SPHEROIDAL GRAPHITE CAST IRON TUBE, AND MANUFACTURING METHOD OF SPHEROIDAL GRAPHITE CAST IRON TUBE

PROBLEM TO BE SOLVED: To provide a spheroidal graphite cast iron tube capable of maintaining hardness in a high temperature range.SOLUTION: A spheroidal graphite cast iron tube is constituted, in which molten metal contains, by wt.%, C:3.20 to 4.00%, Si:1.40 to 3.00%, Mg:0.02 to 0.08%, Cr:0.01 to 0.20%, further Mn:1.20 to 1.70% and Cu:0.60 to 1.20%, and the balance Fe with inevitable impurities, area percentage of pearlite in a matrix structure after firing is 80% or more, area percentage of decomposed cementite is in a range of 10 to 15%. By using the molten metal with the composition, a semi-product with a prescribed shape at cooling rate of 2.0 to 8.0°C/sec., the semi-product is held in a temperature range of 900 to 1100°C for 5 to 30 min., then fooled at cooling rate of 1 to 8°C/min. to manufacture the spheroidal graphite cast iron tube.SELECTED DRAWING: Figure 1 【課題】高温領域における硬度を維持することが可能な球状黒鉛鋳鉄管を提供する。【解決手段】溶湯が、重量％で、Ｃ：３．２０〜４．００％、Ｓｉ：１．４０〜３．００％、Ｍｇ：０．０２〜０．０８％、Ｃｒ：０．０１〜０．２０％を含有し、さらにＭｎ：１．２０〜１．７０％、Ｃｕ：０．６０〜１．２０％となる範囲で含有し、残部がＦｅおよび不可避的不純物からなり、焼鈍後の基地組織におけるパーライトの面積率が８０％以上であり、未分解のセメンタイトの面積率が１０〜１５％の範囲内とした球状黒鉛鋳鉄管を構成する。前記組成の溶湯を用いて、冷却速度２．０〜８．０℃／秒で所定形状の半製品を鋳造し、前記半製品を９００〜１１００℃の温度範囲内で５〜３０分保持した後、１〜８℃／分の冷却速度で冷却して球状黒鉛鋳鉄管を製造する。【選択図】図１