Contribution to the thermal properties of selected steels

The paper deals with the influence of structural changes on heat transport phenomena of steels samples. Three samples of 10GN2MFA steel were thermally treated at quenching temperatures equal to 900 °C, 1 000 °C and 1 100 °C, and temperature of the tempering was 670 °C. Both thermal diffusivity and thermal conductivity increase with the quenching temperature. Specific heat capacity of steel samples after thermal treatment does not change significantly. Further three different high manganese steels were measured. Maximal content of Mn and C was 27 and 0,5 mass percent. From results of thermophysical properties after ageing, one can see the increase of thermal diffusivity up to 20 percent, thermal conductivity up to 15 percent, decrease of specific heat capacity is not significant. All measured values of thermophysical properties are in good agreement with literary data (before ageing).Web of Science54119018

Thermal conductivity of nickel superalloy MAR-M247

The paper presents the narrow connection between γ’ phase dissolving and values of thermal conductivity. In annealing process the free space among γ’ particles (blocks) changes in certain cycle from fine to rough and back to fine. This is accompanied by decrease and subsequent increase of thermal conductivity as well as the sample density. The results of thermal conductivity coarse are supported by image analysis.Web of Science55342242

Corrosion fatigue of austenitic stainless steels for nuclear power engineering

Significant structural steels for nuclear power engineering are chromium-nickel austenitic stainless steels. The presented paper evaluates the kinetics of the fatigue crack growth of AISI 304L and AISI 316L stainless steels in air and in corrosive environments of 3.5% aqueous NaCl solution after the application of solution annealing, stabilizing annealing, and sensitization annealing. Comparisons were made between the fatigue crack growth rate after each heat treatment regime, and a comparison between the fatigue crack growth rate in both types of steels was made. For individual heat treatment regimes, the possibility of the development of intergranular corrosion was also considered. Evaluations resulted in very favourable corrosion fatigue characteristics of the 316L steel. After application of solution and stabilizing annealing at a comparable Delta K level, the fatigue crack growth rate was about one half compared to 304L steel. After sensitization annealing of 316L steel, compared to stabilizing annealing, the increase of crack growth rate during corrosion fatigue was slightly higher. The obtained results complement the existing standardized data on unconventional characteristics of 304L and 316L austenitic stainless steels.Web of Science612art. no. 31

Gass presure sintered Si3N4 – MgSiN2 composites

Si3N4 and MgSiN2-based ceramic composites have excellent thermo-physical and mechanical properties, however with limited industrial applications. In this paper the preparation of Si3N4/MgSiN2 composite by gas pressure sintering (GPS) is described and some of the mechanical properties like Vickers hardness and indentation fracture are characterised and compared with hot pressed (HP) samples. The 15,3 GPa hardness and 7,6 MPa∙m1/2 fracture toughness of GPS composites was slightly lower compared to HP samples (16,5 GPa, 8 MPa∙m1/2).Web of Science55479579

Hydrogen embrittlement of welded joint made of supermartensitic stainless steel in environment containing sulfane

The work is focused on evaluation of resistance of the welded joint made of supermartensitic 13Cr6Ni2.5Mo stainless steel to sulfide stress cracking. Testing method A and solution B in accordance with NACE TM 0177 were used. All the testing samples were ruptured in a very short time interval but welded joint samples were fractured primarily in the weld metal or in heat affected zone and not in the basic material. Material analysis of samples were made with use of a ZEISS NEOPHOT 32 light microscope and a JEOL 6490LV scanning electron microscope.Web of Science61271170

Hot ductility of TiNb IF steel slab after hot torsion testing

The aim of the work was to evaluate the hot ductility loss in TiNb stabilized IF steel directly from the continuously-cast slab using hot torsion testing (plastometry) in the temperature range 600-1250 degrees C according to the basic programme, and also after temperature cycling. A good match of the temperature dependences of number of turns to failure (N-f) and intensity of deformation Se was confirmed. In both cases, the existence of three temperature areas with decrease in plasticity to a minimum was confirmed. The two-stage temperature cycling according to the CT1150 and CT900 programmes mostly resulted in a decrease in plasticity compared to the basic programme. The most significant effect of cycling was related to the CT900 programme below the maximum plasticity in the base programme at 850 degrees C. A less pronounced decrease was observed for CT1150 cycling below the maximum plasticity in the base program at 1050 degrees C. In the case of CT1150 cycling, more complex particles were observed at the fractures compared with the basic programme, namely carbonitrides of Ti and Nb in combination with oxisulfides respectively, then Ti nitrides with oxisulfides or oxides and, in addition, complex (Fe,Nb)P-4, (Ti,Nb)(3)S-4 type particles. Their mean size determined statistically using TEM was much finer, only 20 nm versus 42 nm in the basic programme. Similarly, CT900 cycling revealed finer particles with an average size of 37 nm compared to 105 nm in the basic programme. The observed particles were Al oxides, Ti(N, C) and (Ti, Nb) 2S, in contrast to the particles probably of TiFe and FeMnS in the basic programme. The decrease in plasticity corresponded to the finer particles, newly created in the temperature cycling.Web of Science97art. no. 75

The influence of testing methodology and changes of microstructural parameters on resistance of duplex steel to sulphide stress cracking

The paper is focused on the evaluation of duplex ferritic-austenitic steel resistance to sulphide stress cracking (SSC). The testing was performed in accordance with the NACE TM 0177 Standard using tensile tests and four-point bending tests. The steel was always tested in two diff erent structural states, in the as-received state (marked as AR), and after laboratory annealing by the mode of 800 °C/5h/air (marked as AN). Microstructure of steel in the AR state was formed by ferrite and austenite, the AN state was characterized by an disintegration of the part of ferrite and by formation of brittle σ phase. The aim of this study was to evaluate the eff ect of testing methodologies and changes of microstructural parameters of duplex steel resistance to SSC.Web of Science52331631

Fyzikálně - metalurgické problémy optimalizace tepelného zpracování a hodnocení vlastností austenitických ocelí pro jadernou energetiku resp. chemické strojírenství

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