| 摘要 |
PROBLEM TO BE SOLVED: To provide a tapping screw for high-tension steel sheet which can successfully be used for a high tensile strength steel material having a tensile strength of over 80 kg class by using a material available at a price of near SWCH16A/18A with good workability for screw forming by cold forging, and by improving treatment conditions of a conventional continuous gas carburizing furnace and attaining high hardness and strength. SOLUTION: The tapping screw is for a high-tension steel sheet having tensile strength between 80 kg class and 150 kg class. A steel material is formed into a screw material and subjected to carbonitriding, quenching, and annealing processes. It has a surface hardness of 600-900 Hv, a core hardness of 300-450 Hv, a hardened layer depth of 0.05-0.7 mm, and a tensile strength of 700-1,500 N/mm<SP>2</SP>. COPYRIGHT: (C)2008,JPO&INPIT
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