Microstructure and Mechanical Properties of Welded Joints of 1.4462 Duplex Steel Made by the K-TIG Method

K-TIG (Keyhole Tungsten Inert Gas) method is a new, emerging welding technology that offers a significant acceleration of the joining process, even for very thick plates. However, its potential for welding of certain materials is still unknown. Particularly challenging are duplex steels as this technology does not allow the use of a filler material, which is crucial for these steels and for weld joint microstructure adjustment. In order to demonstrate the suitability of this technology for single-pass welding of 1.4462 duplex steel detailed studies of the microstructure of the weld joints obtained for different linear energies were carried out and discussed with respect to their mechanical properties. According to the results obtained, the heat-affected zone (HAZ) shows a microstructure similar to the HAZ of duplex steel welded with the traditional TIG multi-pass methods. However, the weld, due to the lack of filler material, had a microstructure different to that typical for duplex steel welded joints and was also characterized by an increased content of ferrite. However, all joints, both in terms of microstructure and mechanical properties, met the requirements of the relevant standards. Moreover, the K-TIG process can be carried out in the linear energy range typical of duplex steel welding, although further optimization is needed.

Bonding SiCp/Al Composites via Laser-Induced Exothermic Reactions

In this paper, the SiCp/Al composites were bonded via laser-induced exothermic reactions of a Ni–Al–Zr interlayer. The Ni–Al–Zr interlayer was designed based on its exothermic property and chemical compatibility with the SiCp/Al composites. The influences of the interlayer composition and bonding pressure on the joint microstructure and shear strength were investigated. Results indicated that high exothermic reactions occurred in the Ni–Al–Zr interlayer and realized the reliable bonding with the SiCp/Al composites. The interlayer products were the eutectic structure of NiAl+Ni2AlZr+Ni3Al5Zr2. NiAl3 and Ni2Al3 reaction layers were formed at the bonding interfaces. The interlayer composition and the bonding pressure determined the morphology and distribution of the voids and the reaction layers, thus controlling the joint shear strength. When the SiCp/Al composites were bonded using the interlayer with the Zr content of 15 wt.% under the bonding pressure of 3 MPa, the joint shear strength reached the maximum of 24 MPa.

INVESTIGATION OF A BRAZED JOINT MICROSTRUCTURE FORMATION, MADE OF DISSIMILAR NICKEL SUPER ALLOYS AND THE COMPLEX BRAZING ALLOY

Presents the results of studies on the microstructure an opposite combination of nickel heat-resistant alloys of a brazed joint. The chemical composition of the phases formed as a result of the interaction of the mono-crystal alloy VKNA-25, heat-resistant alloy EP975 and complex alloyed solder VPr56 was investigated. The main regularities of the microstructure of the brazed joint changes during heat treatment were established. The dependence is established and the formula is derived for obtaining the optimal microstructure of the brazed seam with different duration of heat treatment and the size of the assembly gap.

The Analysis of the Microstructure of Welded Joints in Steel P5 after Service

The material subjected to the tests discussed in the article was a section of a welded joint made of bainitic steel P5. The joint subjected to analysis was sampled from a pipe section exposed to the effect of elevated temperature for more than 96 000 hours. The metallurgical tests revealed a relatively low degree of the degradation of the test joint. The microstructure contained retained bainite and precipitates of various morphology. The identification of precipitates revealed the presence of M23C6 and M2C precipitates in the joint. The M23C6 carbides were observed along the boundaries of former austenite grains. The above-named identification of precipitates also revealed the presence of M2C and M23C6 C6 carbides within the grains/laths. The insignificant exhaustion of the joint microstructure might be ascribed to the fact that the joint was subjected to relatively low temperature for a relatively short time.

Study on Welding Adaptability of Spray Formed 2195 Al-Li Alloy Filler Wires

Study on the weldability of Al-Li alloy indicates that the composition design of filler wires, and the morphology and content of the strengthening elements dominate microstructures, mechanical properties and defect control of fusion welding joint; and the welding process can actively correct the joint performances within limits. The filler wires of the both Al-Cu and Al-Cu -Zr alloy systems were developed and comparison and analysis were carried out to their adaptability along with study of the weldability of spray formed 2195 Al-Li alloy. The EDSD (electron back-scattered diffraction) detection method was applied to obtain the statistics of the microstructure fraction, grain size and small angle grain boundary of weld joints and their microstructures and correspondingly establish the interrelationship between the filler compositions and joint microstructure and performances; moreover, a microstructure matching based optimization approach was put forward to the fusion welding filter based on analysis of characteristics between weld joints and the base metal microstructures.