Patent ID: 12006994

Abstract:
A valve spring includes a nitrided layer, and a core portion that is further inward than the nitrided layer. A chemical composition of the core portion consists of, in mass %, C: 0.53 to 0.59%, Si: 2.51 to 2.90%, Mn: 0.70 to 0.85%, P: 0.020% or less, S: 0.020% or less, Cr: 1.40 to 1.70%, Mo: 0.17 to 0.53%, V: 0.23 to 0.33%, Ca: 0.0001 to 0.0050%, Cu: 0.050% or less, Ni: 0.050% or less, Al: 0.0050% or less, Ti: 0.050% or less, and N: 0.0070% or less, with the balance being Fe and impurities. In the core portion, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 500 to 8000 per μm2, and in the core portion, a numerical proportion of Ca sulfides with respect to a total number of oxide-based inclusions and sulfide-based inclusions is 0.20% or less.