa or more can be produced by using a specific steel as the raw material and subjecting the specific steel to quenching and tempering. The specific steel contains 0.40 to 0.70 mass% of C, 0.40 to 2.50 mass% of Si, 0.05 to 1.0 mass% of Mn, either 0.25 to 3.00 mass% of Mo and/or 0.20 to 3.00 mass% of W, and, if necessary, either 0.20 to 1.50 mass% of Cr and/or 0.20 to 1.50 mass% of Ni, or at least one selected from the group consisting of 0.002 to 1.50 mass% of V, 0.002 to 1.50 mass% of Ti and 0.002 to 1.50 mass% of Nb. Further, the specific steel has an α value of 100 or less as calculated from the contents of C and Si according to the formula: α = 19.0 + 76.1×C + 30.0×√Si- 4.5×C×√Si.

KONDO TAKAAKI
YAMADA YUUICHI
MURAKAMI YOUICHI
KIMURA YUUJI (JP)
AKIYAMA EIJI (JP)
TSUZAKI KANEAKI (JP)

PCT/JP2010/067833

April 28, 2011

October 12, 2010

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NISSAN MOTOR (JP)
NAT INST FOR MATERIALS SCIENCE (JP)
KONDO TAKAAKI
YAMADA YUUICHI
MURAKAMI YOUICHI
KIMURA YUUJI (JP)
AKIYAMA EIJI (JP)
TSUZAKI KANEAKI (JP)

C22C38/12; C21D9/00; C22C38/50; F16B35/00

JP2006291295A	2006-10-26
JP2007270293A	2007-10-18
JP2007146284A	2007-06-14
JPH08253843A	1996-10-01

MATOBA, Motonori (JP)
Motonori Matoba (JP)

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