Generally, I'm looking for the effect of grain refinement on cleavage stress, and it's relation to the grain boundaries. Why Ductile to brittle behavior disappears in the ultra fine-grain size region below 1um?
This is what we put on our paper
"A feature of maraging steels, and BCC metals in general, is a marked transition from ductile to brittle behaviour with falling temperature [27]. The ductile to brittle transition temperature (DBTT) is due to the high dependence of the stress required to move a dislocation with temperature in BCC metals; if the temperature is low enough this stress can exceed the stress needed to propagate a crack and result in a brittle failure. Although, this would suggest the DBTT to occur at a distinct temperature, in reality it is spread over a range of temperatures. The DBTT can shift to higher temperatures with larger grain sizes or when the movement of dislocations is inhibited, such as in the presence of precipitates [5,38,39]. Both the yield and fracture stresses are expected to increases with the reciprocal of the square-root of the grain size, but the fracture stress is expected to have a greater grain size dependence [2], which is why a smaller grain size results in a lower DBTT even if it increases the yield stress."
From
[5] Petch, N.J. Fracture: Proceedings of an International Conference on the Atomic Mechanisms of Fracture; Technology Press of Massachusetts Institute of Technology: Cambridge, MA, USA, 1959
[38.] Allen, H.R.; Rees, N.P.; Hopkins, W.P.; Tipler, B.E.Tensile and impact properties of high-purity iron-carbon-manganese alloys of low carbon content.J. Iron Steel Inst.
1953 174, 108.
[39.] Honeycombe, R.W.K.The Plastic Deformation of Metals; Edward Arnold: Maidenhead, Berkshire, England, 1984.
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Article The Influence of Lath, Block and Prior Austenite Grain (PAG)...
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