Weld Cracking Susceptibility of High-Cr Ni-Base Fe Alloys and Its Improvement—Development of Novel Test Method for Ductility-Dip Cracking and New Alloy

The susceptibility to weld cracking such as ductility-dip cracking (DDC), liquation cracking, and solidification cracking, for laboratory melted high-Cr Ni-base Fe alloys was evaluated by Longi-Varestraint, strain to fracture (STF), on-heating on-cooling hot ductility, five-pass four-layer build-up (FPFLB) and axial tensile preloaded thermal cycling (TPLTC) tests, was compared with commercial Alloy 52. The on-heating on-cooling hot ductility and Longi-Varestraint tests showed similar cracking susceptibility, but they were not so suitable for the evaluation of DDC susceptibility. The DDC susceptibility for various materials was evaluated by the FPFLB, STF, and TPLTC tests, and there are no significant inconsistencies for DDC susceptibility between the results of these tests. The TPLTC test which simulates the thermal history at the DDC detected location in FPFLB test specimen and the restrained stress in multi-pass welded joint was performed using the all weld metal round-notched bar specimens. Evaluation was performed by the number of thermal cycles until rupture. It was confirmed that the TPLTC test method is a novel test method that can be easily performed comparing with FPFLB and STF tests. A Nb and C containing 30 pct Cr Ni-base Fe alloy without Mo is suggested as an advantageous new DDC-resistant weld metal.