Piston ring excellent in resistance to scuffing, cracking and fatigue and method for producing the same, and combination of piston ring and cylinder block

Abstract

A piston ring having improved scuffing resistance, cracking resistance and fatigue resistance, consists of a high-chromium martensitic stainless steel and a sliding nitriding layer formed on the surface of said steel. The stainless steel consists of C: 0.3 to 1.0%; Cr: 14.0 to 21.0%, N: 0.05 to 0.50%, at least one of Mo, V, W and Nb: 0.03 to 3.0% in total, Si: 0.1 to 1.0%, Mn 0.1 to 1.0%, P: 0.05% or less, S: 0.05% or less, the balance being Fe and unavoidable impurities. The sliding nitriding layer comprises on its surface hard particles mainly consisting of nitrides in a range of from 0.2 to 2.0 mum of average particle size, 7 mum or less of the longest diameter, and from 5 to 30% in area ratio.

Description

BACKGROUND OF INVENTION[0001] 1. Technical Field[0002] The present invention relates to a piston ring used in an internal combustion engine, particularly, a piston ring consisting of high chromium martensitic stainless steel with nitriding, having improved scuffing resistance (seizure resistance), cracking resistance (failure resistance) and fatigue resistance. The present invention is also related to a production method of the piston ring.[0003] 2. Background Technique[0004] Along with recent demands for low fuel consumption, weight reduction and high performance of internal combustion engines, the piston rings are thinned to reduce weight and to follow the high rotation of the engine. Material properties of the piston rings, such as wear resistance, scuffing resistance and fatigue resistance, and the like must be improved to enable thinning of a piston ring. The conventional cast-iron piston rings have, therefore, been replaced with steel piston rings particularly from a view poin...

AI Technical Summary

Benefits of technology

0032] Any one of Mo, V, W and Nb is a carbide former and enhances wear and scuffing resistances. In addition, Mo prevents softening during the tempering and nitriding treatments and plays an important role in attaining the dimension stability of a piston ring. V promotes nitriding, and therefore the hardness of a nitriding layer containing V is high. Any one of these elements is effective for enhancing the properties of a piston ring. When the total content of at least one of Mo, V, W and Nb is less than 0.03%, their effects are virtually negligible. On the other band, when the total content of these element(s) is more than 3%, the workability is seriously impaired and the toughness is lowered. The total content of at least one of Mo, V, W and Nb is therefore, from 0.03 to 3.0%.

0033] Si is a deoxidizing additives. Si is also dissolved in Fe and enhances the softening resistance in tempering. The so-called thermal setting resistance can therefore, be improved. When the Si content is less than 0.1% its effect is slight. On the other hand, when the Si content is more than 1.0%, the toughness is impaired. The Si content is therefore, in a range of from 0.1 to 1.0%.

0034] Mn is also a deoxidizing additive. When the Mn content is less than 0.1%, its effect is slight. On the other hand when the Mn content is more than 1.0%, the workability is impaired. The Mn content is, therefore, from 0.1 to 1.0%.

0035] P forms inclusions with Mn and the like and lowers the fatigue strength and corrosion resistance. P is an impurity of steel. The less P, the better. The P content is therefore, 0.05% or less from a practical point of view. Preferably, P is 0.03% or less.

0036] S lowers the fatigue strengh and corrosion resistance, as P does. Sis an impurity of steel. The less S, the better. The S content is, therefore, 0.05% or less from a practical points of view. Preferably, S is 0.03% or less.

Problems solved by technology

This phenomenon results in scuffing of the piston ring.

Specifically, in the case of the cast iron monolithic cylinder block having a non-uniform structure as described above, the surface of this block is liable to be roughened by the grinding.

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