Metallurgical Composites Research Articles

Combined CFD and Heat Treatment Simulation of High-Pressure Gas Quenching Process

Abstract To improve the process development for high pressure gas quenching a digital quenching simulation model combining the fields of computational fluid dynamics and heat treatment process simulation has been developed. It was found that the gas flow and hence the quenching properties depend on both local (geometry of parts, carrier and chamber) as well as global influencing factors (fan characteristics, system pressure and hydraulic resistances). Therefore, a computational fluid dynamics model that includes all these factors was realized. The approach includes a heat transfer analysis to determine the local heat exchange coefficients on a component level. By connecting the computational fluid dynamics model and heat treatment simulation the local quenching characteristics are used to compute the temperature history of the quenched part. Based on a thermo-metallurgical heat treatment simulation the computed local cooling curves and metallurgical phase compositions are used to accurately predict the part properties like microstructure and hardness. The applicability of the model has been confirmed by hardness measurements. Hardness results for different batch positions, batch setups or tray systems can now be computed enabling an efficient virtual development of the gas quenching process.

Исследование структуры и свойств износостойкого газотермического покрытия с содержанием вольфрама

The paper presents the results of reverse engineering including metallographic, mechanical, and engineering-technical studies of used rods of a compressor produced by the Dresser-Rand company (Siemens, Germany). The study established that the original product is made of AISI 4140 steel with a working coating based on tungsten carbide applied to a depth of 0.2 mm by the HVOF method. The paper contains the results of the development of an import-substituting technological process for producing a wear-resistant powder coating of the Ni–Cr–B–WC system applied by cold gas flame spraying on the surface of a critical unit of compressor equipment in the oil and gas industry. Microanalysis identified that the sprayed spherical WC particles are evenly distributed in the nickel bond without the formation of free cavities at the lamella boundary, retain the size identical to the original powder composition upon the high-speed collision with the substrate, and minimize the level of residual mechanical stresses in the surface layer. The study shows that the sprayed coating has a high microhardness (the bases – 700 HV0.1, WC – up to 2000 HV0.1), which ensures high wear resistance during operation of the rod in a friction pair. A comparative analysis of the tribological properties of the coatings showed that when changing the shape, particle size distribution, and percentage ratio of tungsten carbide from 20 to 70 % in the nickel matrix, the overall wear resistance of the coating equivalently increases. The authors concluded on the possibility of manufacturing an import-substituting product using the gas flame spraying technology with metallurgical powder compositions containing tungsten. The authors developed an industrial technology for applying a wear-resistant coating on the working surface of a rod made of AISI 4140 steel. The paper presents the results of the analysis of the stress state of a material with a coating produced using the developed technology in comparison with the original product. In the product obtained by the experimental technology, in the process of applying the coating and its subsequent mechanical processing, uniform residual mechanical stresses are formed that do not exceed the value of the difference in the principal mechanical stresses. The paper presents the results of the study obtained both on standard samples and on a pilot part.

Towards high strengthening efficiency by in-situ planting nano-TiB networks into titanium matrix composites

The coarsening of the matrix microstructure and hybrid reinforcements caused by the excessive-high sintering temperature has been a widespread problem for powder metallurgical titanium matrix composites (TMCs). In this study, inspired by the unique eutectic precipitation path in Ti–B system, we innovatively proposed a new strategy to optimize the microstructure by in-situ planting nano-TiB networks into the composite powder. During the hot-pressing process, the pre-planted networks significantly refined the matrix grain and assembled the special interfacial/intragranular structure, containing interfacial submicron-TiB and intragranular nano-TiB. The well-designed TiB/IMI834 composites exhibited a great improvement in mechanical properties, the compressive yield strength was improved to 1438 MPa with an increase of 24.5%, and the tensile strength at 600 °C was increased to 825 MPa, superior to many thermo-mechanically processed TMCs. The grain refinement and the interfacial/intragranular nano-TiB both contributed to the high strengthening efficiency. This new strategy provided a controllable and facile way to refine the microstructure and achieve high strengthening efficiency in TMCs.

A multi-phase linear kinematic elastoplastic model for the HAZ of welded S355J2 steel under low-cycle fatigue

The aim of this paper is to develop a linear kinematic elastoplastic model for simulating the mechanical behavior of a heat-affected zone under low-cycle fatigue for welded S355J2 low-carbon steel. First, an experimental procedure is developed by means of a Gleeble machine for creating macroscopic tensile specimens with different homogeneous metallurgical compositions according to a welding continuous cooling transformation diagram. Then, cyclic tensile tests are carried out by prescribing different strain amplitudes up to 1%. By considering the stabilized behavior at mid-life, the yield stress and hardening modulus are identified as functions of the metallurgical composition by means of a linear mixture rule. Comparisons with numerical simulations are presented to show the efficiency of the multi-phase cyclic linear kinematic elastoplastic model proposed in this work.

Import-substituting technology for manufacturing parts of the oil and gas industry with the application of tungsten based wear-resistant coatings

The results of reverse engineering including metallographic, mechanical, and engineering studies of used compressor rods of foreign manufacture are presented. The structure of surface and the base of the part were examined, mechanical characteristics and types of hardening of pillar threaded portion and working flank were determined. It is concluded that it is possible to manufacture such a product using gas-flame spraying technology with metallurgical powder compositions containing tungsten. An industrial technology has been developed for applying a wear-resistant coating to the working rod surface of steel 45 CrMnMo. The research results made on standard samples and pilot part are presented.

Comparative investigations on sulfidic gold ore processing: A novel biooxidation process option

Microbial enhanced sulfide oxidation is one of the alternatives to roasting or pressure oxidation (POX). High grade whole ores or upgraded sulfide concentrates can be processed using POX or roasting processes but the high capital and operating costs often prohibit to process lower grade materials using these process methods. Sand Farming process is a novel alternative to POX or roasting for medium to low grade materials. The key advantage of the process is to use a relatively coarser material compared to POX or roasting. The POX and roasting processes utilize fine ground materials with P80 75 µm or smaller to achieve higher gold recovery. The Sand Farming process uses agglomerated sample of P80 0.60 mm and the comminution cost saving is significant. Ore samples were collected from a gold mine in Mexico and two metallurgical composites were prepared for the study. Comp #1 contains 2.7 g/t of gold and 15.4 g/t of silver with 0.33% copper and 0.11% arsenic. The total sulfur was 5.7% and the sulfide sulfur was 5.6%. Gold and silver grade of Comp #2 was 1.2 g/t and 8.8 g/t, respectively. Copper and arsenic concentrations were lower than 0.07% and 0.03%. Total sulfur was 5.0% with 4.9% sulfide sulfur. The gold recovery from the Sand Farming was comparable to POX and roasting. Roasting calcine yielded the gold extraction of 70% while gold extraction from POX residue showed about 90%. After 44 days of Sand Farming biooxidation, 80% and 90% gold extractions were observed from Comp #1 and Comp #2, respectively. The gold extractions were further increased to 92% and 96% after 83 days of biooxidation.

Powder metallurgical Ti-Mg metal-metal composites facilitate osteoconduction and osseointegration for orthopedic application

In this work, TiMg metal-metal composites (MMCs) were successfully fabricated by spark plasma sintering (SPS). In vitro, the proliferation and differentiation of SaOS-2 cells in response to TiMg metal-metal composites (MMCs) were investigated. In vivo, a rat model with femur condyle defect was employed, and TiMg MMCs implants were embedded into the femur condyles. Results showed that TiMg MMCs exhibited enhanced cytocompatibility to SaOS-2 cells than pure Ti. The micro-computed tomography (Micro-CT) results showed that the volume of bone trabecula was significantly more abundant around TiMg implants than around Ti implants, indicating that more active new-bone formed around TiMg MMCs implants. Hematoxylin-eosin (H&E) staining analysis revealed significantly greater osteointegration around TiMg implants than that around Ti implants.

Quenched and tempered steel welded with micro-alloyed based ferritic fillers

Quenched and tempered steel welds were made using one ferritic and two different micro-alloyed based ferritic fillers using shielded metal arc welding process. Variable metallurgical compositions in the weld zones of these joints resulted into wide variation in the microstructural phases and microhardness across different zones of these welds, which consequently influenced their tensile and impact toughness performance significantly. Joint welded using filler containing Cr and Mo with Nb, Ti, Al, V, Cu and N as micro-alloying additions resulted into weld metal where martensitic refinement occurred and thus showed highest microhardness of more than 400 HV_1. So this joint exhibited highest yield and ultimate tensile strength but gave least percentage elongation and showed the highest joint efficiency, whereas the other two joints welded using ferritic and less micro-alloyed (containing small additions of Ni, Mo and Cu) fillers fractured in their respective weld zones. High matching index (ratio of yield strength of weld joint to base metal) shifted the plastic strain from the weld metal to the HAZ during tensile loading. High micro-alloyed weld metal also showed the highest Charpy impact toughness value followed by low micro-alloyed and conventional ferritic weld metal. Weld metal with microalloying additions made to the weld metal via using suitable filler resulted into microstructural refinement of the weld metal which improved the tensile and impact toughness performance of quenched and tempered welded joints.

Discrete element simulation of metal ceramic composite materials with varying metal content

Metal–ceramic composite materials are used in several fields of industrial applications. Most of the composites are particulate composites, where metal is the matrix and ceramic the reinforcing particulate material. Oxide dispersion strengthened alloys show increased temperature stability compared to the pure alloy. Theoretical models describing the densification evolution during sintering are only available for particle reinforced materials, but there are no models developed for interpenetrating structures, when both phases are sintering.We present a modelling approach based on the discrete element method, which can be used to investigate the sintering behavior on the whole range of powder metallurgical producible composites. The discrete element method takes the particulate structure of the powder compact into account and allows one to perform detailed modelling of each contact separately. In this paper the metal fraction was varied between 100 and 0 vol.% and the densification was analyzed by the contact radius evolution.

Effect of Laser Cladding Parameters on the Microstructure and Properties of High Chromium Hardfacing Alloys

Mechanical components operating under high-stress and high-temperature environments require enhanced mechanical and tribological properties. In this research, different high chromium steels (Fe-Cr-C-Ni-Mo-Mn) have been coated over a 316L substrate using coaxial laser cladding. Optimized properties of the clad (such as adhesion, compactness, microstructure and dilution rate) have been obtained by a broad parameter search (laser power, powder feeding rate, scanning speed and preheating). Varying such parameters induces change in the microstructure, chemical distribution, morphology and properties of deposits. These have been thoroughly characterized in terms of metallurgical structure, phase compositions and functional properties using dedicated metallurgical mechanical and wear analysis. Samples obtained by laser cladding and plasma arc-transferred cladding have been compared. Laser cladding exhibits a significant strengthening mechanism for this hardfacing alloy. This results from a finer dendritic structure with a modified Chromium and Molybdenum precipitations distribution in the eutectic interdendritic phase.

Effect of the graphite content on the tribological properties of hybrid Al/SiC/Gr composites processed by powder metallurgy

Purpose – The purpose of this paper is to understand the effect of graphite content on the properties of aluminum alloy/silicon carbide/granite (Al/SiC/Gr) composites. Design/methodology/approach – Hardness and wear tests were applied to the powder metallurgical composites, and microstructural characterization was conducted. Findings – Optimum graphite content for maximum wear resistance is reported as weight 6 per cent. Originality/value – Results of this study may help light weight Al/SiC/Gr composites to be used in different industrial applications.

Wetting behavior of eutectic Al–Si droplets on zinc coated steel substrates

Transient spreading behavior, joint properties and metallurgical compositions are investigated for different hot-dip and electro-galvanized zinc coatings. The main focus is set on the effect of coating thicknesses and droplet size. While most of the droplets are observed on surfaces at room temperature, the case of pre-heated substrates is also accounted for. Both the coating thickness and the droplet size have little effect on the resulting wetting angle compared to the effect of preheating or the absence of a coating. The transient spreading behavior significantly differs for different coating types. The coating thickness affects heat transfer into the substrate during the initial stage of wetting. The metallurgical composition shows that the coating is removed over a broad interfacial area, while it accumulates at the toe of the deposited braze metal most likely due to fluid dynamic effects.

The correlation of material characteristics and wear in a laboratory scale cone crusher

Wear of materials is a widely recognised industrial problem. The direct costs of wear failures, such as wear part replacements, loss of productivity as well as indirect losses of energy, and the increased environmental burden, are real problems in everyday work and business. The mineral industry is particularly susceptible to wear part consumption resulting in high expenses. In this study, the performance of various steel-based wear resistant powder metallurgical metal matrix composites (MMCs) was studied for mineral industry applications. The matrix of the composites consisted of various tool steels, manganese steel and martensitic steel and the reinforcements used were tungsten carbides (WC), titanium carbides (TiC) or cemented carbides (WC/Co). Hot isostatic pressing (HIP) was used for compacting the materials. The performance of composite materials was studied in a laboratory scale cone crusher wear test. Correlations between the wear behaviour and microstructure parameters, such as volume fraction and the size of the hard particles and spacing between hard particles were investigated. It was found that the most important parameters in this wear environment were the total volume fraction of the hard phase and the type of the hard phase. A necessary feature of the matrix material is that it is also resistant to abrasion.

Toughness of Fe-Base Materials Containing Hard Phases

AbstractIn the present work the toughness of powder metallurgical tool steels and Metal Matrix Composites (MMC) is being investigated, specifically the influences of heat treatment and the addition of hard phases on the fracture toughness KIc. The experimental materials are cold work tool steel X230CrVMo13-4 as well as hot work tool steel X40CrMoV5-1 with coarse hard phases of the type titanium carbide (TiC), and fused tungsten carbide (FTC) in contents of 0, 10 and 30 vol.-%. The materials were produced by hot isostatic pressing and subsequently heat treated by quenching and tempering in two essentially different treatments. The fracture toughness KIcwas measured at precracked three point bending specimens. Fractographical investigations should characterize the fracture formation, progression and mechanism and give information about the influences of microstructure components on the fracture toughness. The experiments showed that generally an addition of coarse hard phases leads to a large decrease in fracture toughness. However, in case of powder metallurgically produced hot work tool steel X40CrMoV5-1, an increase in fracture toughness was achieved by adding 10 vol.-% of fused tungsten carbide. Even an addition of 30 vol.-% FTC exhibits KIcvalues in the region of a pure cold work matrix. Furthermore it is shown that retained austenite positively affects the fracture toughness

The polishing mechanism of electrochemical mechanical polishing technology

In this paper, the polishing mechanism of the electrochemical mechanical polishing (ECMP) technology for tooling steel SKD11 was investigated. Suitable electrochemical process parameters were evaluated. The electrochemical characteristics of a material such as active, passive and trans-passive (dissolution) can be revealed from its I–V curve. The characteristics of passive and trans-passive have great effects on the ECMP polishing mechanism. Experimental procedures included qualitative, quantitative and surface quality analyses. Qualitative analyses utilized potentiostat to study the I–V curves of a specific specimen in various electrolytes and electrolytic concentrations, and to find out the voltages at each electrochemical state. In quantitative analyses, the electrochemical polishing processes of the ECMP technology were conducted. From the measured and theoretical weight losses, each process state can be verified whether or not it followed the Faraday’s law. Finally, the surface roughness was measured by a surface profiler. The scanning electron microscopy (SEM) was used to observe the surface profile. The energy dispersive spectroscopy (EDS) analysis was employed to analyze the metallurgical compositions of the surface. In summary, the proposed mechanism and analyses were a good methodology in finding suitable electrochemical process parameters for ECMP technology.

Magnetic properties and loss separation in iron powder soft magnetic composite materials

New developments in powder metallurgical composites make soft magnetic composite (SMC) material interesting for application in electrical machines, when combined with new machine design rules and new production techniques. In order to establish these design rules, one must pay attention to electromagnetic loss characteristics of SMC material. In this work, five different series of iron based SMCs are produced and studied: (1) Pure iron powder with resin; (2) sintered iron based powders; (3) pure iron powder with additions of Zn-st and carbon; (4) iron based powder alloys (Fe,Nb,Si); (5) commercially available iron powder “Somaloy.” The specimens were shaped as rectangular rods and characterized on a miniature single sheet tester which was calibrated to Epstein. The measured energy losses are analyzed following the loss separation theory of Bertotti, in which the total energy loss is decomposed into hysteresis loss, classical Foucault loss, and an excess loss component.

Development of Porous Steel Structures for Steam Turbines

Improving thermal efficiency in modern steam turbines can only be achieved by the application of new cooling systems, such as effusion cooling. On the basis of the grid sheet, a new sandwich material with perforated cover sheets and a hollow interlayer containing cavities, a new cooling component for steam turbine casing and rotor parts that fulfills both the mechanical and the functional characteristics can be manufactured. For the low-pressure turbine a process for open porosity powder metallurgical composites has been developed.

溶湯撹はん法で作製したＳｉＣｐ／７０７５アルミニウム合金複合材料の高速超塑性

A SiCp/7075 aluminum alloy composite has been fabricated by a vortex method followed by squeeze casting, extrusion and rolling. The composites were hot rolled to the total rolling reduction of about 94% at temperatures between 573 K to 773 K and at a rolling strain per pass of 0.10. Superplastic characteristics such as microstructure and apparent activation energy were compared with these of the composites made by other processes in order to clarify the superplastic deformation mechanism. Fine grain size of about 1 μm was attained in the composite rolled at a temperature of 573 K and at the strain per pass of 0.1. In the case of rolling at 573 K, the composite obtained exhibited high strain rate superplasticity with a maximum elongation of about 230% at strain rate of 7 × 10−1 s−1 and at 798 K. Plots between e1/n and σ showed linear relation when exponent of n=2 was assumed. Threshold stress obtained from the linear relations were largely dependent on the testing temperature. Apparent activation energy determined from relationship between strain rate and testing temperatures was 244 kJ/mol, which was smaller than that for the powder metallurgical and mechanically alloyed aluminum composites. It seems that there is no substantial difference of high strain rate superplastic mechanism between the composite fabricated by a vortex method and powder metallurgical aluminum alloy composites.

A lot grouping algorithm for a continuous slab caster in an integrated steel mill

This paper discusses a lot grouping problem for a continuous slab caster in an integrated steel mill. Molten steel called 'charge' is transported to the continuous caster to be cast as the elongated rectangular solid steel pieces called 'slabs' of various sizes and metallurgical compositions. In order to enhance the productivity of the continuous caster, it is preferable to group as many charges as possible to form the cast. However, at the same time, lot grouping must be performed in compliance with several operational constraints as well as technological limitations of the continuous caster. The problem is formulated as an integer programming model, and it is shown that the problem is NP-complete. Hence, an efficient heuristic algorithm is developed to solve the problem by employing the column generation approach combined with a simple round-off scheme. In order to evaluate the performance of the proposed heuristic, the computation experiment is performed, and it shows that the proposed heuristic is quite satisfactory in practice.

Friction and wear behavior of CuFe3Al powder metallurgical composites in dry sliding

The dry sliding wear behaviour of unreinforced Cu alloy and on CuFe3Al composites fabricated by a powder metallurgy technique was tested on a block-on-ring test machine. The effects of the contact pressure and the sliding speed on the wear behavior of CuFe3Al composites and wear mechanisms during dry sliding were investigated. The worn surfaces were examined by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). It was found that the coefficients of friction for the CuFe3Al composites were approximately independent of the contact pressure and the sliding speed variation. With increasing volume fraction of Fe3Al particle, wear resistance of the composites increased at lower contact pressures but not at higher contact pressures, and the coefficients of friction slightly decreased. Because of formation of a protective oxide film on the sliding surface of the specimen at a low contact pressure and high sliding speed, and increase in the work-hardening rate in the subsurface layer of the wear specimen, the wear rate of CuFe3Al composites decreased with the sliding speed.