Effect of a Plastic Deformation on the Magnetic Properties of the Fe - 31 . 6 % Mn - 6 . 45 % Si Shape Memory Alloy

Concerning a Fe-Mn-Si shape memory alloy, it was thought of magnetic measurements to follow the evolutions with temperature of an as quenched steel before and after a 2.5% prestrain. INTRODUCTION The shape memory effect, related to the reverse E -. y transformation of a single crystal of FeMn-Si, was fist shown by Sato (1). Many works are devoted to polycrystalline Fe-Mn-Si steels (2,3). The E phase is grown from large stacking faults in the y austenite. From one hand, silicon decreases both the stacking fault energy and the NEEL temperature. On the other hand, to make a clear distinction between thermal induced martensite (~ th) and the stress induced martensite (&def), is not easy. It was thought of the interest of magnetic measurement to precise the differences before and after deformation of an as quenched steel. ALLOY AND EXPERIMENTAL The FM30 alloy was supplied by the " Soci6t6 Aubert et Duval", as 18*18 mm2 bars swaged and 1373K water quenched. The chemical composition ( wt %) is given in Table 1: Fe I Mn I Si I C I N I S Balance 1 31.6 1 6.45 1 0.018 l 0.0052 1 0.0079 -Table 1Structural and physical characterizations were carried out on the as received alloy called AD1.Details were published elsewhere(4), and the results are summarized in Table 2: Lattice parameters of the dual phase alloy (X-ray diffraction) Magnetic transition ( neutron diffraction) Transformation temp. ( elect. resis. meas.). 0,35899 nm a&= 0,25377 nm ce= 0,41452 nm 270 < 5 j Y 295 K MS= 313K As=411K Af= 440K -Table 2Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:1995213 C2-90 JOURNAL DE PHYSIQUE IV Samples of AD1 ( 3 mm in diameter and 20mm in length) were extended on a Instron machine with a strain rate of 1.7 10-4 S-1. The chosen deformation rate was E= 2.5% as controlled by an extensometer. The appearance of the stress induced martensite did not modified the X-ray spectrum of the AD1 alloy (4).Magnetic susceptibility measurements were carried out on the DSM-100 apparatus. Samples were carefully polished in a @?/H202 = 1/15) so1ution.A Faraday device was used,with the sample on a silica tube, during heating from 100 to 610K. Isothermal magnetization curves were recorded under different direct magnetic fields. Then two other temperature ranges were precisely explored ( 1.4-100K and 298-970K)