Carburized and high-frequency hardened part having high strength

A mechanical part, which is obtained by:

• processing a steel into a shape of a part,
• said steel having an alloy composition comprising,
• by weight percent,
• C:
• 0.10 to 0.29%,
• Si:
• 0.50 to 3.00%,
• Mn:
• 0.30 to 3.00%,
• P:
• 0.030% or less,
• S:
• 0.030% or less,
• Cu:
• 0.01 to 1.00%,
• Ni:
• 0.01 to 3.00%,
• Cr:
• 0.20 to 1.00%,
• Al:
• 0.20% or less,
• N:
• 0.05% or less, and
• the remainder of Fe and inevitable impurities, and
• said alloy composition satisfying the following condition:
• [Si %]+[Ni %]+[Cu %]−[Cr %]>0.50,
• wherein [Si %], [Ni %], [Cu %] and [Cr %] represent the concentration of Si, the concentration of Ni, the concentration of Cu and the concentration of Cr in the alloy composition, respectively;
• subjecting the steel to a carburizing treatment in a vacuum, wherein the mechanical part has a surface carbon concentration in the range of 0.85 to 1.50 weight %;
• gradually cooling the steel part after the carburizing treatment is carried out, at a cooling rate where martensitic transformation of the steel does not occur;
• and
• subsequently subjecting the steel to a high-frequency hardening by heating and holding in a temperature in a range of 760 to 900° C. to thereby harden a surface of the steel.

A process for producing a mechanical part, which comprises:

• processing a steel into a shape of a part,
• said steel having an alloy composition comprising,
• by weight percent,
• C:
• 0.10 to 0.29%,
• Si:
• 0.50 to 3.00%,
• Mn:
• 0.30 to 3.00%,
• P:
• 0.030% or less,
• S:
• 0.030% or less,
• Cu:
• 0.01 to 1.00%,
• Ni:
• 0.01 to 3.00%,
• Cr:
• 0.20 to 1.00%,
• Al:
• 0.20% or less,
• N:
• 0.05% or less, and
• the remainder of Fe and inevitable impurities, and
• said alloy composition satisfying the following condition:
• [Si %]+[Ni %]+[Cu %]−[Cr %]>0.50,
• wherein [Si %], [Ni %], [Cu %] and [Cr %] represent the concentration of Si, the concentration of Ni, the concentration of Cu and the concentration of Cr in the alloy composition, respectively;
• subjecting the steel part to a carburizing treatment in a vacuum to provide a surface carbon concentration in the range of from 0.85 to 1.5 weight %, followed by gradually cooling the steel part, after the carburizing treatment is carried out, at a cooling rate of 1° C./sec or less;
• and
• subsequently subjecting the steel part to a high-frequency hardening by heating and holding the steel part at a temperature in a range of 760 to 900° C., to thereby harden a surface of the steel part.

A process for producing a mechanical part, which comprises:

• processing a steel into a shape of a part,
• said steel having an alloy composition comprising,
• by weight percent,
• C:
• 0.10 to 0.29%,
• Si:
• 0.50 to 3.00%,
• Mn:
• 0.30 to 3.00%,
• P:
• 0.030% or less,
• S:
• 0.030% or less,
• Cu:
• 0.01 to 1.00%,
• Ni:
• 0.01 to 3.00%,
• Cr:
• 0.20 to 1.00%,
• Al:
• 0.20% or less,
• N:
• 0.05% or less, and
• the remainder of Fe and inevitable impurities, and
• said alloy composition satisfying the following condition:
• [Si %]+[Ni %]+[Cu %]−[Cr %]>0.50,
• wherein [Si %], [Ni %], [Cu %] and [Cr %] represent the concentration of Si, the concentration of Ni, the concentration of Cu and the concentration of Cr in the alloy composition, respectively;
• subjecting the steel to a carburizing treatment in a vacuum, wherein the mechanical part has a surface carbon concentration in the range of 0.85 to 1.50 weight %;
• gradually cooling the steel part after the carburizing treatment is carried out, at a cooling rate where martensitic transformation of the steel does not occur;
• and
• subsequently subjecting the steel to a high-frequency hardening by heating and holding in a temperature in a range of 760 to 900° C. to thereby harden a surface of the steel.