Research Of Casting FeMnSiCrNi Shape Memory Alloys And Its Pipe Joint

There is a great prospect of FeMnSiCrNi shape memory alloys for the application in one-time connecting pipe joints because of its lower price, better mechanical properties, higher phase transformation temperatures and greater thermal hysteresis. And it has drawn great attention of researchers recently.Currently, FeMnSiCrNi alloys pipe joints are almost prepared by casting,forging and then rolling. However, it's difficult for FeMnSi based alloys to form crossing slip due to its low fault energy. That's the reason why its thermal processing ability is very poor. As the result of poor processing, it is difficult to fabricate pipe joints. Furthermore, only straight pipe joints can be made and it is difficult to make multi-channel or curving pipe joints of complex shape by hot rolling or hot extruding, greatly limiting the application of the shape memory alloys in pipe joints.Casting pipe joints not only avoid the hot forging and thermal processes, but also make the produce of complex shape joints easily. At the same time, it decreases the cost of production which makes a great prospect of the application in engineering.This paper studied the shape memory effect and mechanical properties of as-cast state Fe-19Mn-5.54Si-8.79Cr-5.08Ni-0.012C and Fe-19Mn-5.54Si-8.79Cr-5.08Ni-0.12C and the effects quenching temperature and thermo-mechanical training on them. The pipe joint were manufactured by investment casting and its shape memory effect and joining properties were also tested. At the same time, the microstructures were analyzed by means of optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and X-ray diffraction. The results showed:Good shape memory effect was already found in these two Alloys as-Cast state The shape recovery ratio of Fe-19Mn-5.54Si-8.79Cr-5.08Ni-0.012C and Fe-19Mn-5.54Si-8.79Cr-5.08Ni-0.12C was 83% and 72%, respectively when the bending deformation ratio was 3.75%. Their shape memory effect were improved obviously through quenching between 600～800℃followed by a water quenching The maximum values were 93.8% and 82.3% when the quenching temperatures were 700℃and 800℃respectively. Because the critical stress for stress-inducedεmartensite transformation was the lowest and thus stress-inducedεmartensite transformation occur most easily. As a result, intrusion of permanent slip was not easy.Shape memory effect of casting alloy Fe-19Mn-5.54Si-8.79Cr-5.08Ni-0.012O was not significantly improved by thermal training. But shape memory effect of casting alloy Fe-19Mn-5.53Si-8.79Cr-5.09Ni-0.12C could be significantly enhance by thermal training, especially by thermal training with great amount of deformation.The elongationδand tensile strength of casting alloys Fe-19Mn-5.54Si-8.79Cr-5.08Ni-0.012C achieved maximum by a water quenching at 700℃. And theδand tensile strength of casting alloys Fe-19Mn-5.54Si-8.79Cr-5.08Ni-0.12C remained unchanged when the quenching temperature was below 900℃, But over 900℃, they markedly increased.The pipe joints manufactured by investment casting enjoy good shape memory effect. The leakage does not occur when subjected to 23Mpa oil pressure under no soft gasket material and agglomerant between pipe and joint.