Casting Heat Research Articles

Підвищення тріщиностійкості чавунів з кулястим графітом та їх термічна обробка при виготовленні зносостійких виробів

Methods of achieving the maximum values of crack resistance of Spheroidal graphite cast irons (SGCI) due to the combination of strength of bainite with high plasticity of residual austenite (in the amount of 30-35%) are considered. The results of such studies are suitable for use, in particular, in the manufacture of teeth or crowns of buckets of excavators and other working bodies of mining, earthmoving or earth-moving machinery, as well as parts that function in extreme conditions. These data are comparable to the known results of work on increasing the wear resistance of SGCI for variable parts of agricultural machinery and transport. In addition to crack and wear resistance, the long-term performance and efficiency of the working organs depends on maintaining their pointed part or blade in a sharp condition. The creation of functional-gradient materials, which are characterized by the effect of self-sharpening during their operation and wear, is considered. This effect is proposed to be implemented through the use of gradient heat dissipation in the material of the sand mold, increasing these values by introducing a refrigerant near a specific surface of the casting to accelerate its cooling. For this, casting molds made of loose sand were used in the Lost Foam casting (LFC) process. The method of manufacturing metal working bodies is described on the example of casting by the LFC method of an excavator bucket tooth, it is proposed to obtain its gradient structure according to the regime of heat treatment of castings in a foundry mold due to intensive cooling of its given surface to increase its hardness. At the same time, such conditions were used for the construction and formation of the pattern cluster in the sand, which cause the cooling of the opposite surface to slow down with its lower hardness, which corresponds to the conditions of self-sharpening of the tooth under its operating conditions. Keywords: Spheroidal graphite cast iron, austempering, heat treatment, castings, austenite, Lost Foam casting, bainite.

Ізотермічне гартування залізовуглецевих сплавів, суміщене з їх виливанням

Isothermal hardening (Austempering) of iron-based alloys with medium and high carbon content, which creates a metallic structure called bainite, is used to increase the strength and impact toughness of the metal. The parts are heated to a temperature approximately 200-300 °C below the solidification temperature of the metal, then cooled (hardened) fairly quickly to the temperature of the beginning of the bainite transformation, avoiding the martensitic transformation, and kept for a time sufficient to obtain the given bainite microstructure. IG is particularly advantageous for castings from high-strength cast iron (HC), adding to the high foundry performance of the growth of the mechanical characteristics of this alloy to the level of steel strength at a lower cost, density and energy consumption of HC casting compared to steel. The article examines methods of heat treatment of castings removed in a hot austenitic state from a sand mold, as a type of heat treatment of iron-carbon alloys combined with their casting. For this, casting according to gasification models was used, in which, due to the high fluidity of the dry sand of the casting mold, it is not difficult to remove hot castings from the mold for tempering. A number of IG methods previously patented by the FTIMS Institute of the National Academy of Sciences of the Russian Academy of Sciences have been supplemented by a new method of such hardening in a dosed amount of water, taking into account the effect of its film boiling. The new method includes the calculation of the optimal mass of quenching liquid - water with the aim of heating this mass of water to its boiling point at the time of cooling of the casting to the given temperature of the bainite transformation of the metal. The method saves the quenching liquid, simplifies the control of the duration of cooling, during which it allows the transportation of castings between the foundry and heat-treatment sections, which, in general, saves time, energy resources and the area of the workshop for obtaining heat-treated castings. Keywords: isothermal hardening, heat treatment, castings, austenite, lost foam casting.

Effect of boron addition on the microstructure and wear resistance of laser beam directed energy deposited high chromium white irons

There is a demand for alloys produced by laser beam directed laser deposition (DED-LB) with better wear resistance than the traditionally manufactured alloys. In DED-LB of high chromium white iron (HCWI), the refined carbides at the micron scale can lead to inferior wear performance than the cast alloy of the same composition. In this study, various concentrations of FeB powder were mixed with HCWI powder and produced by DED-LB. The microstructural evolution and its relationship with the wear resistance in high stress abrasion wear test were studied. The B addition is a C equivalent element in HCWI, which can change the composition from hypoeutectic to hypereutectic. In the hypereutectic alloys, B promotes hard phases in the form of M7(C,B)3 and M3(C,B) (M mainly represents Cr and Fe). With the B additions, the volume loss in high stress wear testing is reduced due to the increase in the fraction of the hard phases and their coarsening. With the predominantly austenitic matrix, the alloy with 1.09 wt % B consisting of near 60 vol% hard phases showed a superior wear performance than the heat-treated cast alloy. This was attributed to the microstructure in the contact. The high fraction of refined hard phases and the relatively ductile austenitic matrix (compared with the martensitic matrix) work synergistically, showing a worn surface of plastic deformation without brittle spalling and pitting.

The Microstructure and Magnetic Properties of a Soft Magnetic Fe-12Al Alloy Additively Manufactured via Laser Powder Bed Fusion (L-PBF)

Soft magnetic Fe-Al alloys have been a subject of research in the past. However, they never saw the same reception in technical applications as the Fe-Si or Fe-Ni alloys, which is, to some extent, due to a low ductility level and difficulties in manufacturing. Additive manufacturing (AM) technology could be a way to avoid issues in conventional manufacturing and produce soft magnetic components from these alloys, as has already been shown with similarly brittle Fe-Si alloys. While AM has already been applied to certain Fe-Al alloys, no magnetic properties of AM Fe-Al alloys have been reported in the literature so far. Therefore, in this work, a Fe-12Al alloy was additively manufactured through laser powder bed fusion (L-PBF) and characterized regarding its microstructure and magnetic properties. A comparison was made with the materials produced by casting and rolling, prepared from melts with an identical chemical composition. In order to improve the magnetic properties, a heat treatment at a higher temperature (1300 °C) than typically applied for conventionally manufactured materials (850–1150 °C) is proposed for the AM material. The specially heat-treated AM material reached values (HC: 11.3 A/m; µmax: 13.1 × 103) that were close to the heat-treated cast material (HC: 12.4 A/m; µmax: 20.3 × 103). While the DC magnetic values of hot- and cold-rolled materials (HC: 3.2 to 4.1 A/m; µmax: 36.6 to 40.4 × 103) were not met, the AM material actually showed fewer losses than the rolled material under AC conditions. One explanation for this effect can be domain refinement effects. This study shows that it is possible to additively manufacture Fe-Al alloys with good soft magnetic behavior. With optimized manufacturing and post-processing, further improvements of the magnetic properties of AM L-PBF Fe-12Al may still be possible.

A comparative study on the microstructure, mechanical properties, wear and corrosion behaviors of SS 316 austenitic stainless steels manufactured by casting and WAAM technologies

Replacing the traditional casting method with wire arc additive manufacturing (WAAM) to produce complex shaped parts will lead to using cost-effective technology even for challenging engineering applications depending on their geometry and number of the parts to be produced. This work performed a comparative study on the stainless steel 316 parts manufactured by WAAM and sand casting to reveal the microstructural, mechanical, wear, and corrosion behaviors. The WAAM components were manufactured using three different cooling dwell times and compared in terms of microstructures with the as-cast and heat-treated cast parts to reveal the properties of the WAAM parts. It was concluded that WAAM is a viable engineering alternative to the casting technology. Results showed that the WAAM and cast parts revealed similar microstructures, including delta ferrite and austenite phases, but the cast parts had a coarser grain and lower amount of delta ferrite due to slower cooling during the solidification. The yield and tensile strength of WAAM parts showed an increasing trend with the increase in dwell time, and on average, their yield strength was ∼1.5 times higher than in cast parts due to the smaller grains and more elevated δ-ferrite content resulting from rapid cooling. Furthermore, the greatest wear resistance was obtained in the cast parts after solution annealing heat treatment followed by water quenching. In contrast the highest corrosion resistance was obtained from WAAM parts produced using a dwell time of 120 sec. In conclusion, WAAM technology can be an excellent alternative to casting technology for producing stainless-steel parts with optimized process parameters.

Characterization of heat-treated chitosan cast films and their antimicrobial activity on the growth of natural flora of pasteurized milk

This research aimed to evaluate the physicochemical and biocidal properties of chitosan films obtained through the solvent casting method using two different molecular weights, and thermally treated for an extended time (3 weeks) at 70 °C under vacuum condition (RH 0 %). The effect of storage time (for 30 and 180 days) under ambient conditions (23 °C and RH 40 %) on the properties of heat-treated cast films and their biocidal effectiveness was also assessed. FTIR-ATR, TGA and XRD of resulting films were analyzed to explore the dependency of antibacterial performance on the alteration in molecular and chemical structure. The results demonstrated that the solubility of treated films at 70 °C was proportionally reduced, resulting from the reduction of protonated amines and an increase in crystallinity. Likewise, increasing storage time led to a significant lowering in the solubilization of cast films. It was found that the solubilized fraction of chitosan cast films is the active fraction with the biocide behavior that can act against bacteria. In addition, the effectiveness of migrated chitosan was examined against the natural flora of pasteurized milk, such as Paenibacillus and Pseudomonas fluorescens. The results showed that cast films obtained from chitosan with lower molecular weight caused a reduction in the total count of viable cells without a significant effect on the properties of milk.

Using the Method of Measuring the Microhardness of Different Zones of Welded Joints to Assess the Strength Properties

Corrosion-resistant steels with a high nitrogen content are used as structural materials for high-load critical products. Their high strength and ductility, austenite stability, corrosion and wear resistance are highly relevant for parts and structures operating in marine environments. In addition to a high level of operational properties, they are subject to the requirement of manufacturability, including weldability. Welding of such steels, due to the high concentration of nitrogen, is a complex technological operation, and it is necessary to avoid the appearance of gas nitrogen pores, hot cracks, a sharp drop in mechanical properties in any zones of welded joint. In this work, we investigated the regularities of changes in microhardness in different zones of welded joints (base metal, heat-affected zone of the weld, fusion zone and weld metal) of two grades of austenitic Cr-Ni-Mn-Mo-N high-strength steels with a high equilibrium nitrogen content (up to 0.6%). They fundamentally differ in the structural state of the base metal being welded: deformed (hot-rolled sheet) and cast (metal of a heat-treated cast plate). It has been shown that despite the use of different welding methods (MIG, MMA and TIG), the options for welding fillers and the type of weld groove, there are general patterns for each of the two types of base metal. The work also evaluated the correlation between these regularities and such basic characteristics of the structure and properties of rolled and cast metal of welded joints, such as the grain size and values ​​of the yield stress.

On the Issue of Casting Copper Alloys in Chill Mold

The article describes the features of the process of casting copper alloys in the chill mold. The main properties of alloys depending on the content of various components in it are revealed. The main negative factors leading to a decrease in the casting properties of the process, as well as the quality of the castings obtained, are indicated. Based on the information and analytical review, possible options for improving the efficiency of the process are identified. These include: alloying, refining, modification, the use of various one-time coatings, the use of heat treatment of castings. The use of hard coatings applied by the method of physical vapor deposition in order to increase the efficiency of the entire casting process is proposed.

Heat Treatment of Cast and Cold Rolled Al–Yb and Al–Mn–Yb–Zr Alloys

The microstructure, electrical properties and microhardness of as-cast and cold rolled AlYb and AlMnYbZr alloys were investigated. The addition of Mn, Yb and Zr has a positive influence on grain size. A deformed structure of the grains with no changes of their size was observed after cold rolling. The Al3Yb particles coherent with the matrix were observed in the AlYb alloys. The size of the particles was about 20 nm in the initial state; after isochronal treatment up to 540 °C the particles coarsen, and their number density was lower. The deformation has a massive effect on the microhardness behavior until treatment at 390 °C, after which the difference in microhardness changes between as-cast and cold rolled alloys disappeared. Relative resistivity changes show a large decrease in the temperature interval of 330–540 °C which is probably caused by a combination of recovery of dislocations and precipitation of the Al3(Yb,Zr) particles. Precipitation hardening was observed between 100 and 450 °C in the AlYb alloy after ageing at 625 °C/24 h and between 330 and 570 °C in the AlMnYbZr alloy after ageing at 625 °C/24 h.

The Influence of Load on Dry and Tribocorrosive Sliding of AISI 4330 and 15-5PH against Cast Iron

Environmental conditions, testing variables, and material properties significantly influence the sliding wear behavior of all tribosystems. Such parameters affect the mechanism of wear occurring, govern how the wear scar will be categorized, and control whether transitions occur throughout the test. The present study investigated this through sliding wear tests of AISI 4330, 15-5PH, and heat-treated cast iron in the dry and NaCl regime. Loads of 2, 4, and 6 kg were applied to the cast iron pin in both regimes, with the volume loss results, wear scar morphology, and microstructural evolution analyzed. It was found that the AISI 4330 and 15-5PH discs produced higher volume losses in the dry regime than in the NaCl regime, indicating that the solution had a beneficial effect rather than a detrimental effect versus the dry tribosystem. Beneficial oxidative wear allowed for AISI 4330 to lose less than 15-5PH in the dry regime, with their respective cast iron pins following the same result. Microstructurally, the 15-5PH wear scar cross sections exhibited a mechanically mixed surface layer of refined material mixed with oxides above a layer of grains distorted in the direction of sliding. This highlighted the significant difference between the wear of 15-5PH and AISI 4330, because the latter did not exhibit any areas of interest.

EFFECT OF CARBON CONTENT ON MICROSTRUCTURE EVOLUTION AND PROPERTIES OF HYPEREUTECTIC HIGH CHROMIUM CAST IRON

This study is to reveal the influence of the amount of carbon content on the microstructure evolution, mechanical properties, and wear properties of Hypereutectic High Chromium Cast Iron (HHCCI). The results indicated that the carbon content plays a key role in the regulation of carbides in the cast iron microstructure. As the amount of carbon content rises, the primary carbides in the cast iron microstructure become apparently coarser, and the volume fraction of carbides gradually increases. The carbide volume fraction reaches 62% when the carbon content is 5[Formula: see text]wt.%. When the value of the carbon content increases, the accumulation and growth of eutectic carbides in the heat-treated cast iron become more and more obvious. After heat treatment, a large number of secondary carbides will be precipitated from the austenite matrix, in the form of fine particles or short rods, with a dispersed distribution. The macroscopic hardness of HHCCI has increased. When the carbon content is 3.5[Formula: see text]wt.%, the macroscopic hardness is 61.2 HRC, and when the carbon content becomes 5[Formula: see text]wt.%, it reaches 64.3 HRC. The wear resistance of HHCCI increases with the value of the carbon content increases. When the carbon content was increased from 3.5[Formula: see text]wt.% to 5.0[Formula: see text]wt.%, the wear resistance of the material increased by 85.7%. The wear of HHCCI is mainly adhesive wear and fatigue wear, and the wear morphology is mainly spalling pits and wear debris.

Estimating the Stress-Strain State of Roll by Temperature Gradient in the Course of its Heat Treatment

The paper considers the issue of mathematical simulating the stress-strain state of a roll in the course of its heat treatment. It is shown that a sound heat treatment schedule affects significantly the economic efficiency of a metallurgical enterprise. The mathematical apparatus is provided to estimate the thermal interaction in the casting-furnace system, based on which a program for calculating the thermal state of a roll during heat treatment has been developed. Using this program allows evaluating the thermal stresses occurring in a roll during the heat treatment cycle and reducing the risk of discontinuity in the roll cast billet. Also, using the program developed, allows significant reducing the engineer-technologist man-hours for the design of the process cycle of the casting heat treatment. An example of calculating the thermal state of a roll with a diameter of 930 mm in casting is given. The change in the dynamics of the maximum temperature gradient along the product radius is shown, while correlating it with the furnace setting.

Effect of Heat Treatment on Structure and Properties of Martensite Stainless Steel for Ice-Class Ships Obtained by Direct Laser Deposition Method

At present, to increase competitiveness of shipyards for manufacturing of shipbuilding parts new high technologies are used. Additive production methods, including direct laser deposition (DLD) technology, which meets all the requirements of competitiveness, are increasingly being applied. Heavy-duty large-size parts such as propellers, blades, hubs and other critical parts used in shipbuilding have become possible to produce with DLD. In the process of DLD it is possible to produce parts, including shipbuilding steels used in the Arctic conditions, with the required mechanical characteristics not inferior to similar brands of materials obtained by casting or plastic deformation methods. The work is devoted to research of thermal process influence on structure and mechanical properties formation of deposited samples from steel powder 06Cr15Ni4CuMo. Features of formation of microstructure components by means of optical microscopy, X-ray structure analysis (XRD) are investigated, and also CCT diagram is constructed. Tensile and impact toughness tests have been conducted. As a result, it was found that the material obtained by the DLD method in its initial state significantly exceeds the strength characteristics of heat-treated castings of similar chemical composition, but is inferior to it in terms of plasticity and viscosity. The increase of viscosity and plasticity up to the level of cast material in the grown samples is achieved during the subsequent heat treatment, which leads to the formation of the structure of tempered martensite and reduction of its content in the two-stage tempering in the metal structure. The strength of the material is also reduced to cast metal after heat treatment.

Differentiated welding deposit of soiling parts according to abrasive wear map

The paper proposes the use of maps of the expected abrasive wear of the friction surface of a soil-cutting part, which characterize the wear intensity at various points of the friction surface during its movement in the soil environment. The importance of this work is caused by changes in modern technologies for the cultivation of agricultural crops, requiring changes in the geometric shapes of soil-cutting parts with the need to predict their service life. A study of the physical and mechanical properties and structure of the hardened layer was carried out using gray cast iron. Gray cast iron was preliminarily subjected to heat treatment, which made it possible to increase the tensile strength up to 200 … 250 MPa and hardness up to HRC 50 … 55. To increase the wear resistance of soil-cutting parts operating in an abrasive environment, hardening was carried out by the electric spark method using gray cast iron, previously subjected to heat treatment. The microstructure of the deposited layer became pearlite-ledeburite without graphite precipitation. Electro-spark deposition made it possible to form a wear-resistant layer in several passes, while the structure of the cast iron and the base did not undergo any changes. No increase in grain size was observed in the deposited layer, which favorably affects its properties. The hardness of the deposited layer was higher (4800 … 5000 MPa) than that of the base metal (2300 … 2400 MPa), no softening of the base was observed. According to the test results of hardened products, heat-treated gray cast iron can be recommended for use as a material for hardening, since the thickness of the coating does not lead to changes in the initial geometric dimensions of the soil-cutting tool using differentiated surfacing using abrasive wear maps.

Effect of Cavitation Erosion Wear, Vibration Tumbling, and Heat Treatment on Additively Manufactured Surface Quality and Properties

The paper is devoted to researching various post-processing methods that affect surface quality, physical properties, and mechanical properties of laser additively manufactured steel parts. The samples made of two types of anticorrosion steels—20kH13 (DIN 1.4021, X20Cr13, AISI 420) and 12kH18N9T (DIN 1.4541, X10CrNiTi18-10, AISI 321) steels—of martensitic and austenitic class were subjected to cavitation abrasive finishing and vibration tumbling. The roughness parameter Ra was reduced by 4.2 times for the 20kH13 (X20Cr13) sample by cavitation-abrasive finishing when the roughness parameter Ra for 12kH18N9T (X10CrNiTi18-10) sample was reduced by 2.8 times by vibratory tumbling. The factors of cavitation-abrasive finishing were quantitatively evaluated and mathematically supported. The samples after low tempering at 240 °C in air, at 680 °C in oil, and annealing at 760 °C in air were compared with cast samples after quenching at 1030 °C and tempering at 240 °C in air, 680 °C in oil. It was shown that the strength characteristics increased by ~15% for 20kH13 (X20Cr13) steel and ~20% for 12kH18N9T (X10CrNiTi18-10) steel than for traditionally heat-treated cast samples. The wear resistance of 20kH13 (X20Cr13) steel during abrasive wear correlated with measured hardness and decreased with an increase in tempering temperatures.

Foundry production digitalization

Domestic companies upgrade their production facilities as it is an imperative of the economy changing over to a new technological mode right now. Industrial companies use more automation and robotization of production, and the level of digital intellectualization is growing. Introduced into technological processes, digital technologies save time and costs of production and reduce the human factor effect. Foundry industry is no exception. The authors suggest considering a foundry process as a set of stages: designing and manufacturing casting models, preparation of charge materials, preparation of initial molding materials, smelting, mixing, casting metal in ladles, mold manufacturing, pouring smelt in mold, knocking castings out of mold, stumping and cleaning of castings, heat treatment of castings, quality inspection of castings. The article organizes information about the digital technologies used at each of the selected stages of the foundry castings by pouring the melt into sand molds. The application of computer technology, digital devices, and software is considered in detail at the stages of the casting model design, charging and molding materials preparation, sand mold manufacturing and casting quality inspection. Digital technologies optimize production, save time and costs.

Differential Scanning Calorimetry Fingerprints of Various Heat-Treatment Tempers of Different Aluminum Alloys

Heat-treatable cast and wrought aluminum alloys are widely used for structural applications in the automobile and aerospace industries. To assess and diagnose the production and quality problems related to industrial heat treatments, differential scanning calorimetry (DSC) was used as a tool in the present work to determine the thermal histories of samples that had undergone different tempers of three commonly used aluminum alloys, namely a high-pressure die-cast AlSi10Mg0.3Mn alloy, permanent-mold cast Al-Si-Cu 319 alloy, and extruded Al-Mg-Si AA6082 alloy. Various peaks detected in the DSC curves were analyzed and characterized to identify the precipitation/dissolution reactions of metastable phases, aiming to establish a “fingerprint” of each temper of the three experimental alloys. Results showed that both the number and size of exothermic peaks varied with the temper owing to distinct precipitation behaviors, providing an effective means of fingerprinting the various tempers. Meanwhile, electrical conductivity and microhardness data provided the supplementary support for the fingerprinting. The thermal histories of three experimentally heat-treated alloys were well traced and distinguished by the combination of DSC characteristics and electrical conductivity and microhardness results, promoting the DSC application in the quality control and verification of industrial heat treatments. In addition, the microstructures after the various tempers were observed to confirm the evolution of the precipitation reactions revealed in the DSC curves.

Моделювання формувальних та очисних технологій для ЛТО-процесу, що полягає в термообробці виливків, видалених в гарячому стані із піщаних форм

Моделювання формувальних та очисних технологій для ЛТО-процесу, що полягає в термообробці виливків, видалених в гарячому стані із піщаних форм

In Situ Preparation of Micro–Nano Tantalum Carbide Ceramic

The microstructure and mechanical properties as well as the formation and morphological evolution mechanism of micro–nano TaC carbide prepared by an in situ casting–heat treatment reaction and chemical extraction method have been investigated. The size of the TaC particles was approximately 50–900 nm. The formation process and mechanism included nucleation growth of TaC grains and a diffusion-type solid-phase transition. Due to the “freezing” of the microstructure, the movement of the grain boundaries is inhibited, resulting in ultrafine TaC ceramic particles. The TaC particles preferably grow as cubes enclosed by {100} facets with minimized total surface free energy, indicating that both the intrinsic lattice structure and the growth conditions determine the final morphology of the TaC particles. In addition, the hardness and elastic modulus of the TaC ceramic were found to be 26.5 ± 0.4 GPa and 506.4 ± 5.8 GPa, respectively. Moreover, the fracture toughness was found to be 3.8 ± 0.1 MPa m1/2. The toughening mechanism of the TaC ceramic layer includes crack deflection and crack bridging.

Термічна обробка виливків з використанням тепла ливарного нагріву

Термічна обробка виливків з використанням тепла ливарного нагріву