STEEL WITH HIGH STRENGTH AND EXCELLENT COLDHEADABILITY, FASTENING PARTS, SUCH AS SCREW AND BOLT, OR FORMED ARTICLE, SUCH AS SHAFTS, WITH EXCELLENT STRENGTH AND THEIR MANUFACTURING METHODS 高強度で且つ冷間圧造性に優れた鋼及び強度に優れたねじ及びボルト等の締結部品又は軸類等の成形品並びにそれらの製造方法 - 特許庁