SEAMLESS STEEL PIPE FOR HOLLOW SPRING

摘要

A seamless steel pipe for a hollow spring includes C: 0.2 to 0.7 mass%, Si: 0.5 to 3 mass%, Mn: 0.1 to 2 mass%, Cr: 3 mass% or less (excluding 0 mass%), Al: 0.1 mass% or less (excluding 0 mass%), P: 0.02 mass% or less (excluding 0 mass%), S: 0.02 mass% or less (excluding 0 mass%) and N: 0.02 mass% or less (excluding 0 mass%). A residual austenite content in an inner surface layer part of the steel pipe is 5 vol.% or less. An average grain size of a ferrite-pearlite structure in the inner surface layer part of the steel pipe is 18µm or less. A number density of a carbide having a circle equivalent diameter of 500 nm or more and being present in the inner surface layer part of the steel pipe is 1.8×10 -2 particles/µm 2 or less.