A Study of the Influence of Local Heat Treatment on the Structure of Welded Titanium Pipelines

The article analyzes the results of a study of the influence of zonal heat treatment on the structure of welded joints of pipeline elements made of titanium alloys Ti-3.5Al-1.5Mn. In the manufacture of such structures, the TIG welding method is used to join pipe elements, after which the heat treatment method can be used to relieve residual stresses. The experiments have confirmed the effectiveness of zonal heat treatment preceded by welding. It was revealed that for welded joints made of titanium alloys, heat treatment can stabilize the structure. In experiments conducted by the method of optical metallography, the structure of heat treated and untreated welded joints was investigated. The influence of heat treatment on the weld structure and heat-affected zone was identified.

Assessment of the Thermal Effect on the Surface of Metal Structural Materials on the Stability of Laser-Induced Codes Readability

This work represents the characterization of materials surface before and after laser processing with macrophotography, optical metallography, and scanning electron microscopy before and after thermal exposure. The factors influencing the reliability of the laser-induced code readability have been determined as color and contrast. The range of stability of the code readability under thermal influence on the structural materials under study was determined, which allows improving the reliability of the laser-induced marking codes readability. The research objects in this paper were samples of the following materials: alloys based on copper, aluminum, and iron with laser-induced codes of various types applied on the surface. This work aimed to research the stability of laser-induced codes readability after thermal exposure using macrophotography, optical metallography and scanning electron microscopy on structural materials of various purposes before and after laser processing (when forming a binary matrix code). The research results obtained and presented in this article on the stability of laser-induced codes reading under thermal action on structural materials can be used in different fields of industry, when marking products of heavy, general, medium, and precision engineering, as well as for marking metal products and blank parts. The results of this research are also planned to be used for further analysis of the occurring damage, leading to reading errors due to mechanical and chemical influences. It is planned to evaluate the limit values of the parameters that determine the degree of degradation at which the encoding will be considered to have lost the recognizing ability. Requirements for the quality and permissible code damage will also be developed to ensure their reliable identification.

A study of the influence of high frequency cyclic loading on the structure and properties of weld connections in process pipelines

Introduction. Pipeline systems are exposed to several conditions that lead to a drastic reduction in their durability, primarily due to variable low-frequency and high-frequency loads arising in a process pipeline due to the operation of compressor units. Hence, fatigue failure occurs, leading to the pipeline failure. As early as at the pipeline installation stage, sections of process pipelines have weld connections, and thermal welding cycles have an adverse effect on the properties of materials exposed to fatigue loading. The study of weld connections in steel pipelines exposed to high-frequency vibrations and effects of weld seam defects on durability characteristics are the focus of this research. Materials and methods. Low-carbon pipeline steel St20 was selected for the study. The radiographic inspection method, optical metallography, microhardness of structural phases, and the method of high-frequency fatigue tests were used. Results. The results and principal conclusions about the effect of welding defects on durability characteristics of welded samples, made of pipeline steel and exposed to high-frequency fatigue tests, are presented; structural changes in weld connections are analyzed using optical metallography and microhardness methods. Defects of weld seams and their dimensions were identified by means of radiographic inspection. A comparative analysis of durability limits, demonstrated by the parent metal of the model material that has defective weld connections, and the same limits of defect-free samples is provided. The main causes of failure of weld joints, exposed to high-frequency vibrations, are identified. Conclusions. Having summarized the research findings, we can argue that high-frequency vibrations have a negative impact on the parent metal of a process pipeline and its weld joints. The weld seam is the point of failure; defects trigger destruction, and their presence has a higher impact on fatigue characteristics than their dimensions or types. Characteristics of durability in case of exposure to high frequency loading applied to a weld joint in the gigacycle range are 67 percent below those of the parent metal.

Melt Conditioned Direct Chill (MC-DC) Casting and Extrusion of AA5754 Aluminium Alloy Formulated from Recycled Taint Tabor Scrap

The melt conditioned direct chill (MC-DC) casting process has been used to produce billets and extruded planks of AA5754 alloy formulated from 100% recycled Taint Tabor scrap aluminum. The billets were homogenized and then extruded into flat planks. Optical metallography of the MC-DC cast billets showed equiaxed refined grains in comparison to conventional direct chill (DC) cast and direct chill grain refined (DC-GR) cast billets formulated from the same Taint Tabor scrap. Microstructural evaluation of the extruded planks showed extensive peripheral coarse grain (PCG) for the DC, DC-GR and MC-DC cast planks. The 2 mm and 1 mm MC-DC cast planks produced after cold rolling and heat treatment showed a fully recrystallized microstructure at 380 °C and 300 °C for 10 min respectively with an improvement in mechanical properties over DC-GR cast and similarly processed planks. The as-extruded MC-DC cast planks tensile tested in the transverse direction showed 34% elongation and 213 MPa ultimate tensile strength. These tensile results showed 5.8% higher elongation and 1.2% higher ultimate tensile strength compared with the DC-GR planks after applying high shear melt conditioning.

Structure and properties of high strength low alloyed cold-resistant steel after reheat and direct quenching with tempering

The paper shows comparative investigations of structure of rolled plates from low alloyed coldresistant steel 08CrNi2MoCuNb with guaranteed yield strength 750 MPa after traditional reheat quenching and quenching from rolling heat (direct quenching) with subsequent high temperature tempering. The research is carried out by means of optical metallography, SEM and TEM. The peculiarities of parameters of bainitemartensite structure, which influence the strength level in initial (quenched) state, are revealed. Also, the impact of tempering on structure and properties of rolled plates after reheat and direct quenching is shown.

Microstructural and thermal characteristics of the sintered Al-Fe2O3 composites

This work has as an objective a study of evolution of characteristic properties of crystalline microstructure and mechanical hardening of aluminum by iron oxide (III), (hematite α-Fe2O3) nan energetic material known as thermite, samples of massive alloys, Al (base)-X wt% Fe2O3 (X =2, 4, 16 and 40) were studied.Al-Fe2O3 composite was developed by a sintering technique from the mixtures of compacted powders of Al high purity and α-Fe2O3 under a temperature of 700 °C for 1 hour and then slowly cooled. We have not noted the formation of thermite as foreseen by the chemical reaction due to the mixture of aluminum with hematite. The evolution of crystalline microstructures and the morphologies of surface were determined by means of X-ray diffraction, thermal analysis and optical metallography. The mechanical behavior was characterized by the tests of Vickers indentation and corrosion resistance by electrochemical tests.

Влияние охлаждения подложки на микроструктуру и фазовый состав изделий из титанового сплава Ti-6Al-4V, полученных методами аддитивных технологий

The microstructure, phase composition, and parameters of the -Ti based solid solution in the Ti-6Al-4V alloy obtained by 3D printing without cooling and with water cooling of the titanium substrate were studied by the methods of X-ray diffraction analysis, transmission diffraction and scanning electron microscopy, and optical metallography. It was found that the use of water cooling of the substrate leads to a decrease of the hereditary  grains sizes, an increase in the volume fraction of the  phase, a decrease in the volume fraction of the  phase and the total mean square displacement of atoms in the -Ti crystal lattice, as well as an increase in the elastic macrostrain of the samples.

Improving the Properties of Aluminum Alloy System Al-Cu-Mg, Subjected to Hardening and Severe Plastic Deformation

The tendency of the aluminum alloy D16 system Al-Cu-Mg to natural (NA) and artificial aging (AA) after hardening and high pressure torsion (HPT) under a pressure of 6 GPa at room temperature was studied using optical metallography, scanning electron microscopy, electrical conductivity tests. The dependences of microhardness and electrical conductivity were constructed depending on the exposure time. It is shown that heat treatment (HT) (hardening + HPT + NA) leads to an increase of hardening of the alloy D16 compared to standard HT (T4) in 2,3 times, at preservation of level of conductivity.