Minor Phase Evolution in Homogeneous T24 Welds

Abstract:

This paper deals with the characterization of hardness, microstructure and precipitation processes in homogeneous T24 welds in the as-welded state and after laboratory PWHT at 745°C for 1 and 6 hours, respectively. Tempering of a T24 steel during quality heat treatment is accompanied by intensive precipitation of MX, M₇C₃ and M₂₃C₆ particles in the bainitic matrix. It was found that SAW welding resulted in a pronounced dissolution of minor phases in the base materials close to the joined faces. In the as-welded state microstructure of the CGHAZ was bainitic and the HV10 level in this part of the HAZ reached nearly 400 units. The dominant strengthening mechanism in the CGHAZ was attributed to transformation strengthening due to decomposition of austenite to bainite. Also the HV10 level in the bainitic filler metal (ca 320 HV10) was very close to the maximum acceptable hardness. PWHT at 740°C for 1 hour resulted in a significant decrease of hardness in the weld metal and especially in the CGHAZ. TEM studies revealed that recovery of bainite in the CGHAZ and the weld metal was accompanied by intensive precipitation of MX, M₇C₃ and M₂₃C₆ minor phases. The hardness level in the CGHAZ dropped to approximately 255 HV10. Prolonging of tempering at 740°C to 6 hours resulted in a modest softening in all parts of the weldments due to more pronounced both precipitation processes and recovery of bainite.

• Periodical: Materials Science Forum (Volume 782)
• Pages: 143-148
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.782.143
• Online since: April 2014
• Authors: Vlastimil Vodárek*, Gabriela Rožnovská, Jan Holešinský, Anastasia Maslova, Zdeněk Kuboň
• Keywords: Heat Affected Zone (HAZ), Homogeneous T24 Welds, Precipitation Processes, PWHT

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