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Abstract

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.
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Authors and Affiliations

Minha Park
1
ORCID: ORCID
Gang Ho Lee
2
ORCID: ORCID
Hyo-Seong Kim
2
ORCID: ORCID
Byoungkoo Kim
1
ORCID: ORCID
Sanghoon Noh
3
ORCID: ORCID
Byung Jun Kim
1
ORCID: ORCID

  1. Energy System Group, Korea Institute of Industrial Technology, Busan 46938, Republic of Korea
  2. Energy System Group, Korea Institute of Industrial Technology, Busan 46938, Republic of Korea; Pukyong National University, Department of Materials Science and Engineering, Busan 48513, Republic of Korea
  3. Pukyong National University, Department of Materials Science and Engineering, Busan 48513, Republic of Korea
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Abstract

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.
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Authors and Affiliations

Minha Park
1
ORCID: ORCID
Gang Ho Lee
2
ORCID: ORCID
Gwangjoo Jang
1
Hyoung-Chan Kim
1
Byoungkoo Kim
1
ORCID: ORCID
Byung Jun Kim
1
ORCID: ORCID

  1. Energy System Grou, Korea Institute of Industrial Technology, 46938, Busan, Republic of Korea
  2. Energy System Grou, Korea Institute of Industrial Technology, 46938, Busan, Republic of Korea; Pukyong National University, Department of Materials Science and Engineering, 48513, Busan, Republic of Korea

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