Optical Strain Measurement and Microfractography of the Fractures of Armstal 550 Steel after Temperature Tensile Tests

Abstract

A material strength investigation along with a detailed microfractography analysis of fractures formed during static tensile tests of steel Armstal 550 was performed. The tests in this research were conducted in a temperature range of 298 to 973 K. In addition, during tensile tests at ambient temperature, optical measurements of strain maps and the curvature of the neck were performed. The minimum cross-sectional diameter and the radius of the neck curvature during tensile tests were obtained. The data can be directly used to obtain the true stress–strain curve. The material property analysis confirmed the high strength of the Armstal 550 alloy. The ultimate strength at room temperature equals 2.14 GPa, whereas the yield point equals 1.65 GPa. A decrease in the strength parameters along with an increase in temperature was noted. This is a typical phenomenon related to a change in the density and thermal expansion of steel under the influence of the temperature increase. For example, at a temperature of 500 °C, the ultimate strength is more than 50% less than at room temperature. An in-depth analysis of the metallography and microfractography of fractures resulting from static tensile tests showed the formation of atypical nano- and microstructures with an elongated shape. Local nano- and microstructures were observed at different levels of intensity for different temperatures. The largest clusters of nanoparticles were present on the surfaces of the specimens examined at a temperature of 973 K. Scanning microscopy analysis confirmed the presence of molybdenum oxides.

A New Approach for Evaluation True Stress–Strain Curve from Tensile Specimens for DC04 Steel with Vision Measurement in the Post-Necking Phases

“…It is applied in solving various challenges in materials science [ 7 , 8 ], solid mechanics [ 9 ], civil engineering [ 10 , 11 , 12 , 13 ], etc. It has to be mentioned, that other techniques applied recently for mechanical testing analysis were used successfully, like Acoustic Emission Technique (AET) [ 14 ] or micrography and morphology [ 15 , 16 ].…”

Special Issue “Extreme Mechanics in Multiscale Analyses of Materials”

“…The papers included in this Special Issue deal with a broad spectrum of interests in analytical, computational, and experimental studies on extreme types of material behaviour. The included papers encompass many areas of extreme mechanics modelling including: a strength investigation using detailed microfractography analysis of fractures formed during static tensile tests of steel Armstal 550 [ 1 ], a study on the effect of NTO content on the properties of an HMX-based cast-PBX (polymer bonded explosive) [ 2 ], the dependency of contact length on cutting speed and other variables performed by the optical method in cutting processes [ 3 ], bone molecular models at the nanoscale [ 4 ], molecular models of bones at the nanoscale, the characterisation of composites’ mechanical behaviour at low temperatures [ 5 ], the diffusion of hydrogen atoms through the grain boundaries of materials, the failure properties of batteries under axial forces [ 6 ], the deformation and failure properties of Ni lithium batteries [ 7 ], the effect of material heterogeneity on the environmentally assisted cracking growth rate of Alloy 600 for safe-end welded joints [ 8 ], the high strain yielding of the additive manufacturing of Inconel 625 through laser melting [ 9 ], the effect of the yield strength distribution of welded joints on the crack propagation path and the crack mechanical tip field [ 10 ], the effect of mechanical heterogeneity on strain and stress fields at crack tips of SCC in dissimilar metal welded joints [ 11 ], and the characterisation of mechanical heterogeneity in dissimilar metal welded joints [ 12 ].…”