TEM Microstructure and Chemical Composition of Transition Zone Between Steel Tube and An Inconel 625 Weld Overlay Coating Produced by CMT Method

Abstract

The aim of this work was to investigate the microstructure and chemical composition of the transition zone between 16Mo3 steel and Inconel 625 weld overlay coating produced by the Cold Metal Transfer (CMT) method. Investigations were primarily carried out through transmission electron microscopy (TEM) on thin foils prepared by FIB (Focus Ion Beam).The chemical analysis demonstrated that the amount of certain elements (Fe, Ni, Cr, Mo, Nb) in the transition zone between the base material and the weld overlay changes quickly, from the composition of the steel to the composition of the composite zone. STEM and TEM investigations revealed that two areas are clearly visible in the transition zone. In the narrow band close to the fusion boundary where plates are clearly visible and the M s temperature is higher than room temperature, electron diffraction analyses show reflections of martensite and austenite. Moreover, the crystallographic relations between martensite and austenite can be described by the Kurdjumov-The microstructure of the part of the transition zone with an M s temperature lower than room temperature as well as that of the composite zone is austenite. The investigations proved that the width of the martensitic area can be significantly limited by using the CMT technique for weld overlaying.

Microstructure and Phase Analysis of Multilayer Ni–Cr–Mo Clad for Corrosion Protection

“…Hence, regions B and C create the transition region. The width of the transition region depends on solidification conditions and welding methods [6,[16][17][18][19]. In this case, the width of this region is about 25 microns.…”

“…The chemical EDS maps of this phase, which are presented in Fig. 8b-g, indicate that it is rich in Nb, C and Ti; consequently, the phase could be a MC carbide consisting of Nb and Ti ((NbTi)C) [6,7,16,17]. During solidification, the dendrites of austenite (c), which form at the beginning of solidification, grow and reject Mo, Nb and C to the liquid in the interdendritic regions (L ?…”

“…The planar region, which occurs at the beginning of solidification, manifests nearly featureless at low magnification. This region is often observed at the fusion boundary and is usually relatively narrow [6,[16][17][18][19]. The solidification continues with cellular morphology; then, it quickly breaks down into cellular dendritic growth within some microns of the fusion boundary.…”

Archives of Metallurgy and Materials

“…The likely reason for the increase of hardness on the interface between the base metal and overlay is the presence of martensite. According to the schaeffler diagram, when nickel alloy or austenitic stainless steel is used to clad low-alloyed ferritic steel, between the weld overlay and the steel base, the martensite may form in the transition zone close to the base material [11].…”

Archives of Metallurgy and Materials

“…Carbon and low-alloy steels are the most extensively used materials in industries because of their low cost and good mechanical properties. But, this metal has a limited corrosion resistance and therefore the corrosion of carbon steels is a problem for most industries [1,2]. Therefore, many efforts have been done to increase corrosion resistance and stability of steel materials [3,4].…”