| 921A steel is an important ship-building steel made in China.During using it, brittleness breakage isn't permitted.Toughness demands fully strict.In order to improve quality serving in the condition of low temperature,someone made a dynamic fracture toughness test.By doing that,we can offer some important data for 921A's temperature effects.At the same time it can improve 921A quality,improve on its technique of production and offer some important theory data.In this paper according to the standard of GB/T 229-1994,GB/T 12778-91, ISO 14556: 2000 (E) the Charpy impact test is made.The morphology of dynamic fracture and F-S(F-t)curve acquiring from the instrumented impact machine can make us more clearly learn its rupture process.It confirms dynamic fracture toughness KId, dynamic J-integral, crack initiatioin energy EM, crackpropagation energy EP and converting JId to KIdJ.It finds that impact absorbenergy Ak and fracture fiber rate versus temperature.The ductile-brittle transition temperature is defined.The rule of transition of dynamic fracture toughness versus temperature was first obtained.By series temperature dynamic fracture toughness testing,acquire some dynamic mechanics capability data and build up them relationship.It can offer credibility theory data for material safely design and capability evaluating.The result shows:921A steel's ductile-brittle transition temperature is -100 ℃.It occurs a ductile-brittle transition character from -84℃～-60℃.So the use temperature of 921A should higher than -60℃.It can be improved through fracture and dynamic fracture curve.
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