Characterization of Microstructures and Creep Fracture Characteristics of Dissimilar Metal Welds between Inconel 740H Ni-Based Superalloy and Gr.92 Ferritic Steel

Abstract

Microstructure evolution and the creep fracture characteristics of dissimilar welds between Ni-based superalloy Inconel 740H and High Cr ferritic steel Gr.92 were investigated. The dissimilar welds were fabricated by shielded metal arc (SMA) welding process with Ni-based austenitic Inconel 182 superalloy. Postweld heat treatment at 760 o C for 4 hours was conducted to temper the fresh martensite formed in the heat-affected zone (HAZ) of Gr.92, and to form γ΄ strengthener in Inconel 740H. The weld interface between the Gr.92 and weld metal was characterized by a discrete line with minimal inter-diffusion, whilst the weld interface on the Inconel 740H side showed an unmixed zone having epitaxial columnar growth from the base metal. It was observed that the fresh untempered martensite formed at the Gr.92-sided coarse-grained HAZ next to the weld interface during PWHT. This may be due to higher Ni contents diffused from the Ni-based weld metal. A sharp increase in hardness was detected at the coarse-grained HAZ of Gr.92 while the hardness minimum occurred at the fine-grained and intercritical HAZ (FG/IC HAZ). Fracture after creep at 650 o C/80 MPa and 700 o C/35 MPa occurred at the FG/IC HAZ of Gr.92, commonly known as a type IV fracture. This may be attributed to the strain localization at the FG/IC HAZ due to the smaller grain size as well as the lowest hardness. The elemental migration across the weld interface was not significant. It was also found that a needle-like Nb-rich δ-phase formed at the interdendritic region of the weld metal after creep at 700 o C/35 MPa.

Evaluation of the mechanical properties of Inconel 718 to SCM 440 dissimilar friction welding through real-time monitoring of the acoustic emission system

“…Friction welding is widely applied particularly in the welding of dissimilar metals. [5][6][7][8][9] Since the early 1970s, research on friction welding of dissimilar materials has been increasing, including research on the determination of optimum conditions, the application, and the strength of friction welding. [10][11][12][13][14][15] Chromium molybdenum (SCM440) structural alloy steel is widely used in mechanical parts that require durability such as shafts, gears, and nuts.…”

Characterization of High-Temperature Tensile Properties and Thermal Stability in Gas Tungsten Arc Welds of Ti-added Reduced Activation Ferritic/Martensitic Steel

“…또한, HAZ는 용접 공정에 의해 가열 된 최고온도 (peak temperature, T p )에 따라 4가지 영역으로 구분된다 16) . 조립역 (coarse grained HAZ, 16,17) 13,15,[18][19][20][21][22][23] . 그러나, 국내의 경우 모재 개발에만 집중되어 있으며, 부품 제작 기술 및 용 접부 특성에 관한 연구는 매우 부족한 실정이다 14)…”