Metal treatment – Stock – Ferrous
Patent
1996-08-23
1998-11-03
Yee, Deborah
Metal treatment
Stock
Ferrous
148654, 420121, 420123, 420128, C22C 3804, C22C 3806
Patent
active
058302859
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/JP95/00276 filed Feb. 24, 1995.
TECHNICAL FIELD
The present invention is directed to automobile components and industrial machine members that are processed by hardening and tempering after cold working (forging, cutting, etc.), and more particularly to fine graphite uniform dispersion steel and a production method thereof.
BACKGROUND ART
Apheroidizing annealing techniques for cementite have been employed to improve cold forgeability of steels for machine structures such as steel materials of an AiSi1055 class, and free-cutting elements such as sulfur, lead, etc., have been used to improve cuttability. However, cold forgeability and cuttability, and hardenability and cuttability are mutually contradictory characteristics, and it is technically contradictory to simultaneously satisfy all of them.
As one of the technologies for solving these contradictions, a technical paper relating to a graphite dispersion steel is reported in "Journal of the Japan Institute of Metals", Vol. 30, No. 3(1966), p. 279. This technology converts the ferrite plus pearlite structure in the solid phase to the ferrite plus graphite structure by controlling the chemical components of the steel and the annealing condition. The chemical components are 0.24% of C, 1.18% of Si, 0.24% of Mn and 2.03% of Ni, for example, and the graphitization annealing treatment is carried out at a heating temperature of 650.degree. C. for a heating time of about 28 hours. With regard to cold forgeability of the steels of this system, the technical paper "Journal of the Japan Institute of Metals", Vol. 53 (1989), p. 206 reports that when the ferrite plus pearlite structure of a medium carbon steel is converted to the ferrite plus graphite two-phase structure, its hardness drops from Hv 160 to about Hv 110 in terms of Vicker's hardness, and its cold forgeability becomes higher than that of sulfur free-cutting steels. Cuttability is described also in "Journal of the Japan Institute of Metals", Vol. 52(1988), p. 1285. This article reports that when a graphitization ratio becomes great, a cutting resistance main component of force and a cutting resistance feed component of force drop substantially in half, a shear stress decreases as a shear angle becomes great, a coefficient of friction becomes small, and that a curl radius of a chip becomes small, so that processability becomes higher.
However, existing graphite dispersion steels have not been used industrially because, as described in Japanese Examined Patent Publication (Kokoku) No. 53-46774, graphite particles having diameters exceeding 30 .mu.m exist in the mixture of graphite particles obtained by the present technology. In other words, when the sizes of the graphite particles are large and such particles are dispersed non-uniformly, the graphite is not sufficiently dissolved in the austenite at the time of quench hardening, a diffusion distance becomes longer, and the carbon atoms are segregated. In consequence, insufficiency of quench hardness, non-uniformity of quench hardness, and so forth, occur. Particularly when the heating retention time is as short as several seconds as in the case of induction hardening, the steel structure is likely to become a martensite plus ferrite mixed structure. When the graphite particles become coarse, cracks due to cold forging occur, a limit strain becomes small and coarseness of a cutting finish surface becomes great.
Generally, in order to put the graphite precipitation steel into practical application, it is an essential condition to refine and uniformly disperse the graphite. Therefore, the state of art for controlling the grain diameter of the graphite precipitation steel and its dispersion will be described. First, Japanese Unexamined Patent Publication (Kokai) No. 2-111842 describes that BN can be used as a precipitation nucleus for the graphite and that it is effective to limit the oxygen content to not more than 30 ppm. BN is effective for finely precipitating the graphite as is well k
REFERENCES:
patent: 5476556 (1995-12-01), Hoshino et al.
Patent Abstracts of Japan, vol. 95, No. 10, 30 Nov. 1995 & JP 07 188851 A(Kawasaki Steel Corp.), 25 Jul. 1995.
Patent Abstracts of Japan, vol. 95, No. 10, 30 Nov. 1995 & JP 07 188850 A(Kawasaki Steel Corp.), 25 Jul. 1995.
Patent Abstracts of Japan, vol. 95, No. 8, 29 Sep. 1995 & JP 07 138698 A (Nippon Steel Corp.), 30 May 1995.
"Effect of Pre-quenching Temperatures on the Graphitization of Structural Low Alloy," Tanaka et al., J.Japan Inst.of Metals, vol. 30 (1966), p. 279, published Sep. 24, 1965.
"Pre-Treatments to Enhance Graphitization in a Low Alloy Structural Steel," Fujihira, J.Japan Inst.of Metals, Vol. 43 (1979), p. 640, published Jan. 22, 1979.
"Machinability of Hypo-Eutectoid Graphitic Steels,"Sueyoshi, et al., J.Japan Inst. of Metals, vol. 43 (1979), p. 1285, published Jul. 14, 1988.
"Cold Forgeability and Jachinability after Cold Forging of Hypo-Eutectoid Graphitic Steels", Sueyoshi, et al., J.Japan Inst.of Metals, vol. 53 (1989, p. 206, published Jul. 14, 1988.
Katayama Sakae
Naito Ken-ichiro
Tarui Toshimi
Toda Masahiro
Nippon Steel Corporation
Yee Deborah
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