Remelting Technology Research Articles

A preliminary exploration on improving the solidification quality of electroslag ingot based on laboratory scale experiment

ABSTRACT One of the most important characteristics for electroslag remelting technology is that it can improve the solidification structure of metal. However, with the increase of mould diameter, the cooling effect of mould deteriorates, and the solidification quality of the ingot becomes poor, which is more obvious for large and high-alloy electroslag ingots. Therefore, it is necessary to further develop electroslag technologies to excite the potential of electroslag remelting. In this paper, the principle and practical effect of three technologies, i.e. electroslag remelting with mould rotation, electroslag remelting with ultrasonic vibration, electroslag remelting with electromagnetic stirring, are analyzed in detail. The results show that these technologies can effectively improve the solidification structure of electroslag ingot, and have a good application prospect. It is worth noting that the above technologies and its effects are only obtained under experimental conditions. For industrial application, the process parameters must be carefully selected.

Elimination of Primary NbC Carbides in HSLA Steels for Oil Industry Tubular Goods

Two high-strength low-alloyed steels alloyed with various Nb contents were prepared using continuous casting (CC) technology. In the round Steel 30Nb CC billet, it was the segregation of C and Nb in the central equiaxed zone that promoted the precipitation of primary NbC carbides at grain boundaries. After processing into seamless tubes, micron-sized primary NbC carbides were located in the middle of the segregation bands, surrounded by many nano-sized NbC carbides formed during the post-solidification cooling and/or hot-piercing rolling. Even when the Nb content was decreased down to 0.006 wt.%, there were still coarse primary NbC carbides in the segregation bands. However, no primary NbC carbide was found in the round Steel 30Nb billet prepared using the electroslag remelting technology. Therefore, this study revealed that a rapid solidification rate was relatively effective in eliminating primary NbC carbides compared with merely decreasing the Nb content.

Effect of laser remelting on the surface characteristics of 316L stainless steel fabricated via directed energy deposition

Herein, laser remelting (LRM) technology was adopted for the stainless steel 316L deposited using the directed energy deposition (DED) process. We focused on examining the scanning direction, laser power, and overlap, which are the main parameters of LRM, and changes in the surface characteristics after LRM. The LRM could remove the traces of the spatter, unmelted powder, and deposited tracks remaining on the DEDed surface. Moreover, overlap was the major factor affecting the surface roughness and waviness. The roughness and waviness of the LRM-treated surface decreased as the overlap increased. An interaction was observed between the laser power and overlap in terms of the surface roughness, and when the laser power was high and the overlap was large, the surface roughness was low. Furthermore, the laser power of 1200 W transferred the excess energy to the surface, reducing the surface improvement. After performing LRM, the thermodynamically unstable crystal grains recrystallized. From the X-ray diffraction results, face-centered cubic and body-centered cubic phases were observed; however, no difference was observed in the phase fraction ratio before and after the LRM treatment. Regarding residual stress measurements, no obvious effect was observed on the removal of tensile residual stress formed on the as-prepared surface. For this reason, the change in hardness after LRM was not significant (increased by 10.7%). However, the costs of postprocessing, such as machining and grinding, can be partially reduced using LRM after DED processing.

Microstructure and corrosion properties of laser remelted CrFeCoNi and CrMnFeCoNi high entropy alloys coatings

CrFeCoNi and CrMnFeCoNi coatings were prepared using laser remelting technology. The microstructure and phase composition of coatings were investigated. X-ray diffraction (XRD) results indicated that CrFeCoNi and CrMnFeCoNi coatings presented face-centered cubic structure. Electrochemical measurements were used to reveal the corrosion behavior of coatings. Results showed that CrFeCoNi coating exhibited lower corrosion current density, lower passive current density and higher charge transfer resistance than CrMnFeCoNi coating in H2SO4 solution (0.5 mol/L). This indicated that CrFeCoNi coating possessed higher corrosion resistance. Mott–Schottky analysis revealed that the passive film formed in CrFeCoNi coating possessed lower donor density value in contrast with that of CrMnFeCoNi coating, suggesting that CrFeCoNi coating formed a more protective passive film. The corrosion mechanisms of coatings were also revealed.

Surface modification for AlCoCrFeNi2.1 eutectic high-entropy alloy via laser remelting technology and subsequent aging heat treatment

Eutectic high-entropy alloys (EHEAs) are a class of prospective structural material in advanced engineering applications due to their excellent mechanical properties and castability. However, few researchers focused on the surface modification of these EHEAs. This study aimed to propose an effective method combining laser remelting and heat treatment to modify the surface of classical AlCoCrFeNi2.1 EHEA. After surface modification, the surface microhardness of the EHEA increased by 59%, and the average friction coefficient and wear rate decreased by 26% and 68%, respectively. The improved performance was mainly attributed to the decrease in lamellar spacing between face-centered cubic (FCC)/body-centered cubic (BCC) (B2) and coherent precipitation of nanoparticles in both FCC and B2 phases. A semi-empirical model was built to estimate the contribution of lamellar spacing to microhardness. The method and model might be applied to modify the surface properties of other EHEAs with lamellar structures.

Influence of Plasma Transferred Arc Remelting on Microstructure and Properties of PTAW-Deposited Ni-Based Overlay Coating

Although overlay coatings deposited via plasma transferred arc welding (PTAW) can effectively prolong the service life and improve the performance of components, cracks and pores tend to occur in the high-hardness and wear-resistant coating during the deposition process. Further treatment is thus necessary to improve the coating quality. Herein, PTAW-deposited Ni-based overlay coating was remelted using plasma transferred arc (PTA) under different remelting currents (RCs). The microstructure and phase composition of the coatings were investigated via metallographic microscopy and x-ray diffraction. The hardness, surface quality, and wear resistance of the coatings were also tested. The results show that PTA remelting could effectively eliminate the defects and improve the coating properties when the RC was controlled within a given interval (100-120 A). The type and content of the hard phase in the remelted coating were increased to enhance the microhardness and wear resistance. However, remelting with excessive currents resulted in the agglomeration and growth of the hard phases, which negatively affected the coating hardness and wear resistance. The proper use of PTA remelting technology to treat PTAW-deposited overlay coating is an effective approach for eliminating the coating defects and enhancing the coating properties.

Research of process factors increasing metal yield during aluminum waste remelting

The article presents the results of research determining the most effective technologies for increasing metal yield in the processing of aluminum-containing waste. In particular, peculiarities of the processes of melting aluminum alloys were analyzed using complex methods of furnace and off-furnace processing of charge material containing an increased amount of shovelling scrap and swarf. Studies on the impact of charge preparation and aluminum remelting technology were carried out in SAT-0,16 and IAT-0,4 furnaces on the АК12М2 alloy. Experiments proved that batchwise loading 20 kg of swarf briquette preheated to 300–400 °C into the SAT-0,16 furnace with the addition of flux (composition: NaCl – 50 %; KCl –35 %, Na3AlF6 – 15 %) in the amount of 3 % of total metal mass is the most efficient technology. This technology makes it possible to achieve a metal yield of about 94 %. The study of the remelting technology influence on IAT-0,4 furnace metal yield showed that the greatest effect can be obtained in case of furnace charge (95 kg swarf briquette) by batches of 2 kg into the 7 kg liquid bath with modifier flux (composition: NaCl – 62 %; KCl – 13 %, NaF – 25 %) added in the amount of 2 % from the total metal mass. This technology provides up to 93.5 % of metal yield. Data from 10 series of 5–9 melts were also analyzed with the comparison of metal yield results depending on the mass of briquetted swarf charged into the furnace. A histogram of the change in the porosity of AK12M2 and AK9 samples depending on the content of swarf in the charge (from 0 to 45 %) during remelting. It was found that an increase in the content of swarf in the charge, all other things being equal, leads to an increase in the average porosity score, which indicates the need for additional refining of such melts.

Effect of Laser Remelting on Cladding Layer of Inconel 718 Superalloy Formed by Laser Metal Deposition.

The brittle phase (Laves) of Inconel 718 parts formed by laser metal deposition (LMD) represents a bottleneck of the engineering applications. In order to investigate effectiveness of laser remelting (LR) technology on suppressing the formation of Laves phase, different laser scanning speeds of the LR process were adopted to build and remelt the single-pass cladding layers. The evolution of phase composition, microstructural morphology, and hardness of the LMD and LMD + LR specimens were analyzed. The experimental results show that different laser scanning speeds can obviously change the microstructural evolutions, Laves phase, and hardness. A low laser scanning speed (360 mm/min) made columnar dendrite uninterruptedly grow from the bottom to the top of the cladding layer. A high laser scanning speed (1320 mm/min) has a significant effect on refining Laves phase and reducing Nb segregation. When the laser scanning speed of LR process is equal to that of LMD, the cladding layers can be completely remelted and the content of Laves phase of the LMD + LR layer is 22.4% lower than that of the LMD layer. As the laser scanning speed increases from 360 to 1320 mm/min, the mean primary dendrite arm spacing (PDAS) values of the remelting area decrease from 6.35 to 3.28 μm gradually. In addition, the low content of Laves phase and porosity contribute to the growth of average hardness. However, the laser scanning speed has a little effect on the average hardness and the maximum average hardness difference of the LMD and LMD + LR layers is only 12.4 HV.

Investigation into the Effect of Manufacturing Technology on the Fracture Toughness and Durability of Steam Pipes Made of 10Kh9MFB-Sh Steel

Notched sample modeling was used to demonstrate effect of technology used for manufacturing pipes from steel 10Kh9MFB-Sh (piercing-broaching or electroslag remelting) on metal fracture toughness under creep conditions of 600°C at subcritical and avalanche stages of destruction. According to the subcritical crack growth and metal fracture toughness resistance determined on the samples, the lifespan of pipes having initial defects was evaluated. Calculations were carried out for pipes of two types including a hot reheat (HRH) steam line operating under a pressure of 4.1 MPa and a main steam (MS) line operating under a pressure of 14.0 MPa. Taking into account the obtained characteristics of fracture toughness, the use of electroslag remelting technology was shown to provide a durability of about 3 times that of piercing-broaching approaches. Differences in the pressure level and wall thickness shown to result in a tenfold increase in the durability of the HRH and MS steam pipelines at 600°C justify a different cracking risk classification, which should be taken into account in conducting operational monitoring.

The Methodology Development for Improving Energy Utilization and Reducing Fluoride Pollution of the Electroslag Remelting Process: A Review

Traditional electroslag remelting (ESR) technology using the slag with a high CaF2 content is faced with a high specific power consumption and fluoride pollution. Under double pressure, it is therefore very important to have a good understanding of the ESR process. The energy utilization, η, of the ESR depends on both the electrical, ηE, and thermal efficiency, ηH. Tailoring slag composition is one of the useful techniques to enhance energy utilization, because slag is very important to generate Joule heat for melting electrodes, control horizontal heat transfer, and maintain uniform distribution of alloy elements from the bottom to top of the remelted ingots in the ESR process. Therefore, herein, the aim is to review the effects of slag composition, especially CaF2 content, and temperature on the electrical conductivity and thermal conductivity, which further influence the heat balance during the ESR process. The volatilization mechanism of the liquid fluoride‐containing slag at an elevated temperature is introduced from the perspective of thermodynamics and kinetics. Meanwhile, some of the recent advances and technology improvements in energy utilization and productivity enhancements for the ESR process are summarized, which provide benefits to achieve sustainable development for the ESR process.

Failure Behaviours of Steel Projectiles with Localised Melting Against Armour Plates

The surface remelting technology of high energy beam can locally weaken the case for controlled fragmentation, which may affect the survivability of the impacting projectiles. Failure behaviours of steel projectiles with melted layers grid normally perforating armour plates was investigated. The results reveal that shear fracture mainly occurs in the nose region of projectiles due to high loading, and the melting zone of projectiles can keep integrity with no damage, which means the survivability of projectile can be assured. Furthermore, an analytical model was proposed to the structural analysis of projectile, which is in accordance with the test results.

Investigation on Band Segregate Formation during the Electroslag Remelting of H13 Die Steel

Band segregation has been found in the H13 die steel produced by the electroslag remelting (ESR) technology. Chemical and metallographic studies have been carried out on a one ton ESR ingot of H13 die steel, so as to understand the formation mechanism of the band segregation. The results indicate that the T.O content and S content decreased because of cleanliness improvement of ESR process. Transverse macrosegregation of S content decreased after ESR. The overall removal ratio of the inclusion is around 65.8%. The original complex inclusions would be modified to the CaO·Al2O3 inclusions. Al2O3 and MnS inclusions can be found after ESR. Both of Al2O3 and MnS inclusions were found to be the core of primary carbides. The net like structure in ESR ingot and banded structure in the forged steel were observed. V, Mo, Cr and S are rich in the segregation areas of ESR ingot. Besides, black and white segregation bands can be observed on the forged steel samples after etching. Uneven distribution of carbides rich in V, Mo and Cr was observed in banded structure.

INFLUENCE OF CONSUMABLE ELECTRODE ROTATION ON ANISOTROPY OF PROPERTIES OF THE BILLET OBTAINED BY ELECTROSLAG REMELTING

The article presents theoretical substantiation of the influence of electroslag remelting technology with rotation of consumable electrode on physicomechanical properties of the formed casting (billet). The technology of electroslag remelting with rotation of consumable electrode around its own axis leads to formation of upward flow of heat in the slag bath, making hydrodynamic environment in mold more rational from the point of using generated heat. During rotation of consumable electrode, centrifugal forces act on liquid metal film formed at the end of the electrode, providing radial flow of molten metal droplets. Subsequent separation occurs from the outer perimeter of electrode. Thus, drops of electrode metal fall into the metal bath closer to the wall of the mold, aligning temperature front of the bath. Decrease in temperature gradient of bath over the cross section leads to a flatter crystallization front. Studied technology of electroslag remelting with rotation of consumable electrode should have an impact on physical and mechanical properties of resulting casting (billet). In order to establish effect of rotation of consumable electrode during electroslag remelting on properties of metal obtained, experimental remelting was carried out. The article presents data on experimental electroslag remelting of electrodes of 20Kh13 grade steel using various technologies at A-550 unit. In course of experiment, influence of rotation technology of consumable electrode on conditions of remelting process, billet crystallization, changes in mechanical and physical properties was established. The influence of remelting method on complex properties of resulting billet was analyzed. As the main research tool, processing of the obtained data on microhardness, density, dendritic cell size of experimental samples was used. Analysis of the research results of billets in transverse direction showed an increase in microhardness uniformity in implementation of electroslag remelting technology with rotation of consumable electrode along the course of smelting. It is also shown that use of the rotation technology reduces size of dendritic cell of billet and increases density of the ingot formed in comparison with traditional technology without rotating electrode.

Microstructure and performance of the laser melted aluminum bronze layers with and without using activator

In the present research, the surface-melted aluminum bronze were manufactured by laser remelting technology. The microstructure and properties of the melted layers with and without using activator were investigated. With increasing laser power, the width and depth of the melted layer increased, and the grain size of the melted layer became coarser due to the higher heat input and larger molten pool volume. Under the same conditions (i.e. laser power of 1000 W), the width and depth of the melted layer could be reduced and increased, respectively, with the use of the activator. In particular, the depth of melted layer increased by nearly 50%. Furthermore, to obtain the same penetration of the melted layer, the addition of the activator could reduce the heat input, which led to the decrease of grain size. The relatively small grain size and high dislocation density could improve the hardness and tribological behavior of the melted layers.

Electroslag Remelting Technology for Contemporary Engineering. Retrospection and New Possibilities

New methods are developed for managing the physical chemistry and structural uniformity of electroslag remelted (ESR) ingots with the aim of improving consumer properties for the most critical power generation objects, including atomic and heavy engineering, substantiation and practical verification of the principles of managing physicochemical, and thermophysical processes, approval of monitoring and control methods, and development on this basis of new areas for using ESR during manufacture of solid, hollow, and shaped ingots. Results of the work make it possible to the evaluate the ESR process afresh as an economic effective contemporary method for manufacture of high quality objects.

Electroslag Remelting as a Promising Direction for Producing Hollow and Shaped Objects of Steel 10Kh9MFB-Sh

Preparation of hollow and shaped billets using electroslag remelting (ESR) technology is a promising direction for preparatory manufacture of objects for thermal and atomic power generation, petrochemistry, engineering, and other branches of industry. One of the main factors of ESR determining metal quality is deoxidation and slag regime characteristics. Optimization of slag chemical composition choice of the type and consumption of deoxidizing agent are provided in laboratory experimental melts for solid and hollow ingots of high-chromium heat-resistant steel 10Kh9MFB-Sh. NPO TsNIITMASh together with Energomash (Chekhov) – ChZEM have developed a technology for producing high-quality shaped billets of a shut-off control fitting by ESR of steel 10Kh9MFB-Sh. Laboratory and pilot plant metal structures and properties are studied.

Study on antifriction mechanism of lubricating wear-resistant coating with parallel texture

Purpose – The purpose of this paper is to investigate the effects of parallel texturing coating on antifriction mechanism of lubricating wear-resistant coating. Design/methodology/approach – A KF301/WS2 lubricating wear-resisting coating was prepared on matrix material GCr15 by applying supersonic plasma spraying technology. On the basis of this sample, the KF301/WS2 modified coating with parallel pit-type texture was prepared by laser re-melting technology and a surface texturing technique. Their friction and wear behaviors were evaluated under ambient temperature, and the antifriction mechanism of two kinds of coatings were discussed. Findings – Results showed that parallel texture has a certain impact on the tribological properties of the coating. When friction and wear reach stable state, the value of the friction coefficient of conventional coating was 0.115, while that of parallel texturing coating was 0.09, the latter decreased by 21 per cent. When the friction and wear time was up to 4 hours, the wear loss of the conventional coating was 0.29 mg, while that of the parallel texturing coating was 0.13 mg, the latter decreased by 55 per cent. Originality/value – The tribological properties of parallel texturing coating were higher than conventional coating. That is because the change of three-body layer reduces the friction coefficient and the abrasive particles were collected by parallel texture, reducing the effects of debris.

Numerical Simulation of Electroslag Remelting Process of Hollow Ingot with T-shape Current Supplying Mold

A three dimensional quasi-steady state mathematical model of the slag bath and hollowingot has been established based on the newly developed electroslag remelting( ESR) technology for hollowingot manufacture. The electromagnetic, flowand temperature fields during the electroslag remelting hollowingot process with and without the current supplying mold( CSM)have been simulated using commercial software ANSYS. Computational results showed that the maximum current density and joule heat of the slag bath were obtained in the conductive section of T-shaped CSM,where the fluid flowvelocity was much faster and the temperature field of the slag bath was more uniform,and the metal pool shape was shallower. The CSMcan keep slag bath and metal pool temperature constantly during the exchange of electrodes,which avoided the rapid solidification of liquid metal near the mold wall to generated slag ditchs when the slag bath temperature drops rapidly. The solidification quality and surface quality of hollowingots were thus greatly improved.

Research on the tribological properties of a textured lubricating wear-resistant coating modified by nano-SiC at high temperature

Purpose – The purpose of this paper is to investigate the tribological properties of a textured lubricating wear-resistant coating modified by nano-SiC at a high temperature. Its aim is to explore the influence of a new composite method on the organisation and structure of sprayed coatings as well as the evolution rules governing their high-temperature tribological properties. Design/methodology/approach – A KF301/WS2 lubricating, wear-resisting, coating was prepared on matrix material GCr15 by applying supersonic plasma spraying technology. On the basis of this sample, using nano-SiC particles as a filler, the KF301/WS2 nano-modified coating with its round, pit-type texture was prepared by laser re-melting technology and a surface texturing technique. Two kinds of coating micro-organisations and structures were examined by scanning electron microscopy, and the tribological properties of both the modified and conventional coatings were studied at a high temperature. Findings – Results showed that nano-particles could effectively improve the coating micro-structure, and make the structure denser and more uniform, thus significantly increasing the wear resistance of the coating. When the friction and wear processes were stable, the friction coefficient decreased by 13 per cent, while the wear loss decreased by 45.9 per cent. Originality/value – This research concentrating on the study of the process and performance of coatings doped with nano-particles by laser re-melting incorporating simultaneous surface texturing, and studies of their high-temperature tribological properties. That is because applying nano-particle modification technology to the development of wear-resistant coatings, and by applying the nano-particles to such coatings by thermal spraying technology, they can achieve a modification of the coating which makes the structure denser and more uniform.

Properties of NiCrBSi coating, as sprayed and remelted by different technologies

The work is focused on the evaluation of mechanical properties of thermally sprayed NiCrBSi coatings, as-sprayed and further thermally post-treated by four different technologies (flame, furnace, electric resistance and high power laser remelting). The evaluation addresses specifically the coatings microstructure, hardness, modulus of elasticity, wear resistance and friction behavior. As a result of thermal post-treatment with all four used remelting technologies, the successful elimination of splat boundaries and decrease of coatings porosity were achieved. The difference between used remelting technologies was observed in the amount of dilution between coatings and substrate material, resulting in a decrease of measured Vickers microhardness and surface hardness and causing gradual changes of instrumented hardness and modulus of elasticity. The remelting enhanced the coating cohesion, which led to an increase of the abrasive wear resistance and corrosion resistance, but has low influence on the sliding wear behavior, irrespective of the used remelting technology.