Analysis of Crystallite Size Changes in an Oxide Layer Formed on Steel Used in the Power Industry

Abstract

The paper presents results of studies on the crystallite sizes of oxide layer formed during a long-term operation on steel at an elevated temperature. This value was determined by a method based on analysis of the diffraction line profile, according to a Scherrer formula. The oxide layer was studied on a surface and a cross-section at the inner site on the pipe inlet, at the fire and counter-fire wall of the tube. X-ray studies were carried out on the inner surface of a tube (in a flowing medium environment), then the layer's surface was polished and the diffraction measurements repeated to reveal differences in the originated oxides layer. X-ray phase analysis was performed by the use of a SEIFERT 3003 T/T X-ray diffractometer, with a cobalt source of λCo = 0.17902 nm wavelength. X-ray diffraction measurements were performed in the 20 ÷ 120• range of angles with an angular step of 0.1• . To interpret the results the diffractograms were described by a pseudo Voigt curve using the Analyze software. A computer software and the DHN PDS, PDF4+2009 crystallographic database were used for the phase identification. The results showed that the crystallite sizes have an effect on the properties of the oxide. It has been shown that the outer oxide layer having larger crystallites, is more porous and thus more brittle.

Changes of crystallite sizes in the oxide layer forming during long-term operation of 10CrMo9-10 steel

“…The size of crystallites of oxides was determined by the Scherrer relationship. Methods based on the analysis of diffraction line profile are used to determine the size of crystallites smaller than 100 nm and of lattice deformations (GWOŹDZIK 2016). Based on the width and the position of the main coat and substrate reflections, the size of the crystallites was determined using the Scherrer formula (1):…”

“…A higher chromium content makes that this steel has better anti-corrosion properties as compared with low-alloy steels. However, despite that there is a need to diagnose both this steel and low-alloys steels resistance to the operation of a steam and flue gases environment existing in components operated long time at high temperatures and during a few hundred thousand hours (GWOŹDZIK 2014, 2016, KLEPACKI, WYWROT 2010, KLEPACKI 2006.…”

Surface morphology analysis of oxide layers formed on 10CrMo9-10 steel used in the power industry

“…Corrosion is an issue of high interest to scientists [25][26][27][28][29][30]. In particular, the problem of high-temperature corrosion is particularly important in the case of long-term elements operation in power stations or combined heat and power stations [9,21,[31][32][33][34][35][36][37][38][39]. Niu et al [21] discussed primarily the main problems associated with ash during combustion, such as: alkali-induced slagging, silicate melt-induced slagging (ash fusion), agglomeration, and customized countermeasures including additives, co-firing, and leaching.…”

Microstructure changes responsible for the degradation of the 10CrMo9-10 and 13CrMo4-5 steels during long-term operation

“…Construction steels used in power industry, e.g., 10CrMo9-10 [1,2], 13CrMo4-5 [3,4], 16Mo3 [5,6] or X10CrMoVNb9-1 [7,8] are required to have specific strength properties like guaranteed yield stress and creep strength both at room and elevated temperatures. These requirements are usually fulfilled in a fresh material, where the appropriate microstructure (ferritic-perlitic, ferritic-bainitic, bainitic, martensitic) is adjusted via normalizing or via quenching and tempering.…”

“…An important basis for the description and explanation of the degradation processes running in these steels is their microstructure examination in certain periods of the operation time [9][10][11][12][13][14][15]. For this reason, numerous analytical methods are used that include X-ray diffraction (XRD) analysis [2], optical microscopy (OM) [16,17], scanning electron microscopy (SEM) [16,17], atomic force microscopy (AFM) [4,18,19] and transmission electron microscopy (TEM) [12,20]. TEM allows, in particular, a precise determination of the type of precipitates.…”