Materials Science Forum Vol. 1163

Abstract: A computer program in Python was developed based on the mathematical model, which allows obtaining preliminary calculations of the diffusion coefficient and nitriding time of a punch part. As a result of a numerical experiment, the process of nitrogen diffusion into the depth of the part was studied. The redistribution of nitrogen occurs as a result of diffusion due to the nitrogen concentration gradient in the volume of the part and the high quenching temperature. The numerical experiment confirms the full-scale experiment. Nitrogen penetration into the depth of the metal occurs precisely at the quenching temperature. The nitrogen content in the internal nitriding zone due to the nitrogen released from the surface layer increases and decreases on the surface with the exposure time of the part. Computer modeling and research of the diffusion coefficient in the process of heat treatment after ion nitriding made it possible to establish that for tool steels, diffusion along grain boundaries occurs. Thus, the use of complex ion nitriding (CIN), i.e. ion nitriding and subsequent heat treatment of nitrided parts allows you to change the phase composition and increase the depth of the nitrided layer due to nitrogen doping, control the nitrogen concentration and hardness along the depth of the nitrided layer due to selected modes.

Abstract: The article considers the features of heat treatment of steels, includes quenching, phase transformations and their influence on the structure and properties of the material. The key parameters of heat treatment are described: heating temperature, holding time and cooling rate, as well as their role in forming the required mechanical characteristics of steel. Phase diagrams are considered, in particular for the "iron-carbon" system, and their significance for choosing processing modes. Additional friction-strain hardening (AFSH) of various steel grades (20, 45, U7, U12) after preliminary quenching and low-temperature tempering is studied. An analysis of microstructural changes and microhardness of surface layers after AFSH is carried out, which confirmed the effectiveness of additional hardening. It was found that steels with a higher carbon content, limited to 0.8 %, demonstrate a greater depth of the hardened layer and higher microhardness values, which determines their feasibility for use in conditions of increased wear. The results of the study emphasize the importance of choosing the optimal AFSH mode depending on the carbon content in the steel, which has a significant impact on the formation of the strength characteristics of the material.

Abstract: The study investigates the kinetics of plastic deformation propagation in a welded joint of 10G2FB steel after submerged arc welding. A metallographic analysis of the microstructure of the weld seam, fusion zone, and heat-affected zone was performed. Tensile testing and electron microscopy studies were conducted to determine the mechanisms of plastic deformation and crack initiation. It was found that the fusion zone is the most vulnerable to the formation of deformation defects, which can affect the durability of the structure. Recommendations for optimizing welding parameters to improve the mechanical properties of welded joints are proposed.

Abstract: This paper integrates a comprehensive overview of cylindrical shell simulations by means of finite element analysis, focusing on both ductile and brittle fracture behaviors under explosive loading. Special attention is given to high-carbon alloy steels that exhibit pronounced cleavage or quasi-brittle behavior and can produce smaller, higher-velocity fragments under certain conditions. We discuss key numerical approaches for fragmentation modeling and shrapnel kinetic energy calculations, and explore the relevant constitutive equations—particularly the Johnson-Cook law for high strain-rate plasticity and Linear Elastic Fracture Mechanics (LEFM) parameters for cleavage-type fracture. Emphasis is placed on microstructural factors (grain size, carbide distribution) that govern fracture and fragment mass distribution. We incorporate experimental findings on brittle fracture of steels under internal blast, highlighting how microcrack formation, alloy carbides, and high hardness can alter fragmentation and shell initial velocity.

Abstract: Accurate prediction of steel microstructure is critical for ensuring desirable mechanical properties in industrial applications. This research integrates metallurgical transformation models into a convolutional neural network (CNN) for the classification and quantitative analysis of steel microstructures, including ferrite, pearlite, bainite, and martensite. The model utilizes image-based grain structure recognition in combination with explicit mathematical relations, such as the Hall-Petch equation for yield strength, the Koistinen-Marburger equation for martensitic transformation, and the Avrami equation for ferrite and pearlite phase fraction prediction. By implementing these relations within a Python-based machine learning framework, the network not only classifies steel phases but also estimates grain size, transformation kinetics, and mechanical properties. The developed approach achieves an accuracy of over 90% in microstructure classification and enables real-time prediction of metallurgical characteristics from microstructure images. This research provides a new avenue for computational material science by integrating data-driven neural networks with fundamental physical models.

Abstract: Al-Si-Mg alloy strips with a Si content ranging from 0.5% to 12% were cast using a vertical type high-speed twin-roll caster at a roll speed of 60 m/min. The effect of Si content on ripple marks and cracks on the cast surface, as well as center cracks (crocodile cracks), was investigated. The results show a relationship between the Si content and these defects. When the Si content was higher than 4%, surface cracks and center cracks did not occur. However, ripple marks worsened when the Si content ranged from 3% to 5%.

Abstract: In this study, the bonding of WC-Co cermet to AISI 304L stainless steel was achieved through the flash spark plasma sintering (FSPS) process under a steady pressure of 5 MPa and ultra-short holding durations. The investigation focused on the impact of holding time on interfacial characteristics, diffusion behavior, and mechanical performance. The results demonstrated that prolonged holding times, particularly up to 12 seconds, led to pronounced interfacial deformation and significant diffusion of Co, Ni, and Fe elements across the joint interface. Toughness assessment of the WC-Co cermet near the bonded region was carried out using the Vickers indentation fracture (VIF) technique. The analysis revealed a decline in mechanical integrity with extended holding times, increasing the brittleness of the joint despite the enhanced elemental diffusion between the cermet and the stainless steel.

Abstract: Al-25%Si has excellent fluidity, which allows for the casting of heat sinks with thin and tall fins. During recycling, the content of impurities such as Fe, Cu, and Mg increases. The effect of these impurities on the fluidity of the alloy was investigated. The results show that the influence of impurity elements on fluidity is small. JIS ADC12 is a popular aluminum alloy that is more economical than Al-25%Si. Si was added to ADC12 to reach a 25% Si content, producing an economical Al-25%Si. The fluidity of Si-added ADC12 was almost the same as that of Al-25%Si. Heat sinks with fin heights of 50 mm, fin top thicknesses of 0.5 mm, and a draft angle of 0.5°, were cast using the Si-added ADC12. The molten metal filled the cavity, but solidification cracks occurred when the fin top thickness was 0.5 mm. When the fin top thickness was increased to 1 mm, solidification cracks did not occur.

Abstract: The performance of three kinds of mold lubricants was evaluated by testing the flow length of Al-4.7%Mg alloy. The lubricants tested were a heat-insulating type with inorganic compounds (10~20%), a heat-insulating type with organic acid salts (~10%) and a water-soluble type with mineral oil (20~30%). The flow length of the alloy was longest when using the heat-insulating type with inorganic compounds, and shortest with the water-soluble type with mineral oil. Additionally, data variation was largest with the heat-insulating type with inorganic compounds, and smallest with the water-soluble type with mineral oil.