Papers by Keyword: Weld Metal

Abstract: During underwater wet welding, the environment has a corresponding effect on the mechanical properties of the weld metal. The use of external electromagnetic action (EEA) during welding is promising for influencing the formation of welded joints and the structure formation in physically inhomogeneous environments. Experimental studies have demonstrated the effectiveness of EEA application in reducing the tendency of weld metal to form pores, enhancing degassing, and lowering hydrogen content etc. The paper presents a metallographic study of the welded joint metal of structural steel (St3) after underwater welding with 12Kh18N9T filler wire, both without and with the use of EEA. Based on calculation methods and predictive modelling, optimal operating modes of the electromagnetic system for an experimental study of the EEA effect during underwater welding have been established and implemented. It has been established that the weld metal mainly has a ferrite-pearlite structure, while an austenitic structure with elongated grains is formed in the weld metal. When using the EEA, the grain structure of the weld metal is refined by an average of 1.5 times with an insignificant decrease in microhardness. In the heat-affected zone (HAZ), in the areas of large grain (I HAZ), recrystallisation (II HAZ) and incomplete recrystallisation (III HAZ), a bainitic structure is formed in the presence of ferrite layers. Under the influence of the EEA, the grain size is refined by 1.2 times in the I HAZ and II HAZ with a decrease in the thickness of ferrite layers and an increase in microhardness by an average of 7 ... 10%. The formation of such a structure will provide a set of strength properties and toughness of the welded joint metal. Research has proven that the technology of wet welding under water using the EEA allows for the production of high-quality welded joints with a high set of physical and mechanical properties of the metal of both welded joints and the HAZ.

Abstract: In this paper, the effect of direct and pulsed current in the arc welding with the use of UONI 13/Moroz coated electrodes on the structure and properties of 10KhSND structural low-alloy steel joints was investigated. Welding was performed in winter at an ambient temperature of-40oС. This work is a continuation of the cycle of research on welding of structural steels, carried out by the authors for several years.

Abstract: The operational reliability of rolling production tools depends on the heat resistance of the steel from which they are made. To increase the performance of the rolls, a hardening surfacing with wear-resistant alloys is used. The effectiveness of the applied hardening technology depends on the functional characteristics of the deposited metal. The aim of the work is to study the tempering resistance in the state after heat treatment of the deposited steel (Fe-C-Ni-Mn-Mo-V-Ti-Nb system). It was established that the thermal resistance coefficient of steel 15N8G6M3FTB at temperatures from 650 to 800 °C varies from 0.76 to 0.66, which exceeds the heat resistance of steel 30Kh2V8F by 1.5 times. It is shown that in the fine structure of such a metal after tempering at 800 °C, large amounts of finely dispersed precipitates are observed. These precipitates have a rounded shape up to 100 nm in size and belong to the Laves phases - Fe₂Mo, Fe₂Nb, and Fe₂Ti. The obtained high heat resistance values of 15N8G6M3FTB steel make it possible to recommend it for creating surfacing materials. Flux-cored wire based on this steel can be used for hardfacing hardening of tools operating at temperatures up to 800 °C inclusive.

Abstract: δ-ferrite was formed in the weld metal when the melted metal solidified to the room temperature. The δ-ferrite morphology depended on the composition, temperature gradient and growth rate. Research on the influence of heat treatment temperature (400°C, 600°C, 900°C) on the morphology changes and the δ-ferrite content is presented in this paper using optical microscopy, SEM, TEM. The δ-ferrite concentration reduced continuously in increasing temperature (from 23.5% after welding to 11% at 900°C for 10 hours). Besides, the formation of sigma phase and carbides at 600°C were the main cause of increasing hardness values in the fusion zone. However, the heat treatment at a temperature of 900°C eliminated both the sigma phase and brittleness.

Abstract: Acicular ferrite (AFα) formed on oxide particles in steel weld metals has a positive effect on toughness at low temperature. Good lattice coherency between AFα and oxide is one of the proposed reasons for promotion of AFα formation. Lattice coherency is affected by crystal structure of oxide and crystal orientation relationship (OR) between oxide and AFα. In the present study, ORs among AFα, oxide and γFe are investigated in a low carbon steel weld metal. Cube-cube (C-C) OR is observed between γFe and the oxide. It is probable that the oxide liquefied at high temperature, and then crystalized having the C-C OR with the surrounding γFe during cooling in welding process. Near Kurdjumov-Sachs (K-S) and near Baker-Nutting (B-N) ORs are observed between γFe/AFα and oxide/AFα, respectively. The misorientation from the B-N OR is larger than that from the K-S OR just after nucleation of AFα. This implies that AFα forms satisfying a near K-S OR with γFe essentially. It is supposed that formation of both the C-C (γFe/oxide) and near K-S (AFα/γ) ORs results in apparent formation of the near B-N OR between oxide and AFα.

Abstract: By the non-destructive testing of a dissimilar weld joint (DWJ) of cold collector DN 1100 (CC) on a steam generator, indications were found on inner-side cold collector’s surface at the root position of the examined weld. All the identified indications were very similar in shape and form, therefore, it was decided to cut out a part of the damaged site from this type of DWJ DN 1100 and get the obtained ring (real piece of material) for complex metallographic analysis. This paper briefly describes the results and recommendations found for the future reference during the next long‑term operation induced ageing and degradation of critical steam generator parts in NPP Bohunice Unit 4. There are summarized the results obtained from evaluation of original DWJ material.

Abstract: The study was conducted to evaluate the impact toughness of flux-cored arc welded of SM570-TMC steel joint under different heat inputs, 0.9 kJ/mm (low heat input) and 1.6 kJ/mm (high heat input). Welding wire containing 0.4%Ni was selected on this experiment. Multi-pass welds were performed on SM570-TMC steel plate of 16 mm in thickness with a single V-groove butt joint on flat position (1G). The evaluation consists of observations on microstructure using an optical microscope and SEM-EDS, and mechanical properties including tensile, microhardness Vickers and Charpy V-notch (CVN) impact test at temperatures of 25, 0 and-20 °C. Results showed that the impact toughness of the base metal (BM) was higher than the weld metal (WM) at all test temperatures. Hardness and impact toughness of WM at low heat input was observed higher than when applied a high heat input. The welded samples at low and high heat inputs had high of tensile strength, and the fracture seemly occurs on the BM. Microstructure observation showed that at a high heat input, larger grains and microsegregation were observed. It might affect on decreasing their impact property.

Abstract: Ferrite is well known as a beneficial phase that can prevent hot cracking phenomena and act as strengthening phase in austenitic stainless steel weld metal. This paper investigated mechanical and corrosion behaviour of austenitic weld metal grade 308L which deposited by SMA (Shielded Metal Arc) method with various ferrite content. Several tests such as tensile at room temperature, charpy impact V-notch and lateral expansion at cryogenic temperature-196°C were conducted to observe mechanical behaviour. Electrochemical testings such as Cyclic Polarization method and Electrochemical Impedance Spectroscopy (EIS) were also performed. Controlling weld metal 308L with ferrite number (FN) 2 and manganese content about 1.53 % could achieve excellent toughness and hot cracking resistance as well as improved pitting corrosion resistance for cryogenic purpose.

Abstract: Slag bases for welding materials have been developed from mineral raw materials and man–made mineral formations of the Urals. Successful comprehensive studies and tests of fused fluxes and also of weld metal and weld joints obtained by these welding materials have been carried out. It has been clearly established that the obtained weld metal has low content of harmful impurities ([S] is as low as 0.01 wt%) due to the use of the electric arc furnace method, purity of the feedstock minerals and technogenic raw materials and physicochemical reactions during the welding process.

Abstract: In work the analysis of influence of structurization and nonmetallic inclusions on regularity of change of growth rate of a fatigue crack in different zones of a welded seam of steel X65 is carried out. Welded seams of the pipelines received by a combined method of welding of STT+API were investigated. Growth rate of a fatigue crack low in a root of the seam received when welding in the way STT. On border of the fatigue crack passing in the filling layers of a welded seam the inclusions which are settling down chains on borders of grains are found, being concentrators of tension.