Study on the 40%Ni type Weld Metal for Cryogenic Application (Part 2)

Static Tensile Strength of Butt Welded Joints

Abstract

The 40 % Ni type weld metal is undermatching for 9 % Ni steel with regard to static tensile strength. In this case, the tensile strength of welded joints is influenced remarkably by strength of weld metal and base metal, and by the welding conditions such as heat input, groove shape and so on. Welded joint performance tests were carried out, in this report, to investigate the static tensile strength of MIG welded joints of 9 % Ni steel with 40 %Ni type weld metal. Main experimental results are summerized as follows:
(1) The transverse tensile strength of welded joints increases with decreasing relative thickness (average width of weld metal/plate thickness). Therefore, it is beneficial, both for increasing strength and for improving efficiency, to narrow the groove as far as possible according to the plate thickness.
(2) The transverse tensile strength of welded joints decreases with increasing welding heat input; but, in case of vertical position, it is possible to obtain 66.8 kg/mm² (95 Ksi) or more within heat input of 35 KJ/cm.
(3) It may be considered that, in case of multi-pass weld metal, the strength of intermediate pass weld metal has increased due to the precipitation hardening caused by the fine carbides of molybdenum and chromium.
(4) It was confirmed by center-notched wide plate tension test that the weld metal and fusion zone possess a satisfactory cryogenic fracture toughness as all the fracture occurred in a high-stress ductile manner with fracture stress equal to the cryogenic strength of the 40 % Ni type weld metal.