Comparison of thermally induced and deformation induced martensite in Fe-29% Ni-2% Mn alloy

Thermally induced martensite properties in Fe-29%Ni-2%Mn alloy

Deformation induced martensite characteristics in the austenite phase of Fe–29Ni–2Mn alloy were studied for different austenite grain sizes of alloy. Scanning electron microscopy, transmission electron microscopy, Mossbauer spectroscopy and also differential scanning calorimetry techniques were applied to study in order to clarify the deformation induced martensite characteristics from morphological, crystallographical, magnetical and thermal points of view. Scanning electron microscope revealed that the increasing of deformation amount also increased the amount of existed martensite. Transmission electron microscope observations showed that the crystal structure of these deformation induced martensites morphology was lenticular plates with a bcc crystal structure. Also the magnetism of both austenite and martensite phases were determined with Mossbauer spectroscopy. Mossbauer spectrometer measurements showed paramagnetic character for austenite phases and ferromagnetic character for martensite ph...

Deformation induced martensite characteristics in Fe–29Ni–2Mn alloy

The effects of magnetic fields up to 20 T on the isothermal martensitic transformation were examined in 304L and 316LN stainless steels which were heated at various solution treatment temperatures and cooled from these temperatures at variou rates. In the 316LN steel, since the amount of the martensite induced by the application of the magnetic fields was very small, the effects were not clear. In the 304L steel, a larger amount of α’ martensite was induced by the application of magnetic fields at liquid nitrogen temperature than at liquid helium temperature. The amount of α' martensite which was induced in magnetic fields increased with solution treatment temperatures and cooling rate from the temperatures. The amount of α' martensite did not increase linearly with an increase in the applied magnetic field but seemed to be saturated before the amount of the martensite attained 10 volume %.

Effects of High Magnetic Fields on Martensitic Transformation at Cryogenic Temperatures for Variously Heat Treated Stainless Steels

The effect of high pulsed magnetic fields on the martensitic γ → α transformation in Fe–Ni and Fe–Ni–Mn alloys characterized by dual kinetics has been analyzed. It has been shown that the higher the iron content and the lower the martensitic transformation temperature, the more substantial the effect of pulsed magnetic field on the athermal martensitic transformation (MT) in the Fe–Ni alloys. The possibility of athermal martensite nucleation at magnetic inhomogenities of austenite, which is characterized by disordered magnetic moments (antiferromagnetic contribution) within a local area that assumes coherent conjugation at the interface, has been discussed. It has been suggested that athermal MT in Invar Fe–Ni alloys characterized by dual kinetics occurs in a pulsed magnetic field via a first-order magnetic phase transformation.

Effect of Magnetic state of Austenite on Martensitic transformation in Fe–Ni Alloys in High and Zero Magnetic Fields

Magnetic field-induced transformation from paramagnetic austenite to ferromagnetic martensite in an Fe-21Ni-4Mn (wt%) alloy with dual martensitic transformation kinetics has been studied by magnetization measurement and optical microscopy, applying a pulsed ultra-high magnetic field. As a result, the following were found. A magnetic field higher than a critical one is needed to induce the martensitic transformation above Ms. The critical magnetic field increases with increasing temperature, and when plotted against the temperature difference (ΔT) from Ms, it lies on a straight line not passing through the origin. This result and thermodynamical analysis suggest that pulsed magnetic field strongly promotes the athermal martensitic transformation and restrains the isothemal one. The influence of magnetic field on martensitic transformation in the present Fe-Ni-Mn alloy is mainly due to Zeeman effect. The entropy change for athermal transformation at Ms, ΔSΔMsat is obtained to be 4.13 J/mol·K. The amount of magnetic field-induced martensites increases linearly with the maximum strength of pulsed magnetic field. Lath, plate and butterfly martensites are formed under magnetic field.

E. X. Sun

Papers

Pulsed magnetic field-induced martensitic transformation in an Fe-21Ni-4Mn alloy.