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 μm of average particle size, 7 μm or less of the longest diameter, and from 5 to 30% in area ratio.

1 . A piston ring having improved scuffing resistance, cracking resistance and fatigue resistance, consisting of a high-chromium martensitic stainless steel and a sliding nitriding layer formed on the surface of said steel, characterized in that said high-chromium martensitic stainless steel consists, by weight %, 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; and, further said sliding nitriding layer comprises on its surface hard particles mainly consisting of nitrides in a range of from 0.2 to 2.0 μm of average particle size, 7 μm or less of the longest diameter, and from 5 to 30% in area %.  
     
     
         2 . A piston ring according to  claim 1 , characterized in that the grain boundary nitride observed in the longitudinal cross-section of a nitriding layer is 20 μm or less in size(length).  
     
     
         3 . A piston ring according to  claim 1  or  2 , wherein the N content of said high-chromium martensitic stainless steel is from 0.05 to 0.20%.  
     
     
         4 . A piston ring according to any one of claims  1  through  3 , wherein the hardness of the sliding nitriding layer is in a range of from Hv 900 to 1400.  
     
     
         5 . A method for producing a piston ring having improved scuffing resistance, cracking resistance and fatigue resistance, by means of subjecting the high-chromium martensitic stainless steel to nitriding treatment, characterized in that the high-chromium martensitic stainless steel consists, by weight %, 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; and, further the quenching of said high-chromium martensitic stainless steel prior to bending it into a ring shape is carried out from a temperature in a range of from 850 to 1000° C.  
     
     
         6 . A combination of the piston ring according to any one of claims  1  through  4 , and a cast-iron monolithic cylinder.