| 摘要 |
PURPOSE: A manufacturing method of a U-bolt is provided to omit a spheroidizing process and a correction process, thereby reducing manufacturing costs. CONSTITUTION: A manufacturing method of a U-bolt comprises the following steps. A steel material is drawn, where the steel material is composed of, in wt: C 0.15-0.50; Si: 1.5 or less; Mn 0.25-2.0; P: 0.03 or less; S: 0.03 or less; and the remainder Fe and other inevitable impurities. The steel material is heat-treated through quenching with successive tempering to have tensile strength: 70-130Kgf/mm^2; yield ratio: 85-97%; sectional reduction ratio: 50% or more; and austenite crystal particle: ASTM No.9 or more. The steel material which is heat-treated through tempering is drawn to reach the diameter of a U-bolt. The drawn steel material is cut at the length of a U-bolt, and processed with rolled screwing. The rolled screwing processed steel material is bent into a U shape. The bent steel material is heated at 300-600°C, maintained for more than 30 minutes at the temperature, and then rapidly cooled by using water and oil or slowly cooled in the air for sufficient stress relieving. The surface of the steel material is plated or painted. [Reference numerals] (AA) Wire; (BB) Tempering; (CC) Drawing; (DD) Cutting; (EE) Sign; (FF) U curve; (GG) Stress relieving and annealing; (HH) Plating; (II) Low temperature annealing; (JJ) Product |
