SELECTIVELY QUENCHED NAIL

摘要

PROBLEM TO BE SOLVED: To provide a nail quenched only in a selected position by heating a part of the nail up to a temperature higher than a specific temperature, and quenching the part in the next place. SOLUTION: A lower axial part 15 of a positive placement nail 10 is selectively quenched. The selectively quenching action is performed by quenching the nail in the next place by selectively heating the lower axial part 15 from at least about 1400 deg.F, desirably, about 1500 deg.F up to about 2000 deg.F. A heated part of the nail typically made of carbon steel changes to an austenite metallographic structure from a ferrite pearlite metallographic structure by selective heating. A resultantly formed and selectively processed nail has different hardness in a different axial position running along the nail. The lower axis 15 is harder than a residual part of a body part 14 in the other axial position, and a value of Rockwell hardness of a selectively quenched axial part is at least about 45.