Analysis of Nb-rich and Ti-rich particles in Fe-Nb and Fe-Ti melt additions and J55 steel

Analysis of Nb-rich and Ti-rich particles in Fe-Nb and Fe-Ti melt additions and J55 steel

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Unformatted text preview: I; Matenals nology Laboratory flaw- ' 9 Analysis of Nb—Rich and Ti-Rich Particles in F e-Nb and Fe—Ti Melt Additions and J55 Steel PROTECTED BUSINESS INFORMATION MTL 2005-4(CF) O. Dremajlova, V.Y. Gertsman, J. Li and J .TLBlowk-Ier February 2005 I zithis project was funded by IPSCO. 'bfthis report is restricted to IPSCO. nuutributioin is at their discretion. CANMET-MTL i PROTECTED BUSINESS INFORMATION OANMEfri-MATERIALS TECHNOLOGY LABORATORY ' -' REPORT MTL 2005-4(CF) ANALISIS 0F Nb-RlCH AND Ti-RICH PARTICLES IN Fe—Nb AND Fe—Ti ' MELT ADDITIONS AND J55 STEEL. by O. Dremailova, V.Y. Gertsman, J. Li and J.T. Bowker '5 EXECUTIVE SUMMARY At the request Of IPSCO, Ti-rich and Nb-rich particles present in three different supplied materials including a low carbon J55 steel, and two melt additions, F e-Nb and FeuTi, were characterized. The characterization techniques employed included scanning electron microscopy, electron probe microanalysis and transmission electron microscopy (TEM). FocuSed Ion Beam (FIB) microscopy was used for TEM specimen preparation. In the case of the J55 steel three types of large particles were identified. Type I was shown to be NbC with an f.c.c. structure and lattice parameter of 0.447 11111. Type II particles were confirmed to be (Ti,Nb)N. Complex inclusions containing Fe, Ca, S, Mg, 0 and C surrounded by Ti-l‘iCh particles characterized as TiN or (Ti,Nb)N were labelled as Type III inclusions. Two finer types of particles extracted using a two-stage replica technique were identified as Ti(C,N) and NbC. TEM conducted on samples taken from the Fe—Nb alloy melt addition revealed two phases, the first being a solid solution of Fe in b.c.c. Nb and the second an intennetallic Fer phase. TEM of the Fe—Ti alloy confirmed the presence of four phases: 1“ — solid solutiOn based on oc-Ti; 2nd w solid solution based on [El—Ti; 3rd 7 Ti(C,N) and 4‘h m phase X based on a b.c.c. structure with an approximately 1.3 nm lattice parameter. CANMET-MTL PROTECTED BUSINESS INFORMATION ii CONTENTS EXECUTIVE SUMMARY 1. INTRODUCTION 2. EXPERIMENTAL PROCEDURE 2.1 SCANNING ELECTRON MICROSCOPY 2.2 ELECTRON PROBE MICROANALYSIS 2.3 FOCUSED ION BEAM ANALYSIS 2.4 TRANSMISSION ELECTRON MICROSCOPY 3. RESULTS 3.1 SCANNING ELECTRON MICROSCOPY 3.2 ELECTRON PROBE MICROANALYSIS 3.3 FOCUSED ION BEAM ANALYSIS 3.3.1 References 3.4 TEM RESULTS OF TYPE-l PARTICLE (NB-RICH) 3.4.1 Experimental and Results ' 3.4.2 Conclusion 3.5 TEM RESULTS OF TYPE—Ii PARTICLE (Tl-RICH) 3.5.1 Experimental and Results 3.5.2 Conclusion 3.5.3 Smaller Type-ll Particle 3.6 TEM RESULTS OF TYPE—III PARTICLE 3.7 TEM RESULTS OF FINE PARTICLES 3.7.1 Experimental 3.7.2 Results 3.7.3 Discussion 3.8 TEM INVESTIGATION OF FE-NB ALLOY 3.9 TEM INVESTIGATION OF FE-TI ALLOY 3.9.1 Experimental and Results 3.9.2 Conclusions 3.9.3 References 3.9.4 Appendix 4. GENERAL CONCLUSIONS 5. CONCLUDING REMARKS 6. RECOMMENDATIONS 7. ACKNOWLEDGEMENTS CANNIET-MTL. PROTECTED BUSINESS INFORMATION 1'. INTRODUCTION Twelve fractured samples of carbon steel J55 were received from IPSCO Inc. for quantitative microanalysis cf large Ti-rich and Nb—rich particles. A sample identified as E4098 containing the largest particles was selectedfor study. An additional two alloys, one containing Fe—Ti and the other Fe—Nb, were received for the same investigation. To determine the chemical composition and crystallographic-name of these particles, scanning electron microscoPy (SEM), electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) were used. A Micrion-2500 focused beam (FIB) was used to prepare some of the specimens for TEM analysis. Several other techniques of sample preparation were also employed depending on the material and size of particles. The detailed description of quantitative microanalysis of fine and large Ti-rich and Nb-rich particles that were studied is given below. 2. EXPERIMENTAL PROCEDURE 2.1 SCANNING ELECTRON MICROSCOPY : The Philips XL—3O scanning electron microsoopy (SEM) was used at an accelerating voltage of 20 kV to identify particles present on the fracture surface as well as in the polished sample. 77?“ Back scattered electron (BSE) imaging was carried out to assist in identifying regions richer in high atomic number elements such as niobium. To identify the elements present in particles, energy dispersive X—ray microanalysis was conducted. I' ' 2.2 ELECTRON PROBE MICROANALYSIS Based on the detailed observations made using SEM, as-polished specimens were taken for - further chemical composition analysis using a Cameca SX-51 electron probe micro-analyzer . (EPMA) equipped with four wave-length X—ray spectrometers. It was necessary to use samples in the polished condition. Due to the small particle size, an accelerating voltage of 10 kV was used to minimize the beam—specimen interaction volume. The analysis was performed using a relatively large beam current of 20 HA and counting time of 30 s. 2.3 FOCUSED ION BEAM ANALYSIS For the specific kinds ofinclusion particles that were identified using SEM-EDS analyses, TEM J Specimens were prepared using a Micrion-2500 focused ion beam (FIB) microsc0pe. I The FIB. is perhaps the most powerful tool currently available, which can be used to extract site- - specific TEM specimens. The various FIB-TEM Specimen preparation techniques and their ~~J advantages and shortcomings have already been well documented. With the capability of high— resolution imaging coupled. With st_r_e_ss~free fine ion—beam micro-machining, FIB is by far the most powerful tool in site-specific TEM sample preparation. _ __cANME'r-MT:_L;¢ I PROTECTED BUSINESS INFORMATION 2 2.4 TRANSMISSION ELECTRON MICROSCOPY Samples for TEM investigation were prepared by different techniques. some sections of large inclusions were prepared by FIB. Smaller particles were analyzed by means of two-stage extraction replicas. Thin foils from Fer and Fe-Ti alloys were prepared by combination of _. mechanical polishing and ion milling with high-energy Ar ions. A Philips CM20 FEG TEM equipped with a Schottky field emission gun was operated at a _ voltage of 200 kV. Conventional bright-field TEM image modes were used to visualize the particles. The crystal structure of the phases was determined by means of selected area electron diffraction (SAED) and, for finer particles, convergent beam electron diffraction (CBED). Chemical microanalysis was performed using an Oxford Instruments thin—window energy- dispersive spectrometry (EDS) detector with an INCA System analyzer. Condenser aperture C2 of 50 um and spot size 5, giving the probe size of 10 nm, were employed. Electron energy loss spectroscopy (EELS) was employed for identifying nitrogen in the presence of titanium. Gatan Image Filter model GIF 678 was used for that. TEM was used to analyze large Ti—rich and Nb-rich particles present in the as-polished specimen that were previously observed using SEM and EPMA. In addition fine particles that were present but could not be seen in the SEM or EPMA because of a spot size limitation were analysed after extraction using a two-stage replica technique. Further TEM investigation was performed for Fe-Nb and Fe—Ti alloys. 3. RESULTS The chemical composition of J55 steel supplied by IPSCO is listed in Table 3.1 below. Table 3.1. Chemical composition of 155 steel received from IPSCO. . Ta 013 0.04 0.02 0.04 0.002 S J 0.002%, P — 0.01%, N — 0.008%, B - 0.0002% ' 3.1 SCANNING ELECTRON' MICROSCOPY Individual Nb—rich and Ti—rich particles in the range 2 ,um to 145 ,um were qualitatively analyzed by SEM/EDX. A low magnification SEM image of the fractured sample E4098 is shown in Fig. 3.1(a), revealing two different-fracture morphologies. Two kinds of large particles,'Nb~rich and Ti-rich, were obseIVed on the fracture surface. Nb-rich particles were identified as Type 1 particles and the Ti—rich as Type-II} The maximum size of the Ti—rich particles present on the fractured sample [Figs’g 3j.;l'_(b)_and 3.1(d)] was 14.5 X 14 H.111 and the size of Nb—rich particles was slightly smaller. one "f-‘Nb-rich particles is presented in CANMET-MTL 3 PROTECTED BUSINESS INFORMATION lire surface identified in Fig. 3.1(a). Two EDX spectra Fig. 3.1(c).withi-I_ _ rticles are shown in Figs. 3.1(e) and 3.1(t), reSpectively. - obtained from3N: ri'c A transverse section oh __ _. ample was prepared for further qualitative microanalysis. The as-polished specimen again revealed the presence of Type I and Type II particles as shown in Figs. 3.2 and 3.3, respectively; The Type I Nb—rich particles were in the form of a segregation line of bright rectangular shaped particles. EDX spectra from these particles confirmed the presence of niobium [Fig 32(0)]. A small peak of iron was also present. The Type II large cubical shape particles enriched with titanium were observed in the matrix of the as—polished specimen. The BSE image and EDX spectrum of the Ti-rich particle are presented in Figs. 3.3(a) and 3.303), respectively. Elements such as Nb, N and Mg were also present in this particle. It appears that the Type II particle could be Ti, Nb nitride. A third type of large particle was observed in the as—polished specimen, as revealed in Fig. 3.4(a), containing of a round—shape dark area surrounded by a grey cuboid reminiscent of a ‘ Type II particle. The EDX spectrum of the dark particle identified by the arrows, revealed the presence of elements such as Fe, Ti, Ca, S, Mg, 0 and C, as shown in Fig. 3.400). Similar observations were made for several others dark areas of Type III particles. EDX spectra from the grey cuboids COnfirmed them as Type II particles containing Ti, Nb. and N. 3.2 ELECTRON PROBE MICROANALYSIS The same as-polished Specimen was used to determine the detailed chemical composition of a j, group of elements (Ti, Nb, N, .C, Fe, 0, Ca, Si, Al and B) present in the'large particles (size range from 2 to 5 tam) using EPMA. Prior to the measurements, various standards were scanned. in order to calibrate the microprobe to ensure precise measurements; The standards used in the f current calibration are listed in Table 3.2. The summarized results of four large Ti-rich and three. "" Nb-rich particles are listed in Table 3.3. The following sunnnarizestthegfindings: _ 1. Type I (Nb—rich) particles contained more carbon and iron, and less nitrogen than Type II (Ti—rich) particles. However; the Nb-rich particles are in general quite small which ,3 approaches the interaction volume under the current beam condition. Hence, it is possible that the higher iron and-carbon concentration could be attributed to the surrounding matrix. Further TEM analysis is needed to clarify this matter. No oxygen was observed in Type I - particles. 2. Type II (Ti—rich) particles are mainly-composed of Ti and N. A significant amount of Nb ‘ was also detected: Unlike the Type Iparticles, a small amount of oxygen existed in these particles. ' ' 3. The particle identifiedin the table as Ti-rich *—3 was a Type III particle and contained even higher amounts of oxygen,,carbon and silicon than Type II. ' a CANMETTMTF i easi'mmmmmmam Whamafiaimu a...“ ' ' _CANMET-MTL PROTECTED BUSINESS INFORMATION 4 3.3 FOCUSED ION BEAM ANALYSIS The FIB microscope was used to prepare TEM specimens containing large Ti-rich and Nb-rich particles. Figures 3.5(a) and 3.5(b) show FIB secondary electron images of the Type I and Type 11 particles taken from a mechanically polished sample surface. Once these particles were identified in the FIB, precise ion beam milling was used to create trenches around it and leave a thin membrane of approximately 20 x 10 x 5 pm in size. At this point, the feature of interest was isolated in this thin slab. This thin slab was subsequently cut free in the FIB using the same ion beam. A so-called “lift-out” process was used to transfer this small slab to a carrier, which was subsequently mounted on a TEM copper grid. The mounted slab containing the feature of interest was then further thinned to become electron transparent using the FIB. Details of the technique can be found in open literature [1—3]. TEM specimens from all three types of inclusions were prepared using this technique. Figures 35(0) and (d) show examples of the small sample approximately 20 x 10 x 5 pm in size ' containing the feature of interest that had been lifted-out and mounted onto a carrier. This sample will be further milled (thinned) in a FIB microscope so that the feature of interest (particles) will be electron transparent in TEM. 3.3.1 References l. M.W. Phaneuf, and J. Li, FIB Techniques for Analysis of Metallurgical Specimens, Microscopy and Moroanalysis 6 (Suppl 2: Proceedings) (2000), 524-525. 2. J. Li, G.S. McMahon and M.W. Phaneuf, “FIB Techniques for Microscopy Applications”, Proceedings of the Microscopy Society of Canada, vol. XXVIII, (2001), 26-27. 3. Jian Li, V.Y. Gertsman, and J. Lo, “Preparation of Transmission Electron Microscope Specimens from Ultra—Fine Fibers by a FIB Technique”, Microscopy and Moroanalysis 9 (2003), 888-889. ‘ 5 PROTECTED BUSINESS INFORMATiON I = "MM-a Vi 2 A \ Table 3.2. standards and corresponding reflecting crystals. Standards Table 3.3. Chemical compositions of large particles obtained by EMPA. Particle Mm Ti Nb 5 '5; - :- --: .' _: ._ ' .i"':-f'i :.' i Ti—rich-l 0 - Ti-rich -4 3 -~.' ; Nb-rich -2 2.5 * Type III particle CANMET-MTL PROTECTED BUSINESS INFORMATION 6 (a) Low magnification SEM image of as-received sample. :mm ¥%&”m{fffi?€:¥fi (d) BSE image shown Ti-rich particle. m E‘OSEHHGIB] [55.4453 kcoum, EIDBB-flinclzl anusu ' ' Rev D 2 4 5 a 10 keV n 2 4 . s e 10 (e) EDX spectrum of Nb-rich particle. (f) EDX spectrum of Ti—rich particle. Fig. 3.1. SEM images and EDX spectra of fractured ass-received E4098 sample. CANMET—MTL_ _; Luau! 7 PROTECTED BUSINESS INFORMATION (b) High magnification BSE image of Type 1 particles. Fig. 3.2. Type Iparticles (Nb—rich). CANME‘IT” . PROTECTED BUSINESS INFORMATION 8 kCounts E40993:l Blinc3 _ _ FS=BS4B keV (c). EDX spectrum of Type I particles. Fig. 3.2 (continued) CANMET-MTL PROTECTED BUSINESS INFORMATION - (a) BSE image of Type II particle. kCaunts . E 4UBBIFI B Iinc1 3 F5 $533 Ti ke'V' u 2 , 4 s '- a w (b) EDX of Type [I particle. - . Fig. 3.3. . Type II particle. CANMET L 10 PROTECTED BUSINESS INFORMATION f Type 111 particle. 1mage 0 (21) ESE F5 =37SD EdflflfllFlfllincIEb kCaLmts ke‘v' Isle. ed by the arrow above of Type 1]] part indicat (b) X- ray spectrum of dark area 165. Type IEI part' 4 1g. 3 F 16 L. T M. T E. M N. A. C 11 PROTECTED BUSINESS INFORMATION (a) FIB secondary electron image showing the (b) FIB secondary electron image showing the Type-l inclusions to be examined in TEM. " Type-II inclusion to be examined in TEM. (0) Small sample containing Type—l inclusion. (d) Small sample containing Type-HI Inclusion is mounted on a carrier. inclusion. Inclusion is mounted on a carrier. Fig. 3.5. FIB secondary electron image showing lifted—out specimen containing the feature of interest to be FIB thinned. CANMET-MTL' PROTECTED BUSINESS INFORMATION 12 3.4 TEM RESULTS OF TYPE-l PARTICLE (Nb-RICH) 3.4.1 Experimental and Results The sample was prepared by FIB—milling. The left photo of Fig. 3 .4.1 represents almost the entire sample, while the right photo is a higher magnification image of the particle in question. Several locations on the inclusion were examined by EDS (Table 3.4.1). Two other regions on the sample exhibiting somewhat similar contrast were also analyzed (spectra 4 and 5, see Table 3.4.1), but those appeared to be simply ferrite matrix. A series of diffraction patterns was taken from the particle at different goniometer tilts (Fig. 3.4.2). The EDS data (see Table 3.4.1) suggest that the particle is Nb with a little Ti and Fe (the latter signal could have come from the surrounding matrix and/ or smearing of the material during F [B- milling). However, diffiaction patterns could not be indexed as metallic Nb, which has a b.c.c. structure with a = 0.33 nm, but are perfectly matched by the NbC f.c.c. structure with a = 0.447 nm. Careful re-examination of the EDS spectra indeed revealed a small carbon peak (an example is shown in Fig. 3.4.3). Apparently, the C signal is very weak because the sample is thick and heavy element (Nb) absorbs most of characteristic C X—rays. 3.4.2 Conclusion The inclusion is niobium carbide with a little bit Ti (and possibly Fe). menu-rt. .,,.-...-.. PROTECTED BUSINESS INFORMATION stilts as given by the ]NCA software. CANMET ° ° 9 9. n {I g n G 8354 S355 Fig. 3.4.2. Selected area electron diffraction patterns indexed as an f.c.c. structure with a = 0.447 11111, Le. NbC. 'MlTL . .2 t “m . 7 5 3 S . em. . 0.. w. . \rl. mu. Q, .me 8 . M 5 /l\ e 3 2 .G .r n S 4 : 3 i. '1 F o . a , .m.w 6 K .m 5 a 3. ...e ‘ S a a . D U PROTECTED BUSINESS INFORMATION- CANMET-MTL. w» PROTECTED BUSINESS INFORMATION D 1 uil Scale 42‘] ds Cursor: 0.803 keV (12356 (:13) Fig. 3.4.3. LOW—energy part of EDS spectrum. CANMETeMTL PROTECTED BUSINESS INFORMATION 16 3.5 TEM RESULTS OF TYPE-II PARTICLE (Tl-RICH) 3.5.1 Experimental and Results Sample was prepared by F IB milling. The left photo of Fig. 3.5.1 represents almost the entire sample, while the right photo is a higher magnification image of the particle in question. Several locations on the inclusion were examined by EDS (Table 3.5.1) and two selected area diffraction pattern Were taken at different gonimeter tilts. The inclusion is a single crystal of Ti(+Nb)N. The particle shape (see Fig. 3.5.1) is consistent with such identification and selected area diffraction patterns (see Fig. 3.5.2) confirm that. EDS results are presented in Table 3.5.1. Spectra were acquired in two different regimes, 0—20 keV and 0—10 keV. The latter range is a little more sensitive for light elements, but may miss Nb, which is definitely present in small amount. Nitrogen concentration is less than would be expected from the equiatomic stoichiometry, but this is a common effect in EDS analysis due to absorption of light element X—rays by heavier atoms in the sample. Because of that, the measured concentration of N is higher at the foil edge (see Table 3.5.1) where the sample is thinner. Carbon signal was only occasionally detected and was probably due to surface contamination. Iron signal most likely came from spurious X-rays from the surrounding steel matrix and/or frOm some smearing of the material during FIB milling. 3.5.2 Conclusion This inclusion is titanium nitride with some Ti substituted by Nb and small amount of Zr. CANMET-MTL-j. ' Sectrum18* PROTECTED BUSINESS INFORMATION I results as given by INCA system. ~ 0"” I Results in at. % Nb Spectrum” 1 Spectrum 2* I Sectrum 3* Spectrum 4 Spectrum 5 S ectrum 6* Spectrum 7* Spectrum 8 Sectrum 9 Spectrum 10* Spectrum 1 1"= Sectrum 12 Spectrum 13 Spectrum 14* S Spectrum 16 ectrum15* Spectrum 17 * - spectra acquired in the 0—10 keV range only CANMET-MTL PROTECTED BUSINESS INFORMATION Fig. 3.5.1. Bright-field TEM images of the inclusion. Locations of EDS measurements are #2: _ S384 Fig. 3.5.2. Selected area electron diffiaction pattei‘ns indexed as an f.c.c. structure CANMET-MTL 18 shown. - B.'TiN. S385 (iii: 3 PROTECTED BUSINESS INFORMATiON Fig. 3.5.4. Enlarged TEM image of the particle. Fig. Sale 6' area electron diffraction pattern — corresponds to [100] f.c.c. ' ' ' with a = 0.424 11111, i.e. TiN: ' CAN MET-MT L. _ . v «- PROTECTED BUSlNESS INFORMATION 20 Table 3.5.2. EDS measurements on two areas of the particle. Ti 74.6 65.1 Nb 13.7 6.0 N 9.9 28.9 No carbon was found in the particle. at. % 66.1 7.8 26.1 wt% 3.6 TEM RESULTS OF TYPE-Ill PARTICLE The TEM sample was prepared by FIB milling. The sample contains an inclusion of Ti (carbo—)njtride along with some other particle. The presence of C in the inclusion could not be reliably confirmed, since a high level of carbon was also measured in the steel matrix (see Tables 3.6.1, 3.6.2), indicating contamination of the sample (probably by the epoxy used t...
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