1、December 2015 English price group 11No part of this translation may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).ICS 71.040.50!%JwX“2398453www.din.d
2、eDIN ISO 16592Microbeam analysis Electron probe microanalysis Guidelines for determining the carbon content of steels using a English translation of DIN ISO 16592:2015-12Mikrobereichsanalyse Elektronenstrahl-Mikroanalyse Leitfaden fr die Bestimmung des Kohlenstoffgehalts von Sthlen mittels einer Kal
3、ibrierkurven-Methode (ISO 16592:2012),Englische bersetzung von DIN ISO 16592:2015-12Analyse par microfaisceaux Analyse par microsonde lectronique (microsonde de Castaing) Lignes directrices pour le dosage du carbone dans les aciers par la droite dtalonnage (ISO 16592:2012),Traduction anglaise de DIN
4、 ISO 16592:2015-12www.beuth.deDocument comprises 15 pagesDTranslation by DIN-Sprachendienst.In case of doubt, the German-language original shall be considered authoritative.calibration curve method (ISO 16592:2012),12.15National Annex NA (informative) Bibliography 3 1 Scope 4 2 Procedure .4 2.1 Gene
5、ral 4 2.2 Reference materials .4 2.3 Specimen preparation .4 2.4 Measurement of carbon K X-ray intensity 5 2.5 Background subtraction .6 2.6 Establishment of the calibration curve .7 3 Evaluation of uncertainty 9 4 Test report 9 Annex A (informative) Method of estimating the uncertainty of the calcu
6、lated value using a calibration curve 11 Annex B (informative) A practical example of the determination of the mass fraction of carbon and the evaluation of uncertainty in a steel 13 Bibliography 15 A comma is used as the decimal marker. Contents Page National foreword 3DIN ISO 16592:2015-12 2 Natio
7、nal foreword This document (ISO 16592:2012) has been prepared by Technical Committee ISO/TC 202 “Microbeam analysis” (Secretariat: SAC, China). The responsible German body involved in its preparation was DIN-Normenausschuss Materialprfung (DIN Standards Committee Materials Testing), Working Committe
8、e NA 062-08-18 AA Elektronenmikroskopie und Mikrobereichsanalyse. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. DIN and/or DKE shall not be held responsible for identifying any or all such patent rights. The DIN Standards corres
9、ponding to the International Standards referred to in this document are as follows: ISO 5725-6 DIN ISO 5725-6 ISO/IEC 17025 DIN EN ISO/IEC 17025 ISO 22309 DIN EN ISO 22309 National Annex NA (informative) Bibliography DIN EN ISO/IEC 17025, General requirements for the competence of testing and calibr
10、ation laboratories DIN ISO 5725-6, Accuracy (trueness and precision) of measurement methods and results Part 6: Use in practice of accuracy values DIN ISO 22309, Microbeam analysis Quantitative analysis using energy-dispersive spectrometry (EDS) for elements with an atomic number of 11 (Na) or above
11、 DIN ISO 16592:2015-12 3Microbeam analysis Electron probe microanalysis Guidelines for determining the carbon content of steels using a calibration curve method1 ScopeThis International Standard gives guidance on a method for the determination of the carbon content in steels containing other alloyin
12、g elements (less than 1 % to 2 % by mass) using the calibration curve method. It specifies the sample preparation, X-ray detection, establishment of the calibration curve and the procedure for the determination of the uncertainty of the measured carbon content. It is applicable to steels containing
13、a mass fraction of carbon of less than 1,0 %. The method is not applicable to steels with higher carbon contents, which could significantly affect the accuracy of the analysis results.This International Standard applies to analyses performed using normal beam incidence and wavelength-dispersive X-ra
14、y spectrometry; it is not designed to be used for energy-dispersive X-ray spectrometry.2 Procedure2.1 GeneralIn order to determine the carbon content in steels using a calibration curve, suitable reference materials should be prepared. For accurate analysis, extreme care should be used to prevent ca
15、rbon contamination which would otherwise increase the apparent carbon content of the specimen.The measurement of C K intensity should be carried out using the same procedures for the specimen and the reference materials; that is, specimen preparation, beam energy, beam current, beam diameter, point
16、counting mode, step between points in case of line analysis, and also the method of background subtraction.2.2 Reference materialsTo establish the calibration curve to determine the carbon content, a suitable reference material or set of reference materials should be used. Examples of reference mate
17、rials are as follows: Fe-C solid-solution reference materials which are manufactured by quenching from the austenite region at high temperature; these reference materials should be homogeneous and contain different carbon concentrations; Fe-C compound Fe3C1.Reference materials with a different C K p
18、eak shape compared to the unknown materials should not be used because the use of these reference materials causes a lowering of the quantitative accuracy.2.3 Specimen preparation2.3.1 GeneralThe presence of carbon and/or its compounds as contamination on the specimen surface as a result of specimen
19、 preparation significantly affects the accuracy of carbon analysis. Extreme care should be used to prevent this contamination. The specimen preparation (mounting, grinding and polishing) procedures should be the same for both the reference material and the unknown material.DIN ISO 16592:2015-12 4 2.
20、3.2 Specimen mountingAlthough it is often possible to analyse a specimen without the use of a mounting medium, for small or irregularly shaped specimens mounting will be necessary. It is important to realize that the mounting material can act as a source of carbon contamination. Various mounting med
21、ia are available, such as Bakelite and copper-filled or aluminium-filled (or even graphite-filled) resins, and it is recommended that the user evaluate the different types.Where a mounting medium is used, areas chosen for analysis should, if possible, be close to the centre of the specimen to avoid
22、smearing effects close to the mounting medium/specimen interface.A conductive path must be established from the specimen or reference material to ground to prevent charging.Outgassing of the specimen-mounting medium should be minimized. Virtual leaks from porosity in the specimen and gaps in the mou
23、nting medium/specimen interface will degrade the vacuum, resulting in higher contamination levels.2.3.3 Specimen polishing and cleaningThe surface finish of the specimen to be examined should be flat, clean and dry. The specimen should be prepared in the standard metallographic manner, using silicon
24、 carbide papers for grinding and diamond-impregnated pads for polishing, etc. Final polishing should be with a carbon-free material such as alumina powder. After polishing, it is important to thoroughly clean the specimen so as to remove any residue resulting from the preparation, using a carbon-fre
25、e liquid, such as ultrapure water, for ultrasonic cleaning.2.4 Measurement of carbon K Xray intensity2.4.1 Beam energy and beam currentThe X-ray emission level of carbon is low due to low ionization probability and also because the absorption of C K radiation is very strong in almost all matrix mate
26、rials. Increasing the beam energy above the excitation potential of C K increases the depth of penetration of the electrons, which increases the number of X-rays generated. However, the emitted fraction of X-rays is strongly decreased compared to the generated intensity because of the high absorptio
27、n of X-rays before reaching the surface (see Figure 1). The optimum beam energy, which produces the maximum emitted X-ray intensity, is specimen-dependent. Although the optimum beam energy for many types of carbide which commonly occur in steels is in the region of 6 keV 2, in practice a value of 10
28、 keV to 15 keV is more usually used when measuring carbon composition from the viewpoint of intensity of C K and beam diameter. The use of a high beam current will increase the total number of X-rays, but with an associated increase in beam diameter. Unless the beam diameter is an issue, the beam cu
29、rrent for analysing carbon in steels should be set at a high value so as to be consistent with good counting statistics. The beam current should be kept constant when measuring the unknown and reference specimen. Normalization of the counts is acceptable if the current is measured at frequent interv
30、als.DIN ISO 16592:2015-12 5KeyX beam energy, keVY measured C K intensity, cps/nAFigure 1 Effect of the beam energy on the measured C K intensity (see Reference 2)2.4.2 Counting timeFor best results, the EPMA instrument should have an effective anti-contamination device with a liquid-nitrogen cooling
31、 plate and/or a microleak of air or oxygen on the specimen to limit the contamination. In this case, the procedure should include a fixed time (depending on the instrument) on each point to stabilize the count rate before starting the measurement for both the reference material and the unknown speci
32、men.NOTE 1 For an instrument with high contamination rates, a better strategy might be to collect as many counts in as short a time as possible before the contribution of counts due to the contamination becomes unacceptably large. The preferred strategy will be different from instrument to instrumen
33、t.NOTE 2 The origins of the carbon that might contaminate the surface of the specimen by the electron irradiation are numerous (the specimen itself, residual gas inside the specimen chamber, oils associated with the vacuum pumps, lubrication of the spectrometer mechanics, etc.). As mentioned above,
34、the contamination which arises from the electron irradiation can be reduced by a liquid-nitrogen cooling plate and/or a jet of air or oxygen on the specimen2.2.4.3 Pulse height analyser (PHA) settingThe PHA settings should be adjusted to remove all high-order diffraction lines at the wavelength used
35、 for the measurement of C K.NOTE It is easier to adjust the PHA settings when using a specimen with a high carbon content such as Fe3C.2.4.4 Crystal choiceTo obtain good counting statistics, the crystal used should provide a high count rate and a good peak-to-background ratio at the wavelength used
36、for the measurement of C K. Older instruments use a lead stearate crystal, but synthetic multi-layer crystals with optimized d-spacing and much better intensity and peak-to-background values are available now.2.5 Background subtractionWhen performing quantitative analyses of heavier elements, care i
37、s taken in choosing suitable background positions either side of the peak to be measured. The choice of positions is determined by the avoidance of additional peaks from other elements that might be present within the specimen. In the case of carbon analysis, however, the measured C K intensity is t
38、he sum of five X-ray intensities, as shown in Figure 2. These five DIN ISO 16592:2015-12 6 contributions to the total measured intensity are the intensity from the carbon atoms in the specimen, the intensity from the carbon contamination on the specimen surface due to specimen preparation (curve 4 i
39、n Figure 2), the intensity from the carbon contamination due to electron irradiation during measurement (curve 3), the intensity of continuous X-rays (curve 6) and the intensity of any overlapped peak (curve 5). In order to determine the net C K intensity generated in the unknown and reference mater
40、ial, these additional intensities should be subtracted from the measured total intensity.KeyX wavelengthY measured C K intensity1 total measured intensity2 net intensity from carbon in specimen3 intensity from contamination due to electron irradiation during measurement4 intensity from contamination
41、 due to specimen preparation5 intensity of overlapped peak6 continuous X-ray intensityFigure 2 Contributions to the measured C K intensityThe peak profile method may be used to determine the level of continuous X-ray generation (curve 6). However, the resultant peak height and/or area does not give
42、the net intensity in the specimen because the intensities resulting from contamination (curves 3 and 4) are still included. To estimate the net intensity generated in the specimen without the contributions due to contamination (curves 3 and 4), it is very useful to measure C K intensity on a pure ir
43、on reference specimen under conditions identical to those used for the unknown. This method involves collecting counts on pure iron from the maximum peak intensity position for C K, without moving to background positions, to determine the X-ray intensity related to the zero carbon content. Where ove
44、rlapping peaks are present, the contribution made by the element(s) must be estimated using appropriate reference materials.2.6 Establishment of the calibration curveThe calibration curve for the determination of the carbon content of steels should be established from the relationship between the ne
45、t C K intensity and a number of certified reference materials of differing carbon contents, as shown in Figure 3.DIN ISO 16592:2015-12 7As there is a linear relationship between the carbon contents and the C K intensity in the range 0 % to 1,0 % carbon (by mass), the calibration curve is given by Eq
46、uation (1):IbbCii=+01(1)whereIiis the X-ray intensity measured on the reference material;Ciis the mass fraction of carbon in the reference material;b0is the intercept on the intensity axis;b1is the slope of the calibration curve.The coefficients b0, b1may be calculated by the linear least-square fit
47、ting procedure (see Annex A).When using pure iron for background subtraction, the net intensity when the carbon content is zero should theoretically correspond to zero, but will always have a finite value due to the effects of contamination. For this reason, care should be taken to reduce the carbon
48、 contamination.KeyX mass fraction of carbon, %Y C K intensity, cps/nA1 total measured C K intensity2 C K intensity after subtracting the contributions from overlapped peaks and continuous X-rays3 net C K intensity after subtracting the background obtained on pure ironb1slopeFigure 3 Calibration curv
49、e for determining carbon content in steelsDIN ISO 16592:2015-12 8 3 Evaluation of uncertaintyValidation of the method should be carried out prior to any analyses. This may be accomplished using certified reference materials. The analyst should establish the repeatability, reproducibility and uncertainty of measurement for typical samples analysed in the laboratory. The analyst should also validate the method to ensure that it is fit for the intended purpose.Factors that contribute to the uncertainty of measurement should be i
