Tiのβ→α変態におよぼす冷却速度の影響について

Abstract

Using a hot-stage microscope with cinecamera, the kinetics of β-α transformation of titanium was observed by means of the surface relief associated with the martensitic transformation, especially the effect of the rate of cooling. on the β-α transformation of titanium was studied. When the rate of cooling was below 20°C/min, the kinetics of the transformation showed the following results:-(1)The growth rate of α needles was proportional to the rate of cooling, and increased with the increasing rate of cooling. (2) The maximum height of surface relief of α needles was inversely proportional to the rate of cooling, and decreased with the increasing rate of cooling.(3) The grain size of α crystal decreased and the its hardness increased with increasing rate of cooling. However, the increase of hardness was saturated at the rate of cooling of 20°C/min. (4) The Ms point was 885°, the Mf point was 860° and the range of transformation temperature was 25°. (5) The β-α transformation of titanium was athermal martensitic transformation and the kinetics of the transformation was the nucleation and growth process, i.e.the “Schiebung” martensitic transformation.