Carbonitrided induction hardened steel part superior in surface fatigue strength at high temperature and method of production of same

A method of production of a carbonitrided induction hardened steel part superior in surface fatigue strength at high temperature characterized by using steel including, as chemical ingredients, by mass %,

• C:
• 0.005 to 0.8%,
• Si:
• 2.0% or less,
• Mn:
• 0.2 to 3.0%,
• P:
• 0.03% or less,
• S:
• 0.005 to 0.10%,
• Ni:
• 3.0% or less (including 0%),
• Cr:
• 5.0% or less (including 0%),
• Mo:
• 2.0% or less (including 0%),
• W:
• 1.0% or less (including 0%),
• B:
• 0.0050% or less (including 0%),
• O:
• 0.0050% or less, and
• N:
• 0.003 to 0.03%,
• further containing one or both of
• Al:
• 0.005 to 0.2% and
• Ti:
• 0.005 to 0.2% and
• one or both of
• V:
• 0.3% or less (including 0%) and
• Nb:
• 0.3% or less (including 0%), and having a balance of substantially iron and unavoidable impurities, so as to form a part, carbonitriding it, then oil or salt quenching it, then induction heating it and hardening it by water or a polymer quenching agent of a temperature of less than 40° C. to give that part a surfacemost N concentration of 0.1 to 0.8 mass % and sum of the N concentration and C concentration of 1.0 to 2.0 mass %, making the amount of surface residual austenite less than 15 vol %, making the depth of the incompletely hardened layer from the surface less than 5 μm, and further making the surface X-ray diffraction half width 6.0 degrees or more.