| Based on the previous researches, the paper devoted to improve the shape memory effect and recovery stresses, decrease the recovery stresses relaxation at low temperature and improve the corrosion resistance of Fe-Mn-Si-Cr-Ni-based shape memory alloys. The effects of solution time, tempering following deep cooling, pre-deformation temperature, alloying and different ageing technology on the structures and performance of Fe-Mn-Si-Cr-Ni-based SMA were investigated. The recovery stresses relaxation at low temperature and corrosion resistance of the alloys subjected to different treatment were also studied in detail. The paper drew some original results as follows.After alloying with C and Nb elements and subsequent solution treatment, the SME and recovery stresses are improves due to the solution strength by C and Nb. After subsequent ageing, many tiny NbC particles are precipitated and remarkably strengthen the matrix. The obstacle effects of NbC particles on 112<110> dislocations are bigger than on <112>/6 Shockley partial dislocations and as a result, the SME and recovery stresses are improved. Addition of proper amount of N elements (0.1％) can also improve the SME and recovery stresses, especially the latter, which is 26％higher than those without N.Solution time has an obvious effect on SME. For Fe-Mn-Si-Cr-Ni-based alloy annealed at optimal temperature 973K, better SME can be obtained through adjusting the holding time. The optimal time is confirmed to be 10min for getting the bestηof 78％. On the other hand, tempering following deep cooling can also change the structures of the alloy and obtain theηof 15％higher than the alloy tempering following water quenching.Pre-deformation temperature has different effects on alloys with different chemical composition. This difference is mainly originated from the difference of stress-induced martensite transformation and cross of thermal martensite in different alloys.The paper study the effect of ageing after deformation on structures and performance for the first time, ageing after deformation can remarkably improve the SME and recovery stress. The paper found that in the alloys subjected to ageing after deformation, a lot of aligned carbides are distributed in the grains, instead of distributing in the grains boundaries in the alloys being aged without deformation. These carbides can effectively strengthen the matrix and suppress the plastic strain. Meantime, aging after pre-deformation can decrease the critical stress for inducingεmartensite (critical stress) for stress-induced martensite transformation, and thus can prompt theγ→εtransformation. The results show that shape recovery ratio of the alloys aged after deformation is 45～135％higher than those aged without pre-deformation and 5％～24％higher than those quenched at optimal temperature. Meantime, the maximum recovery stressσ_h and room recovery stress of the alloys aged after deformations are 72％and 34％higher than those aged without deformation, respectively.The influence factors on recovery stress relaxation at low temperature were investigated. While the increasing pre-strain, the relaxation ratio increases and when the pre-strain is about 5.5％～7.0％, the relaxation ratio is biggest. With the further increasing pre-strain, the relaxation ratio decrease. The paper study the effect of amount of carbides on relaxation ratio for the first time, precipitation of proper amount of carbides can decrease the relaxation ratio. On the other hand, recovery stress at low temperature of the alloy bearing higher carbon (0.16％C) is higher than the alloy bearing the carbon less than 0.02％. And meantime, the relaxation ratio of the former is also lower than that of the latter. The reason is that in the alloy bearing higher amount of carbon, more carbides can be produced, suppressing the nuclei and growth of martensite and decreasing the Ms, although the drive stress for inducing martensite is increased. Ageing after pre-deformation has little effects on relaxation ratio when remarkably improving the SME and recovery stress.The paper suggested the practical methods to decrease the relaxation at low temperature. For example, to control the recovery stress and drive stress for inducingεmartensite by controlling the pre-strain can decrease the recovery stress relaxation. To suppress theεmartensite transformation by alloying with carbon and Ti,Nb,V to produce carbides can also decrease the relaxation. At last, on the premise of obtaining the good SME, decreasing of Ms can decrease the relaxation.The paper study the effect of ageing after deformation on corrosion resistance for the first time, The erosion resistance of alloys fabricated by aging after pre-deforming is little lower than 18-8 stainless steel, especially in the basic condition, the erosion resistance is as good as 18-8 stainless steel. It shows that alloys fabricated by aging after deformation have the comprehensive performance, better SME, recovery stress and erosion resistance and can be applied in pipe-joint and some other joint equipments. On the other hand, addition of N, C, can both increase the erosion resistance. For the alloy adding with Nband C, the precipitations are mainlyNbC and thus avoid the inter-crystalline corrosion. The alloy bearing N has better corrosion resistance in basic condition, because N element can strength and stabilize the passivating film, improve the electrode potential and decrease the corrosion current.
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