INFLUENCE OF WELDING PROCESSES ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF DISSIMILAR AUSTENITIC-FERRITIC STAINLESS STEEL WELDS

Abstract

Dissimilar metal welding of austenitic (AISI 304)-ferritic (AISI 430) stainless steel has been taken up to understand the influence of the welding process on microstructure and mechanical properties. Fusion welding processes, namely, gas tungsten arc welding (GTAW), electron beam welding (EBW), and friction welding, have been employed. The GTAW and EBW processes were selected to understand the heat input effects, while friction welding was included to compare fusion and solid-state welding processes. The material used for fusion welding studies is 20-mm-thick, hot-rolled, and annealed plate. Rods of 18 mm diameter machined from the same plate material were used for friction welding studies. In GTAW, ER 430 filler material was employed for dissimilar metal combination, while other welds are autogenous. Gas tungsten arc welds consisted of coarse columnar grains. In electron beam welds, the microstructure consisted of predominantely equiaxed grains on the austenitic stainless steel side, while columnar grains were observed on the ferritic stainless steel side. Epitaxial solidification was noted on the ferritic stainless steel side, while no such features were evident on the austenitic stainless steel side. Electron probe micro analysis (EPMA) revealed that inter diffusion of elements was significant in GTAW, intermediate in EBW, and insignificant in friction welds. Notch tensile and impact properties of ferritic stainless steel and dissimilar metal combination of austenitic-ferritic stainless steel friction welds are superior to gas tungsten arc welds and electron beam welds. Electron beam welds of austenitic stainless steel exhibited superior notch tensile and impact toughness compared to friction welds. Gas tungsten arc welds exihibited the lowest pitting corrosion resistance, while friction welds possessed the highest pitting corrosion resistance. In general, pitting was confined to Cr-depleted regions adjacent to the carbide precipitates.

Key Words:

• Dissimilar metal welding
• Electron beam weld
• Friction weld
• Gas tungsten arc weld
• Mechanical properties
• Pitting corrosion
• Residual stresses

ACKNOWLEDGMENTS

We express our gratitude to the Defence Research and Development Organization for the financial support to carry out this program and to Dr. D. Banerjee of CC (R&D) Aeronautics and Materials. The authors are thankful to Dr. A. M. Srirama Murthy, Director, DMRL, for his continued encouragement and support. We are thankful to members of SAFG and EMG groups for permitting support to carry out metallography and scanning electron microscope examinations. We are grateful to Mr. N. Vishwanathan and C. V. S. Murthy, Scientists, DRDL, for extending electron beam welding facilities for this program.

Notes

Note: All-weld mechanical properties: 0.2% yield strength (MPa), 320; ultimate tensile strength (MPa), 400; elongation (%), 16.

Note: AISI 430 parent metal: 570 MPa (NTS), 7 Joules (impact toughness) AISI 304 parent metal: 860 MPa (NTS), 214 Joules (impact toughness). Reported values correspond to average of three test specimens.

Note: AISI 430 parent metal: 988; AISI 304 parent metal: 914. Reported values correspond to average of three test specimens.