In this work the influence of the particular stages of a multi-stage heat treatment on microstructure and properties of the Ti-47Al-2W-0.5Si alloy was presented. The alloy was melted in a vacuum induction furnace at a special graphite crucible. The received alloy in form of cylindrical ingot with a diameter of 16 mm and a length of 120 mm was homogenized at 1400°C for 1 h with furnace cooling (Stage 1). The proposed further treatment consists of a cyclic heat treatment (Stage 2), under-annealing carried out in a two-phase α+γ area (Stage 3) and a short full annealing conducted in α-phase area (Stage 4). Selection of particular stage parameters including the upper cycle temperature, the soaking time at the upper cycle temperature, the cooling rate from the upper cycle temperature and number of cycles for the second stage and the temperature and time of annealing for the third and forth stage was presented. The purpose of the proposed treatment is microstructure refining. This refinement is associated with the massive transformation that occurs in the alloy after heating to a temperature of 1405°C, short soaking time and cooling in air. The effect of heat treatment parameters on the microstructure and hardness of the investigated alloy was characterized.
Understanding the effect of multi-stage heat treatment on the microstructure of cryogenic structural steel
