In-situ Observation of Martensite Decomposition in HAZ of Cr-Mo Steel Weldment

  • Isaratat Phung-on King Mongkut's University of Technology Thonburi
  • Sudarat Khetsoongnoen Suranaree University of Technology
  • Jongkol Srithorn Suranaree University of Technology
  • Chanan Euaruksakul Synchrotron Light Research Institute (Public Organization), Nakhon Ratchasima, Thailand
  • Pat Photongkam Synchrotron Light Research Institute (Public Organization), Nakhon Ratchasima, Thailand
Keywords: PWTH, heat-affected zone (HAZ), martensite decomposition, LEEM, in-situ observation

Abstract

In-situ observation of martensite decomposition at Heat Affected Zone (HAZ) was investigated on a dissimilar joining between 2.25Cr-0.5Mo grade T22 as base material and ER90S-B9 as filler metal using GTAW process using LEEM at a synchrotron facility. A post weld heat treatment (PWHT) cycle was simulated on a welded specimen in high vacuum chamber by heating cartridge and electron bombardment. Both effects PWHT duration and weld areas were studied for comparisons. At the simulated PWHT between 690oC -700oC in CGHAZ, martensite started to decompose by the dissolution of carbide flakes. The prior-austenite grain boundaries were also shown during the process. The same phenomena were also observed in FGHAZ with different extent. In un-affected base material, ferrite and new pearlite grains presented and grew at the expense of old pearlite. Longer PWHT duration resulted in more ferrite formed in all weld areas. Raising PWHT temperature to 730oC could push the reaction above Eutectoid temperature as the new austenite formed at grain boundaries. The proposed mechanism for martensite decomposition would be in steps as dissolution of carbide followed by formation of ferrite and growth as PWHT proceeded.

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Author Biographies

Isaratat Phung-on

Maintenance Technology Center, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand

Sudarat Khetsoongnoen

Industrial Engineering, Institute of Engineering, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand

Jongkol Srithorn

Industrial Engineering, Institute of Engineering, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand

Chanan Euaruksakul

Synchrotron Light Research Institute (Public Organization), Nakhon Ratchasima 30000, Thailand

Pat Photongkam

Synchrotron Light Research Institute (Public Organization), Nakhon Ratchasima 30000, Thailand

Published In
Vol 23 No 5, Sep 30, 2019
How to Cite
[1]
I. Phung-on, S. Khetsoongnoen, J. Srithorn, C. Euaruksakul, and P. Photongkam, “In-situ Observation of Martensite Decomposition in HAZ of Cr-Mo Steel Weldment”, Eng. J., vol. 23, no. 5, pp. 59-70, Sep. 2019.