Characterization of Precipitates in a Microalloyed Steel Using Quantitative X-ray Diffraction

Abstract

Quantitative X-ray diffraction (QXRD) (also known as the Rietveld method) was used to analyze the precipitates present in Grade 100 microalloyed steel. The precipitates were extracted from the steel using electrolytic dissolution and the residue from the dissolution was analyzed using XRD. The XRD pattern exhibited three (3) distinct diffraction peaks, and significant broadening of a fourth peak corresponding to the <10 nm size precipitates. QXRD analysis was applied to the XRD pattern to obtain precipitate size, composition, and weight fraction data for each of the four diffraction peaks observed. The predicted mean precipitate diameter and average atomic composition of the nano-size (<10 nm) precipitates was 4.7 nm and (Nb 0.50 Ti 0.32 Mo 0.18 )(C 0.59 N 0.41 ), respectively. The predicted precipitate size correlates well with the average size of precipitates measured in previous work by the authors using both transmission electron microscopy (TEM) and small angle neutron scattering (SANS). The average atomic composition correlates well with the composition measured in this work using energy dispersive X-ray (EDX) analysis of individual nano-sized precipitates. The calculated weight fraction of the nano-size precipitates in the extracted residue was 42.2 wt. %. The calculated atomic compositions of the other three diffraction peaks were TiN, (Ti 0.87 Nb 0.13 )N, and (Nb 0.82 Ti 0.18 )(C 0.87 N 0.13 ) with weight fraction values of 12.9 wt. %, 31.7 wt. %, and 13.1 wt. %, respectively. The sizes of both the (Ti 0.87 Nb 0.13 )N and the (Nb 0.82 Ti 0.18 )(C 0.87 N 0.13 ) groups of precipitates were directly measured and were observed to range from 150 nm to 570 nm and from 90 nm to 475 nm, respectively. QXRD was unable to determine a reasonable mean precipitate size for either of these two groups of precipitates. The wide compositional range (i.e., varying levels of Nb and Ti) of these precipitates (as measured by EDX) resulted in XRD peak broadening that was erroneously interpreted as a size broadening effect.

Single-Particle Mass Spectrometry of Titanium and Niobium Carbonitride Precipitates in Steels

“…Larger sample volumes are accessible through matrix dissolution, which provides extracted particles that can then be analyzed with X-ray diffraction (XRD), for example. , A representative steel sample is dissolved electrolytically or by chemical etching to leave only the targeted particles in the residue. The residue is analyzed using XRD with Rietveld refinement to obtain phase information and crystallite size.…”

Comprehensive Inspection on the Experimental Ferritic Stainless Steel by Means of Transmission Electron Microscopy and Neutron Diffraction Techniques

“…The correlation between (1/d hkl ) and (2sinϴ/λ) was determined by the least square (LS) method [16], [17]. Figure 4 shows the calibration curve of the JCPDS data between 2ϴ and d hkl obtained by the LS-method.…”

Theoretical and Experimental Nucleation and Growth of Precipitates in a Medium Carbon–Vanadium Steel

“…The distribution of precipitate sizes was always determined on a population of close to 200 precipitates. This technique is widely used, but there are other competitive techniques such as quantitative X-ray diffraction (QXRD) [13].…”