Formation Of Metallic Structures Research Articles

The Role of the Weld Metal Structure Formation in Selecting Rational Cooling Rates When Welding K80 Strength Grade Steel

The Role of the Weld Metal Structure Formation in Selecting Rational Cooling Rates When Welding K80 Strength Grade Steel

Study of the Effect of Selective Laser Melting Parameters on the Structure and Physico-Mechanical Properties of a Blank Made of Stainless Chromium-Nickel Steel

Currently, there are a number of additive technologies that are used in various industries (laser fusion of powder materials, electron beam melting, etc.). The formation of metal structures and products by methods of additive technologies occurs by adding a new layer of material and its further melting (sintering), ensuring the adhesion of each subsequent layer with the previous one in accordance with digital model data. The advantages of using and developing additive technologies include the possibility of using a wide range of materials, obtaining finished products with complex geometries, restoring and repairing damaged structures, as well as the possibility of applying protective and anticorrosive coatings. Metal powder materials with specified physical and mechanical properties are of crucial importance in additive manufacturing. The main requirements for such powders include requirements for their shape and size. The preferred particle shape is spherical, as it provides a more compact installation in a given volume and the necessary fluidity of the material, which is due to the low resistance in the supply systems of powder materials in 3D printers. The aim of the work is to study the influence of the parameters of the SLM printing process on the structure and mechanical properties of products made of 12Cr18Ni10Ti alloy. Samples obtained by selective laser melting were subjected to pycnometric and metallographic analysis. Based on the obtained microstructure images, a digital porosity analysis of the work piece under study was performed in the Thixomet Pro software package. The microhardness and acoustic characteristics were also measured over the entire section of the work piece under study. It was revealed that with an increase in the distance from the substrate (0...112 mm) in the transverse and longitudinal sections, the tendency remains to decrease the density values and increase the volume fraction of pores. It is shown that the acoustic parameter Dc can be used to control changes in the physical and mechanical properties of stainless chromium-nickel steel blanks obtained by selective laser melting.

Physical modeling of the effect of refilling the melt into an ingot knock-off head on solidification and structure formation

The paper presents the results of a laboratory study of the effect of refilling the ingot knock-off head with melt in a certain time interval after pouring the ingot body on solidification and structure formation of the model ingot. The research was carried out by the method of physical (cold) modeling for which a laboratory installation (casting form-mold) was developed and manufactured. It allows visually studying the processes occurring during solidification and structure formation on a 19.6-ton model ingot. We used sodium sulfuric acid (crystalline hyposulfite) as a modeling solution. Correspondence of the processes occurring on the model and in real conditions of industrial ingots casting was evaluated using similarity criteria obtained on the basis of dimension theory with analysis of physico-chemical processes occurring during casting and crystallization of the ingot. Casting of the melt into the casting form-mold was downhill. In order to assess changes in the temperature field during casting and crystallization of the ingot in the entire solidification time, we performed thermometry of the mold model surface. Analysis of the conducted studies results showed that refilling the melt before 40 min leads to stimulation of early settling of crystals (“rain of crystals”), which contributes to an increase in the crystallization directivity in vertical direction. It was established that in a conventional ingot up to 40 min solidification proceeds by a sequential mechanism, and after that the crystals begin to settle (“rain of crystals”) and the solidification of the ingot passes through a volume-sequential mechanism. Refilling the ingot knock-off head with melt 40 min after pouring the ingot body contributed to the continuation of the sequential mechanism of ingot solidification, which led to the formation of a monolithic defect-free structure in the ingot body and the least development of shrinkage shell in the knock-off head. The results obtained make it possible to develop a technology for differentiated ingots casting when filling their knock-off heads with melt in a certain time interval after pouring the ingot body, which will affect the process of metal structure formation and reduce defective zones.

Investigation of Metal Structure Formation During Ingotless Rolling-Extrusion of Aluminum and Its Alloys

Investigation of Metal Structure Formation During Ingotless Rolling-Extrusion of Aluminum and Its Alloys

Control of properties and structure of steel vessels by cooling in various media at the outlet of rolling and pressing lines

When controlling the mechanical properties and structure of vessels made of carbon structural steels manufactured by hot deformation on rolling and pressing lines (PPL) of machine-building enterprises of Russia, such cooling media as water, I20 industrial mineral oil, air are used. The applied cooling media are able to provide the workpieces with a given structure with a wide range of mechanical properties. However, the cooling media have a number of technological limitations and conditions of the use, non-compliance with which leads to reject. When cooled in oil, the probability of ignition is high; when cooled in water, hardening cracks may form, and air is not always able to provide the required rate and uniformity of heat transfer to the environment. The efficiency of control of physical and mechanical properties and structure of deformed vessels made of 50 steel by cooling in TERMAT polymer aqueous solutions in different concentrations on PPL of the plant of JSC NPO Pribor was studied. The effect of varying the concentration from 2 to 9% of TERMAT polymer on the formation of metal structure, as well as physical and mechanical properties of hot-deformed vessels was studied. The results of testing the strength and plastic characteristics of vessels by destructive and non-destructive control methods are presented. According to the results of physical and mechanical properties, regression equations were obtained with at least 95% reliability of R2, which establish the relationship between the controlled plastic and strength parameters of the vessel metal`s properties. The conducted researches allowed to compare the indicators of the main physical and mechanical properties of steel vessels at the PPL outlet and to propose methods of inhomogeneity control that reduce time and material costs by 5–10% during the tests.

Improvement of Technology for Producing Rolled Sheet from Continuously Cast Steel Slabs. Part 2. Physical Modeling of Low-Carbon Steel Strip Rolling*

Features of metal structure formation in the finishing group of a continuous broad-strip mill are studied using a physical modeling method. Wedge-shaped samples of low carbon steel are rolled in a two-roll laboratory mill at 880–1070 °С in one and two passes. Results of modeling rolling conditions for low-carbon steel strips and subsequent cooling make it possible to establish the main laws governing metal structure formation. Industrial testing of the calculated rolling regimes and subsequent cooling of low-carbon steel strips in the 2000 NLMK mill confirm the possibility of improving finished rolled product mechanical properties.

Фізичні методи управління формуванням структури металів

Фізичні методи управління формуванням структури металів

Technology Development for Producing Hot-Rolled Sheet Steel from Continuous-Casted Slab

To improve the quality of continuous-casted slabs and to reduce the cost of the produced rolled steel by ₽258 per ton, a resource-saving technology and submerged casting nozzle with eccentric holes are proposed. The experimental industrial tests of this technology for low-carbon and low-alloyed steel show an increase in the strength and toughness of the obtained hot-rolled metal. The results of the economic calculations at casting of 1.5 million tons of slabs and production of hot-rolled steel from them are provided. The computations of the ultimate strength and relative elongation of sheet steel were performed using well-known equations. The physical simulation results of sheet rolling in the finishing group of NShS and subsequent cooling establish the laws of metal structure formation.

Effect of layer-by-layer formation of ingot during electroslag remelting on the quality of its surface and solidification structure

ABSTRACT The article presents the results of experimental studies of the features of forming the side surface and the crystallization structure of steel ingots, produced by the method of electroslag remelting with a layer-by-layer formation. The ingots with diameters of 160 and 220 mm were produced by remelting consumable electrodes in a pulsed mode, providing the periodicity of the processes of electrode melting and metal solidification. This was achieved due to a cyclic change of the slag pool voltage from operating values to the values, at which the electrode melting ceased, as well as due to a corresponding change in the electrode feed rate. It was shown that layer-by-layer formation of the ingot allows reducing the volume of the liquid metal pool, equalizing the crystallization front and controlling the metal structure formation while maintaining a good quality of the side surface.

Stabilization of metal structure formation in directed energy deposition by applying a coolant system

Directed energy deposition (DED), which is one of additive manufacturing processes applicable to metals, is suitable to produce a large-scale complex-shaped part in aerospace and automobile industries. However, mechanical characteristics in a DED-produced part often varies according to the thermal conduction at each deposition point. To ensure quality uniformity in a DED-produced part, a cooling process also should be actively performed to control the thermal condition. This study evaluates variation in crystal structure in parts produced with DED applying a coolant system. By performing the cooling process at certain intervals during deposition, the variations in Vickers hardness and crystal structure are effectively suppressed in DED of Inconel 625.

Cellular automata for simulation of dendritic growth with surface active refractory inoculants

Purpose: During weld metal structure formation the possibility of impact on its mechanical properties are much more limited in comparison with metallurgy and technology of steel production. Adding of the inoculants to the welding pool is one of the promising methods of influencing the structure and mechanical properties of the weld metal. Design/methodology/approach: Cellular automata (CA) with additions of finite difference method (FDM) is one of the best ways to simulate dendritic growth process with the surfaceactive inoculants. It`s easy to add new rules of interaction between the inoculants and dendrite surface to the cellular automata model. Findings: It was found that average distance between primary dendrites axis decrease with increase of the inoculants wetting angle by melt iron. Obtained results were confirmed experimentally on weld metal samples that were obtained by the welding of HSLA steels with the surface-active inoculants. Research limitations/implications: The inoculants with size that comparable with cells size of the model (!0.4 microns) were distributed evenly in computational area. Practical implications: Adding of surface-active inoculants to the melt metal improve structure and mechanical properties of weld metal. Different refractory particles (TiC, TiN, SiC, TiO2, Al2O3 and ZrO2) can be used. Originality/value: Refractory inoculants adding to the melt metal are wide used in metallurgy as crystallization centers and heat absorbers. Inoculants that were added to the welding pool of high-strength low-alloyed (HSLA) steel welds could also influence on crystallization processes of weld metal as surface active particles. In the contact point between the dendrite surface and the surface-active inoculant, a surface energy is change depending of the inoculant surface properties. Different refractory particles (TiC, TiN, SiC, TiO2, Al2O3 and ZrO2) were used.

Features of the Metal Structure Formation in Cryogenic Equipment during Long-Term Operation at 4.2 K

This study discusses the role of thermal processes, including repair welding, and maintenance heat-up of cryogenic equipment, in the alteration of the properties of base metal and formation of thermal impact zones during repair and installation of joints from chromium-nickel steels with different nickel content. The tests have confirmed the primary role of nickel in the change of the properties of base metal and welded joints of low-temperature structures during operation and maintenance heat-up. It was shown that maintenance, repair and welding heat-up can lead to structure alteration and material embrittlement, which occurs in all steels, regardless of nickel content. The research has identified the areas that are potentially dangerous from the perspective of the brittle defect evolution in cryogenic equipment operating under complex thermal cycles during operation or maintenance heat-ups.

PRODUCTION TECHNOLOGY OF HOT ROLLED PLATE OF SPECIFIED QUALITY USING NEW TECHNICS OF LARGE SECTION SLABS CASTING

Development of new methods for production of continuous cast slab blanks shall not be based on low speed equilibrium crystallization processes in steel. Feeding melt into crystallizer side-wall layers through feed rising construction of submerged nozzle with eccentric outlet holes allows a significant increase in steel crystallization rate during slab casting. The main results of large section slabs casting using new technology providing improvement of their quality are given. When casting steel through an experimental nozzle, considerable decrease in width of columnar crystals zone and increase of disoriented crystals zone are observed, as well as decrease in index of centerline segregation. When casting with a new technology, heat transfer in crystallizer increases by 10 – 12 %. In impact test, a number of qualitative characteristics of metal have been identified that are not captured in other types of tests. The main regularities in metal structure formation in continuous finishing mill group of continuous wide strip mill (CWSM) and subsequent cooling were studied using physical modeling method. Wedge-shaped samples of industrial melted low-carbon steel, withdrawn from semi-finished rolled stock cooled on CWSM intermediate rolling table, were rolled in one and two passes on twohigh speed laboratory rolling mill with a bypass device. Geometric and kinematic resemblance of rolling process was observed. Rolled samples, after fixed exposures on air, were dropped by a special device onto the lateral edge for partial hardening in cooling solution. A set of relative reductions were received longwise the sample, a set of cooling rates – edgewise. Based on results of physical modeling, the main formation regularities of low-carbon steel structure during rolling and accelerated cooling of strips on continuous wide strip mill were established. Using these regularities and the Hall-Petch equation, it is possible to provide specified structure and flow limit of the finished hot-rolled plate. By eliminating of additional heating of slabs for rolling and improving quality of rolled products, a significant economic effect can be obtained.

From Impurity Doping to Metallic Growth in Diffusion Doping: Properties and Structure of Silver-Doped InAs Nanocrystals.

Tuning of the electronic properties of presynthesized colloidal semiconductor nanocrystals (NCs) by doping plays a key role in the prospect of implementing them in printed electronics devices such as transistors and photodetectors. While such impurity doping reactions have already been introduced, the understanding of the doping process, the nature of interaction between the impurity and host atoms, and the conditions affecting the solubility limit of impurities in nanocrystals are still unclear. Here, we used a postsynthesis diffusion-based doping reaction to introduce Ag impurities into InAs NCs. Optical absorption spectroscopy and analytical inductively coupled plasma mass spectroscopy (ICP-MS) were used to present a two-stage doping model consisting of a "doping region" and a "growth region", depending on the impurity to NC ratio in the reaction vessel. X-ray absorption fine-structure (XAFS) spectroscopy was employed to determine the impurity location and correlate between the structural and electronic properties for different sizes of InAs NCs and dopant concentrations. The resulting structural model describes a heterogeneous system where the impurities initially dope the NC, by substituting for In atoms near the surface of the NC, until the "solubility limit" is reached, after which the rapid growth and formation of metallic structures are identified.

Structure Formation in Metal Complex/Polymer Hybrid Nanomaterials Prepared by Miniemulsion

Polymer/complex hybrid nanostructures were prepared using a variety of hydrophobic metal β-diketonato complexes. The mechanism of structure formation was investigated by electron paramagnetic resonance (EPR) spectroscopy and small-angle X-ray scattering (SAXS) in the liquid phase. Structure formation is attributed to an interaction between free coordination sites of metal β-diketonato complexes and coordinating anionic surfactants. Lamellar structures are already present in the miniemulsion. By subsequent polymerization the lamellae can be embedded in a great variety of different polymeric matrices. The morphology of the lamellar structures, as elucidated by transmission electron microscopy (TEM), can be controlled by the choice of anionic surfactant. Using sodium alkylsulfates and sodium dodecylphosphate, "nano-onions" are formed, while sodium carboxylates lead to "kebab-like" structures. The composition of the hybrid nanostructures can be described as bilayer lamellae, embedded in a polymeric matrix. The metal complexes are separated by surfactant molecules which are arranged tail-to-tail; by increasing the carbon chain length of the surfactant the layer distance of the structured nanomaterial can be adjusted between 2 and 5 nm.

Communication: Coalescence of carbon atoms on Cu (111) surface: Emergence of a stable bridging-metal structure motif

By combining first principles transition state location and molecular dynamics simulation, we unambiguously identify a carbon atom approaching induced bridging-metal structure formation on Cu (111) surface, which strongly modify the carbon atom coalescence dynamics. The emergence of such a new structural motif turns out to be a result of the subtle balance between Cu-C and Cu-Cu interactions. Based on this picture, a simple theoretical model is proposed, which describes a variety of surface chemistries very well.

Kinetic self-assembly of metals on copolymer templates

In this work, we seek to understand some of the fundamental processes that govern self-assembly at the nanoscale in the context of the formation of metallic structures on patterned copolymer templates. To this end, we focus on recent experiments where morphologies resulting from the evaporation-deposition of different metals on PS- b -PMMA phase-separated templates were studied. We show that the different morphologies obtained can be understood in terms of the relative importance of the energetics and kinetics. We then focus on a particular morphology: micron-long wirelike states obtained by the evaporation deposition of silver on the template. We show the existence of "nontrivial" correlations between adjacent wires that can be understood based on a purely kinetic mechanism. We also compare these correlations quantitatively to those obtained from simulations done with the relevant experimental parameters and find them in good agreement.

High-Porosity Metal Structure Formation under Stationary Nonequilibrium Condensation Conditions

A substantially new technological approach to the formation of high-porosity metal layers is proposed, which is based on the process of stationary nonequilibrium vapor condensation inside a hollow cathode. The conditions necessary for the manifestation of such a spatially distributed selective nucleation and growth of metal condensates are the realization of only monoatomic critical nuclei and the existence of a critical energy for the binding of adatoms to the growth surface (below this level, the probability of condensate formation is negligibly small).

Kinetics of silver structures growth by electrodiffusion in quartz crystals

Silver layers were grown in quartz crystals by electrodiffusion from an anodic layer of AgNO 3. Different experimental arrangements were employed in order to obtain such layers in a reproducible way. We performed DC ionic conductivity measurements on Z-cut and X-cut samples as a function of temperature in the heating up phase and as a function of time at the electromigration temperature. The metal structures and the quartz samples were analyzed by electron microscopy and electron diffraction. Based on the experimental results and on the observations a model for the metal structure formation is proposed.

Microcontact Printing of Palladium Colloids: Micron-Scale Patterning by Electroless Deposition of Copper

This paper describes a new method for forming micron- and submicron-scale patterns of copper on surfaces. This method uses microcontact printing (μCP) to deposit colloids that serve as catalysts for the selective electroless deposition of copper. A patterned elastomeric stamp fabricated from poly(dimethylsiloxane) was used to deliver the catalystpalladium colloids stabilized with tetraalkylammonium bromidesto the substrate surface. The electroless deposition of the copper on the sample occurred only where palladium colloid was transferred to the substrate. Electroless deposition catalyzed by the colloids resulted in the formation of metal structures with features having submicron dimensions, with an edge resolution in the range of 100 nm. This technique of activating substrates for electroless metalization was successfully used to pattern glass, (Si/SiO2), and polymers; both flat and curved substrates were used. Microcontact printing of colloids was also used to fabricate metal structures whose thicknesses were varied in different regions of the sample (multilevel metal structures). Free-standing metal structures were produced by dissolving the substrate after the metal film had reached the desired thickness.