Hajime Nakamura1, Yoshikazu Kuriyama1 and Yasuhisa Yamazaki1
1Ishikawajima-Harima Heavy Industries Co., Ltd., Tokyo
A new ultra-high-strength steel of 100 kg/mm2 was developed jointly by the Ishikawajima-Harima Heavy Industries Co., Ltd. and the Yawata Iron and Steel Co., Ltd. Prior to use for structures and pressure vesseles, various weldability tests were undertaken. It has been established that the mechanical properties of the HT-100 steel weld-joint was satisfactory excepting H.A.Z. deterioration, and it is quite comparable to that of commercial heat treated 80 kg/mm2 high-strength steels. Many investigators, have pointed out that there exists a remarkable brittle zone in the weld-heat-affected zone of the heat-treated high tension steel, and such a brittle zone causes deterioration of weld-joint properties. The following conclusions were obtained as the result of investigation.
(1) Brittleness of HT-100 steel was observed in the results of pressed-notch charpy, notched slow bend, drop weight and weld-joint wide tension tests.
(2) When weld defects such as under-cut and angular distortion exist tensile strength decreases to below the yield point of HT-100 steel in the weld-joint wide tension tests.
(3) Successful results in improving for over-all weldment properties were obtained by deposition of a protective weld bead called A.C.I. bead in this investigation. These effects were believed to be due to micro-structure refining, removing of stress consentration at weld toes, and increasing of thickness in the weld-heat-affected zone.
Please do not copy without permission.