TIG WELDED JOINT AND ITS WELDING METHOD

摘要

PROBLEM TO BE SOLVED: To provide a TIG welded joint part with high toughness having an impact value of 50 J/cm2 or over at 20 deg.C, at which a brittle fracture is said avoidabl, to the welded joint part of refining type low alloy steels manufactured by singly adding or adding after mixing W, V or Nb to 1 to 2.25 CrMo steel, and its welding method. SOLUTION: In this welding, the number of the layers of welded metal layers (average depositing quantity of one pass) is three layers or more, and the welded metal layers other than a final welded metal layer have the fine martensite structure of a grain size No.6 or over. And, the TIB welded joint whose impact value is 50 J/cm2 or over at 20 deg.C, which is measured with a 2 mmV notch test piece, is obtained, and the welding speed of the welded metal layers on and after a second pass is made to be 7 cm/min or below. The deposition quantity per pass is adjusted to a rage of 0.7 g/cm to 2.5g/cm, or the height of a deposition layer per pass is adjusted to a range of 1.0 mm-3.6 mm.