Formation of martensite crystals in the limiting case of a supersonic growth rate

Abstract

A brief overview of the basic concepts and achievements of the dynamic theory of supersonic growth of martensite crystals is given. It is shown that a consideration of the limiting case of a high growth rate allows for achievement of the physical transparency and mathematical simplicity of the description. Attention is focused on a number of topical problems of a new stage of investigations.

Elastic fields of (774)γ[4 4 $\overline {14} $ ]γ crystons and the formation of a lath structure of bainitic ferrite

“…In accordance with [10], as the model set of elastic mod uli, we chose С L = 0.2508, C' = 0.0271, and C 44 = 0.1034 TPa for the Fe-31.5Ni alloy at a temperature T = 673 K. Compared to the case of the carrier of shear (558) γ considered in [9], the transition to the shear (774) γ (apart from the interest in the consideration of a variant > 1) requires that we increased tanψ. In accordance with the results of [6], we assume that tanψ = 0.22.…”

“…At present, this scenario can only be considered to be the most likely. In connection with this, it is worthy of noting that, in [6], the formation of austenite twins was noted to accompany the formation of lath crystals of bainitic ferrite.…”

“…Just as in [4], we will assume that the lath crystals are formed in the supersonic regime via the martensi tic mechanism [5,6]. This means that, in the elastic fields of defects there exist local regions with lowered interphase barriers for the development of initial excited states (IESs) in the form of extended rectangu lar parallelepipeds.…”

Estimation of the effective growth rate of a plate of bainitic ferrite in dynamic theory

“…One should note that a specific feature of the γ-α martensitic transformation (MT) in steels is an extremely high (supersonic) rate of crystal growth, which is adequately described [7][8][9] in terms of the concept of the control wave process (CWP). The wave mechanism of controlling growth is associated with the specific process of heterogeneous nucleation of crystals, which is related to the appearance of an initial excited (oscillatory) state (in the form of an elongated rectangular parallelepiped) in the elastic field of a defect (as a rule, of an individual dislocation).…”

“…The aim of this work is to show the similarity of the mechanisms of the formation of lath crystals of bainite and of packet martensite in terms of the dynamic the ory of the formation of martensite crystals [7][8][9] based on experimental information concerning the morpho logical signs of bainitic ferrite, as well as to give an ade quate interpretation of the effective rate of growth of a bainitic ferrite plate.…”