Intermediate Heat Treatment Research Articles

Microstructure characteristics and properties of yttrium-bearing 9Cr ferritic-martensitic steel cladding tubes

Thin wall cladding tubes of yttrium-bearing 9Cr ferritic-martensitic steel have been fabricated by cold-rolling process, with the final dimensions of 6 mm outer diameter, 0.5 mm thickness and 3 m length. The changes of microstructure of hot-rolled plate, forged rod and the final tubes were attributed to the cold-rolling process and the intermediate heat treatment. Mechanical properties were tested from room temperature to 600 °C. The final tubes showed the strength level between the traditional ferritic-martensitic steel and the metallurgy alloyed oxide dispersion strengthened steel. It was also found that the degradation of ductility at 400 °C was related to the dynamic strain ageing (DSA) effect. At last, ultra-sound test, flattening test and flaring test were carried out to evaluated the qualities of the final tubes.

Effect of ECAP on Change in Microstructure and Critical Current Density of Low Temperature Super-Conducting Monowire

The critical current density (Jc), which is a major performance parameter of low temperature superconducting Nb-46.5 wt%Ti wire, can be improved by uniformly dispersed fine α-Ti precipitates since they serve as a flux pinning center. The high volume fraction of α-Ti precipitates at grain boundary intersections can be achieved by repetitive large deformation and intermediate heat treatments. For this aim, we investigated effect of severe plastic deformation of Nb-46.5 wt%Ti billet on the changes in microstructure and Jc by assigning equal channel angular process (ECAP) followed by groove rolling and drawing. In addition, intermediate heat treatments with different heating condition and holding time after each process were assigned to precipitate the fine α-Ti. It was observed that the curled flow lines like shear bands with the highly dense dislocations were formed after ECAP leading to recrystallization and the high volume fraction of α-Ti after subsequent heat treatment. The additional plastic deformation by groove rolling and drawing increased the volume fraction of the α-Ti and the aspect ratio of its shape. As a result, the critical current density at the lower range of magnetic field was enhanced with increasing the number of ECAP pass.

Microstructure and properties of Cu–Fe deformation processed in-situ composite

Focus on the preparation process of Cu–14Fe deformation processed in-situ composite, by studying the stage of solidification, deformation, and heat treatment, the evolution of microstructure and the improvement of material properties have been investigated. The primary Fe phase distributed parallel on the longitudinal section and bent on the cross section under the shear stress, finally form the lamellar fiber structure in the deformation process. With cumulative cold deformation strain, the enhancement of tensile strength is attributed to the combined action of fiber strengthening, dislocation strengthening and precipitation strengthening. The strengthening mechanism of Cu–Fe deformation processed in-situ composites follows Hall-Petch relation with heavy strain. Due to the resistivity depends on the influence of impurity scattering and dislocation scattering, the intermediate heat treatment can improve conductivity effectively.

Enhanced strength and ductility of A356 alloy due to composite effect of near-rapid solidification and thermo-mechanical treatment

The coarse dendritic microstructure with non-uniform distribution of eutectic Si particles leads to poor ductility of A356 alloy, thus challenging the enhancement of mechanical properties through deformation at room temperature. Here, a new processing protocol was proposed by combining near-rapid solidification with two-step thermo-mechanical treatment (TMT). To significantly improve the ductility of the alloy, near-rapid solidification, in combination with first-step TMT including equal channel angular pressing (ECAP) and intermediate heat treatment, was applied to refine eutectic Si particles and make them evenly distributed in the matrix. On this basis, a high ultimate tensile strength ∼483 MPa, with relatively good elongation to failure ∼8.1% can be achieved by the subsequent ageing treatment and composite deformation (ECAP + cryorolling) of second-step TMT. The excellent combination of strength and ductility was mainly attributed to the synergistic effect of high density of dislocations, refined nanoscale Si particles and uniform distributed eutectic Si particles arising from this fabrication processing. This work provides a new idea for the preparation of high strength Al-Si cast aluminum alloy, so that the application of Al-Si cast alloy is promisingly expected to expand.

Hidden Potential of Cold Sheet Rolling

Symmetric rolling (SR) where the roll speeds are equal and rolling-drawing (RD) where the roll speed ratio is limiting are versions of general rolling (GR). An advantage of GR is in a greater number of independent control parameters than in SR and RD (three against two and one, respectively). In this regard, GR is more flexible, thus allowing rolling schedules that ensure a fuller utilization of equipment capabilities, a reduction in the number of passes or intermediate heat treatments, a reduction in the minimum possible thickness of the strip, etc. The developed mathematical model of GR, the program for optimizing the rolling schedules against various criteria, and its numerical implementation confirm these conclusions. If compared with SR, the efficiency of GR increases with increase in the friction coefficient and the diameter of the work rolls, decrease in the elastic characteristics of the rolls, expansion of the range of mill products, increase in the strength of the strip, and decrease in its thickness. When compared with RD, the situation is opposite. An analysis of the variation in the control parameters during passages shows that as the thickness of the strip increases (decreases), the rolling schedules of GR tend to those of SR (RD).

Medium carbon fully pearlitic steel: microstructures and properties after wire drawing

ABSTRACTIn the current work, fully pearlitic microstructure was initially developed in a medium carbon steel by isothermal holding at different temperatures. Subsequently, these samples were drawn in laboratory scale wire-drawing machine without any intermediate heat treatment. Microstructures and mechanical properties of as-heat-treated and heat-treated plus drawn samples were characterised. The results were also compared with some commercially produced steel. It was found that the new steel can offer a very good wire drawing behaviour. The steel possesses a good combination of strength and ductility along with a high-value torsion, bending and reverse bending properties after drawn condition as well.

Microstructural and Property Evolution of Continuous Columnar-Grained Polycrystalline Copper during Extreme Plastic Deformation at Room Temperature

An extreme extensibility with a true strain of 11.12 has been obtained for continuous columnar-grained (CCG) polycrystalline copper at room temperature, which was cold-drawn from a 10-mm-diameter as-cast rod into a 38.5-μm-diameter ultra-fine wire without any intermediate softening heat treatment. During the extreme plastic deformation, the ultimate tensile stress increased from 140 MPa for as-cast CCG copper to 525 MPa for the deformed sample at a true stain of 11.12, while the relative electrical conductivity maintained a high value of 97.6% IACS. On this basis, CCG copper is an excellent raw material for the fabrication of ultra-fine wires with both high strength and high electrical conductivity. The original columnar grains experienced grain subdivision and formed fibrous grains along the drawing direction with a fibrous longitudinal morphology and curly transverse microstructure at medium to high strain. The subdivision of the fibrous grains then went on as the extreme plastic deformation continued. Large amounts of strain-induced boundaries and microstructural refinement facilitated the storage of abundant glide dislocations created by extreme plastic deformation. Thus, extreme plastic extensibility can be achieved through continuous work hardening of CCG copper.

Effect of Intermediate Heat Treatment on the Formation and Structure of Superconducting Layers in Multifilamentary Nb<sub>3</sub>Sn- Based Wires

In the present study, the Nb3Sn-based multifilamentary wires with coupled Nb filaments have been investigated by SEM and TEM after various regimes of intermediate annealing including short high-temperature heat treatments and after two-staged diffusion annealing. The formation of some amount of pre-reacted Nb3Sn layers has been revealed in all the wires studied, and their amount depends on the wire diameter, temperature and duration of the intermediate heat treatment. The structure of final diffusion layers is also affected by the regimes of these preliminary treatments. This research enables the revealing of the optimal heat treatment schedules for the formation of most perfect nanocrystalline structure of superconducting layers ensuring the highest critical current densities.

Development and Introduction of Technology and Equipment for Multiple Drawing of Copper Alloy Thin-Walled Tube on a Long Movable Mandrel Without Intermediate Heat Treatment

Thin-walled and extremely thin-walled tubes made of copper alloys, i.e., brass grades L96, L68, L63, LANKMts, and the bronze grades BrOF6.5-0.15, BrOF4-0.25, are in great demand in the aircraft, shipbuilding, automotive, defense, diesel-locomotive building, and instrument-making industries. A promising manufacturing method is multiple drawing on a long movable mandrel without intermediate heat treatment due to such advantages as high total elongation ratios (λ = 3.0–6.0), simplicity of the equipment of the flow line, high productivity equal to 1200–1600 m/h, as well as good pipe surface quality and size precision. These advantages of the new method of manufacturing cold-deformed pipes make it possible to reduce the cyclic nature of manufacturing and processing costs. The work provides a methodological basis of theoretical analysis and design of rational routes for manufacturing colddeformed pipes by multiple deformation without intermediate heat treatment. As an example, the results are presented for calculation of three-fold drawing of thin-walled pipes made of brass grades L96, L68 and L63. Research results are used in the development of innovative technology for pipe manufacture from copper alloys at the PAO Revda Non-Ferrous Metal Processing Plant using a highly efficient three-fold drawing line on a long movable mandrel. One of the versions for line equipment layout is provided.

Effect of Processing Techniques on the Mechanical Property of New Zirconium Alloy Strip

In this paper, a typical new zirconium alloy (Zr-Sn-Nb system) was used as the research object. The zirconium alloy strip was prepared from a series of production processes from smelting. By optimizing the process of cold processing with the change of the deformation amount and the intermediate heat treatment, the mechanical properties of the zirconium alloy were studied by different processing. The results are as follows: (1) The mechanical properties of the new zirconium alloy have reached the mechanical properties of Zirlo alloy with the optimization of the alloy composition, and (2) The zirconium alloy can refine the grain strength by the control of deformation degree and annealing temperature during cold deformation. The larger of the cold deformation, the smaller the average of the grains and the higher the yield strength of the material. The yield strength of the material was decreased by cold rolling and annealing more than once; (3) The larger the cold rolling variable of the zirconium alloy in cold deformation, it is beneficial to the second phase to be fine, dispersed and uniformly distributed, thus improving the strength of the material.

Eccentric rotary swaging variants

Rotary swaging is an incremental cold forming process that changes beneath the geometry also the microstructure and mechanical properties of the workpiece. Especially a new process design with Eccentric Flat Shaped Dies (EFSD) influences both the kind and amount of stress and plastic strain and consequently the material structure, and hence the material and workpiece properties. Eccentric rotary swaging typically provides a helical material flow. According to the process parameters the microstructure features a typical eddy pattern with a spiral shaped grain orientation. The forming process can be carried out in one or more process steps. In a multistage process, it is possible to change the feed direction and, hence, the material flow helix direction. This approach can be used as a possibility to improve the homogeneity of the workpiece and material properties. In addition, for this aims an intermediate heat treatment in multistage forming operations could be realized. Following the goal of optimizing the final properties, the question arises how these mechanical and thermal treatments affect the material microstructure and the forming properties of the workpiece and how they interact. Experiments were conducted with austenitic stainless steel rods of grade AISI304. The effects of the varied feed direction, feed velocity and heat treatment between the forming operations are discussed.

Determination of Hardness and Other Mechanical Properties of Thin-Sheet TRIP Steel by Indenting

In this paper, we studied the microstructure and mechanical properties of thin-sheet TRIP steel VNS9-Sh obtained by cold rolling of a hot rolled sheet for several transitions with intermediate heat treatment and supplied in the form of a strip with a thickness of 250–260 μm. The structure of the TRIP steel is deformation martensite and metastable hardened austenite. On the basis of the average grain size (35 μm) and the strip thickness, the optimum loading of the Vickers pyramid equal to 1 kgf (9.81 N) was determined when determining the hardness. Under this load, the indent covers several grains of steel and the ratio of the tape thickness to the indent depth is at least 20, which excludes the influence of the substrate (the instrument stage or other equipment) on the hardness values. To evaluate other mechanical properties, a kinetic (instrumental) indentation by a spherical diamond indenter with a radius of 0.2 mm was used. A methodolgy for determining the normal elastic modulus, yield stress, and time resistance is proposed. It is shown that the maximum deviation of the values of the indicated mechanical characteristics found by instrumented indentation from the values of these characteristics determined by the sample tension test did not exceed ±7%.

Improved photoelectrochemical performance of molybdenum (Mo)-doped monoclinic bismuth vanadate with increasing donor concentration

Molybdenum (Mo)-doped Monoclinic Bismuth Vanadate (Mo-BiVO4; BVO) catalysts were fabricated via a simple dip coating method. We systematically studied the effect of Mo-doping with various concentration (1–5%) in BVO electrode through photoelectrochemical (PEC), Mott-Schottky and impedance measurement. Intermediate heat treatment and number of successive dip coating deposition were utilized to control the monoclinic crystallization and thickness of Mo-BVO photoanodes. Furthermore, the effect of Mo-doping in morphology, structure, chemical states and optical properties of the obtained electrodes were characterized by different physico-chemical and morphological methods BVO with 2% Mo doping (2% Mo-BVO) showed the best PEC performance, of about 15 times higher than that of the pure BVO. Improved charge carrier transport and optimized light absorption obtained upon Mo doping into the BVO crystal lattice while the monoclinic scheelite structure with small band-gap was retained. To understand the effect of Mo-doping, Mott Schottky and Impedance measurement carried out, in order to evaluate the donor concentration and conductivity of pure BVO and Mo-BVO. Interestingly, 2% Mo-BVO showed the maximum donor concentration (5.7E + 27) and minimum flat band potential (Vfb = −0.45) compared to other prepared electrodes. Furthermore, we attempt to discuss the improved PEC performance of Mo-BVO using high donor concentration, up-shifting of Fermi level and consequently facilitating electrons transport in Mo-BVO compared to pure BVO.

Experimental Measurement of Residual Stresses in Cr-Mo-V Steel Restrained Welds with High Thickness

Abstract This experimental work is focused on the residual stresses induced by multi-pass welding of thick components. Two samples were produced, inspired by the nozzle-vessel geometry, with Submerged Arc Welding buttwelding, performed according to the standard welding procedures employed by Belleli Energy CPE. The components were characterized by different sizes and groove positions. Measurements of residual stresses were carried out by hole drilling according to ASTM E837-13a, Standard Test Method for Determining Residual Stresses by the Hole-Drilling Strain-Gage Method, in different positions of the samples. The measurements were performed on welded, and Dehydrogenation Heat Treatment (350°C, 4h), and Intermediate Stress Relieving treatments. The obtained results allowed a discussion of the influence of the component size on the residual stresses and the effectiveness of an intermediate heat treatment for reducing the stress state.

Influence of thermomechanical process and Fe addition on microstructural evolution and properties of Cu-26 wt%Ag composite

We investigated the microstructure and mechanical properties of deformed Cu-26 wt%Ag alloy and Cu-26 wt%Ag-0.1 wt%Fe alloy superimposed by thermomechanical process. The addition of 0.1 wt% Fe into Cu-26 wt% alloy refined the eutectic lamella spacing and the spacing between Ag precipitates. Magnetization measurements of containing-Fe composites indicated that the transformation from γ-Fe to α-Fe was induced during cold deformation and the volume fraction of α-Fe increased as the strain increased. Intermediate heat treatments caused the precipitation of γ-Fe precipitates out of Cu matrix. The solid solution as well as addition for the Cu-Ag alloy with high Ag content was beneficial to the strength rather than the electrical conductivity. Although intermediate heat treatments (IHTs) improved electrical conductivity effectively, the strength of IHT samples was lower than that of solid-solution-treated samples.

A study on forming process of AA5083 alloy with an infrared local heat treatment

Although the demand of aluminum alloys has been increasing to reduce vehicle’s weight in automotive industries, the low formability of aluminum alloys has made a limit on industrial applications. This work presents an infrared ray (IR) local heat treatment in the purpose of improving formability of aluminum alloys. The concept of the IR local heat treatment is focusing IR rays on target areas where the level of plastic deformation reaches the fracture level. The local heat treatment employs the intermediate heat treatment scheme that is conducted between two stages, 1st forming and 2nd forming. In the 1st forming, the blank is deformed until a part of the blank reaches 15% strain. Then, the part is locally heat treated. After the heat treatment, the 2nd forming makes the heat treated blank match the target shape. Authors recently conducted this heat treatment with an IR local heating method to resolve the formability problem of an AA5083 alloy [1]. However, in the paper, the IR heat treatment was applied to only a linear heating shape. Neither the heat treatment for a curved shape nor local heating effect in temperature distribution was discussed in the paper. In this work, the IR heat treatment is studied in three points of view. The first is to shortly introduce the IR heat treatment in the purpose of improving formability with the AA5083 alloy. The second is studying the local heating effects in temperature distribution and application of a curved shape. Finally, an industrial application of tailgate is discussed with reduction of heating energy. The results show that this focused IR heating can improve formability with reducing heating energy for industrial applications.

Intermediate annealing and strong cube texture of Ni8W/Ni12W/Ni8W composite substrates

The deformation and recrystallization of Ni8W/Ni12W/Ni8W composite substrates by means of cold rolling and intermediate annealing have been studied. The work reveals the increase in the brass orientation fractions, accompanied by the decrease in the copper and cube orientation fractions during the deformation process. A typical brass-type rolling texture is obtained finally. To get the deeper understanding of the intermediate heat treatment effect at different levels of deformation and recrystallization, four intermediate anneals (i.e., 550 °C/120 min) were introduced at the rolling thickness of 4, 2, 1, and 0.5 mm, and 2, 1, 0.5, and 0.25 mm, respectively. The result shows that the transformation from the copper type to the brass type of the former deformation set occurs at 0.5 mm, while for the latter one, it is detected at 0.25 mm. Furthermore, the EBSD maps of the cross sections of the recovery samples reveal that the decrease of the shear structure and the increase of the copper, S and cube orientation are the main sources for promotion of the homogeneous deformation. This can enhance the formation of the copper-type deformation texture and hence finally promotes the formation of strong cube texture.

Evaluation of the impact of the natural seasoning process on post-machining deformation of thin-walled elements made of aluminium alloy EN AW-2024

The study attempts to evaluate the impact of short-term natural seasoning process on the state of post-machining deformations of thin-walled elements made of the EN AW-2024 aluminium alloy. Analyses were made of the impact of the technological history of the semi-finished product, in this case – the rolling direction of the plate (perpendicular and parallel to the feed direction) as well as high-performance machining strategies, such as High Speed Cutting (HSC) and High Performance Cutting (HPC) on the value of deformations of thin-walled samples, directly after machining and after seasoning. Application of natural seasoning at reducing deformations of thin-walled elements made of aluminium alloys may prove an alternative to the difficult intermediate heat treatment. The expected reduction of deformations is a result of reducing residual stresses in the material, in the course of the relaxation process. The dynamics of the natural relaxation is highly correlated with the properties of materials. The study includes an analysis of the effects of a short-term relaxation, accepted in industrial conditions (up to 1 month since the end of machining) for the EN AW-2024 alloy. If the proposed solution gives positive effects, it can bring measurable economic benefits in industrial applications. The study is completed with general and practical conclusions.

Effect of Sn Concentration in Bronze Matrix on the Pre-Reaction Formation of Nb3Sn Layers in Bronze-Processed Superconducting Strands of Different Design

The goal of this paper is to study and analyze the effect of Sn concentration (14% or 16%), the mode of Ti-doping and the shape of Nb filaments on the thickness of the “parasitic” layers of prereacted Nb 3Sn grains (formed before the diffusion annealing) in the ITER-type strands and strands for high field applications processed by bronze technology. The use of short (of total duration not more than 1 h) intermediate heat treatments at 500 °С does not allow avoiding the prereaction formation of Nb3Sn in all the samples under study. Sn concentration in bronze decreases by 1.5–2.0% after heat treatments compared to the initial state in all samples. In the samples with Ti-doped bronze matrix and coupled Nb filaments, the average thickness of “parasitic” layers is 112 nm in the case of 14% Sn in bronze and 140 nm for a bronze matrix with 16% Sn. In the sample with 16% Sn in matrix and extended Nb filaments of intricate shape the average thickness of prereacted layers reaches 200 nm. It is concluded that to minimize the parasitic layers formation the strands with high tin bronze matrix should be subjected to short intermediate heat treatments at temperatures lower than 500 °C.

Evaluation of numerical and experimental investigations on the hybrid sheet hydroforming process to produce a novel high-capacity engine oil pan

The engine oil pan is used for restraining pollutant and gathering greasing oil from the engine components’ surface which is significant for thermal dissipation and preventing deterioration of oil quality. The study intended to investigate and develop a hybrid sheet hydroforming process for fabricating an innovative high-capacity oil pan that has the characters of asymmetrical cavity depth and major lateral bulging. Firstly, a two-stage hydromechanical deep drawing (HMDD) process was accomplished, which included precedingly regional and eventually integral deep drawing assisted by fluid counter force. The finite element modeling (FEM) was employed to study the impact of the die fillet dimension as well as the loading routes on the formability of the preformed part. The limited drawing ratio can be enhanced from 2.34 to 2.77 for AISI 304 by HMDD. Hydro-bulging was subsequently investigated by the simulations accompanied by the relatively experimental verification. Both the simulated and experimental results showed that there is a remarkable influence of lubrication condition and intermediate heat treatment on the formability of the final part. The cracks occurred at the corners of the main bulging area can be alleviated by reduction of friction coefficient. Furthermore, wrinkles and cracks have been completely eliminated and the thinning ratio can be reduced to 31.8% for the final part, when intermediate heat treatment is additionally employed. It was concluded that the present hybrid sheet hydroforming process is feasible and sufficient to manufacture a sound engine oil pan without any defects through the optimization of the process parameters.