This paper presents results obtained from a laboratory investigation conducted on material from a pressure vessel after longterm operation in the oil refinery industry. The tested material contained structural defects which arose from improper heat treatment during steel plate manufacturing. Complex tensile tests with acoustic emission signal recording were conducted on both notched and unnotched specimens. The detailed analysis of different acoustic emission criteria allowed as to detect each stage of plastic deformation and microstructural damage processes after a long-term operation, and unused carbon steels during quasi-static axial tension testing. The acoustic emission activity, generated in the typical stages of material deformation, was correlated by microscopy observations during the tensile test. The results are to be used as the basis for new algorithms for the assessment of the structural condition of in-service pressure equipment.
This paper shows results of researches of a structure and mechanical properties of metal sheets of IF steels subjected torecrystallization annealing. The annealing was held in the scope of the temperature of 600-900°C over 25 min time. The impact of heat treatment on changes of properties and structure of the researches steel has been analysed. During annealing typical processes of rebuilding of the structure deformed as a result of cold deformation in the form of forming new recrystallized grains and their growth were observed. As the temperature of annealing increases the hardness of the material gradually decreases.
In this paper small punch test (SPT) which is one of miniaturized samples technique, was employed to characterize the mechanical properties of carbon steel P110. The tests were carried out in the range of –175°C to RT. Results obtained for SPT were compared to those calculated for tensile and Charpy impact test. Based on tensile and SPT parameters numerical model was prepared. 8 mm in diameter and 0.8 mm in height (t) discs with and without notch were employed in this research. The specimens had different depth notch (a) in the range of 0.1 to 0.4 mm. It was estimated that α factor for comparison of Tsp and DBTT for carbon steel P110 is 0.55 and the linear relation is DBTT = 0.55TSPT. The numerical model fit with force – deflection curve of SPT. If the factor of notch depth and samples thickness is higher than 0.3 the fracture mode is transformed from ductile to brittle at –150°C.
The effect of CaSiAl modification (43-49% Ca, 43-48% Si, 2% Al) on the non-metallic inclusions and mechanical properties of cast lowcarbon steel is discussed. Tests were carried out on the cast steel with 0.2% C and micro-additives of V and Nb, used mainly for heavy steel castings (e.g. slag ladles). The modifier in an amount of 1.5 and 3 kg / Mg was introduced to the liquid steel before tapping the metal into a ladle. Test ingots of Y type and a weight of 10 kg were cast and then subjected to a normalizing heat treatment. Using light microscopy and scanning electron microscopy, qualitative and quantitative evaluation of the non-metallic inclusions present in as-cast samples was carried out. Additionally, tests of mechanical strength and impact strength were performed on cast steel with and without the different content of modifier. It was found that increasing the modifier addition affected impact strength but had no significant effect on tensile strength and yield strength. The material with high impact strength had the smallest area fraction of non-metallic inclusions in the microstructure (0.20%). The introduction of modifiers changed the morphology of non-metallic inclusions from dendritic to regular and nodular shapes.