Effect of Nb and Mo on the Microstructure, Mechanical Properties and Ductility-Dip Cracking of Ni-Cr-Fe Weld Metals

• Published in: Acta metallurgica sinica : English letters Vol. 29; no. 10; pp. 928 - 939
• Main Authors: Zhang, Xu, Li, Dian-Zhong, Li, Yi-Yi, Lu, Shan-Ping
• Format: Journal Article
• Language: English
• Published: Beijing The Chinese Society for Metals 01.10.2016; Springer Nature B.V
• Subjects: Alloys; Carbon steel; Characterization and Evaluation of Materials; Chemistry and Materials Science; Chromium; Corrosion; Corrosion and Coatings; Ductility; Grain boundaries; Impact strength; Impact tests; Investigations; Iron; Laves phase; Materials Science; Mechanical properties; Metallic Materials; Metals; Microscopy; Microstructure; Molybdenum; Morphology; Nanotechnology; Nickel; Niobium; Optical microscopy; Organometallic Chemistry; Spectroscopy/Spectrometry; Stress corrosion cracking; Tensile tests; Tribology; Ultimate tensile strength; Weld metal; Welding wire; Mechanical properties; Mo; Nb; Microstructure; Laves phase
• ISSN: 1006-7191; 2194-1289
• DOI: 10.1007/s40195-016-0469-z

A series of Ni-Cr-Fe welding wires with different Nb and Mo contents were designed to investigate the effect of Nb and Mo on the rnicrostructure, mechanical properties and the ductility-dip cracking susceptibility of the weld metals by optical microscopy （OM）, scanning electron microscopy, X-ray diffraction as well as the tensile and impact tests. Results showed that large Laves phases formed and distributed along the interdendritic regions with high Nb or Mo addition. The Cr-carbide （M23C6） was suppressed to precipitate at the grain boundaries with high Nb addition. Tensile testing indicates that the ultimate strength of weld metals increases with Nb or Mo addition. However, the voids formed easily around the large Laves phases in the interdendritic area during tensile testing for the weld metal with high Mo content. It is found that the tensile fractographs of high Mo weld metals show a typical feature of interdendritic fracture. The high Nb or Mo addition, which leads to the formation of large Laves phases, exposes a great weakening effect on the impact toughness of weld metals. In addition, the ductility-dip cracking was not found by OM in the selected cross sections of weld metals with different Nb additions. High Nb addition can eliminate the ductility-dip cracking from the Ni-Cr-Fe weld metals effectively.