Heat Treatment Operations Research Articles

Transfer of Self‐Sustained Reactions between Thermally Coupled Reactive Material Elements

System engineering requires the implementation of assembly methods allowing the formation of functional elements according to a desired system design. This is possible by joining prefabricated elements on a desired place in the system or by forming functional materials at wanted locations. Both approaches need temperature treatment. A typical system in part consists of materials restricting the use of annealing procedures above 300 °C. For this reason, higher‐temperature operations have to be localized to the point of use and transferred to the next reactive element. A further requirement is the reduction of the thermal budget of the localized joining process implementing ultrashort heat treatment operations. Reactive metallic multilayer offers the combined possibility of implementing a localized heat source and the formation of a functional intermetallic alloy. The article demonstrates the feasibility of a heat and reaction transfer chain in a topological structured pattern consisting of localized reactive multilayer materials under conditions of their gasless combustion. For the used Ni/Al multilayer material system, the critical (obstacle thickness) dimensions for the reaction and heat transfer are determined using a high‐speed camera and pyrometer measurements.

Properties of Ni-B/B Composite Coatings Produced by the Electroless Method under Semi-Technical Line Conditions

Composite coatings have been successfully fabricated at the laboratory scale in many research centers around the world; however, it is still a major challenge to transfer the positive results of the work to the industrial scale. This paper presents the technology for the production of Ni-B and Ni-B/B composite coatings on a pilot experimental semi-technical line by chemical reduction. A process scheme for the fabrication of Ni-B layers and composite coatings with a nickel–boron matrix and a dispersive phase in the form of boron nanoparticles was developed. All stages of the fabrication process were described in detail. The dispersion phase of the boron particles was characterized, and the performance properties of the Ni-B and Ni-B/B composite coatings produced on a pilot electroplating line were studied. The structure and morphology of the Ni-B/B composite coatings were characterized for comparison with nickel–boron coatings. Their mechanical and tribological properties and adhesion to the substrate were studied. The influence of the dispersion phase of boron particles on the structure and functional properties of the composite coatings was evaluated. In order to improve the performance of the fabricated coatings, a heating process at 400 °C was carried out, and the performance of Ni-B and composite Ni-B/B coatings was studied after the heat treatment operation.

Investigation of the fracture resistance of high strength ferritic steel welds in gaseous hydrogen environment

Hydrogen is expected to play a major role in the decarbonization of the energy grid. As a fuel, it possesses an elevated energy density per unit mass, about twice as much as natural gas but also a very low mass density; for this reason, it is preferably stored and transported at elevated pressures in the gas phase to achieve a comparable volumetric energy density. High strength quenched and tempered ferritic steels are widely used for gaseous hydrogen storage despite the fact that hydrogen affects material properties and result in higher fatigue crack growth rate and lower fracture toughness.This work presents the results of a comprehensive fracture toughness test program in gaseous hydrogen for the characterization of base metal, heat affected zone and weld metal on a high strength, quenched and tempered steel, suitable for the construction of hydrogen pressure equipment.Full penetration, butt welded joints were made using partly mechanized gas metal arc welding technique on a weldable, high strength steel, namely EN 101216-3 grade P690 QL2. Two different welding procedures were evaluated, and fracture toughness tests were conducted according to ASTM E1820 requirements, in high purity (99.9995%) hydrogen gas at a pressure of 200 bar on specimens extracted from base metal, heat affected zone and weld metal. While base metal and weld metal exhibited stable crack growth behavior, heat affected zone showed variable behavior as a function of the post-weld heat treatment conditions. It was found that local micro-hardness spots are a concern and should be controlled through dedicated post weld heat treatment operation to limit hardness values for use of welds in H2 gas conditions.

Thermal post-treatment and material characterization of laser powder bed fusion additively manufactured Ti-6Al-4V

Laser powder bed fusion of Ti-6Al-4V (PBF-LB/Ti-6Al-4V) alloy results in the formation of non-equilibrium microstructures due to very high cooling rates, causing them to be unfit for direct applications; therefore, post-heat-treatment operations are required. This paper investigates the effects of different heat treatment operations on the microstructure, hardness and phase composition of as-built PBF-LB/Ti-6Al-4V samples. Six sets of heat-treatment operations have been designed in which samples have been first subjected to either above or below the beta (β) transus zone of 980 °C, then subjected to air cooling or water quenching followed by ageing at 510 °C. The novelty of this article is performing double quenching on as-built Ti-6Al-4V parts. Optical microscopy, Vickers microhardness testing, and XRD analysis have been performed on heat-treated samples for material characterization. Microstructural studies have revealed that depending upon the cooling medium and subjected temperature during heat treatment, the extent of dissolution of martensitic (α′) needle-like phases present in as-built samples into α-β phase varies, resulting in variation of hardness values. XRD analysis confirmed the presence of β-phase along with the α-phase in the matrix in air-cooled heat-treated samples. Maximum hardness was obtained in the case when the sample was solutionized at 1050 °C, followed by water quenching and ageing due to the formation of intermetallic precipitates.

Peripheral coarse grain formation in AA2024 and AA6063 aluminium alloys- A comparative study

Multifaceted mechanical and physical characteristics such as light weighting, high strength to weight ratio, electrical conductivity, and ease of fabrication have helped aluminium alloys to find its application in aerospace and automobile sectors. The most famous aluminium alloy used in extrusion is AA 6063 because of its 100% extrudability. AA2024 is from the family of hard alloys which finds its applications in the strength requirements and major alloying additions comprise of Cu, Mg which contributes to age/precipitation hardening phenomena. Because of its inherent nature of high strength, it is challenging to extrude. Extrusion is one of the major metals forming processes which involve several process parameters such as, temperature, strain rate, ram speed and post forming heat treatment operations. To attain the specific mechanical properties, microstructure of the extrudate is of utmost importance and evolution of the same needs to be understood. Heat treatable aluminium alloys series of 2xxx, 6xxx or 7xxx are prone to peripheral coarse grain structure, which is responsible for the loss of mechanical and corrosion performance. To eliminate PCG entirely or to minimize it is the fundamental interest of extrusion industries and to come up with a workable solution, it is necessary to twig the microstructure evolution of AA6063 and AA2024 alloy during extrusion and after heat treatment. The present work is aimed at comparative study of the PCG formation of press quenched samples in AA6063 and heat-treated (T6) samples of AA2024.

Application of the heat treatment in the welding process of ferritic stainless steels – causes and effects

This paper aims to analyse the application, importance and impact of heat treatment operations used in ferritic stainless steel welding processes on the properties of the welds obtained. In addition, the article aimed to formulate the main problems that occur during the welding process of ferritic stainless steels, including, in particular, the phenomenon of ferrite grain growth due to thermal processes.The analysis of the available literature covered issues related to heat treatment processes used in the welding of ferritic stainless steels, taking into account the issue of the growth of the ferrite grain under the influence of heat supplied during welding and the possibility of heat treatment of the obtained welds. The analysis also included determining the possibility of inhibiting the growth of ferrite grains by using elements such as titanium, niobium, and molybdenum, thus improving the strength properties of welds.Organisation of knowledge in the field of the impact on the mechanical properties of ferritic stainless-steel welds and heat treatment processes used before, during, and after welding.Properly selected parameters of the welding process of ferritic stainless steels, especially the amount of heat input, together with appropriate heat treatment parameters, should improve the mechanical properties of ferritic stainless steels.The analysis of the possibility of a wider application of ferritic stainless steels allowed to draw one of the main conclusions stating that the limited possibilities of using ferritic stainless steels in heavy industry are related to their high susceptibility to ferrite grain growth under the influence of high temperature during welding and, consequently, decreases in strength properties of welding joints made of ferritic stainless steels. Additional heat treatment operations are introduced before, during, or after the sapping process to improve their mechanical properties.

Experimental and numerical analyses of residual stress redistributions in large steel dies: Influence of tempering cycles and rough milling

The aim of the present research was to study the residual stress variations induced by heat treatment and rough milling operations of large forged steel blocks. The heat treatment process includes quenching and tempering operations. An efficient strategy based on a size sensitivity analysis (SSA) was proposed to reach the actual values of residual stresses in large-size steel blocks by using small-size workpieces in laboratory scale without damaging the blocks. The residual stresses were measured and compared after the first and second tempering and the rough milling. A 3D finite element (FE) model was developed to predict superficial residual stresses and was then calibrated experimentally. The results showed that the residual stresses after the first and second tempering were highly compressive on and near the surface. In addition, the resultants of the residual stresses after double tempering processes were almost equal. Therefore, the second tempering could be omitted from the manufacturing process. It was also found that both surface and sub-surface hoop and radial residual stresses were highly tensile after the rough milling. Finally, the 3D FE model can be used as a predictive tool to predict residual stresses for rough milling to avoid conducting expensive, time-consuming experimentations and measurements.

Microstructure and Mechanical Properties of Tungsten Heavy Alloy Prepared Using Tungsten Metal Powder Produced from Heavy Alloy Scrap

Tungsten metal powder, using a hydrometallurgical route, was extracted from tungsten heavy alloy scrap that was generated during machining of penetrator cores for the manufacture of Fin Stabilised Armour Piercing Discarding Sabot (FSAPDS). The powder was subjected to extensive characterisation that included physical property evaluation and analysis of the alloy chemistry in order to assess its suitability for the preparation of tungsten heavy alloys with enhanced mechanical properties. Subsequently, a tungsten heavy alloy based on W-Ni-Co was consolidated using this powder through liquid phase sintering followed by heat treatment and swaging operations to realize long rods (~500 mm). This was followed by a detailed characterisation that included microstructure and mechanical property. The mechanical properties of these rods are promising, exhibiting a good balance of tensile and impact properties, which in turn underscores the potential of these recycled powders in the production of premium quality heavy alloy long rods for stringent applications such as kinetic energy penetrators.

On the role of residual austenite in improving the complex of properties of ductile cast iron

This article is analyzing the prospects and ways to expand the field of applying ductile cast iron-high-strength cast iron in technology. Ductile cast iron occupies a special place among structural materials. With the same level of mechanical properties, having less specific weight than steel, it provides less weight of products in comparison with steel. This reduces the consumption of raw materials and energy resources in the manufacture and operation of machines and mechanisms. There is a positive effect both in terms of economy and ecology. In addition, ductile cast iron has better casting properties than steel. In recent years, scientists and engineers have focused their efforts on finding new ways to improve the complex of mechanical and operational properties of ductile cast iron. This will make it possible to expand the field of their application and obtain additional advantages. A very effective direction – obtaining bainite matrix and a great amount of stable austenite in the structure of ductile cast iron by heat treatment allows to realize martensitic transformation in the most loaded parts during their operation and thereby increases adaptability. In this case, in addition to the traditional type of heat treatment - one-stage isothermal hardening, the technology of two-stage isothermal hardening is actively implemented, which allows for providing more dispersed ferrite and more stable austenite in the structure. A fundamentally new approach to obtaining the favorable microstructure of ductile cast iron is the organization of a foundry and heat treatment complex that makes it possible to obtain the ferrite-austenite mixture in the structure of ductile cast iron directly from the cast state, bypassing a separate heat treatment operation

Influence of mechanical properties and alloying elements of low carbon steels on fine blanking and heat treatment processes response

The effect of the negative clearances between punch and die of a flange with different fine blanking half-cutting depths was investigated for two low carbon steels with various elongation rates, C18E (0.18%C) and 20MnB5 steels (0.2%C, with upper mechanical properties than the carbon steel), industrially used for forming car seat parts. A specific tool adaptable on a tensile machine was built to determine the force needed to fine blank a simple geometry, in the objective to further transpose the obtained results to the complex geometry of industrial parts. Heat treatment was carried out to optimize the microstructure, hardness and dimensional modifications for the combination material/clearance/half-cutting height tested. Increasing the elongation rate of the raw material allows to reach a better formability and reduces the force needed to create a given geometry, but cracks were detected for the extreme deformation rate. Moreover, after fine blanking and heat treatment operations, different microstructures were observed according to the material grade, stable for low alloy 20MnB5 steels (martensitic microstructure) while non reproducible for the low carbon steel (mix of ferrite, bainite and martensite).

Efficient reconstruction of prior austenite grains in steel from etched light optical micrographs using deep learning and annotations from correlative microscopy

The high-temperature austenite phase is the initial state of practically all technologically relevant hot forming and heat treatment operations in steel processing. The phenomena occurring in austenite, such as recrystallization or grain growth, can have a decisive influence on the subsequent properties of the material. After the hot forming or heat treatment process, however, the austenite transforms into other microstructural constituents and information on the prior austenite morphology are no longer directly accessible. There are established methods available for reconstructing former austenite grain boundaries via metallographic etching or electron backscatter diffraction (EBSD) which both exhibit shortcomings. While etching is often difficult to reproduce and strongly depend on the investigated steel’s alloying concept, EBSD acquisition and reconstruction is rather time-consuming. But in fact, though, light optical micrographs of steels contrasted with conventional Nital etchant also contain information about the former austenite grains. However, relevant features are not directly apparent or accessible with conventional segmentation approaches. This work presents a deep learning (DL) segmentation of prior austenite grains (PAG) from Nital etched light optical micrographs. The basis for successful segmentation is a correlative characterization from EBSD, light and scanning electron microscopy to specify the ground truth required for supervised learning. The DL model shows good and robust segmentation results. While the intersection over union of 70% does not fully reflect the model performance due to the inherent uncertainty in PAG estimation, a mean error of 6.1% in mean grain size derived from the segmentation clearly shows the high quality of the result.

The Effect of Quenching Media on the Hardness of Low Carbon Steel

Steels with desired properties are essential and always required by many industries. This paper highlights some heat treatment operations with various cooling media to achieve different rapid cooling rates. This was carried out by heating samples of low carbon steel to a specific temperature and then cooling them rapidly in 8 different quenching media in order to obtain a specific microstructure of steel. These heat-treated samples were then tested mechanically using the Brinell hardness test (BH). The results show that the quenching mediums affect the mechanical properties and hence the microstructures of low carbon steels and the effect varies depending on the types of quanchants employed.

ELECTRODEPOSITION OF NICKEL ON HEAT-TREATED LOW CARBON STEEL FOR YAM POUNDING BEATER

This work focused on the mechanical and corrosion behaviors of electroplated nickel on heat-treated low carbon steel serving as an alternative to austenitic stainless steel for the yam beater in a yam pounding machine. Four standard samples were prepared for electrodeposition from the steel samples by heating to a temperature of 920°C with a 60-min holding time. One of the samples was air-cooled while the remaining three were quenched in H2O and later tempered at 450°C, 550°C and 650°C for 60[Formula: see text]min. After the heat treatment process, the ultimate tensile strength, toughness, and microhardness of the samples were obtained. Nickel electrodeposition was later carried out on the heat-treated mild steel using Watt standard bath concentration. Optical Microscopy (OM) and Scanning Electron Microscope equipped with energy dispersion spectroscopy (SEM/EDS) were used for the characterization of the heat-treated and nickel-electrodeposited samples. More so, the electrochemical behavior of the nickel-plated samples was studied in a yam fluid environment using the potentiodynamic polarization technique. X-ray fluorescence (XRF) was used to analyze the chemical and oxide composition of the samples. The results showed that among all the heat treatment operations, the sample heat-treated at 920°C and tempered at the highest tempering temperature of 650°C gave the highest toughness value (102[Formula: see text]MJ/m3) when compared with stainless steel at 124[Formula: see text]MJ/m3. The sample heat-treated at 920°C and tempered at 550°C displayed a corrosion rate of 0.022182[Formula: see text]mm/yr as against the stainless steel sample with a value of 0.0031864[Formula: see text]mm/yr. From the analysis, the nickel deposited on the heat-treated samples enhanced corrosion resistance in the yam fluid. XRF analysis of the yam before pounding, after processing with nickel electroplated, and stainless beaters shows the content of nickel as 0.0941%, 0.109%, and 0.1113%, respectively. It was concluded that the materials for the yam pounding beater, therefore, perform better if they were both heat-treated and nickel-plated. Invariably, stainless steel could be successfully replaced with heat-treated and nickel-plated mild steel for use as a yam pounding beater.

Providing steel with an approximate application of the mechanical properties of wire rod 5.5-6.5 mm from sreel grades 70-75 based on a conventional twin of the Stelmor process

In 2019, the air-cooling line of Mill 170 of PJSC MMK (Magnitogorsk Iron and Steel Works) was upgraded. The main task of modernization was to obtain wire rod sorbitized in the initial state. The use of such products makes it possible to abandon one intermediate heat treatment operation in the wire production process, and should also ensure the stability of the mechanical properties of the finished wire of the entire size range of OJSC MMK-METIZ. On the part of OJSC MMK-METIZ, the following high requirements were imposed on the uniformity of the mechanical properties of the wire rod obtained at the mill - no more than 40 N/mm2 along the length of the convolution, 50 N/mm2 along the length of the coil, 60 N/mm2 within the melt. When analyzing samples of rolled products from steel grades 70-75 with a diameter of 5.5-6.5 mm, it was found that compliance with the requirements in the modes operating at the mill is difficult. By the order of PJSC MMK, as part of scientific research on the development of wire rod production technology using a digital twin of an air cooling line, a mathematical model was developed, the adequacy of which was proved by developing rolling modes based on it, followed by evaluation of the resulting product. Upon further analysis of the obtained rolled products, it was found that the products manufactured according to the new modes meet the requirements for uneven mechanical properties along the length of the convolution and the coil to a greater extent.

Evolution of residual stress through the processing stages in manufacturing of bore-chilled sand-cast aluminum engine blocks with pressed-in iron liners

To minimize the carbon footprint of the transportation industry, manufacturers and engineers are continuously trying to improve the efficiency of the combustion engine. However, due to the presence of iron cylinder liners in the engine block, high tensile residual stresses are generated during the manufacturing process which leads to a large reduction of the alloy’s useable strength. Thus, the present study utilized neutron diffraction to study, for the first time, the evolution of residual stress of sand-cast aluminum engine blocks that have eliminated the iron cylinder liners from the casting process and mechanically inserted them after heat treatment and machining operations. Moreover, this study also examined the effects that cylinder bore chills have on the resulting residual stress profiles. The replacement of the iron liners shifted the stress mode from purely tension to purely compression until the bore chills were removed. Following the removal of the bore chills, the maximum tensile stress at the top of the cylinder bridge was ~ 70% lower than the engine’s predecessor which was produced with iron liners. Moreover, in the production-ready state (i.e., T7 heat treated and press-fit liners inserted), the stress mode maintains the partially compressive nature, thereby lowering the material’s susceptibility to crack growth and propagation.Graphical Abstract

Simulation modeling and optimization of bitumen –palm kernel oil blend for austempering of cast iron and steel

The study combines both simulation modeling and optimization of bitumen-palm kernel oil blend for austempering of cast iron and steel. Two independent factors namely austenitizing temperature (A) and holding time (H) were evaluated while five responses which includes ultimate tensile strength (u.t.s), hardness (h), impact strength (i), percentage elongation (e), percentage reduction in area (r.i.a) were evaluated. 3-D response surface and 2-D contour plots through response surface methods were used to estimate multi-response mathematical models. Desirability function approach provided by MINITAB 18 was used to determine the optimal settings of the response and factors after adequacy of the models to approximate the measured data had been established at 0.10 confidence level. From the result, optimum conditions for austenitizing temperature was 916.50C and 5 min while the predicted values of quenching hardness, ultimate tensile strength, impact strength, %elongation, %reduction in area were 1327.29MPa, 29.36J, 72.77%, 86.79% and 175.59HRC for 0.56%C-Steel; 1407.97MPa, 20.04J, 50.80%, 49.17% and 196.13 for 0.76%C-Steel; 1235.01MPa, 32.42J, 60.39%, 55.99% and 234.99HRC for ductile cast iron. Great improvement was seen in the steel performance after austempering process which gave rise to the conclusion that as the austempering time and holding time increases, that the mechanical properties of the steel were affected. Quenching of 0.56%C, 0.76%C-steel and ductile cast iron at the optimal settings using B-PKO saved one thousand naira (₦1000.00) showing 28.57% profit. The developed empirical models are recommended in some of the automobile and engineering industries during heat treatment operations so as to save time and energy.

Mechanical Testing of Additively Manufactured Superalloy Lugs

Abstract Additively manufactured parts, in spite of their many advantages, face substantial challenges on the path toward certification. This challenge is more pronounced in the quality-demanding aviation industry, where the safety considerations are paramount. A major reason for this challenge is the lack of history associated with additively built parts compared to the traditional cast and wrought components. In assessing the structural integrity of cast and wrought components, material properties obtained from laboratory coupon tests are routinely applied for design calculations of large components. However, for additive manufacturing (AM) parts, questions remain over transferability of properties over multiple length scales due to possible variations in material chemistry, microstructure, and defect. In this work, this issue is investigated by conducting mechanical tests on small simplified lugs of nickel-based superalloy Haynes 282. The lugs are produced by the laser powder bed fusion process. After appropriate heat treatment and machining operations, the lugs are subjected to strength, low cycle fatigue, and crack propagation tests. Multiple tests are carried out in order to assess repeatability. Design calculations are performed to assess whether the test results can be predicted with standard methods. The results in this work generate confidence in predictable, repeatable behavior of the AM built lugs. Continuation of this approach over larger length scales has the potential to build enough confidence so that additively manufactured parts can be used in load-bearing structural elements of the aircraft engine.

Isothermal Oxidation Behaviour of 800H Nickel-Based Alloy

The behaviour of 800H nickel (Ni)-based alloy under isothermal oxidation condition was study in this paper. The isothermal oxidation behaviour was examined in terms of fine grained and coarse grained 800H Ni-based alloy obtained from heat treatment operation at 1000 °C and 1150 °C, respectively. The heat treated samples were undergo an isothermal oxidation attempt at 500 °C in laboratory air for 500 hours exposure duration. The effects on the oxidation kinetics was examined in terms of weight change measurement. In addition, the effects on the oxide scale growth was observed in terms of phase analysis using XRD technique and surface morphology analysis using FESEM outfitted with EDX spectrometer. As a results, both fine grained and coarse grained 800H Ni-based alloy were obey a parabolic rate law showing that the oxide growth rate was followed a diffusion controlled mechanism. Additionally, fine grained 800H Ni-based alloy sample exhibited a inferior oxidation rate compared to coarse grained sample. The XRD analysis exhibited that the oxides scale composed of Cr2O3, TiO2 and MnCr2O4. The observation on the oxide scale morphology indicate that uniform oxide scales were formed on the alloy surface of both samples. However, coarse grained 800H Ni-based alloy recorded an oxide exfoliation which indicate poor oxidation protection.

A Study of the Convective Cooling of Large Industrial Billets

The thermodynamic heat-transfer mechanisms, which occur as a heated billet cools in an air environment, are of clear importance in determining the rate at which a heated billet cools. However, in finite element modelling simulations, the convective heat transfer term of the heat transfer mechanisms is often reduced to simplified or guessed constants, whereas thermal conductivity and radiative emissivity are entered as detailed temperature dependent functions. As such, in both natural and forced convection environments, the fundamental physical relationships for the Nusselt number, Reynolds number, Raleigh parameter, and Grashof parameter were consulted and combined to form a fundamental relationship for the natural convective heat transfer as a temperature-dependent function. This function was calculated using values for air as found in the literature. These functions were then applied within an FE framework for a simple billet cooling model, compared against FE predictions with constant convective coefficient, and further compared with experimental data for a real steel billet cooling. The modified, temperature-dependent convective transfer coefficient displayed an improved prediction of the cooling curves in the majority of experiments, although on occasion a constant value model also produced very similar predicted cooling curves. Finally, a grain growth kinetics numerical model was implemented in order to predict how different convective models influence grain size and, as such, mechanical properties. The resulting findings could offer improved cooling rate predictions for all types of FE models for metal forming and heat treatment operations.

Investigation of Heat Treatment on Mechanical Properties of Medium Carbon Steel

The effect of various heat treatment operations (annealing, normalizing and hardening) on mechanical properties of medium carbon steel was investigated. The samples were prepared and heat-treated at 770 ºC subsequently was cooled by different quenching media. The mechanical properties of the treated and untreated samples were determined using standard methods. Results showed that the mechanical properties of carbon steel can be changed and improved by various heat treatments. It was also found that the annealed samples has the lowest tensile strength and hardness value and highest ductility, while hardened samples has the highest tensile strength and hardness value and lowest ductility value.