Effect of Hot Working Technology on Shape Memory Effect of Fe-24Mn-3Si-7Cr-3Ni Alloy Pipe Joints

The application of shape memory alloys is very suitable for developing pipe joints, and Fe-Mn-Si memory alloy pipe joints show great promise. This paper studied the variation rule and microscopic mechanism of the strain recovery rates of Fe-24Mn-6Si-7Cr-3Ni alloy pipe joints made by three different hot working technologies: casting, forging, and rolling. The strain recovery rate of as-cast pipe joints rose monotonously with the increasing thermomechanical training cycle. As-cast pipe joints’ superior shape memory effect mainly came from the large grain size of 662.70 μm and the low density of annealing twin boundaries. On the other hand, the shape memory effects of forging and rolling pipe joints were restricted by the high densities of annealing twin boundaries and grain boundaries, respectively. Although the shape memory effects had a lower upper limit, their strain recovery rates climbed quickly. Following the third annealing, the remaining second-phase particles precipitated according to the (varepsilon)-martensitic distribution orientation, and this contributed to the shape memory effects of as-cast and forging pipe joints. During adjusting the solution treatment parameters for as-cast pipe joints, it was found that as-cast pipe joints without solution treatment exhibited a notable superiority over the solution-treated ones when less thermomechanical training was performed.