The number of carbide particles stringers at boundaries and subboundaries of martensite per unit of surface decreases with the third root of tempering time at 1073 K. The accelerated creep rate at ...853 K depends on the number of stringers of carbide particles per unit of surface, and below an inflection point, the creep rate increases strongly. Equations relating for creep rate are discussed in terms of experimental creep rate, number of carbide particles stringers and average particles spacing.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Two creep resistant steels, P91 and X20, were tempered for 17520 h at 650 °C or 8760 h at 750 °C to study the growth and redistribution of carbide precipitates in martensite. On specimens annealed ...for a different time, yield stress at room temperature and accelerated creep rate at 580 °C were determined. With increasing yield stress in the range from 350 to 650 MPa the accelerated creep rate decreased continuously by about 2 orders of magnitude from 8·10−7 s−1 to 5·10−9 s−1. For equal yield stress, the creep rate was slightly lower for the steel P91 than for the steel X20.
A high strength low alloyed (HSLA) V-Nb steel was heat treated to martensite and lower bainite with different grain size, reheated for 3 seconds at 750 degree C and air cooled. Charpy notch tests ...were performed from-100 degree C to 60 degree C and the hardness assessed at room temperature. For as delivered steel and lower bainite, the upper shelf toughness was above 200 J and the transition temperature low, while, for martensite the upper shelf toughness threshold was aproximateky at 0 degree C. After reheating, notch toughness was decreased moderatly for martensite and strongly for lower bainite. Independently on grain size, lower bainite was more propensive than martensite to embritlement after short reheating in the ( alpha + gamma ) range. For martensite, the change of notch toughness was not related to change of hardness, as by lower hardness lower, also toughness was lower.
The fracturing of structural steels in Charpy ductile range is investigated. The dependences load versus deflection and time were recorded and the consumption of energy for different fracturing ...events, as f.i. plastic deflection and crack propagation was assessed. The micromorphology of the crack surface and lips is examined and the succesions of decohesion mechanims is deduced. The aproximate change of fracturing temperature due to adiabatic dissipation of deformation energy as heat is deduced, also.
Theoretical analysis of the dependence microstructure creep rate. Discussion on the effects of carbide particles size and their distribution on the base of accelerated creep tests on a steel ...X20CrMoV121 tempered at 800 deg C. Analysis of the stability of carbide particles size in terms of free energy of formation of the compound. Explanation of the different effect of VC and NbC particles on the resistance to accelerated creep rate.
By lowering the testing temperature down to below the nil ductility temperature (NDT −20°C) the yield stress, tensile strength and the uniform elongation are increased, while the reduction of area is ...slightly decreased and the Charpy notch toughness strongly decreased. After strain ageing, the tensile properties are increased, the uniform elongation strongly decreased and the reduction of area slightly decreased. The effect of low temperature on the tensile properties is similar for as-delivered and strain-aged steels. The tensile fracture of as-delivered and strain-aged steels at the NDT −20°C is ductile, while the Charpy-V notch toughness (CVN) fracture is brittle at a significantly higher temperature. The fracture of CVN specimens in the transition temperature range is basically similar to the fracture of notched tensile specimens tested with loading rates in the range 0.1–1500
m/s at the NDT. The mechanism of CVN fracture is discussed.
A storage tank for 93 % phosphoric acid was built in Luka Koper from 7 mm thick ground hot-rolled plates of 316L stainless steel. The capacity of the storage tank is of the 750 m3, diameter of 11 m ...and the height of 8,2 m. The shell plates were welded manually using the shielded metal-arc and gas-metal-arc processes. Before the erection, welding procedure tests according to EN 288-3 were carried out. During the construction several non-destructive examination methods were used, such as radiographic testing and visual and liquid penetrant examination. After the entire tank and roof structure were completed, a hydrostatic leak test was carried out. The surfaces of all the welds on the internal surface of the vessel were ground and the roughness was checked on site. The surfaces of the base material and the ground welds were passivated and tested for resistance to corrosion with electrochemical measurements.
The number of carbide particles stringers at boundaries and subboundaries of martensite per unit of surface decreases with the third root of tempering time at 1073 K. The accelerated creep rate at ...853 K depends on the number of stringers of carbide particles per unit of surface, and below an inflection point, the creep rate increases strongly. Equations relating for creep rate are discussed in terms of experimental creep rate, number of carbide particles stringers and average particles spacing. PUBLICATION ABSTRACT
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Local brittle zones (LBZ) cause the unstable fracture behaviour of weld metals. This threatens the safe service of welded structures and makes structural assessment procedures difficult. Therefore, ...the unstable fracture behaviour of an overmatched high strength low alloyed steel weldment was experimentally investigated. It showed that any interaction between two adjacent weld metal matrix and soft weld metal inclusions produces LBZ, causing local unstable fracture behaviour. The formation of a low hardness region is attributed to the multipass welding reheating process between Ac
1 and the self-tempering temperature. The presence of partly solid metallic inclusions with a high content of alloying elements and pro-eutectoid ferrite microstructure were found to be additional causes for the local unstable fracture behaviour of the weld metal. Local strength mis-match induced the yielding and strain hardening in the soft weld metal inclusions, contributing significantly to unstable fracture behaviour. Thus, a significantly different scatter of experimental results can be obtained. In the cases of specimens with through-the-thickness crack, not only is the scatter significantly lower, but the toughness itself.
The fracture toughness of some areas in the multi-pass heat affected zone (HAZ) of a high strength low alloy (HSLA) structural steel was analysed in a straightforward way using precracked, ...cylindrical specimens tested on a conventional tensile machine. The specimens were made from samples with a simulated HAZ microstructure; however, the size of the samples was restricted by the limitations of the Gleeble machine. The brittleness of the samples was an indication of the detrimental effect of welding on their toughness. The specimens were not large enough for a direct K
Ic
measurement over a wide testing temperature range; it was necessary to modify the results. The low fracture toughness and the substantial shift of fracture transition temperatures suggest that welding of the investigated steel could be a delicate procedure.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
