Microstructure evolution and grain refinement mechanism of Inconel 601H alloy welded joints under compound physical fields of vibration and rapid cooling

Abstract

The method and mechanism of suppressing grain growth and microstructure coarsening in nickel-based alloy welded joints were studied herein. First, sodium thiosulfate was used to simulate the crystallization processes of the welding pool. Then, on this basis, the compound physical fields of low-frequency mechanical vibration and rapid cooling on the microstructure of the Inconel 601H alloy welded joint were investigated. Finally, the joint grain refinement behavior and mechanism were analyzed based on the experimental and physical simulation results. The experimental results indicate that only the low-frequency mechanical vibration acting in the welding process caused the center of the weld to be mostly composed of equiaxed grains. The epitaxial solidification phenomenon near the fusion line disappeared, but there were still many fine columnar grains in the upper part of the weld edge. The heat-affected zone (HAZ) morphology was eventually dominated by coarse grains, and the width of the HAZ increased. However, with the compound physical fields, the weld was mainly composed of equiaxed grains, and the grain size and width of the HAZ decreased. Thus, an increased hardness distribution was also achieved. Moreover, the γ ′ phase exhibited a dispersed distribution and the alloy elements were very uniformly distributed in the γ ′ phase, which helped to prevent the initiation of hot cracking of the weld comprising nickel-based alloys. In addition, the results demonstrated that the generation of additional crystal nuclei and the increase in the cooling rate from the compound physical fields were the main mechanisms for the grain refinement.

Keywords

• nickel-based alloy
• welded joints
• compound physical fields
• physical simulation
• hot cracking