Two-piece oil ring for use in internal combustion engine, steel wire of

Abstract

A two-piece oil ring, for use in an internal combustion engine, with the oil ring being made from a martensitic stainless steel material having high consisting essentially of more than 0.8 wt % but less than 0.95 wt % of C, not more than 1.0 wt % of Si, not more than 1.0 wt % of Mn, from 15.0 wt % to 20.0 wt % of Cr and a balance substantially Fe and incidental impurities. The oil ring has a hardness ranging from HV300 to HV450 and a substantially H- or X-shaped cross-section. A web portion interconnecting left and right halves of the H- or X-shaped cross-section has a thickness not greater than 0.3 in terms of the ratio of the total thickness of the ring. Oil passage holes are formed in the web portion. A nitrided layer is formed on the sliding surface thereof which makes a sliding contact with the inner surface of a cylinder of the engine. The material may further contain suitable amounts of at least one of Mo, W, V, Nb, Ni and Co. The oil ring is produced by bending a wire of the martensitic stainless steel material by a process including warm roll dies plastic working and a subsequent cold roll dies plastic working through which a modified cross-section is imparted to the material, continuous annealing, punching for forming oil passage holes by punching, and continuous hardening and tempering.