The Microstructure and Mechanical Properties of Multi-Strand, Composite Welding-Wire Welded Joints of High Nitrogen Austenitic Stainless Steel

Abstract

A multi-strand composite welding wire was applied to join high nitrogen austenitic stainless steel, and microstructures and mechanical properties were investigated. The electrical signals demonstrate that the welding process using a multi-strand composite welding wire is highly stable. The welded joints are composed of columnar austenite and dendritic ferrite and welded joints obtained under high heat input and cooling rate have a noticeable coarse-grained heat-affected zone and larger columnar austenite in weld seam. Compared with welded joints obtained under the high heat input and cooling rate, welded joints have the higher fractions of deformed grains, high angle grain boundaries, Schmid factor, and lower dislocation density under the low heat input and cooling rate, which indicate a lower tensile strength and higher yield strength. The rotated Goss (GRD) ({110}⟨1 1 ¯ 0⟩) orientation of a thin plate and the cube (C) ({001}⟨100⟩) orientation of a thick plate are obvious after welding, but the S ({123}⟨63 4 ¯ ⟩) orientation at 65° sections of Euler’s space is weak. The δ-ferrite was studied based on the primary ferrite solidification mode. It was observed that low heat input and a high cooling rate results in an increase of δ-ferrite, and a high dislocation density was obtained in grain boundaries of δ-ferrite. M23C6 precipitates due to a low cooling rate and heat input in the weld seam and deteriorates the elongation of welded joints. The engineering Stress–strain curves also show the low elongation and tensile strength of welded joints under low heat input and cooling rate, which is mainly caused by the high fraction of δ-ferrite and the precipitation of M23C6.

Persistent Homology on Electron Backscatter Diffraction Data in Nano/ultrafine-grained Metallic Materials

“…It is known that low angle KAM (less than 1°) represents recrystallized material, whereas high angle KAM (greater than 1°) represents deformed material 19 . Since dislocations are mainly concentrated in deformed grains and sub-boundaries rather than subgrains and recrystallized grains, high KAM (greater than 1°) corresponds to deformed grains and lower KAM (less than 1°) to recrystallized grains 21,22 . Fig.…”

“…Orientation imaging microscopy (OIM) such as electron backscatter diffraction (EBSD) is a powerful technique which is used to characterize the spatial distribution of crystallographic orientation within a wide range of polycrystalline materials and associated microstructures [19][20][21][22] . In the last twenty years of the developments in the automated EBSD technique, it has become an important tool for quantitative metallography 23 .…”

“…It is thought regions with higher concentrations of low angle boundaries (2-15°) have concentrated "geometrically necessary" dislocations density, where subgrain boundaries form 19 . Both kernel average misorientation (KAM), which captures the distribution of the dislocation density, as well as the Schmid factor of EBSD, which evaluates the ease of dislocation movement within a grain, are used to relate material structure and behavior 21,22 . The EBSD technique can obtain the data required for quantitative microstructural analysis, especially the direct characterization of every crystal in a microstructure.…”

A New Test Method for Evaluation of Solidification Cracking Susceptibility of Stainless Steel during Laser Welding

“…According to the welding metallurgy of stainless steel and previous researches, the microstructures of the weld bead are dependent on the solidification mode [ 26 ]. At the same time, the value of Cr eq /Ni eq can determine the solidification mode of the welding.…”

The Effect of Electrochemical Composite Coatings with LaF3-LaB6 Particles in Nickel–Copper Matrix on the Metallurgical Processes in Arc Welding of Low Alloy Ferrite-Pearlite Steels

“…Welded steel structures are used at low temperatures, often in hydrogen-containing and aggressive environments. The weldability of steels becomes more complicated due to the grain coarsening, hydrogen embrittlement, hydrogen-assisted cracking (HAC), and reduced impact toughness at low temperatures [ 1 , 2 ]. The main method that is used to weld these steels is a metal active gas (MAG) and metal inert gas (MIG) welding with solid wire, because it ensures the lowest level of diffusible hydrogen in welds [ 3 , 4 ].…”