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2 Archives of Metallurgy and Materials

2 2024

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The Effects of Post Weld Heat Treatment on Microstructure and Mechanical Properties of API X70 Linepipe using Submerged Arc Welding

Park Minha, Lee Gang Ho, Jang Gwangjoo, Kim Hyoung-Chan, Kim Byoungkoo, Kim Byung Jun

Archives of Metallurgy and Materials

2024

Vol. 69, iss. 1

99--102

API X70 steel requires high strength and toughness for safety in extreme environments like high pressure and low temperature. Submerged Arc Welding (SAW ) is effective for manufacturing thick steel pipes. However, the welding heat input during SAW alters the microstructure and mechanical properties of the heat affected zone (HAZ). Therefore, investigating the correlation between microstructure and mechanical properties in welded X70 pipes is important to address potential degradation of HAZ and weld metal (WM). In this study, post weld heat treatment (PWHT) was performed to improve mechanical properties of HAZ and WM and to reduce residual stress caused by the welding process. We performed PWHT at 640°C for 15 hours and followed by air cooling. After heat treatment, we observed the microstructure through OM and SEM analysis, and investigated the mechanical properties through tensile test, hardness test, and Charpy impact test.

Effect of Cooling Rate on Microstructure and Mechanical Properties According to Heat Treatment Temperature of Inconel 625

Park Minha, Lee Gang Ho, Kim Hyo-Seong, Kim Byoungkoo, Noh Sanghoon, Kim Byung Jun

Archives of Metallurgy and Materials

2024

Vol. 69, iss. 1

95--98

Inconel 625 is typically used in extreme environments due to excellent mechanical properties such as high strength, corrosion resistance, abrasion resistance and low-temperature toughness. When manufacturing a hot forged flange with a thick and complex shape, the cooling rate varies depending on the location due to the difference in thermal gradient during the cooling process after hot forging. In this study, to evaluate the microstructure and mechanical properties of Inconel 625 according to the cooling rate, we performed heat treatment at 950°C, 1050°C, and 1150°C for 4 hours followed by water cooling. Additionally, temperature data for each location on the flange were obtained using finite element method (FEM) simulation for each heat treatment temperature, revealing a discrepancy in the cooling rate between the surface and the center. Therefore, the correlation between microstructure and mechanical properties according to cooling rate was investigated.