A new ledeburite cast steel was designed based on a matrix precipitation hardened with intermetallic compounds of a chemical composition enriched by adding about 4.25% V totally balanced with carbon. A martensitic-austenitic matrix with a ledeburite network at the crystallite boundary prone to the strengthening effect with intermetallic compounds was obtained. Both hardness (about 400 HV20) and fracture energy KV (about 3 J) of the new material are only slightly superior to the same properties offered by the cast G200CrNiMo4-3-3 steel used so far for the section rolls operating in medium and large rolling mills. The applicability of the new cast steel in industrial practice will mainly depend on its tribological properties.
Keywords: ledeburite cast steel, precipitation hardening, microstructure, toughness, metallurgical mill rolls,
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Microscopic observations and quantitative analysis of the microstructure image were used to analyze the solidification course and morphology evolution in polyphase eutectics in the AlSi casting alloys with transition metals Fe and Mn. The utility of the analytical test procedures was demonstrated. It was stated that their precision and repeatability should be improved. Further works on quantitative morphological coefficients used as objective discriminators of the particular morphological form of phase constituents should be continued.
Nevertheless, obtained results of the microstructure image analysis indicated that in a concentration range of transition metals: Fe 0.5-1.5 wt. % and Mn 0-0.5 wt. %, the total Vv of the eutectic intermetallics has increased with a total content of the transition metals (Fe + Mn). In both group of alloys hypo- and eutectic the final results of the competition between phases αc-AlFeMnSi, αH-AlFeSi and β-AlFeSi have been explained as affected by non-equilibrium microsegregation of Fe, Mn and Si in solidifying liquid, and by the actual value of the Fe/Si coefficient. Preferences for αc-AlFeMnSi phase were reinforced by a decrease in the value of Fe/Mn coefficient.
Keywords: aluminium alloys, transition metals, intermetallic phases, eutectic,
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Adam Kokosza, Jerzy Pacyna
Stress measurements were taken on three castings made on the laboratory scale by different technologies from ledeburite alloy steel; the obtained results were subjected to a detailed analysis. The first casting was made by a conventional technique, i.e. by pouring metal through the riser into a bentonite sand mould. In the case of the second casting, the mould pouring process was additionally assisted by vibrations applied in order to reduce to a minimum the stresses formed in the casting. The process of making the third casting included a metallurgical treatment of molten metal, which comprised deoxidation using CaSi (0.1 wt. %), inoculation with a complex Reseed® inoculant (0.1 wt. %) and argon blowing of the melt. Stresses were measured by a magnetic method based on the Barkhausen noise effect. It has been found that mould vibrating immediately after pouring did not yield the expected result of stress level reduction. Only the additional vibration treatment and stress relief annealing conducted on raw castings 1 and 2 slightly reduced the stress level in the surface layer of these castings. On the other hand, very satisfactory results were obtained with the secondary metallurgical treatment of molten metal. This treatment has contributed to a very significant stress reduction in the surface layer of the examined castings.
Keywords: stress state, Barkhausen noise method, stress relief annealing, cast alloy steel, surface layer,
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Łukasz Pałyga, Mateusz Stachowicz, Kazimierz Granat
The article presents the results of investigations of the effect of selected casting parameters on the structure of casts made under high pressure by means of the casting machine produced by BÜHLER, type H630-B, out of the AlSi9Cu3 alloy from the EN AB-46000 group, with varying parameters of the piston operation. The investigations were performed on appropriately prepared specimen sampled from casts of an armchair back bracket. For the evaluation of the cast structure a scanning electron microscope was used, whose EDS software allows for determining the composition of the alloy with the consideration of the distribution of the elements. Also, measurements of the cast hardness and the structure component microhardness were performed. After a series of tests, evaluation of the structure of the microsections of the samples of casts made with varying casting parameters, during phase II and III of the pressure casting process, was performed. It was established that, at low piston rates, larger precipitations crystallize, which were characterized by very high hardness. Increasing the piston rate causes refinement of the product structure; however, decreasing the pressure of intensification of phase III leads to a drop of the cast hardness.
Keywords: pressure casting, structure, silumin, microhardness, SEM,
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Mateusz Stachowicz, Kazimierz Granat, Łukasz Pałyga
An attempt has been made to determine the effect of the addition of an agent wetting the surface of silica sand grains, introduced in order to increase the hardening efficiency of selected physical methods applied to the ecological foundry sands bonded with sodium water glass. The effect of water used as a wetting agent of the silica sand grains, added during the mixing process prior to the introduction of unmodified inorganic binders, was evaluated by comparing the mechanical and technological parameters of green sands and sands hardened by drying at 100°C. Tests and studies were carried out on silica sand of medium grain size and on three grades of hydrated sodium silicate, i.e. 137, 140 and 145. It has been found that modification of the method of the base sand processing by adding water prior to the addition of a small amount (1.5 parts by weight) of binder has a beneficial effect on the technological and mechanical parameters of moulding sands obtained after the hardening process. The results of measurements were confronted with the SEM studies of bonds formed between the grains of silica sand. The studies were completed with photographs and chemical analysis of the surface of silica sand grains. Based on a comprehensive evaluation of moulding sands hardened by the conventional drying process, the beneficial effect of a wetting agent, added to the sand mixture in an amount optimum for a given type of binder, has been confirmed.
Keywords: foundry industry, drying, moulding sand, water glass, strength, wettability,
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