Characterisation of Microstructure of Isothermally Transformed Martensite in Low Temperature in Powder and Bulk State of Fe–23Ni–3.6Mn (mass%) Alloy by Rietveld's Method

Abstract

The present study concerns X-ray characterisation of the microstructures of the martensites of Fe–23Ni–3.6Mn alloy, transformed isothermally at low temperature. Along with the austenized powder and bulk forms of the alloy, coldworked powders have also been analysed. The methodology adopted is Rietveld's whole profile fitting technique which incorporates correction for preferred orientation of the crystallites. The results reveal important information on the crystallite (domain) sizes, residual microstrains, preferred orientation, stacking and compound fault probabilities, dislocation density etc., for both the austenite and martensite phases of the alloy. The martensite has smaller crystallite sizes and larger microstrain values, both of which are isotropic in nature for the transformed bulk and the austenized powders but anisotropic for the coldworked powders. The transformed matrix revealed high percentage of martensites in coldworked powder and bulk whereas annealed powder revealed about 8% volume fraction of martensites. The dislocation density values evaluated from the respective crystallite sizes and r.m.s. strain values are high (∼1011 cm/cm3) in the martensitic phase by almost an order of magnitude compared to their respective austenite phase. The coldworked powder reveals high propensity of faulting. The hardness value of transformed bulk (191 kg/mm2) is more than double the value for the austenite bulk (95 kg/mm2). The results have been compared and correlated with those in two previous studies on the same alloy system having 3.3 and 3.8 mass% of Mn.

Austenitizing Behavior of Laser Solid Formed Ultrahigh-Strength 300 M Steel

“…The growth of this new martensite lath will stop, when it encounters next adjacent lath. It is well known that the lath martensite has a very high density of dislocation of an order of 10 14 –10 15 m −2 , implying a high nucleation rate. However, in the lath's length direction, the growth of the new martensite lath can only be hindered by the grain and packet boundaries.…”

Lattice imperfections in intermetallic Ti–Al alloys: an X-ray diffraction study of the microstructure by the Rietveld method

“…In continuation of recent studies on the microstructural characterization of the industrially important structural materials, namely martensites in Fe-Ni-Mn, Fe-Mn-C and AISI type 300 steel [14][15][16][17][18], by analyzing the X-ray diffraction (XRD) pattern through the Rietveld whole profile fitting method [19,20], the author has undertaken the study of the microstructure in terms of various lattice defect parameters (crystallite size, rms strain, stacking and twin fault probabilities, etc) in three intermetallic titanium aluminides, having compositions close to (Ti:AlZ1:1), in both the homogenized bulk and plastically deformed (ground) powder forms. The present study revealed a 2 /g phase transformations due to plastic deformation in the considered alloy compositions.…”

“…Instrumental parameters, like 2q correction, peakasymmetry, peak broadening parameters (U, V, W) [25,26] of a Si standard sample, assumed to have no size and strain broadening, have been used as fitting parameters in the software following the procedure indicated by Lutterotti et al [27] and reported elsewhere [14][15][16][17][18]22,23]. The crystallite size (D) and the microstrain (h3 2 i 1/2 ) values were evaluated using the Popa model [28] of anisotropic 'sizestrain' broadening.…”

Dislocation Density of Lath Martensite in 10Cr-5W Heat-Resistant Steels

“…[5][6][7][8][9][10] The dislocation density can be measured by transmission electron microscopy (TEM) techniques, X-ray diffraction (XRD) and neutron techniques. These experimental methods complement each other.…”