The brittle‐ductile transition temperature in the solidification range depends on the composition of the phase which solidifies as the last one. The paper presents a thermochemical study of Fe‐Mn‐C‐P system, determining the conditions of crystallisation of carbides, phosphides and the pseudo‐ternary eutectic ML‐M3C‐M3P. Manganese raises the phosphorus concentration in eutectic. The eutectic temperature attains its maximum at about 6% of Mn. Then the brittle‐ductile transition temperature is about 30 K higher than in ternary Fe‐C‐P alloy. A further raise is possible when the alloy is modified by an element forming stable, solide carbide, for ex. titanium.
The results of theoretical analysis were verified by experimental work. The influence of titanium on the inclusions appearing in the vicinity of hot cracks of Hadfield cast steel has been studied.
Over-all mechanical properties of alloys are extremely low at the last stage of solidification where alloy exists at brittle temperature range (BTR). When the solidification process is completed a sudden and marked change in strength and ductility of metal is observed. It means that as long as liquid phase is present, metal will fail in a brittle manner. There are known different theories of brittleness of alloys in existence of liquid phase. The idea involved by authors of the paper is as follows: three major factors caused by presence of liquid may be taken into account:-decreasing the energy needed for crack nucleation, -increasing atomic diffusional flux out of the crack tip, -creating a path for abnormally quick diffusion of atoms from the crack tip. Keywords: high temperature brittleness, hot tearing, shrinkage brittleness, mushy state Własności mechaniczne stopów są bardzo niskie w ostatnim stadium krzepnięcia, w którym stop wykazuje kruchość wysokotemperaturową. Przy końcu procesu krzepnięcia obserwuje się nagłą zmianę wytrzymałości i plastyczności metalu. Dopóki występuje faza ciekła metal ulega zniszczeniu w sposób kruchy. Przyczyną tego mogą być trzy główne czynniki związane z obecnością fazy ciekłej: a) spadek energii potrzebnej do zarodkowania pęknięcia, b) wzrost strumienia dyfuzji atomów od wierzchołka pęknięcia, c) utworzenie ścieżki do anomalnie szybkiej dyfuzji atomów od wierzchołka pęknięcia.
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