The effects of room temperature soaking and deep cryogenic treatment on the stress relief phenomenon of Ti–Mo maraging stainless steel: experimental evidence and critical patents investigation

Abstract

By using different microstructural analysis techniques, the present study explored the influence of the soaking period before deep cryogenic treatment (DCT) on the microstructural characteristics and mechanical properties of Ti–Mo maraging stainless steel. It is found that the effect of the soaking periods before DCT on the related metallurgical phenomena is primarily associated with the amount of lattice strain remaining within the matrix before DCT. The corresponding scanning electron microscope (SEM), electron backscattered diffraction (EBSD), and Kernel Average Misorientation (KAM) analyses showed that the lattice strain within the martensite matrix would be relieved after a longer soaking time before DCT. This consequence is also consistent with the results of mechanical tests. The yield strengths (YSs) of tested samples with different soaking periods before DCT exhibited a clear decrement trend as the soaking period increased, thus also resulting in a decrement of the yield ratio. For example, the YS of tested samples with 2-h and 60-day soaking periods before DCT were 663 ± 11 MPa and 489 ± 15 MPa, respectively. On the other hand, regardless of the length of the soaking period, numerous η-Ni3Ti intermetallic compounds were randomly distributed within the matrix after ageing treatment, and they had adopted a specific Burgers orientation relationship, i.e., {011}α′// {0001}η ; <111¯>α′// <112¯0>η, with the martensite matrix.