Piston ring and its production method

Patent metadata

Field	Value
Publication number	US-10227670-B2
Application number	US-201515113631-A
Country	US
Kind code	B2
Filing date	Jan 22, 2015
Priority date	Jan 23, 2014
Publication date	Mar 12, 2019
Grant date	Mar 12, 2019

Abstract

To provide a piston ring of low-alloy steel having excellent nitridability, namely, a piston ring of low-alloy steel having excellent thermal conductivity and capable of being provided with a sufficient nitrided layer, steel comprising by mass 0.45-0.65% of C, 0.15-0.35% of Si, 0.65-1.00% of Mn and 0.60-1.10% of Cr as indispensable alloy elements, and less than 0.35% of Mo, less than 0.25% of V and less than 0.001% of B as optional alloy elements, the total amount of the indispensable alloy elements and the optional alloy elements being less than 3.0% by mass, is formed into a piston ring; and the nitrided layer is formed on its surface.

First claim

What is claimed is:

1. A piston ring made of steel comprising C, Si, Mn and Cr as indispensable alloy elements, and Mo, V and B as optional alloy elements;
said indispensable alloy elements having a composition comprising by mass 0.45-0.65% of C, 0.15-0.35% of Si, 0.65-1.00% of Mn, and 0.60-1.10% of Cr;
said optional alloy elements having a composition comprising by mass less than 0.35% of Mo, less than 0.25% of V, and less than 0.001% of B;
the total amount of said indispensable alloy elements and said optional alloy elements being less than 3.0% by mass; and
a nitrided layer being formed on the surface;
wherein the outermost surface of said nitride layer is a diffusion layer exposed by removing a compound layer;
wherein said diffusion layer has hardness of 700-900 HV0.05 to the depth of 40 μm from said outermost surface and a hardness reduction ratio of 3 HV0.05/μm or less in a depth direction to the depth of 40 μm from said outermost surface; and
wherein said steel contains C concentrated in prior austenite grain boundaries.

2. The piston ring according to claim 1 , whose base material has hardness, which is 90-100% of the hardness before nitriding.

3. The piston ring according to claim 1 , wherein prior austenite grains in said steel have a grain size number of 8 or more.

4. The piston ring according to claim 1 , wherein said steel has a structure in which spheroidal cementite is dispersed in a tempered martensite matrix.

5. The piston ring according to claim 1 , which is a compression ring having said nitrided layer formed on side surfaces of the piston ring.

6. A method for producing the piston ring recited in claim 1 from a wire made of steel comprising C, Si, Mn and Cr as indispensable alloy elements, and Mo, V and B as optional alloy elements; said indispensable alloy elements having a composition comprising by mass 0.45-0.65% of C, 0.15-0.35% of Si, 0.65-1.00% of Mn, and 0.60-1.10% of Cr; said optional alloy elements having a composition comprising by mass less than 0.35% of Mo, less than 0.25% of V, and less than 0.001% of B; and the total amount of said indispensable alloy elements and said optional alloy elements being less than 3.0% by mass; comprising
conducting oil tempering at a quenching temperature of 820-930° C. and a tempering temperature of 440-500° C. before forming said piston ring; and
conducting a strain-removing heat treatment at a temperature of 420-480° C., lower than said tempering temperature, and nitriding at a temperature within ±30° C. from said tempering temperature, after forming the piston ring.

7. The method for producing a piston ring according to claim 6 , wherein annealing is conducted before said oil tempering.

Assignees

• Kk Riken

Inventors

• Shima Yuji

Classifications

• C22C38/32

  with boron · CPC title

• C21D1/58

  Oils · CPC title

• C22C38/24

  with vanadium · CPC title

• C22C38/22

  with molybdenum or tungsten · CPC title

• C22C38/02

  containing silicon · CPC title