Title:
ROLLED ROUND STEEL MATERIAL FOR STEERING RACK BAR, AND STEERING RACK BAR
Document Type and Number:
WIPO Patent Application WO/2014/167891
Kind Code:
A1
Abstract:
The purpose of the present invention is to provide a rolled round steel material for a steering rack bar having a high base material toughness and an excellent machinability for machining a deep hole in the length direction of the radial center part, without performing a refinement treatment. A rolled round steel material for a steering rack bar having a chemical composition containing 0.38 to 0.55% of C, no more than 1.0% of Si, 0.20 to 2.0% of Mn, 0.005 to 0.10% of S, 0.01 to 2.0% of Cr, 0.003 to 0.10% of Al, and 0.003 to 0.03% of N, with the remainder being made up by Fe and impurities, the impurities containing no more than 0.030% of P. The microstructure comprises ferrite (F), lamellar pearlite (LP), and cementite (C). In a cross-section perpendicular to the rolling direction, the average grain diameter of the F in a region extending from the surface to a position halfway along the radius is no greater than 10 μm, the area ratio of the LP is less than 20%, and the number of spherical cementite (SC) among the C is greater than or equal to 4 × 105 per mm2. In the center part, the area ratio of the LP is greater than or equal to 20% and the number of SC is less than 4 × 105 per mm2. In a cross-section which passes through the center line of the round steel material and is parallel to the rolling direction, the average aspect ratio of the F in the region extending from the surface to the position halfway along the radius is equal to or greater than 3.
Inventors:
HORIKAMI SADANORI (JP)
HIGASHIDA MASASHI (JP)
OKADA TAKAHIRO (JP)
EGASHIRA MAKOTO (JP)
NEISHI YUTAKA (JP)
HASEGAWA TATSUYA (JP)
MATSUMOTO HITOSHI (JP)
HIGASHIDA MASASHI (JP)
OKADA TAKAHIRO (JP)
EGASHIRA MAKOTO (JP)
NEISHI YUTAKA (JP)
HASEGAWA TATSUYA (JP)
MATSUMOTO HITOSHI (JP)
Application Number:
PCT/JP2014/053052
Publication Date:
October 16, 2014
Filing Date:
February 10, 2014
Export Citation:
Assignee:
NIPPON STEEL & SUMITOMO METAL CORP (JP)
International Classes:
C22C38/00; B21B1/16; B21B3/00; C21D8/06; C22C38/60; F16H55/26
Domestic Patent References:
| WO2014030327A1 | 2014-02-27 |
Foreign References:
| JP2010168624A | 2010-08-05 | |||
| JP2010144226A | 2010-07-01 | |||
| KR20080109351A | 2008-12-17 |
Attorney, Agent or Firm:
CHIHARA, Kiyosei et al. (JP)
Kiyomasa Chihara (JP)
Kiyomasa Chihara (JP)
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