Title:
ROLLED ROUND STEEL MATERIAL FOR STEERING RACK BAR, AND STEERING RACK BAR
Document Type and Number:
WIPO Patent Application WO/2015/029553
Kind Code:
A1
Abstract:
A rolled round steel material for steering rack bars that has a chemical composition which comprises 0.38-0.55% C, up to 1.0% Si, 0.20-2.0% Mn, 0.005-0.10% S, 0.01-2.0% Cr, 0.003-0.10% Al, 0.0005-0.0030% B, up to 0.047% Ti, 0-1.0% Cu, 0-3.0% Ni, 0-0.50% Mo, 0-0.10% Nb, 0-0.30% V, 0-0.005% Ca, 0-0.30% Pb, and Fe and impurities as the remainder, the contents of P and M among the impurities being P≤0.030% and N≤0.008%, and which satisfies 3.4N≤Ti≤3.4N+0.02, and that has a microstructure which comprises ferrite (F), lamellar pearlite (LP), and cementite (C). In a cross-section thereof, a region ranging from the surface to a depth which is 1/2 the radius has an average F-grain diameter of 10 µm or smaller and an areal LP proportion less than 20% and contains spherical cementite (SC), of the C, in an amount of 4×105 grains/mm2 or larger. In a central part thereof, the areal LP proportion is 20% or higher and the number of SC grains is smaller than 4×105 grains/mm2. In a longitudinal section thereof, the F grains contained in a region ranging from the surface to a depth 1/2 the radius have an average aspect ratio of 3 or higher. This steel material has high base-material toughness and satisfactory cuttability without necessitating a tempering treatment.
Inventors:
EGASHIRA MAKOTO (JP)
HORIKAMI SADANORI (JP)
HIGASHIDA MASASHI (JP)
OKADA TAKAHIRO (JP)
NEISHI YUTAKA (JP)
HASEGAWA TATSUYA (JP)
MATSUMOTO HITOSHI (JP)
HORIKAMI SADANORI (JP)
HIGASHIDA MASASHI (JP)
OKADA TAKAHIRO (JP)
NEISHI YUTAKA (JP)
HASEGAWA TATSUYA (JP)
MATSUMOTO HITOSHI (JP)
Application Number:
PCT/JP2014/066200
Publication Date:
March 05, 2015
Filing Date:
June 18, 2014
Export Citation:
Assignee:
NIPPON STEEL & SUMITOMO METAL CORP (JP)
International Classes:
C22C38/00; C22C38/38; C22C38/58; C21D8/06
Foreign References:
| JP2011241468A | 2011-12-01 | |||
| JP2013147728A | 2013-08-01 | |||
| JP2011214130A | 2011-10-27 | |||
| JP2011241466A | 2011-12-01 |
Other References:
JIS Z 2242, 2005
JIS Z 2241, 2011
JIS Z 2241, 2011
Attorney, Agent or Firm:
CHIHARA, Kiyosei et al. (JP)
Kiyomasa Chihara (JP)
Kiyomasa Chihara (JP)
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