SPIRAL STEEL PIPE AND MANUFACTURING METHOD THEREOF

• Main Authors: FUJIYAMA NAOTO, ITO TADASHI, ORUI SUGURU
• Format: Patent
• Language: English; Japanese
• Published: 11.10.2023
• Subjects: ALLOYS; CHEMISTRY; FERROUS OR NON-FERROUS ALLOYS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS; MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; TREATMENT OF ALLOYS OR NON-FERROUS METALS

To satisfy a required specification by improving toughness, while allowing some degree of strength lowering on the premise to reduce Ni and Mo, in a 570 MPa class spiral steel pipe.SOLUTION: By forming a texture that does not contain martensite, which deteriorates toughness, and has a bainitic ferrite single phase or main phase (90% or more), which improves toughness while maintaining a certain level of strength. Furthermore, in order to compensate for the deterioration in toughness due to the formation of pearlite and polygonal ferrite in some parts due to fluctuations in manufacturing conditions, the crystal grains of bainitic ferrite were made finer.SELECTED DRAWING: None 【課題】本発明は、５７０ＭＰａ級スパイラル鋼管において、ＮｉやＭｏを削減することを前提に強度低下はある程度許容しつつも、靭性を向上させることで要求仕様を満足させることを課題とする。【解決手段】靭性を悪化させるマルテンサイトを含まず、ベイニティックフェライト単相もしくは主体（９０％以上）の組織にすることにより一定の強度を担保しつつ靭性を向上させた。さらに、製造条件のゆらぎのため一部にパーライトやポリゴナルフェライト生成することによる靭性低下を補償するため、ベイニティックフェライトの結晶粒を微細化させた。【選択図】なし