Solid State Phenomena Vol. 386

Abstract: Final turning, which is a finishing process for obtaining components with specific precise parameters, affects the integrity of the surface and its properties, whether hardness or surface residual stresses. The synergistic effect of these factors affects the susceptibility of the material, to stress corrosion cracking. In this work, 2 types of austenitic stainless steel, namely AISI 304 and AISI 321, were turned. Tool with positive cutting geometry was used for turning. The cutting parameters that varied were the cutting speed (100 and 250 m.min⁻¹) and the tool feed (0.12, 0.2 and 0.3 mm·rev⁻¹). The depth of cut was the same for all turnings (0.8 mm). Subsequently, the prepared samples were exposed in MgCl₂ solution based on the ASTM G36 for 96 hours. After this time, the samples were analysed using SEM, where the density of surface cracks was monitored. When comparing the crack density, an increase in density was visible for AISI 304 compared to AISI 321. It was shown that with increasing cutting speed, the density of cracks increased significantly, as well as with increasing tool feed. On the cross-sections the depth and length of the cracks were analysed. Crack depth and length increased with increasing feed too.

Abstract: Diamond-like carbon (DLC) coatings are valued for their excellent wear resistance and ability to extend the life of mechanical components, supporting resource conservation. However, high residual stress and poor adhesion limit their practical use. Silicon-doped DLC (Si-DLC) can reduce stress and improve adhesion, though excess silicon lowers hardness, creating a trade-off. This study aimed to optimize both adhesion and hardness by adjusting the silicon-containing gas ratio and the number of stacked layers. Si-DLC was deposited on austenitic stainless steel (SUS304) using acetylene (C₂H₂) and tetramethylsilane (TMS) via plasma enhanced chemical vapor deposition (PECVD) at 170 °C with a 1.2 µm thickness. Higher TMS ratios increased silicon and hydrogen content in the Si-DLC layer. More layers reduced hardness and low-load wear resistance but enhanced durability under high loads.

Abstract: Steel 22MnB5 is widely used in the automotive industry for manufacturing high-strength structural car body parts. To achieve desired mechanical properties, hot-stamping is used, during which the Al-Si coating plays a critical protective role against oxidation. This study investigates the structural evolution of the Al-Si coating under various austenitization durations at 920 °C. Intermetallic phase formation and coating morphology are analyzed.

Abstract: This paper presents a metallographic and fractographic study of AISI 304 austenitic stainless steel subjected to mechanical loading in the sensitized condition. Static three-point bending tests and impact tests were carried out to evaluate how sensitization affects the mechanical response and fracture behaviour of AISI 304. The study compares the initial state of the material with its condition after sensitization at 700 °C for 10 h, with emphasis on changes in plastic deformation and fracture mechanisms. Microstructural evaluation was performed using light microscopy, while Vickers microhardness measurements provided insight into local mechanical changes. Fractographic analysis using scanning electron microscopy revealed differences in fracture surface morphology. Results demonstrate a decrease in microhardness, reduced impact energy, and noticeable differences in fracture morphology following the sensitization treatment, indicating that the heat treatment influences both the mechanical response and failure behaviour of AISI 304.

Abstract: In the paper the detailed structural changes in the cutting zone were determined using metallography. Accurate determination of parameters such as shear angle, slip angle, chip thickness, cutting ratio, chip separation point, etc. required metallographic analysis on a relatively complex sampling of the cutting area. We performed the analysis on an orthogonal cutting. We achieved orthogonal cutting by turning a thin-walled Inconel 718 and C45 alloy tubes and setting the lath bit cutting edge perpendicular to the tube axis. In real state, the shapes in the cutting zone are more complicated therefore the chip thickness was determined using quantitative metallography from the equality of areas and the resulting point of transition between the chip and the machined surface. The shear angle starts from this point and is a tangent to the cutting edge, the direction of which was determined using the Thales circle. The distance between this point and the machined surface which represents a layer which is not separated from the machined material but is planar deformed was determined too. The depth of the deformed layer and the value of deformation on the machined surface was determined by quantitative metallography. A much simpler numerical simulation was performed with the same parameters using Deform 2D/3D software package. Numerical simulation could not fully replace metallographic analysis, but to some extent numerical simulation can be used instead of metallographic analysis.