Papers by Keyword: Hot Forging

Abstract: Hot forging of nickel-based superalloys involves severe thermo-mechanical loading of the forming dies due to the high strength of these materials, even at elevated temperatures. Under industrial production conditions, forging dies are subjected to repeated heating-cooling cycles, which progressively degrade the mechanical properties of the tool steel and increase the risk of die plastic deformation. Reliable assessment of die performance therefore requires material characterisation that accounts for both temperature effects and service-induced degradation. In this work, an H13 tool steel used in an industrial hot forging application (nickel-based superalloy case study), was experimentally and numerically investigated in both its raw and service-degraded conditions. Hardness measurements, microstructural analysis, uniaxial compression tests, and quasi-static tensile tests were carried out from room temperature up to 600 °C. An artificial degrading heat treatment was applied to reproduce the mechanical state of the most degraded die regions, and the resulting data were used to quantify the temperature-dependent reduction in yield strength with service exposure. Finite element simulations of the industrial forging process were then carried out using deformable dies to evaluate temperature evolution and stress levels in critical die regions. The risk of die plastification was assessed by comparing simulated von Mises stresses with the experimentally determined temperature-dependent yield strengths for the raw and degraded conditions. The results show a significant reduction in yield strength due to both increasing temperature and service-induced degradation, leading to a substantially higher risk of die plastic deformation under production conditions. The study underlines the importance of incorporating degraded material properties into tool design and process assessment, and motivates improved cooling systems to enhance tool life and process stability.

Abstract: In recent years, the weight reduction of components in the automotive and aircraft industries has become a major issue in achieving sustainable development goals (SDGs), as it is critical to reducing fuel and energy consumption. Magnesium (Mg) alloys have the lowest density among all practical metals and have attracted attention as lightweight materials. For weight reduction, rims and wheels are fabricated by the hot forging of Mg alloys, and the shortening of the die life is a problem because of the high load on the die and the tendency to burn and wear caused by adhesion in the hot forging of Mg. The T-shape compression test (TSCT) can evaluate friction in complex deformations involving both extrusion and compression and can achieve a surface area enlargement greater than 50%. In this study, a hot V-groove friction test based on the TSCT is proposed as a friction test that simulates hot extrusion and forging. The friction coefficient is identified from the aspect ratio of the product after compression, as either longitudinal extrusion or transverse compression is the preferred deformation due to the effects of friction. The proposed test combines extrusion and compression deformation, has a high surface area expansion ratio of a greater than 50%, and produces a two-dimensional deformation in which the circle collapses. In addition, the dimensions and compression ratio can be easily changed. In this study, as part of the development of a V-groove friction test, we examine the tool dimensions and mechanism of adhesion under different temperatures and compression ratios. Using the AZ80 alloy as experimental material and varying the temperature and stroke amount, we investigate the effects of the working temperature on adhesion growth during hot forming.

Abstract: SACM 645 nitriding steel is a commercial Cr-M0-Al medium carbon low alloy steel. Due to its good balance of strength, toughness and wear resistance the steel has been widely used for several general-purpose parts. Hot forging is a heat treatment method commonly used to increase the hardness of steel. The temperature and strain rate used in hot forging of steel results in changes in grain shape and size through a mechanism known as recovery, recrystallization and grain growth. There are common problems such as defect, net shape and cracked. The designer lacked of knowledge and understanding of the behavior of materials in hot forging process. This research aimed to study material properties under Hot forging at high temperature and effect of times annealing. Experiment, it was found that at 5 temperature levels, which were 850, 950, 1,050, 1,150 and 1,200 °C and annealing test in furnace temperature constant 800°C, holding time in furnace for 6 different times (1-6 hour). Therefore hot forging and the annealing test after hot forging concluded low temperatures, annealing time less result in small grain sizes and high hardness values. On the other hand, the higher temperature, annealing time long the larger the grain size and the lower the hardness. Consequently, the designer can use the information to improve the hot forging process, annealing determines the material properties of the finished products to the design of the part fabrication process.

Abstract: This study investigates the impact of lubrication on friction factors during the hot ring compression test of BS 080M46 medium carbon steel. Hot forging processes are crucial in industries due to the strength and durability of forged products, but friction-related issues can arise. Four lubrication conditions are focused: dry, oil to black graphite, water to black graphite, and water to colorless graphite. The ring compression test procedure, including sample dimensions and lubrication application, is explained. By employing predictive calibration curves generated through FEM which monitored height and internal diameter changes during compression. The study successfully aligns FEM simulation results with experimental data, thereby enhancing the accuracy of friction factor estimations and visualizing material behavior under various lubrication conditions. Results indicate that lubrication significantly affects friction factors, with oil to black graphite performing the best, yielding a friction factor of 0.15. A comparison between theoretical and experimental friction factors shows varying agreement levels, with water-to-black graphite, and water-to-colorless graphite respectively demonstrating excellent alignment with 0.990% and 0.971%. This study has practical implications for selecting lubricants in industrial applications, potentially enhancing manufacturing processes and product quality.

Abstract: Hot-forming tools are subjected to high thermal and mechanical stresses during their application. Therefore, a suitable design of the tool die is important to ensure a long tool life. For this purpose, numerical simulations can be used to calculate the occurring stresses and the temperature development in the tools during the course of a stroke or over several forging cycles. The aim of this research is to investigate the effect of different radii on the resulting stresses in the lower die of the forming tools. Furthermore, the temperature evolution over several cycles is analysed to determine their effect on the temperature. When investigating the stress, it was found that a larger radius leads to a reduction in stresses. In addition, it could be numerically proven that the base temperature of the die levels off after a certain number of cycles. These findings will be used in further research dealing with the service life calculation of dies subjected to thermo-mechanical alternating stresses.

Abstract: Hot forging is a complex process involving the mutual influence of numerous thermo-mechanical-metallurgical material phenomena. In particular, the strains of transformation-induced plasticity (TRIP) have a significant influence on the distortions and residual stresses of the components. The TRIP strains refer to the anisotropic strains depending on the orientation and significance of the stress conditions during cooling superimposed to the phase transformation. With the use of numerical models, the impact of this effect can be investigated in order to ensure the production of high quality components. However, an experimental determination of the characteristic values of TRIP is challenging, which is why only few corresponding data are available in the literature. Therefore, this paper presents an experimental and numerical methodology as well as the results of studies on the interaction between stresses and phase transformations in the materials AISI 4140 and AISI 52100. The investigations of the TRIP strains are carried out using hollow specimens, which are thermo-mechanically treated in the physical forming simulator Gleeble 3800-GTC. The specimens are austenitised, quenched to test temperature and held there while diffusion controlled phase transformation takes place. The extent of TRIP as a result of different superimposed tensile or compressive loads is determined by means of dilatometry. In addition, the extent of TRIP for diffusionless martensitic phase transformations was investigated by continuous cooling tests under tensile and compressive loads. It was found that the transformation plasticity varies depending on the material, the phase type, the temperature and the tensile or compressive stresses. Subsequently, simulations of the physical experiments using the FE software Simufact.Forming verified the determined phase specific values of TRIP.

Abstract: Al-Mg alloys with 3, 4.7, 6, 8, and 10%Mg were fabricated using gravity casting with a copper mold at a cooling rate of 30.6 °C/s. Hot forging was conducted at 500 °C with 50% reduction. An increase in Mg content increased the tensile stress but decreased the elongation in the as-cast ingot. The tensile stress and especially the elongation were increased by hot forging. The tensile stress, 0.2% proof stress, and elongation for hot-forged Al-8%Mg were 337 MPa, 154 MPa, and 24%, respectively. These mechanical properties were obtained without heat treatment. The results show that Al-Mg is suitable for cast forging in terms of mechanical properties and energy consumption.

Abstract: Al-4.7%Mg alloy with 0, 0.2, 0.4, 0.6 and 0.8% Fe added was cast using a copper mold and an insulator mold. The cooling rates of ingots cast using the copper mold and the insulator mold were 30.6 ^°C/s and 0.5 ^°C/s, respectively. The tensile stress and elongation of the ingots cast by the copper mold were superior to those cast by the insulator mold. The addition of Fe did not lead to tensile stress, but the elongation became smaller as the Fe content increased. The elongation of the ingot cast using the copper mold became much smaller on addition of only 0.2% Fe. The tensile stress and elongation were improved by hot forging with 50% reduction. The elongation of the ingots with Fe added was significantly improved by the hot forging. The degree of improvement of the tensile stress and elongation for the ingots cast using the insulator mold was remarkable.

Abstract: The damping capacity improvement in under seawater for torpedo cone is the main of the research work. In the proposed work, an induction furnace was used to fabricate aluminum alloy AA7075 by melting individual elements such as pure Al, Zn, Mg, and Cu, followed by 10 wt.% graphite with varying sizes of reinforcement C1 (3 to 10μm), C2 (53 to 66μm), and C3 (106 to 150μm). Ingot casting was made in steel mold of 45 45 120mm³ and then hot forged at 490ᵒC, followed by solutionizing and artificial aging. Composites characterized for optical, SEM, hardness, and DMA analysis for loss factor. The improved performance in damping capacity by 50% observed for the threshold modulus of particulate (volume to the surface) for C2 composite. The processing cycle of fabrication of composites has been established.

Abstract: The effect of strain rate on the β texture evolution during two-step hot forging of Ti-6246 alloy was investigated. The two-step forging consisted of 15% or 50% prior-β forging at 980°C and subsequent 60% or 25% forging at 870°C in the (α + β) dual-phase region. The total compression ratio was 75%, and the investigated strain rates were 0.01 and 1.0 s⁻¹. The β forging texture showed typical {001} and {111} body-centered cubic textures. With increasing compression ratio in the (α + β) region and at a strain rate of 0.01 s⁻¹, the amount of precipitated α phase increased. Dynamic recrystallization was rarely observed after forging in the (α + β) region at a strain rate of 0.01 s⁻¹. Large amounts of α precipitates lowered the {001} β texture intensity through slip transmission between the α and β phases under the Burgers orientation relationship. However, in specimens forged at a strain rate of 1.0 s⁻¹, as the compression ratio in the β single-phase region increased, the growth of dynamic-recrystallized β grains was promoted at the prior-β grain boundaries, where α-phase precipitation was not substantial. These effects resulted in a higher {001} texture intensity of the β phase in specimens forged at 1.0 s⁻¹ compared with that of the β phase in specimens forged at 0.01 s⁻¹.