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Analysis of Oxide Inclusions in Steel by Fast Laser-Induced Breakdown Spectroscopy Scanning: An Approach to Quantification
Abstract
Laser-induced breakdown spectroscopy (LIBS) measurements were performed on a steel sample to investigate the feasibility of obtaining fast information on cleanness. A calibration approach was considered to enable the quantification of the elemental composition of non-metallic inclusions; the same data was also used to estimate the size of the inclusions. For the first time, the quantified chemical composition data obtained by LIBS for non-metallic inclusions was compared to the corresponding results obtained from scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis, the conventional method used for steel cleanness assessment, and proved successful. Due to the speed of analysis and the systematic recording of the signal from the scanned area, LIBS enables the analysis of larger areas of sample and in significantly shorter time than with automated SEM-EDX. This paper summarizes the hitherto obtained results for the fast analysis of inclusions in steel by LIBS.
- ... Acicular ferrite has been known to provide an optimal combination of high strength and good toughness due to its refined and interwoven structure234. The role of oxide inclusion sites on the transformation austenite→acicular ferrite in steel weld metal deposits has been well analyzed in the last 20 years123456789101112131415. Authors of the main publications are not of the same opinion about nucleation of acicular ferrite [5]. ...The goal of this project (BK-284/RT1/2007) is to chose the proper method of car body welding. SMAW could be treated as the main method used in the transport industry. Properties of metal weld deposits depend on many conditions. This paper attempts to study first of all the role of oxide inclusion sites on the transformation austenite->acicular ferrite in steel weld metal deposits and their toughness. Properties of metal weld deposits depend on the amount of acicular ferrite in them. For good toughness over a range of temperatures, metal weld deposits should have a high amount of acicularferrite. Different basic and rutile electrodes were used in order to obtain different asdeposited weld compositions. Impact toughness tests of various deposits were carried out. The microstructure of the welds with different oxygen levels, the inclusion size distribution and approximate chemical composition of inclusions are characterized. Mostobservations and measurements were done with a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer. The result of the present study implies that it is advantageous to keep oxygen contents in basic and rutile deposits as low as possiblewhen well-developed microstructures of acicular ferrite are desired.
- ... 10) In detection of oxide inclusion particles in steel materials, several papers reported on the distribution analysis of them by using LIBS. [11][12][13][14][15][16] Boue-Bigne suggested a LIBS method for obtaining the chemical composition as well as the size of inclusion particles in a steel sample, in order to estimate the cleanness of the metallurgical structure. 11) Kuss et al. published a paper which discussed a method for determining the position of inclusion particles from variations in the emission signals under a statistical analysis. ...This paper described how the lateral resolution of an elemental mapping was estimated in laser-induced breakdown optical emission spectrometry (LIBS), when the focus point of a high-frequency Q-switched Nd: YAG laser was moved on a sample surface, along with measuring the emission signal from the resultant plasma. Several measuring parameters were optimized to improve the lateral resolution; namely, they were an averaged laser power of 1 mJ/pulse, a laser repetition frequency of 1 kHz, a scanning rate of the laser beam of 0.5 mm/s, and an atmospheric gas pressure of He 1000 Pa. Using these optimal parameters, a lateral resolution was obtained to be ca. 20 μm in the one-dimensional direction of laser scan. Furthermore, two model samples, in which regularly-aligned copper circles were deposited on a nickel plate, were irradiated by a scanning laser beam to determine actual resolving abilities both in a line direction along travelling the laser and in a two-dimensional direction over a certain sample area. The sample having an interval of 85 μm between the copper circles could give an emission image which was appropriately resolved in the two-dimensional as well as the one-dimensional direction; however, in the other sample having the 25-μm interval, the two-dimensional resolution became degraded compared to the resolution of the line scan, probably because the ablation grooves, which were left on the sample surface, had a width of more than 100 μm and were overlapped with each other in the observed area.
- ... Quantitative mapping with a spatial resolution as small as 3 μm was reported for elemental mapping in different materials [11]. The development of LIBS scanning measurements for the characterization of steel cleanness led to the generation of microscale elemental maps by either using a line-focused laser beam [12], or by using fast repetition rate lasers, pulsing at 1 kHz [13][14][15]. The analyses of segregation and decarburization in steel samples are the applications considered in this paper. ...Rapid chemical analysis is increasingly a prerequisite in the steel making industry, either to check that a steel product complies with customers' specifications, or to investigate the presence of defects that may lead to mechanical property failure of the product. Methods conventionally used for assessment, such as the monitoring of decarburization and segregation, performed by chemical etching of a polished surface followed by optical observation, tend to be relatively fast, simple and applicable to large sample areas; however, the information obtained is limited to the spatial extent of the defect. Other techniques, such as electron probe microscopy and scanning electron microscopy — energy dispersive X-ray, can be used for providing detailed chemical composition at the micro-scale, for a better understanding of the mechanisms involved; however, their use is limited to analyzing comparatively very small sample areas (typically a few mm2).The ability to rapidly generate chemical concentration maps at the micro-scale is one of the many positive attributes of laser-induced breakdown spectroscopy (LIBS) that makes it a useful tool for the steel industry as a laboratory or near-the-line analysis facility. Parameters that influence the detailed mapping of large sample areas were determined and optimized. LIBS scanning measurements were performed on samples displaying segregation and decarburization. A 60 × 60 mm2 area, with a step size of 50 μm, was measured in 35 min on segregation samples, and a 4 × 1 mm2 area with a step size of 20 μm in 2 min on a decarburization sample. The resulting quantified elemental maps correlated very well with data from the methods used conventionally.In the two examples above, the application of LIBS as a micro-analysis technique proved to bring very valuable information that was not accessible previously with other techniques on such large areas in such a short time.
- ... Laser-induced breakdown spectroscopy has been found to be a powerful analytical technique suitable for determining elemental composition of different types of materials, either in solid, liquid or gaseous phase, with advantages of lack of any previous sample preparation and on-line measurement capability [1][2][3][4]. In the recent decades, laserinduced breakdown spectroscopy (LIBS) has gained much attention in many fields, including in process analytical applications [5], microanalysis [6,7], biomedical applications [8,9] and in situ chemical analysis of extraterrestrial surfaces [10]. ...A time and spatially resolved technique was used for the investigation of emission signal enhancement in collinear double-pulse LIBS. Two Q-switched Nd:YAG lasers at 1064 nm wavelength have been employed to produce laser-induced plasmas on aluminum-based alloys by single- (SP) and doublepulse (DP) LIBS. Time and spatial evolution of the plasma temperature and electron number density was investigated in these two experimental schemes. The enhancement of the emission line intensities was investigated, and a relation between the increases in intensity and excitation energy level was established. The results shows that the production of the second plasma by second laser pulse was important in DP experiment in collinear geometry.
- ... In the literature, we find that the direct observation of coinciding LIBS intensity peaks of two or more chemical elements was used to identify simple diatomic inclusions in steel, such as TiN, or for the qualitative identification of more complex inclusions that have distinct elemental compositions [4][5][6][7]. Previous work also included the identification of large inclusions, as found in solidified samples of liquid steel [8], where univariate calibration was used to quantify the inclusions' chemical content to distinguish them apart. In this case, the inclusion sizes were larger than the laser beam diameter, insuring that the ablation took place on oxide inclusion material only, minimising the variation of matrix effects during LIBS measurements and removing the effect of inclusions size on the LIBS signal. ...
- ... As a result, there have been numerous alloys developed for particular applications, because they have one or several specific properties. Accordingly, in connection with increasing industrial demands for process control and quality assurance of steel production, the LIBS technique has been progressively developed, both on-line and in the laboratory, for the rapid, precise and accurate chemical composition analysis of these elements [e.g., [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. ...
- ... Principal component analysis (PCA) was used to classify the profile data. Compared to SEM analyses, elemental information of larger areas of steel samples can be monitored due to the increased speed of LIBS measurements, while SEM analysis provides more precise morphological information, such as the shape and size [24]. The combination of energy dispersive X-ray fluorescence spectrometry (EDXRF) and LIBS was used to detect P, K, Ca, Mg, S, Fe, Cu, Mn and Zn in wheat flour [25]. ...The fast detection of classical contaminants and their distribution on high-voltage transmission line insulators is essential for ensuring the safe operation of the power grid. The analysis of existing insulator contamination has traditionally relied on taking samples during a power cut, taking the samples back to the lab and then testing them with elemental analysis equipment, especially for sugars, bird droppings, and heavy metal particulates, which cannot be analysed by the equivalent salt deposit density (ESDD) or non-soluble deposit density (NSDD) methods. In this study, a novel method called laser-induced breakdown spectroscopy (LIBS) offering the advantages of no sample preparation, being nearly nondestructive and having a fast speed was applied for the analysis of metal contamination. Several LIBS parameters (laser energy and delay time) were optimized to obtain better resolution of the spectral data. The limit of detection (LOD) of the observed elements was obtained using a calibration curve. Compared to calibration curves, multivariate analysis methods including principal component analysis (PCA), k-means and partial least squares regression (PLSR) showed their superiority in analyzing metal contamination in insulators. Then, the elemental distribution of natural pollution was predicted using LIBS to fully capture information about the bulk elements (Na, Ni, Cu, Mn, Ca, etc.) of entire areas with PLSR. The results showed that LIBS could be a promising method for accurate direct online quantification of metal contamination in insulators.
- This review is focused on a comparison of LIBS with the two most common plasma Optical Emission Spectroscopy (OES) techniques for analysis of metals; spark OES and glow discharge (GD) OES. It is shown that these two techniques have only minor differences in analytical performance. An important part of the paper reviews a direct comparison of the analytical figures of merit for bulk analysis of steels using spark and LIBS sources. The comparison was carried out using one instrument with interchangeable sources, eliminating differences related to the optical system and detectors. It was found that the spark provides slightly better analytical figures of merit. The spark analysis is considerably faster, the simple design of the spark stand has enabled complete automation, both properties of great importance in the metallurgical industry for routine analysis. The analysis of non-metallic inclusions (NMI) with spark and LIBS is presented, in the case of the spark this has become known as Pulse Distribution Analysis (PDA). A very significant difference between the techniques is that the electrical spark typically evaporates ~ 100 times more material than a single laser pulse, resulting in complete evaporation of an NMI present in the evaporated metal. The major advantage of LIBS is that it is localised with very good lateral resolution. The major advantages of spark is that it is much faster (can be done simultaneous with the bulk analysis) and easier to quantify. Compositional Depth Profiling (CDP) is compared for GD-OES and LIBS. It is shown that for applications where GD-OES is well suited, e.g. coated metallic sheet, GD-OES still performs slightly better than LIBS. Similar to the case of NMI analysis, the major advantage of LIBS is the great lateral resolution. This allows elemental surface mapping, as well as CDP of very small areas on μm scale. One further advantage of LIBS is that samples of almost any material, shape and size can be analysed, whereas GD-OES has only limited capabilities for non-flat and small samples. A general conclusion of this review is that LIBS is not likely to replace spark and GD-OES in the foreseeable future, for applications where these techniques are well suited. On the other hand several new applications, particularly in the field of on-line monitoring of industrial processes, are making great inroads for LIBS in the metallurgical and manufacturing industries.
- This paper describes an analytical method for determining the spatial distribution of alumina inclusion particles in several ferritic stainless steels by laser-induced breakdown optical emission spectrometry with a single-shot laser scanned on the sample surface. For this purpose, an irradiation system, which comprised a Q-switched Nd:YAG laser with an average energy of 50 mJ/pulse and a precisely driven X-Y-Z sample stage, was prepared. A Czerny–Turner-mounting spectrograph equipped with an ICCD detector was employed for a time-resolved measurement of the laser-induced breakdown optical emission spectrometry signal. The intensity ratio of Al I 396.152 nm to Cr I 396.368 nm was measured each for the single shot, while the irradiation positions were step-wise moved in the X-Y direction and then the same sampling area was repeatedly irradiated by subsequent laser shots in the Z direction. The number of alumina particles was mapped from the intensity ratio of Al/Cr each for the irradiation points in both the lateral and in-depth directions, enabling the distribution of alumina particles to be presented. The resolution of our measuring system was 40 μm in the lateral position and 6–7 μm in the depth direction, which were mainly determined by the crater size of a laser shot. A typical size of the alumina particles (several μm) was smaller than their resolutions; nevertheless, the suggested method would be still more effective to give the distribution of alumina particles, especially the coarse ones, because of its rapid response for the analytical result. Copyright
- Grade assessment of steel is generally performed via the metallographic method, which is timeconsuming and is not able to provide the elemental distribution information. In this paper, we present a method to measure the globular oxide inclusion ratings in steel using laser-induced breakdown spectroscopy (LIBS). The measurement is performed in two basic steps: steel samples are polished using metallographic sand paper and the Al2O3 inclusion number and size distribution in a marked area are observed using scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDS) for further LIBS scanning analysis. The threshold intensity that distinguishes soluble aluminum and insoluble aluminum inclusions is determined using LIBS combined with the SEM/EDS statistical data. Carbon steel (the sample number is S9256) and bearing steel (the sample number is GCr15) are analyzed in scanning mode, and the number of Al2O3 inclusions in different size ranges is obtained from the statistical information derived from the Al2O3 size calibration curve. According to heavy and thin series for globular oxide inclusions grade assessment, the method we propose is comparable to the traditional metallographic method in terms of accuracy; however, the process is simplified and the measurement speed is significantly improved.
- Laser spectroscopy utilizes the specific properties of atoms and molecules to gain information about the chemical composition of the test object. The principle of laser material analysis is described as well as the important underlying physical processes. The evaluation of the emitted spectra yields the composition of the material. Examples of applications for mix-up detection, material-specific recycling and inline process control tasks are presented. Light detection and ranging—LIDAR—is a spectroscopic method for the remote analysis of the composition of gases in the atmosphere. The working principle and the methods for the signal evaluation are presented. Examples of applications are described such as measurements of atmospheric gas constituents, aerosol particles, atmosphere dynamics and organic pollutions in water. Coherent anti-Stokes Raman spectroscopy—CARS—is based on the non-linear interaction of laser light with matter. By this, information about the temperature and concentration of molecules in gas atmospheres is gained. Examples of applications are combustion processes such as Diesel and Otto engines, gas discharges, graphite furnaces or novel types of microscopy to make visible cellular structures of living cells.
- This chapter describes a selection of industrial applications of LIBS systems based on methodical approaches and instrumental system designs presented in the previous chapters.
- Laser-induced breakdown spectroscopy (LIBS) is an upcoming technique for element analysis of solid, liquid, and gaseous material. We give a brief introduction to LIBS, estimate the optical emission for most chemical elements in laser-induced plasma, and discuss the achievable limits of detection. An overview of industrial materials analyzed by LIBS is given. Secondary raw materials are a relevant resource in production and can be measured by LIBS sensors under harsh conditions. We present LIBS analysis of waste polymers, metal oxide powder, and metallurgical slags from steel production. Heavy metals in polymers and impurities in powders are detected with ppm sensitivity. Slags are analyzed by a calibration-free method.
- The feasibility of steel materials classification by support vector machines (SVMs), in combination with laser-induced breakdown spectroscopy (LIBS) technology, was investigated. Multi-classification methods based on SVM, the one-against-all and the one-against-one models, and a combination model, are applied to classify nine types of round steel. Due to the inhomogeneity of steel composition, the data obtained using the one-against-all and one-against-one models were ambiguous and difficult to discriminate; whereas, the combination model, was able to successfully distinguish most of the ambiguous data and control the computation cost within an acceptable range. The studies presented here demonstrate that LIBS-SVM is a useful technique for the identification and discrimination of steel materials, and would be very well-suited for process analysis in the steelmaking industry.
- A review of publications regarding detection of non-metallic inclusions in metal alloys using optical emission spectrometry with single-spark spectrum registration is presented. The main advantage of the method - an extremely short time of measurement (~1 min) – makes it useful for the purposes of direct production control. A spark-induced impact on a non-metallic inclusion results in a sharp increase (flashes) in the intensities of spectral lines of the elements that comprise the inclusion because their content in the metal matrix is usually rather small. The intensity distribution of the spectral line of the element obtained from several thousand of single-spark spectra consists of two parts: i) the Gaussian function corresponding to the content of the element in a dissolved form, and ii) an asymmetric additive in the region of high intensity values ??attributed to inclusions. Their quantitative determination is based on the assumption that the intensity of the spectral line in the single-spark spectrum is proportional to the content of the element in the matter ablated by the spark. Thus, according to the calibration dependence constructed using samples with a certified total element content, it is possible not only to determine the proportions of the dissolved and undissolved element, but also the dimensions of the individual inclusions. However, determination of the sizes is limited to a range of 1 – 20 µm. Moreover, only Al-containing inclusions can be determined quantitatively nowadays. Difficulties occur both with elements hardly dissolved in steels (O, Ca, Mg, S), and with the elements which exhibit rather high content in the dissolved form (Si, Mn). It is also still impossible to determine carbides and nitrides in steels using C and N lines. The use of time-resolved spectrometry can reduce the detection limits for inclusions containing Si and, possibly, Mn. The use of the internal standard in determination of the inclusions can also lower the detection limits, but may distort the results. Substitution of photomultipliers by solid-state linear radiation detectors provided development of more reliable internal standard, based on the background value in the vicinity of the spectral line. Verification of the results is difficult in the lack of standard samples of composition of the inclusions. Future studies can expand the range of inclusions to be determined by this method.
- The development of a direct, rapid, and sensitive spectroscopic method for the analytical quantification of light (low atomic number) elements represents an important ongoing challenge. For the first time, we review the evolution of laser-induced breakdown spectroscopy (LIBS) technique for trace analysis of light elements in steels. We present studies carried out in both far/vacuum UV and UV–visible spectral regions, and focus on the elements carbon, sulfur, phosphorous, and nitrogen as their presence and content determine key properties of all steel products. In order to facilitate tracking down the evolution of the technique for a particular element/matrix, the review is organized in such a way that a chronological order has always been obeyed. Moreover, important information regarding characterization of a specific element in a given steel sample is tabulated, so that interested readers can easily locate relevant resources. Furthermore, typical examples of recent developments and advances in terms of LIBS instrumentation and systems regarding light elements in steels are summarized. Finally, the article suggests in brief some approaches for further raising the analytical capability and figures of merit of LIBS regarding trace compositional analysis of light elements. In this respect, we suggest combining LIBS with recently developed diode laser-based techniques such as DLIFS and DLAAS.
- In industrial recycling processes secondary metals need to be separated by material grades before they can be further processed. The identification and separation into different material classes lead to higher value-added industrial feedstock and prevent downgrading processes. Secondary raw materials can be used more efficiently resulting in an increased use of waste products in resource-intensive production processes. Laser-induced breakdown spectroscopy (LIBS) offers a contact free, multi-elemental and fast method for the inline quantitative analysis of single objects in moving particle streams. The LIBS method presented in this paper is based on a 3D object detection combined with a scanning LIBS setup. The optical system consists of a pulsed Nd:YAG laser running at 40 Hz, delivering a 200 mJ double pulse for plasma generation. A high performance three axis galvo-scanner guides the laser beam onto single pieces moving at 3 m s−1 through a measuring volume of 600 × 600 × 100 mm3 with a precision of ±1.5 mm. Twenty channels of a high resolution Paschen–Runge spectrometer are simultaneously processed within a few microseconds enabling multi-elemental analysis of different aluminium (Al) alloys. A dimensionless figure of merit is introduced for the evaluation of the analytical performance. Sorting measurements of Al post-consumer scrap charges, consisting of wrought and cast alloys were carried out. After discarding 20% of the data as outliers low and high silicon alloyed Al pieces were identified with a correctness of >96%. In a second sorting scenario the analytical discrimination of 8 different Al alloys of production scrap, requiring high analytical precision, is investigated. A mean identification correctness of wrought Al alloys >95% is demonstrated successfully for the first time.
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H. M. Kuss and H. Mittelstädt, G.Müller, J. Anal. At. Spectrom. 20, 730 (2005).- Fast scanning laser-induced optical emission spectrometry (scanning laser OES) is applied to estimate the content of non-metallic inclusions in ferrous materials within a few tens of minutes. The emission intensity after each single laser pulse is recorded in 41 element channels. Signals of inclusion related elements are evaluated by different statistical algorithms. The goal of the data treatment is to distinguish between emission peaks representing laser pulses focussed on the non-metallic inclusions and the class of low intensity signals from the element share dissolved in the metallic matrix. Criteria for the distinction are the 3-sigma (plus mean) threshold, the skewness of the histogram by Pearson, and a modified outlier test based on the Nalimov test. Correlations between the statistical approaches for signal evaluation and the inclusion contents in synthetic Fe-base standards are discussed.
- Spatially resolved information about the distribution and chemical composition of inclusions in steel are gained by scanning methods, such as scanning electron microscopy with energy dispersive X-ray spectroscopy, electron probe microanalysis or capillary-X-ray flourescence. Scanning laser-induced breakdown spectroscopy (LIBS) offers distinct advantages in contrast to these conventional methods. Sample polishing or high vacuum conditions are not necessary, a simple grinding of the sample is sufficient for the preparation. Analysing times can be reduced significantly. At Fraunhofer ILT a measuring system was developed enabling for the first time high-speed scanning LIBS with measuring frequencies of up to 1000 Hz. Sample surfaces with dimensions up to 110×45 mm2 can be analyzed. Light elements such as C, N, O, P, and S are detected, which is demonstrated by the identification of nonmetallic inclusions in steel. Principle, features and results of high-speed scanning LIBS with a spatial resolution<20 μm are presented.
- Pulsed laser sources with high repetition rates, high beam quality and pulse-to-pulse stability are available since few years. These sources can be applied to micro-analytical scanning techniques requiring high number of laser pulses in a short time, low signal deviation and good focusability. A scanning laser-induced optical emission spectrometer (Laser-OES) using such a laser source was built up and applied to steel cleanness analysis. This novel analytical technique enables to distinguish between different inclusion types based on their chemical compositions. Coincidences of high intensity peaks for single elements at the same co-ordinates can be connected to specific inclusion types.
- Single spark evaluation (SSE) needs time resolved multispectral detection of individual emission intensities from the spark plasma. The classification and statistical evaluation of these data, typically 300 data per second and spectral channel have to be processed. Experiments with metal samples have shown that the single spark pulse height distributions can be satisfactorily approximated by a Gaussian function if the respective element is homogeneously distributed within the sample. If there are nonhomogeneities of the analyte concentration in the sample, such as inclusions, than significant deviations from the Gaussian distribution are observed. The integrals over the Gaussian and non-Gaussian parts can be used to quantify the respective components of the analyte. This procedure could be succesfully applied to calibrate the contents of soluble and insoluble Al in a set of steel samples. SSE allows also the calculation of correlations between pulse height distributions of different emission lines. One finds a range from anticorrelation to correlation for various line combinations. This information can help to select reference lines for improving the precision.
- For the first time laser-induced breakdown spectrometry, with laser pulse repetition frequencies of up to 1 kHz, with single pulse evaluation is realized for scanning microanalysis of macroscopic samples. The tightly focused beam of a diode-pumped Q-switched Nd : YAG-laser is scanned with a step size of 20 µm across a sample surface. The emission spectrum of each laser-induced plasma generated by a single laser pulse of 2 mJ energy is guided to a spectrometer of the Paschen–Runge type to detect the line radiation of up to 24 elements simultaneously covering a spectral range from the vacuum ultraviolet to the near infrared. The time resolved spectral signals linked to the respective detector channel are processed to generate maps of the spatial distribution of elements in the sample surface. In a measuring field of typically 1 × 1 cm2 250 000 measurements are performed within 11 min. The spatial resolution achieved, in terms of the diameter of the crater produced by a single laser pulse in steel samples, is better than 15 µm. The experimental system is applied to investigate inclusions in steel samples. These inclusions influence the quality of steel grades for the production of spring steel, thin sheets and wires. They consist of oxides, nitrides or sulfides. Correlating the maps of different elements allows us to identify the type of inclusion, this is demonstrated for aluminium oxide, aluminium nitride and manganese sulfide.
- An automated line imaging arrangement for two-dimensional (2D) and three-dimensional (3D) generation of chemical maps of inclusions in stainless steel by laser-induced plasma spectrometry (LIPS) is presented. The plasma was generated in air at atmospheric pressure by focusing a flat-top Nd:YAG laser beam operating at 532 nm to a microline on the sample surface. The emitted light from the microline plasma was projected through an imaging spectrograph onto a charge-coupled device (CCD) detector to generate a spatially and spectrally resolved data set. Compositional distribution maps of inclusion constituents (Mn, Mg, Ca, Al, and Ti) in stainless steel of different grades have been generated. Comparative studies with the point-to-point LIPS mapping method have been performed, resulting in a 51-fold reduction in the number of pulses and analysis time when the microline imaging approach is employed. The results illustrate the capability of microline imaging LIPS for fast-automated acquisition of tomographic maps with spatial resolution of 50 microm between adjacent craters and 4.8 microm along the microline.
- With the help of an automated SEM/EDX analysis system non-metallic micro-inclusions in steel can be detected on a metallographically prepared surface area. The system makes it possible to determine position, size, shape and composition of each particle. Usually more than 1000 inclusions are found on one scan area. Therefore a new offline evaluation method has been developed to classify the large amount of inclusions and calculate specific size and shape data. A summary sheet is created to show the area contents and the mean values of all important properties for each class. Size and XY distributions as well as binary and ternary phase diagrams are drawn to depict the results. The strengths of this analytical technique are demonstrated by evaluation of an LC (low-carbon) steel. Alumina, common spinel, sulfide and oxisulfide inclusions could be identified as dominant inclusion types in LC steel.
