Microstructural Variations Across a Dissimilar 316L Austenitic: 9Cr Reduced Activation Ferritic Martensitic Steel Weld Joint

Abstract

This paper discuss the microstructural variations across a dissimilar weld joint between SS316 and 9Cr-RAFM steel and its modifications on post weld heat treatments (PWHT). Detailed characterization showed a mixed microstructure of austenite and martensite in the weld which is in agreement with the phases predicted using Schaeffler diagram based on composition measurements. The presence of very low volume fraction of d-ferrite in SS316L has been identified employing state of the art electron back-scattered diffraction technique. PWHT of the ferritic steel did not reduce the hardness in the weld metal. Thermal exposure at 973 K (700°C) showed a progressive reduction in hardness of weld joint with duration of treatment except in austenitic base metal. However, diffusion annealing at 1073 K (800°C) for 100 hours resulted in an unexpected increase in hardness of weld metal, which is a manifestation of the dilution effects and enrichment of Ni on the transformation characteristics of the weld zone. Migration of carbon from ferritic steel aided the precipitation of fine carbides in the austenitic base metal on annealing at 973 K (700°C); but enhanced diffusion at 1073 K (880°C) resulted in coarsening of carbides and thereby reduction of hardness.

Decisive impact of Filler-free joining processes on the Microstructural evolution, tensile and impact properties of 9Cr-1Mo-V-Nb to 316 L(N) dissimilar joints

“…Based on the chemical compositions of the weld metal (Table 4), the mixing ratio of the dissimilar metals for the ATIG and LBW process is calculated by using equation (1). 19 …”

“…17 However, the post-weld heat treatment (PWHT) of dissimilar ferritic martensitic/austenitic weld configurations is very complex due to the location dependant compositional variations, carbon diffusion and softening, sensitization of austenitic stainless steel at the temperature range of PWHT, a significant loss in hardness in 9Cr-1Mo-V-Nb side HAZ. 18,19 Hence it is crucial to select appropriate PWHT procedure to achieve the properties at the desired level.…”

Influence of Immersion Corrosion on Mechanical Properties of AISI 430/AISI 316L Dissimilar Welded Joints

“…Additionally, phase transformations of these dissimilar welded joints have been extensively investigated. Both ferritic and austenitic stainless plates of steels may undergo coarsening and refinement of grain at different regions, as well as, several phase transformations along the heat-affected zone [16][17][18]. All these metallurgical changes may modify the corrosion behavior of welded joints and they are functions of several factors, such as the as-received condition of base metals, shielding gas mixtures, thermal cycling, heat input, temperatures, and cooling rates imposed during the welding process.…”

Microstructure and alloy element distribution of dissimilar joint 316L and EH36 in laser welding

“…Macrostructure and microstructure of the Al 5083-H321 and 316L stainless steel joint were examined using optical microscope and scanning electron microscope (SEM) [2]. The microstructural variations across a dissimilar weld joint between SS316 and 9Cr-RAFM steel were analysed, and further regulated by the post weld heat treatment [3]. Bonding mechanism and interface characterisation for dissimilar joints (copper with steel [4], aluminium with titanium [5] and high-density polyethylene [6]) were researched by SEM and energy dispersive X-ray spectroscopy.…”