High-Concentration Carburized/Low-Strain Quenched Member and Process for Producing the Same

A process for producing a super carburized, low-distortion quenched member, which comprises a primary treatment of heating a steel member for a machine structure to a temperature within an austenite region by vacuum carburizing (low-pressure carburizing) to have carbon dissolved at least at a eutectoid carbon concentration of a surface layer portion of said member and then quenching said member at a cooling rate of from 3 to 15° C./sec from said temperature within said austenite region to a temperature not higher than an A1 transformation point to have at least one of ultrafine carbide and nuclei of said carbide formed in said surface layer portion of the said member;

• and a secondary treatment of subsequently heating and soaking said member to a temperature within said austenite region and then conducting rapid quenching to have ultrafine carbide precipitated in a range of from 10 to 30% in terms of effective case depth percentage in an outermost surface layer portion.