The dependences of the macro-and microstructures as well as the hardness of local TiC-Fe-type reinforcements (LR) fabricated in situ in steel casting using compacts containing different contents of TiC reactants and the addition of an Fe moderator have been investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Vickers hardness (HV) tests. Five powder mixtures were selected for compact preparation; one of them contains only TiC reactants, while the other four contain TiC reactants as well as 10, 30, 50, and 70 wt pct Fe moderator additions, respectively. Next, the ready compacts were introduced to the mold cavity and poured by cast steel for the in situ LR fabrication. This is the first time, through this study, that the fragmentation phenomena was revealed by macrostructural observations of the LR produced with only the TiC reactants. The increasing Fe content gradually limited the fragmentation and infiltration processes and stabilized the dimensions of the LR. With the increasing contents of the Fe moderator, the refinement of the TiC particles in the LR was observed. Due to the limited infiltration process and high surface content of the TiC, the LR produced with 30 wt pct Fe exhibited the greatest hardness.
Compacts for the synthesis of composite zones in castings were obtained by cold pressing powders of the TiC reactants under a pressure of 250, 300, 500 and 600 MPa. The all compacts made under different pressures were placed in a mould cavity and poured with liquid unalloyed low-carbon steel. From the resulting casting, four composite zone A, B, C, D, produced in this casting by in situ method. In all composite zones, TiC and ferrite (αFe) were obtained. Additionally, in zones A, B and C the presence of graphite (Cgr) was also stated. The surface friction (Sf) of Cgr decreases in composite zones A ÷ D, while both the Sf of TiC and hardness VH30 increase in these zones with increasing compaction pressure of the reactants. Too low compaction pressure applied to the TiC reactants impedes the effective propagation of the reaction of synthesis.
Application of in-situ technique allows for fabrication of composite zone in the casting with a matrix of cast steel with low carbon content. The reinforcing phase in the composite zone is titanium carbide, produced by the synthesis of substrates introduced into the mould in the form of pressed compacts. Metallographic studies were performed in order to determine of homogeneity of composite zones and characteristic features existed in transition area between the composite zone and core of the casting. The transition areas of composites zone were blurred and there were no discontinuities caused by poor bonding between the composite zone and the core of the casting. To confirm the correct run of the TiC synthesis, phase analysis was performed of the base alloy as well as composite zone. The results of this examination indicated that there were two phases in composite zone, i.e. α Fe and TiC and only α Fe was observed in base alloy. Changes of mechanical properties in the composite zone were examined, measuring its hardness HV. The average hardness values of the base alloy and composite zone were 175±4 and 696±201 HV, respectively.Keywords: composite zone, in situ, TiC, MMC, cast steel, microstructure W odlewie z ferrytycznego staliwa o niskiej zawartości węgla, otrzymano strefy kompozytowe. Fazą wzmacniającą strefy kompozytowej był węglik tytanu TiC, uzyskany w wyniku syntezy in situ substratów, wprowadzonych do formy w postaci wyprasek. Przeprowadzono badania metalograficzne stref kompozytowych w celu określenia jednorodności otrzymanej strefy kompozytowej oraz charakteru obszaru przejściowego: strefa kompozytowa -rdzeń odlewu. Obszar przejściowy, pomiędzy strefą kompozytową, a rdzeniem odlewu, charakteryzował się gradientowym rozkładem TiC oraz brakiem nieciągłości. W celu potwierdzenia prawidłowego przebiegu procesu syntezy TiC, przeprowadzono analizę fazową stopu bazowego oraz otrzymanej strefy kompozytowej. Potwierdzono, że w obrębie strefy kompozytowej występują dwie fazy tj. α Fe i TiC, a stop bazowy zawiera wyłącznie α Fe.Analizowano zmiany mechaniczne w obrębie otrzymanej strefy kompozytowej, badając jej twardość HV. średnia wartość twardości stopu bazowego oraz strefy kompozytowej wynosiła odpowiednio 175±4 i 696±201 HV.
This article addresses the effect of cooling rate and of titanium additions on the exhibited microstructure of thin-walled compacted graphite iron (TWCI) castings as determined by changing molding media, section size and Ferro Titanium. The research work was carried out on TWCI castings and reference castings of 2-5 mm and 13 mm wall thickness, respectively. Various molding materials were employed (silica sand and insulating sand ''LDASC'') to achieve different cooling rates. Thermal analysis was implemented for determinations of the actual cooling rates at the onset of solidification. This study shows that the cooling rates exhibited in the TWCI castings varies widely (70-14°C/s) when the wall thickness is changed from 2 to 5 mm. In turn, this is accompanied by a significant variation in the compacted graphite fraction. The resultant cooling rates were effectively reduced by applying an insulating sand in order to obtain the desired graphite compactness. In addition, good agreement was found between the theoretical predictions of the solidification process and the experimental outcome. Ti additions in combination with LDASC sand molds were highly effective in promoting the development of over 80% compacted graphite in castings with wall thicknesses of 2 and 3 mm as evidenced by quantitative metallographic analyses.
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