1. Introduction Iron-based shape memory alloys have widely been stud- ied due to their low cost and large hysteresis. 1–6) Among the iron-based alloys FeMnSiCrNi alloys have the best shape memory effect (SME). 7) The theory of the composition de- sign to obtain the best SME has been developed. 12) SME of FeMnSiCrNi alloys is based on a g (f.c.c)→e (h.p.c) trans- formation by the extension and contraction of stacking faults. Thermomechanical training which increases the amount of directional e phase is one of the most important measures used to improve the SME of iron-based shape memory alloys. 8—12) In the industrial application of SME alloys for couplings of pipes, the amount of absolute recoverable strain and the corrosion resistance are the important properties. The for- mer is related to the possibility of sealing and joining of pipes, and to the working life of the couplings. Then, the effects of the chemical compositions of the alloys, the train- ing mode on the absolute recoverable strain and corrosion resistance of the alloy are studied. Aspects of the manufac- turing technique of joint also need to be considered. 2. Experimental Procedures The alloys were prepared from Fe, Mn, Si, Cr, Ni and Co with purities of 98.0, 99.7, 99.0, 99.0, 99.9 and 99.3 % which were melted in a vacuum induction furnace and cast into ingots. The composition of the alloy is Fe14Mn6Si9Cr5Ni (wt%). The ingots were hot rolled to f 36 mm pipe with 3 mm in thickness. The pipe was solu- tion-treated at 1 373 K for 1 h and quenched into water. The specimens for corrosion tests were obtained by cutting the ingot using a Mo wire cutter. The specimens for the loss weight measurements were soaked in 1.1 M HCl (1.1 mol. HCl in 1 000 ml distilled water) or 2.8 M NaOH (2.8 mol NaOH in 1 000 ml distilled water) solutions at 287 K for 700 h. The weight loss was measured by an analytical balance. The electrochemical pa- rameters are measured at 298 K (changing rates of voltage are 0.01 and -0.01 mV/s). Experiments of creep under constant stress and stress re- laxation under constant strain were performed using a self- built loading device. The testing times used were 3 200 and 2 600 h. The constant stress for the creep experiments is 190 MPa corresponding to the low yield stress of the austenite in the range of s s =180–300 MPa. 1,2,13) A constant strain of 4% was employed for the stress relaxation. The constant strain corresponds to a stress of 533 MPa to seal and join the pipes. 3. Results and Discussion The results of loss weight measurements are shown in Table 1. The corrosion resistance of the alloy is excellent compared with those of 304, 316 and 1 020 steels in NaOH solution, the loss weight of the alloy being about one-fourth of those in 304 and 316 steels. The corrosion resistance of the alloy in HCl solution is better than that of 1 020 steel, but worse than those of 304 and 316 steels. Figure 1 shows the polarization curves of the alloys (Tafal curve) in HCl and NaOH solutions. The correspond- ing electrochemical parameters are shown in Table 2. In NaOH solution the polarization curve of the Fe14Mn6Si9Cr5Ni alloy locates upper side of Fig. 1a, whose corrosion current (I corr ) is the smallest among the ISIJ International, Vol. 40 (2000), No. 11, pp. 1124–1126 © 2000 ISIJ 1124 Shape Memory Effects in an Fe14Mn6Si9Cr5Ni Alloy for Joining Pipe J. C. LI, X. X. LÜ and Q. JIANG Department of Materials Science & Engineering, Jilin University of Technology, Changchun 130025 P. R. China. Email: jiangq@post.jut.edu.cn. (Received on May 2, 2000; accepted in final form on July 12, 2000 ) The shape memory effect (SME) of an Fe14Mn6Si9Cr5Ni alloy has been studied, and resulted to be the best for joining pipe. Training can improve the SME of the alloy. Fe14Mn6Si9Cr5Ni alloy shows good creep and stress relaxation resistance. Its corrosion resistance in alkaline solution is 4–5 times better than that of 304 and 316 stainless steels. The tensile force of 20 KN and sealing pressure of 6 MPa can satisfy usual re- quirements for joining pipe in general industrial applications. KEY WORDS: iron-based shape memory alloy; joint pipe; creep; corrosion. Table 1. The experimental results of loss weight. (g/m 2 h )