PSI - Issue 65

D.S. Bezverkhy et al. / Procedia Structural Integrity 65 (2024) 17–24 D. S. Bezverkhy and N. S. Kondratev / Structural Integrity Procedia 00 (2024) 000–000

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manufacturing processes is carried out at elevated and high temperatures above 0.5 – 0.7 from the homological one. Under such forming conditions recrystallization and recovery processes occur in the materials, which have a significant influence on the internal structure. This paper examines discontinuous dynamic recrystallization, which occurs during plastic deformation in the specified temperature range. Multistage hot upsetting is considered as an example of a technological process. Examples of products produced using hot upsetting are railway axles, plates, disks, cubes, bars, shafts, workpieces for valve boxes, plungers, box wheels, ball valves, bushings, etc. (Rathi M. G. & Jakhade N. A. (2014)). Products produced using hot upsetting often have improved physical and mechanical characteristics compared to cast or mechanically processed products (Gardner S. et al. (2016)). Traditionally, industrial production of products using technological processes is based on the experience of operators, often carried out by trial and error (Tzou G. Y. et al. (2017), Mwema F. M. et al. (2019)). This is reflected in the product price and production costs (Tzou G. Y. et al. (2017), Mwema F. M. et al. (2019)). Numerical modeling methods are designed to improve this process, improving product quality and optimizing production costs. To improve production processes, it is possible to use multilevel constitutive models. Such models allow one to investigate not only the stress-strain state, but also the evolution material structure (Åkerström P. (2006), Karbasian H. & Tekkaya A. E. (2010)). Currently, finite element software packages Ansys, Abaqus, Fidesys and others are widely used to describe technological processes. Often, the material models embedded in them do not allow one to take into account the complex mechanisms and accompanying phenomena of high-temperature inelastic deformation such as recrystallization, superplasticity, etc. To take them into account, some FE software allows to encapsulate custom models. Constitutive multilevel models are promising for a detailed description of material behavior (Trusov P. V. et al. (2017)). Using custom constitutive models in conjunction with finite element software can be implemented in several methods. The first method is direct including the constitutive model in finite element software for the entire computational domain. This approach is the most accurate, but requires a significant amount of computing resources. The second method, which is considered in this paper, reduces the computational resource intensity of multilevel models. It can be divided into two stages. First, the problem is solved for the workpiece using a phenomenological model, after which, for its critical areas, the found solution is refined using a constitutive model of material. This method makes it possible to investigate in detail the material characteristics (grain size, defect density, phase properties, etc.) in the most loaded areas of the workpiece. Forging is one of the oldest metal forming processes, dating back several thousand years (Rathi M. G. & Jakhade N. A. (2014)). As a result of repeated and intermittent exposure to the processing tool, the metal is successively plastically deformed and gradually acquires the required shape and size (Choi S. K. et al. (2006)). The manufactured products have high structural integrity, good fatigue life, homogeneity, and high impact strength (Ruban P. et al. (2020)). Forged products examples are such critical parts as engine turbines, propeller and crank shafts, disks, flanges, connecting rods, gears and others (Rathi M. G. & Jakhade N. A. (2014)). Thus, the design of a modern car contains about 250 forged parts and an airplane contains more than 18 thousand (Ruban P. et al. (2020)). One of the types of forging is upsetting. Upsetting is an intermediate technological stage to which the vast majority of workpieces are subjected before their further forming and thermomechanical processing (Rathi M. G. & Jakhade N. A. (2014)). The simplest and most common upsetting is carried out by flat presses (Kajtoch J. (2007), Rathi M. G. & Jakhade N. A. (2014)). During upsetting, the size of the workpiece decreases in the direction of the applied force with a simultaneous increase in the cross section (Kajtoch J. (2007)). Thus, the workpiece undergoes uneven deformation due to the influence of frictional forces on the contact planes between the workpiece and the presses (Kajtoch J. (2007)). The unevenness of deformation and temperatures during hot upsetting leads to an uneven distribution of grain sizes throughout the volume of the forging, including as a result of recrystallization (Kajtoch J. (2007)). During the workpiece producing process, giving it the required shape is often carried out in several successive stages. During processing, the workpiece is manipulated and/or rotated between upsetting stages on the machine (Choi S. K. et al. (2006), DiDomizio R. et al. (2006), Ruban P. et al. (2020)). Figure 1 shows a diagram of a typical multistage upsetting with rotations. The workpiece is preheated in a furnace to high homological temperatures of the 2. Hot upsetting multistage process