Microstructural characterization and hardness of an electron beam welded low carbon Ni-Cr-Mo low alloy steel

Abstract

In this paper the microstructure and hardness of electron beam weld joints of 16NCD13, low alloy steel in the as-welded and post weld heat treated (PWHT) conditions have been explored. The as-received base metal (BM) was in annealed condition. The BM microstructure depicted ferrite and carbides (Fe3C). In the as-welded condition the fusion zone(FZ) contained martensite in coarse grains and small amount of ferrite. The as-welded joints exhibited high hardness in the FZ and heat affected zone (HAZ) due to the occurrence of martensite during the weld thermal cycle. The PWHT employed is low temperature tempering commercially designed to preserve hardness and strength of as quenched martensite while relieving the internal stresses and providing small increase in toughness.The PWHT did not cause any significant reduction in hardness in the FZ and HAZ as tempering is carried out at 150 °C for 2 h and air cooled.The BM and FZ were characterised using optical microscopy, field emission scanning electron microscopy (FE-SEM), electron back scattered diffraction (EBSD) and Xray diffraction techniques. The current study is pursued with the aim of obtaining a comprehensive understanding of the fusion zone (FZ) and heat affected zone (HAZ) developed during electron beam welding process in as-welded and post weld heat treated conditions.