The experimental coarsening rate of M sub(23)C sub(6) particles at 800 degree C was about three times greater than that calculated from the slightly modified Lifshitz-Slyozov-Wagner equation. ...Applying a simplified relation, the coarsening rate was deduced for M sub(23)C sub(6) particles in range 800-550 degree C. The calculated coarsening rates are compared to data in references. The coarsening rate of carbide particles at 800 degree C is determined experimentally and calculated. By substituting in LSW equation molar carbide content with atom content of chromium in solid solution, the difference of both rates is lower by 2 orders of magnitude. It is confirmed that the smaller difference is due to the shorter diffusion time for chromium atoms from solid solution than from decomposing carbide particles.
The experimental coarsening rate of M23C6 particles at 800°C was about three times greater than that calculated from the slightly modified Lifshitz–Slyozov–Wagner equation. Applying a simplified ...relation, the coarsening rate was deduced for M23C6 particles in range 800–550°C. The calculated coarsening rates are compared to data in references.
The coarsening rate of carbide particles at 800°C is determined experimentally and calculated. By substituting in LSW equation molar carbide content with atom content of chromium in solid solution, the difference of both rates is lower by 2 orders of magnitude. It is confirmed that the smaller difference is due to the shorter diffusion time for chromium atoms from solid solution than from decomposing carbide particles.
The results of an investigation into the hot stretch reducing of high-frequency welded steel tubes are presented. The internal stresses were determined after every processing pass. The selected ...processing parameters ensured that the coefficient of plastic extension was maintained in the range that prevents the tearing of the tube wall and achieves the required geometrical shape as well as the planned properties of the finished tube.
Fe-NiCrMo alloys were aged for up to 17 520 h in the temperature range 290-350 deg C to achieve the spinodal decomposition of delta-ferrite. The tensile properties and the Charpy notch toughness were ...determined at room temperature and at 290 deg C. The ageing affected the tensile properties only a little, but decreased very strongly the notch toughness and to a greater extent the content of alpha-ferrite. The tensile properties were lower at 290 deg C than at room temperature and the difference was virtually independent of the content of ferrite. The notch toughness was significantly higher at 290 deg C, and the difference amounted to three times the lowest toughness of the aged alloy with the maximum content of delta-ferrite. The different effects of ageing are explained in terms of the ferrite microhardness, the strain hardening of the austenite and the mechanisms of deformation and fracturing.
Tensile tests were carried out on specimens of the same micro-alloyed structural steel after different thermal treatments, with the aim being to obtain the microstructure in a weld's heat-affected ...zone. The mechanical properties were determined at a temperature below the brittle threshold transition Charpy temperature, the fracture surfaces were examined, the cleavage strength was deduced and the space orientation of the cleavage facets was determined. No relation was found between the results of the tensile tests and the previously determined Charpy properties after an identical thermal treatment.
A survey of the solidification structure of austenitic stainless steels is presented. The solidification occurs, depending on the content of the main alloying elements, with the primary formation ...ofdelta-ferrite or austenite. In the case of primary solidification of 8-ferrite, this phase reacts with the residual melt producing austenite with a peritectic reaction. The hot workability of the as-solidified microstructure is better in the case of primary solidification of 5-ferrite, since, in this case, the accumulation of impurities in the final melt is prevented. Some impurities, slightly soluble or insoluble in the solid phase at solidification, e.g., lead, decrease the hot workability significantly, which is also lowered in the case of the segregation of soluble impurities at the boundary of austenite and 8-ferrite. The integrity of the continuous cast slab can be improved and the cracking by hot rolling can be prevented by an optimal adjustment of the steel chemical composition and the parameters of continuous casting. Laboratory tests of one-pass rolling of wedge-shaped specimens of industrial steels have confirmed the recommendations and the conclusions in the quoted references.
Steels with carbon content from 0.13 to 0.04% were rolled in temperature range 1220 to 750°C and subsequently air cooled. The microstructure as well as mechanical properties were investigated. The ...grain size in steels is first gradually decreased with lowering rolling temperature, and then it is fastly increased with further lowering of rolling temperature down to ferrite range. The microstructure is the more coarse and heterogeneous the less completed was the interpass recrystallisation of austenite and the more ferrite was present in steel during the rolling. The rolling in ferrite range produces a strong anisotropy in tensile ductility.
Five objects were chosen for metallographic examinationsfrom the hoard of Roman weapons found at Grad near Šmihel,dated to the end of the 3rd or in the first half of the 2nd centuriesBC. The ...sword, catapult bolt, and simple rod with an unsymme-trical point predominantly have a ferrite or ferrite pearlite mi-crostructure. The shafts of two pila with flat hafts also have aferrite microstructure. The point of one of the pila is made froma soft (ferrite) center and a hard pearlite layer on the surface.Evidently the earliest pila already had a hard point with a softshaft, as was noted in much later historical sources. The relati-vely poor quality of the weapons (soft steel) is explained by therapidity of production, considering also that the catapult boltsand simple rods with an unsymmetrical point were probably weaponsfor one-time use.
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