Characterization and comparison of the carbides morphologies in the near surface region of the single- and double layer iron-based hardfaced coatings

Abstract

The properties of the high-chromium white iron (HCWI) hardfaced materials, such as hardness, toughness and wear resistance, are affected by the morphology of their reinforcing phase, the Cr-carbides. In this work, the influence of the 1) welding parameters, 2) welding procedures and 3) chemical composition on the near-surface Cr-carbides morphology is presented. Additionally, the effects of the nucleo C® formula (Castolin Eutectic Ltd.) of unknown composition are evaluated. The hardfaced coatings are deposited by using the submerged metal arc welding (SMAW) process. The obtained near-surface structures are observed with scanning electron microscope with energy dispersive system (SEM-EDS). The structure morphological parameters are quantitatively determined by use of the ImageJ software. In the single-layer HCWI hardfaced coatings, larger heat input per unit length (≈ 4.1 kJ/mm) is leading to a formation of the hypoeutectic structures. An approximately two times lower heat input (≈ 1.8 kJ/mm) stimulates the solidification of the near-eutectic structures with presence of spheroidized eutectic and primary Cr-carbides (the Nucleo C effect). The double-layer coatings deposited with the ≈ 1.8 kJ/mm possess the hypereutectic structures with blade-like primary and needle-like eutectic carbides (the absence of the Nucleo C effect). The lower heat input (≈ 1.4 kJ/mm) and increase of the chromium and carbon content result in a formation of the hypereutectic structures with presence of the primary rod-like Cr-carbides embedded in the eutectic matrix with coarser and irregular eutectic Cr-carbides. The influence of the nucleo C® formula on the Cr-carbides morphology is more pronounced in the single-layer HCWI hardfaced coatings than in the double-layer coatings.