Hot Working Research Articles

Microstructure evolution after hot working and heat treatment in 6082 aluminum alloy manufactured by horizontal continuous casting

In this paper, 6082 aluminum alloy manufactured by horizontal continuous casting was subjected to high-temperature plastic deformation under 20–70 % deformation levels with following T6 heat treatment process. Microstructural and phase changes were investigated by light and scanning electron microscopy together with energy dispersive spectroscopy, while grain, grain boundary, dislocation and texture evolution was studied by electron-backscattered diffraction. The results are showing that continuous dynamic recrystallization processes are active during the hot working while influence of static recrystallization is significant only for highest deformation degrees. The abnormally coarse-grained microstructure does locally occur in the subsurface layer after the 70 % deformation and T6 heat treatment. Crystallographic texture components are gradually evolving from the various types (Goss, Brass, D) for the low deformations (up to 40 %) into fiber-type textures (α-fiber, γ-fiber or C2-fiber) for high deformations due to the inhomogeneity of plastic deformation. The formation of AlMnSi dispersoids, CSL-boundaries Σ25b and an increase in fraction of GND, MgSi and Fe-based intermetallic particles was observed during the phase transformation which promotes ongoing nucleation of recrystallization processes.

Research on hot workability and deformation mechanism of as-extruded Ti-6554 alloy over a broad temperature range

The favorable mechanical characteristics of Ti-6554 offer potential uses in the aerospace industry. To broaden the potential uses of as-extruded Ti-6554 alloy, it is essential to conduct additional assessments on its hot workability and deformation mechanisms. This study, through a series of hot compression tests conducted over a broad temperature range using a thermal simulation testing machine, established the activation energy map and the hot processing map, while examining the evolution of microstructures and deformation mechanisms. The findings indicate that the activation energy of the Ti-6554 alloy reduces as strain rises. The ideal conditions for hot processing are 850-900 °C and 10-3-10-2s-1. The precipitation of the α phase occurs when deforming in the two-phase region, some maintain burgers orientation relationship (BOR) with the matrix, and some maintain random orientation with the matrix. In addition, the α phase precipitation significantly promotes dynamic recrystallization (DRX), resulting in obvious flow softening. The examination of misorientation angles reveals that DRX mechanisms of the β phase. At a slow strain rate, DDRX gradually dominates as the temperature rises. At constant temperatures, CDRX increasingly takes precedence with the increase of strain rate.

Hot Ductility Behaviour of AA7075-T651 Aluminium Alloy

Abstract This study focused on examining the hot ductility characteristics of aluminium alloy 7075-T651. Hot ductility is the capacity of a substance to undergo deformation at high temperatures without fracturing. Aluminium alloys typically demonstrate favorable hot ductility, rendering them appropriate for a wide range of high-temperature applications. The investigation entails performing hot tensile tests for AA7075-T651 aluminium alloy at different deformation temperatures (350°C-525°C), followed by fractography to ascertain the fracture mode. The ductility of the AA7075-T651 alloy was greatly enhanced during this procedure. The findings indicate that the hot working range of the aluminium alloy 7075-T651 can be expanded to 525°C instead of a liquidus start temperature of 477°C with a maximum of 30% ductility. The fractography results demonstrate that the fracture mode remains ductile. The AA7075-T651 aluminium alloy exhibits excellent thermal stability, allowing it to be hot worked at temperatures as high as 525°C without experiencing any sudden alterations in its characteristics or fracture behaviour.

Impacts of age, type 2 diabetes, and hypertension on circulating neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 after prolonged work in the heat in men.

Prolonged work in the heat increases the risk of acute kidney injury (AKI) in young men. Whether aging and age-associated chronic disease may exacerbate the risk of AKI remains unclear. We evaluated plasma neutrophil gelatinase-associated lipocalin (NGAL) and serum kidney injury molecule-1 (KIM1) before and after 180min of moderate-intensity work (200W/m2) in temperate (wet-bulb globe temperature [WBGT] 16°C) and hot (32°C) environments in healthy young (n = 13, 22years) and older men (n = 12, 59years), and older men with type 2 diabetes (T2D; n = 9, 60years) or hypertension (HTN; n = 9, 60years). There were no changes in NGAL or KIM1 concentrations following prolonged work in temperate conditions in any group. Despite a similar work tolerance, the relative change in NGAL was greater in the older group when compared to the young group following exercise in the hot condition (mean difference + 82ng/mL; p < 0.001). Baseline concentrations of KIM1 were ~ 22pg/mL higher in the older relative to young group, increasing by ~ 10pg/mL in each group after exercise in the heat (both p ≤ 0.03). Despite a reduced work tolerance in the heat in older men with T2D (120 ± 40min) and HTN (108 ± 42min), elevations in NGAL and KIM1 were similar to their healthy counterparts. Age may be associated with greater renal stress following prolonged work in the heat. The similar biomarker responses in T2D and HTN compared to healthy older men, alongside reduced exercise tolerance in the heat, suggest these individuals may exhibit greater vulnerability to heat-induced AKI if work is prolonged.

Preparation and properties of room temperature foaming lignin-based non-isocyanate polyurethane foams

The preparation and application of biomass-based non-isocyanate polyurethane (NIPU) is an essential and meaningful hot topic research work in the field of polyurethane industry, due to its advantages of sustainability of raw materials and no highly toxic isocyanate used in the synthesis. Lignin, as the second most renewable natural polymer on earth, was used in this paper to synthesize lignin-based non-isocyanate polyurethane (L-NIPU) resins. Subsequently, L-NIPU foams were prepared by self-foaming at room temperature with the addition of maleic acid as an initiator and glutaraldehyde as a cross-linker, and their properties were investigated. Results show that L-NIPU foams are lightweight (0.11–0.18 g/cm3), have low thermal conductivity (0.033–0.04 W/m·K), and have excellent compressive strength. When the addition of maleic acid and glutaraldehyde is respectively 18 % and 25 % (based on L-NIPU resin quality), the compressive strength can be as high as 0.5 MPa, and the thermal conductivity is only 0.03559 W/m·K, so it can be used as an insulating board in buildings. In addition, FT-IR and XPS analyses showed that maleic acid and glutaraldehyde can react with the amino group in L-NIPU to form a cross-linked network structure, which ensures the favorable mechanical properties of the foam.

Thermal Processing Map Study of the GH99 Nickel-Based Superalloy Based on Different Instability Criteria

The thermal compression experiments of the GH99 alloy were carried out at different strains from 1020 °C to 1170 °C and 0.001 s−1–1 s−1 conditions using a Gleeble-3800 thermal compression simulation tester. Construction of thermal processing maps with four instability criteria were superimposed on Murty, Prasad, Gegel, and Malas at different strains based on stress-strain data. Based on the theoretical basis, prediction results, and EBSD microstructure characterization method of four instability criteria, the suitable forming processing region and rheological instability region of the alloy were predicted. It was found that the Prasad instability criterion had the most accurate prediction results. The instability range predicted by Murty was accurate under minor strains, but as the strain increased, the expected instability range slightly increased compared to the actual range. However, the Gegel and Malas criteria have biases in predicting alloys under low-rate conditions at different strains. A scientific and rational optimization was carried out to select hot working process parameters for GH99 alloy in response to the influence of strain on its hot deformation behavior.

Effect of Machining Parameters on the Surface Roughness of Hot Die Steel

H13 tool steel is frequently used in hot work dies, hot forging, hot extrusion, and mold materials for casting ferrous and nonferrous materials. Surface roughness is of key importance in case of dies and moulds, as it insures the finish of the final product. After studying the work done by the researchers in field of machining and its impact over surface roughness, it was found that machining behaviour of H13 steel at the annealed state is not being studied. The surface finish obtained during turning of H13 steel are not studied on a greater scale, so the present study includes the analysis of finish (surface roughness) generated. Turning operation is carried out on the CNC machine at dry condition with an aim to find systematically the effect on surface roughness by distinct machining variables like feed rate, depth of cut and speed. RSM model using Box Behnken design is used to predict the roughness developed during turning of annealed H13 steel using carbide tool. It was found that feed rate and the depth of cut have a direct relation with the surface finish and the value of surface roughness increases with increase in these parameters. On the other side, cutting speed has a less impact over the surface roughness &amp; is inversely related.

High and very high cycle fatigue behavior of an additive manufactured hot-work tool steel

In the present study, the fatigue response of an additive manufactured H13 type hot-work tool steel is investigated across the High Cycle Fatigue (HCF) and Very High Cycle (VHCF) regimes. The primary focus encompasses the interpretation of fatigue strength models, the defect type analysis along with a detailed examination of crack initiation and growth mechanisms. Despite the tremendous development in AM technology, experimental data regarding advanced mechanical properties, and particularly fatigue behavior, are still limited. Here, microstructural analysis of a modified AMed H13 hot-work tool steel, a combination of HCF and VHCF testing methodologies implemented for the characterization of the fatigue behavior, as well as a thorough fractographic analysis of the fractured surfaces were performed. Results are compared with historical data of a conventionally ingot cast and forged grade to assess the influence of the AM process on the fatigue response of H13 hot-work tool steels. It proves to be comparable to the conventionally manufactured grade, showcasing the potential utilization of AM in the production of components used in high-demanding applications, and in hot work tooling applications. However, the type of critical defects identified in the AM grade was found to be process-induced, emphasizing the need to optimize process parameters to reduce both the number and size of defects and also to ensure component reliability and high performance in various industrial applications.

Influence of hot rolling on microstructure, mechanical properties, and martensitic transformation of TiNiCuNb shape memory alloy

TiNiCuNb shape memory alloys are a promising new class of materials with the potential to be applied as elastocaloric components. However, the mechanical processing of these alloys remains a challenge and new insights on this topic must enlighten the knowledge about this system. In this work, the effects of hot rolling on Ti46Ni38Cu10Nb6 alloy were investigated. The results showed that hot rolling leads to the increase of martensitic transformation temperatures and the formation of a matrix containing both B2 and B19 phases. The coarsening of the lamellar eutectic constituent was observed, and part of the β-Nb phase precipitated into the matrix after being dissolved due to hot work. Microstructural aspects and ultra-microhardness measurements suggest that dynamic recrystallization occurred during hot rolling.

Deformation behaviour and microstructure evolution of Ti-2.3Al-2.6Zr alloy in the temperature range of 700–1000 °C

Ti-2.3Al-2.6Zr alloy was hot deformed at temperatures from 700 to 1000 °C and strain rates from 10−2 −30 s−1. The uniaxial compression tests were conducted in vacuum to a true strain of 1 for this alloy. Strain rate sensitivity was calculated from the true stress- true strain data and plotted as contour plots to generate the strain rate sensitivity map. The hot working condition of this model α-Ti alloy was optimized by using the strain rate sensitivity map. The optimized hot workability domains were identified for α-phase as (a) 780–900 °C at strain rate of 10−2 to 0.3 s−1 and (b) 825–900 °C at strain rate of 3–30 s−1. The domain of hot processing condition for β-phase was found at 930–1000 °C for all strain rates. In α-phase domain the strain rate sensitivity was about 0.3, the stress exponent was 4.3 and the activation energy for deformation was 285 kJ mol−1 whereas in β-phase domain the strain rate sensitivity was about 0.34, the stress exponent was 5.3 and the activation energy for deformation was 210 kJ mol−1. These deformation parameters suggest the deformation process to be a dislocation based mechanism. Samples deformed within the high strain rate sensitivity domains showed microstructural features of dynamic recrystallization. In α-phase fine equiaxed recrystallized grains with high angle boundaries were observed. Deformation at 900 °C and 0.01 s−1 resulted in fully recrystallized equiaxed grains in the α-phase, whereas the β-phase showed lamellar grain morphology with very fine recrystallized grains.

Evolution mechanism of Mo-rich, B2-NiAl, and Cu-rich particles under aging and its influence on strength and elongation in a maraging hot work steel SDH88

A novel maraging hot work steel, SDH88, is developed to achieve a balance between ultimate tensile strength (UTS), yield strength (YS), and elongation by combining nanometer-scale precipitates of B2-NiAl, Cu-rich, and M2C carbide. The peak-aging sample demonstrates a YS of ∼1281.8 MPa, a UTS of ∼1665.9 MPa, and an elongation (EL) of ∼17.5 % at room temperature. The microstructure and precipitation changes from peak aging (8h) to over-aging (48h) were examined using different techniques. Under peak aging condition, the precipitates consist of four nanoparticles: 9R-Cu, B2-NiAl, Cu-NiAl, and M2C carbides. However, at over-aging condition, the type of particles changes and consist of B2-NiAl, M6C, Laves phases and FCC-Cu. This study systematically investigates the precipitation evolution of Mo-rich, B2-NiAl, and Cu-rich particles from peak-aging to over-aging conditions. The high YS at peak aging condition is attributed to high precipitation strengthening of ∼553.3 MPa and dislocation strengthening of about 430.8 MPa. The number densities of NiAl (<3.8 nm) particles are more than that of Cu particles which indicates that the NiAl nanoparticles are the dominant strengthening phase. Finally, this work clearly demonstrates that the new alloy composition design allows the application of aging steels in die casting steels with great advantages and potential for obtaining balanced mechanical properties through the systematic study of the aging process and mechanism of precipitation evolution. Proposing a new approach for designing hot work die steel without quenching treatment during mold processing.

Revealing the Dynamic Recrystallization Mechanism and Hot Workability of Fe–0.15C–10Mn Medium‐Mn Steel through Grain Size Distribution and 3D Processing Maps

Revealing the Dynamic Recrystallization Mechanism and Hot Workability of Fe–0.15C–10Mn Medium‐Mn Steel through Grain Size Distribution and 3D Processing Maps

Flow behavior and microstructural evolution of Al-1.2Mg-2.4Si-1.2Cu-0.6Mn alloy during hot compression

Thermal compression tests were conducted on Al-1.2Mg-2.4Si-1.2Cu-0.6Mn alloys with process parameters including deformation temperatures ranging from 400°C to 550°C and strain rates ranging from 0.05 s⁻¹ to 1 s⁻¹. The hot working properties of aluminum alloys were evaluated with intrinsic equations and machining diagrams. The results show that the processing safety zones of the alloy are 425–450℃ and 0.05–0.1 s−1, 450–475℃ and 0.1 s−1-0.5 s−1, and 475–500℃ and 0.5 s−1. The microstructure of the aluminum alloy following hot pressing was investigated through the use of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and backscattered electron diffraction (EBSD). When the deformation temperature of the alloy is below 450°C, the alloy organization exhibits a greater prevalence of inhomogeneous defects, which manifest as coarser granular regions in the micro-morphology. Upon reaching a deformation temperature of above 525°C, the deformed alloy organization exhibits an evident thermal cracking phenomenon. At the same temperature, an increase in strain rate is accompanied by a decrease in the Mg2Si phase and an increase in the precipitation of the Al(Fe,Mn)Si eutectic phase. Furthermore, the precipitated phase tends to become coarser. The presence of certain Mn-containing nanoparticle dispersions can impede the migration of subgrain grain boundaries, while simultaneously pinning dislocations and accelerating the generation of dislocation entanglement. This also can serve to inhibit the coarsening of the grains to some extent.

Melt Pool Changes Characterization in Laser-Processed H11 Hot Work Tool Steel Using Point-by-Point Scanning Mode towards LPBF Process Optimization.

Additive manufacturing techniques employing laser-based metal melting have garnered significant attention within the scientific community. Despite a decade of comprehensive research on the fundamentals of these techniques, there still remain unexplored facets related to heat flux impact on metallic alloys' properties. Particularly, the effects of point-by-point laser operation on melt pool formation in metallic materials still remain unclear. Thus, this study focuses on the implications of laser metal melting, particularly investigating a point-by-point laser mode operation's influence on melt pool formation and its geometry in the phase-transformation-sensitive material H11 hot work tool steel. To examine the melt pool, singular laser tracks with various laser parameters were scanned across H11 sheet metal, which allowed for the elimination of layer-by-layer heat cycles' influence on the melt pool's microstructure. Samples were examined by means of metallography, revealing significant differences in the melt pool's depth, influenced mostly by exposure time rather than volumetric energy density. Heat-affected zone effects were found to have a limited range and thus potentially marginal effects in layer-by-layer manufacturing conditions. At the same time, retained austenite concentrations near fusion lines have been found within melt pools, suggesting potential micro-segregation of the alloying additions. The results present guidelines towards laser melting processes optimization.

Термомеханическая прокатка при производстве обсадных труб (обзор исследований)

Introduction. The modern oil and gas industry requires the development of high strength materials for well casing. Changes in rolled steel production technologies are one of the urgent tasks. Reducing the cost of high quality steel well casing is becoming a major challenge for the oil and gas industry. Multiphase microstructures containing acicular ferrite or an acicular ferrite-dominated phase exhibit good complex properties in HSLA steels. This paper focuses on the results obtained using modern methods of thermomechanical rolling. Results and discussion. This work analyzes the characteristics of thermomechanical rolling technologies and its impact on the microstructure of rolled steel for well casing. It is shown that predicting mechanical properties based on the microstructural characteristics of steel is complicated due to the large number of parameters involved. This requires an optimal microstructure of the steel. A satisfactory microstructure depends on several factors, such as chemical composition, hot work processing, and accelerated cooling. Alloying elements have a complex effect on the properties of steel, and alloying additives are usually introduced into the steel composition. From a metallurgical point of view, the choice of alloying elements and the metallurgical process can greatly influence the resulting microstructure. Conclusion. This review reports the most representative study regarding thermomechanical rolling technologies and microstructural factors in well casing steels. It includes a summary of the most important process variables, material properties, regulatory guidelines, and microstructural and mechanical properties of the metal for well casing production. This review is intended to benefit readers from a variety of backgrounds, from non-metal forming or materials scientists to various industrial application specialists and researchers.

Study on microstructure and properties between alloy steel and powder steel via hot isostatic pressing diffusion bonding

PM23 powder steel and H13 hot working die steel and 9Cr2Mo cold working die steel bimetallic composite components were successfully prepared by hot isostatic pressing powder-solid diffusion bonding process. The interfacial behavior of H13-PM23 and 9Cr2Mo-PM23 bimetals was studied by SEM and EBSD techniques; the mechanical properties of the two bimetals were evaluated by universal testing machine. The results indicated that the element diffusion occurred in the interfacial bonding region, and an obvious decarburized layer was observed in the 9Cr2Mo-PM23 bimetals, whose surface was enriched with small rod-like and dot-like MC and M6C carbides.The tensile strength of H13-PM23 and 9Cr2Mo-PM23 bimetals could reach 882 MPa and 772 MPa, respectively, and the fracture occurred exclusively on the side of PM23 powder steel, which could achieve good metallurgical bonding and stable connection. This study provides potential application guidance for enhancing efficiency while reducing costs in composite bimetallic spinning rollers.

A polycrystal plasticity-cellular automaton integrated modeling method for continuous dynamic recrystallization and its application to AA2196 alloy

Continuous dynamic recrystallization usually dominates the microstructural evolution in hot working of aluminum alloys, in which the high-angle grain boundaries of new grains mainly originate from the gradual increase in subgrain misorientation angles. In this work, an integrated computational method is proposed to simulate continuous dynamic recrystallization process of aluminum alloys by coupling three-dimensional cellular automaton and visco-plastic self-consistent models. The stress response, dislocation accumulation and recovery, and evolution of crystal orientations are computed in the context of polycrystal plasticity; the formation and rotation of subgrains, followed by stored energy and curvature-driven boundary migration, are captured and visualized by cellular automaton. The non-octahedral slip mode {110}<110> is additionally introduced to capture the 〈001〉 texture during hot compression. A universal cell topology deformation method is adopted to achieve an effective track of grain morphology evolution during plastic deformation. The proposed simulation framework is validated through simulating the isothermal uniaxial compression process of AA2196 alloy under different temperatures and strain rates. The orientation dependence of CDRX during compression is numerically reproduced by correlating the subgrain formation and rotation process with the activation state of slip systems. The simulated macroscopic flow stress, 3D microstructure and inherent microstructural characteristics such as subgrain size, subgrain boundaries and textures are in good agreement with the experimental results. The proposed method provides an effective and efficient tool for multi-scale simulation of hot forming process of aluminum alloys.

Analisa Keberadaan Jamur Trichophyton rubrum pada Kuku Kaki Petugas Kebersihan Dinas Lingkungan Hidup Surabaya

Sanitation workers play a vital role in maintaining environmental cleanliness. However, many of them neglect their personal hygiene. Sanitation workers are professions that regularly wear closed shoes for long periods,the humid, hot, and dirty work environment promotes fungal infections in toenails, known as onychomycosis. The purpose of this study is to analyze the presence of the fungus Trichophyton rubrum on the toenails of the sanitation workers of the Surabaya Environmental Service Department. This study is a descriptive laboratory observation. The research was conducted from February 23 to March 13, 2024. Sample collection took place at Surabaya Environmental Service Department, and the study carried out at Mycology Laboratory of the Medical Laboratory Technology Department, Poltekkes Kemenkes Surabaya. The samples in this study consisted of toenails from 30 sanitation workers members. The examination was conducted using the culture method on SDA media, incubated for 7-14 days, followed by macroscopic and microscopic observations. The results showed that 2 samples were positive for Trichophyton rubrum (6.7%), 23 samples were positive for Aspergillus sp., (76.7%), 4 samples were positive for Rhizopus sp., (13.3%), and 1 sample was positive for Penicillium sp., (3.3%). The conclusion is, out of 30 samples, 2 individuals (6.7%) tested positive for Trichophyton rubrum, while the remaining 28 samples (93.3%) tested negative for Trichophyton rubrum.

Thermal deformation behavior of a Ni-Cr-Fe superalloy and its effect on corrosion resistance: A comprehensive analysis of strain rate and temperature effects

Thermal deformation behavior of a Ni-Cr-Fe superalloy billet were investigated by hot compression experiments under temperatures of 900–1200 °C and strain rates of 0.001–1 s−1, and the corrosion properties of the superalloy after thermal deformation were also evaluated by electrochemical tests. Compression experiments determined that lower strain rates and higher temperatures reduce the superalloy's stress levels. The Arrhenius-type model accurately described the thermal deformation behavior of the superalloy. Furthermore, the optimal hot working domain was identified between 1120 and 1170 °C and strain rates of 0.001–0.01 s−1. Microstructure observations showed that the dynamic recrystallization (DRX), characterized by grain boundary bending nucleation and consumption of numerous dislocations is the main mechanism leading to grain refinement during thermal deformation. The results of the electrochemical corrosion tests proved that the corrosion predominantly occurred near the grain boundaries (GBs) of deformed grains, worsening with increased deformation temperatures.

Study of the thermal effect of hot and cold working on the mechanical properties of medium carbon steel

Medium carbon steel is widely used in industries due to its favourable strength and flexibility. However, they are highly prone to deformation processes that affect their impact resistance and corrosion rate. This research examines the effects of hot and cold working on the mechanical properties of medium-carbon steel. Experimental tests were conducted on medium carbon steel samples subjected to hot and cold working treatment procedures via funnels for the hot working. Deformation techniques such as rolling and bending are employed by subjecting the materials to a high temperature of 900oC. At the same time, in this study, cold working uses room temperature between 0oC to 22 oC for both rolling and bending. The results show that hot bending improves the hardness property in the bending analysis, having 185.64, as opposed to cold bending, which is 174.33. It can be seen that the cold rolling treatment of medium carbon steel increases the hardness property by 179.84 compared with hot rolling techniques, which have a hardness of 161.63. The results from the rolling test show that the tensile stress at the yield point of the zero slopes is lower during the hot working process, having 598.05090 MPa, compared with the cold working results of 665.43718 MPa. However, the results of the elasticity modules show that hot working increases it with a value of 32885.24170 MPa compared with 28923.17810, respectively. It can be concluded that parameter optimization of the specification of medium carbon steel determined the specific treatment needed for the manufacturing industry to produce quality materials.