| 摘要 |
<p>PURPOSE:To obtain a PC steel bar excellent in delayed fracture resistance by providing a compressive residual stress of specific value to the part between the surface and the position at a specific depth from the surface of a PC steel bar. CONSTITUTION:A compressive residual stress in the range of 40-90% of 0.2% yield strength is provided to the part in the range between the surface and the position at a depth of 100mum from the surface of a PC steel bar. In order to produce such a PC steel bar a steel having a composition containing, e.g. about 0.2% C, about 1.1% Si, and about 1.5% Mn is hot-rolled into a wire bar of about 9.2mmphi and formed into a martensitic structure by means of controlled cooling and then subjected to straightening by means of repeated bending, by which the PC steel bar having about 120kgf/mm<2> of 0.2% yield strength and about 150kgf/mm<2> tensile strength can be produced. Shot peening is applied to this PC steel bar at about 85-40m/s projection speed for about 120sec projection time by using steel shots of about 0.2-1.2mm grain diameter, by which desired compressive residual stress can be provided.</p> |
