Metal treatment – Stock – Ferrous
Patent
1997-10-27
1999-10-26
Yee, Deborah
Metal treatment
Stock
Ferrous
420 17, C22C 3708
Patent
active
059721286
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to cast iron and a piston ring, with improved seizure resistance and wear resistance.
BACKGROUND TECHNIQUE
Wear resistance of high level is required for the piston ring used in a reciprocating internal combustion engine. Therefore, flaky graphite cast-iron material (FC250 or FC300), nodular graphite cast-iron material (FCD700 or the like), and compacted varmicular (CV) graphite cast-iron material proposed in Japanese Unexamined Patent Publication No. Hei 5-86473 or the like have been extensively used heretofore for the piston rings of an internal combustion engine. Also, a cast iron or steel piston-ring, provided with a hard chromium plating layer or a composite dispersion plating layer on the outer peripheral sliding surface for imparting wear resistance, is widely used.
Nevertheless, since the piston ring is caused to slide on the cylinder inner surface at high speed, the piston ring should not only have excellent wear resistance in itself but should also have such property that it does not abrade the cylinder inner-surface, which is the opposed material. Particularly, when the opposed material of the piston ring, i.e., the cylinder liner, is a flaky graphite cast iron, the ferrite precipitation amount of which is increased by lowering the cooling rate at the casting and hence the hardness of which is from HRB approximately 85-95, since the wear resistance of the liner itself is low, a property of the piston ring, that does not abrade the opposed material, is an important factor of the piston ring.
The cast-iron or steel piston ring, which is provided with a hard chromium plating layer or a composite dispersion plating layer on the outer peripheral sliding surface, has an excellent wear resistance in itself but also has a strong abrasive tendency on the flaky graphite cast-iron liner as the opposed material. The above cast-iron or steel piston ring has, therefore, been occasionally used for the 1st ring which is required to have breaking resistance. It was, however, seldom used as the 2nd ring. For the 2nd ring, a piston ring made of flaky graphite cast-iron material or CV graphite cast-iron material has, therefore, been used heretofore, without being provided with a surface-treatment layer. A piston ring consisting of these materials has, however, low wear resistance in itself and low seizure resistance with respect to the opposed material (flaky graphite cast iron). Improvement of these properties is, therefore, desired.
DISCLOSURE OF INVENTION
Considering the above described points, it is an object of the present invention to provide a cast iron with improved seizure resistance and wear resistance, and also to provide a piston ring, which has improved wear resistance in itself, and improved seizure resistance with respect to the flaky graphite cast iron having low hardness of from HRB85-95, and abrades only slightly the opposed material of a liner.
The present invention, which attains the above mentioned object, relates to a cast iron, which has a composition containing C: 3.0-3.5%; Si: 2.2-3.2%; Mn: 0.4-1.0%; P: not more than 0.2%; S: not more than 0.12%; Cr: 0.1-0.3%; V: 0.05-0.2%; Ni: 0.8-1.2%; Mo: 0.5-1.2%; Cu: 0.5-1.2%; and B: 0.05-0.1%, by weight, the balance being essentially Fe and unavoidable impurities, in which cast iron from 2 to 10% by area of the undissolved carbides and fine graphite are dispersed in a matrix consisting of either tempered martensite or bainite or both, and which cast iron has a hardness of from ERC 32-45. The present invention is also related to a piston ring constitued of this cast iron.
The present invention is based on the conventionally used, fine graphite cast-iron material, the chemical composition of which is C, Si, Cr, Ni, Mo and V. B is added to this fine graphite cast iron for the purpose of enhancing the wear resistance in the present invention. A characteristic of the present invention resides in the point that Cu, which has been generally alleged to be not very effective as regards its sliding property is
REFERENCES:
Giesserei-Praxis [Foundry Practice]; 1976, 23/24, pp. 351-384.
Konstruktion [Construction] 44 (1992) pp. 193-204.
Giesserei-Praxis [Foundry Practice]; 1982, 1/2, pp. 1-28.
K. Rohrig and D. Wolters: "Legiertes Gusseisen" [Alloyed Cast Iron], vol. 1, Giesserei-Verlag Gmbh [Foundry Publications], Dusseldorf, 1976, pp. 26 and 41-43.
Kabushiki Kaisha Riken
Yee Deborah
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