X-Ray Diffraction Profile Analysis for Characterizing Isothermal Aging Behavior of M250 Grade Maraging Steel

Abstract

X-ray diffraction (XRD) studies were carried out to characterize aging behavior of M250 grade maraging steel samples subjected to isothermal aging at 755 K for varying durations of 0.25, 1, 3, 10, 40, 70, and 100 hours. Earlier studies had shown typical features of precipitation hardening, wherein the hardness increased to a peak value due to precipitation of intermetallics and decreased upon further aging (overaging) due to reversion of martensite to austenite. Intermetallic precipitates, while coherent, are expected to increase the microstrain in the matrix. Hence, an attempt has been made in the present study to understand the microstructural changes in these samples using XRD line profile analysis. The anisotropic broadening with diffraction angle observed in the simple Williamson-Hall (WH) plot has been addressed using the modified WH (mWH) approach, which takes into account the contrast caused by dislocations on line profiles, leading to new scaling factors in the WH plot. The normalized mean square strain and crystallite size estimated from mWH have been used to infer early precipitation and to characterize aging behavior. The normalized mean square strain has been used to determine the Avrami exponent in the Johnson-Mehl-Avrami (JMA) equation, which deals with the kinetics of precipitation. The Avrami exponent thus determined has matched well with values found by other methods, as reported in literature.

Line profile analysis of synchrotron X-ray diffraction data of iron powder with bimodal microstructural profile parameters

“…3 and 7(b). The estimated average maximum microstrain (Stokes & Wilson, 1944) values for the narrow and broad components of the microstructure are comparable to the reported literature values (Lutterotti & Scardi, 1990;Langford, 1992;Ustinov et al, 2004;Rai et al, 2004;Mahadevan et al, 2008;Martínez-Blanco et al, 2008;Kremenović et al, 2010;Bhakar et al, 2017).…”

“…Fe is abundantly used in the production of steels (Bhadeshia & Honeycombe, 2017), magnetic alloys (Yoshizawa et al, 1988;Yoshizawa & Yamauchi, 1990;Herzer, 1997), powder metallurgy (Roll & Johnson, 1968;Gaiduchenko & Napara-Volgina, 1996) and catalysts (Liu et al, 1996;Boddien et al, 2011;Lendzion-Bieluń et al, 2011;Wilk et al, 2017). Knowledge of their microstructural parameters plays a vital role in evaluating the processing conditions of these materials as well as their performance under operative conditions (Taylor, 1945;Rai et al, 2004;Radzikowska, 2005;Mahadevan et al, 2008;Raghavan, 2011;Rajan et al, 2016). An understanding of microstructural parameters is also helpful in designing new products with improved properties (Arora et al, 2019;He et al, 2017;Li et al, 2016;Wang et al, 2002).…”

In situ X-ray diffraction study of the δ to α′ isothermal martensitic transformation kinetics in a Pu–Ga alloy

“…For martensitic transformations, n is reported to be between 2 and 3 [25][26][27]. While values of n as low as 0.34-0.49 have been reported for maraging steel [28,29], these weak exponents are not well defined in current formulations of the JMAK model.…”

The origin of the effect of aging on the thermoelectric power of maraging C250 steel

“…Currently, the identification of the aging state of maraging steel is mostly based on destructive measurements, semi-non-destructive microhardness tests and nondestructive resistivity and magnetic measurements [1,[10][11][12][13]. Another potential non-destructive method for monitoring the aging state of maraging steels is the measurement of thermoelectric power (TEP), also known as the Seeback coefficient (S).…”