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1、BRITISH STANDARD BS ISO 16592:2006 Microbeam analysis Electron probe microanalysis Guidelines for determining the carbon content of steels using a calibration curve method ICS 71.040.50 ? Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 05:43:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS IS
2、O 16592:2006 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 October 2006 BSI 2006 ISBN 0 580 49320 2 National foreword This British Standard was published by BSI. It is the UK implementation of ISO 16592:2006. The UK participation in its
3、preparation was entrusted to Technical Committee CII/9, Microbeam analysis. A list of organizations represented on CII/9 can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct applica
4、tion. Compliance with a British Standard cannot confer immunity from legal obligations. Amendments issued since publication Amd. No. DateComments Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 05:43:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Reference number ISO 16592:2006(E) INTERNATIONA
5、L STANDARD ISO 16592 First edition 2006-09-15 Microbeam analysis Electron probe microanalysis Guidelines for determining the carbon content of steels using a calibration curve method Analyse par microfaisceaux Analyse par microsonde lectronique (microsonde de Castaing) Lignes directrices pour le dos
6、age du carbone dans les aciers par la droite dtalonnage BS ISO 16592:2006 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 05:43:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 05:43:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iii Conte
7、nts Page Foreword iv 1 Scope . 1 2 Procedure 1 2.1 General. 1 2.2 Reference materials 1 2.3 Specimen preparation 2 2.4 Measurement of carbon K X-ray intensity . 2 2.5 Background subtraction 4 2.6 Establishment of the calibration curve. 5 3 Evaluation of uncertainty. 6 4 Test report . 6 Annex A (info
8、rmative) Method to estimate the uncertainty of the calculated value using a calibration curve. 8 Annex B (informative) A practical example of the determination of the mass fraction of carbon and the evaluation of uncertainty in a steel. 10 Bibliography. 12 BS ISO 16592:2006 Licensed Copy: sheffieldu
9、n sheffieldun, na, Mon Nov 27 05:43:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out thr
10、ough ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collabo
11、rates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Stand
12、ards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of
13、this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 16592 was prepared by Technical Committee ISO/TC 202, Microbeam analysis, Subcommittee SC 2, Electron probe microanalysis. BS ISO 16592:2006 Licensed Copy: sheffiel
14、dun sheffieldun, na, Mon Nov 27 05:43:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 1 Microbeam analysis Electron probe microanalysis Guidelines for determining the carbon content of steels using a calibration curve method 1 Scope This International Standard gives guidance on a method for the determ
15、ination of the carbon content in steels containing other alloying 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
16、 measured carbon content. It is applicable to steels containing 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 per
17、formed using normal beam incidence and wavelength-dispersive X-ray spectrometry; it is not designed to be used for energy-dispersive X-ray spectrometry. 2 Procedure 2.1 General In order to determine the carbon content in steels using a calibration curve, suitable reference materials should be prepar
18、ed. For accurate analysis, extreme care should be used to prevent carbon 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, s
19、pecimen preparation, beam energy, beam current, beam diameter, point counting mode, step between points in case of line analysis, and also the method of background subtraction. 2.2 Reference materials To establish the calibration curve to determine the carbon content, a suitable reference material o
20、r set of reference materials should be used. Examples of reference materials 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 concent
21、rations; Fe-C compound Fe3C 1. Reference materials with a different C K peak shape compared to the unknown materials should not be used because the use of these reference materials causes a lowering of the quantitative accuracy. BS ISO 16592:2006 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 2
22、7 05:43:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 2 2.3 Specimen preparation 2.3.1 General The presence of carbon and/or its compounds as contamination on the specimen surface as a result of specimen preparation significantly affects the accuracy of carbon analysis. Extreme care should be used t
23、o prevent this contamination. The specimen preparation (mounting, grinding and polishing) procedures should be the same for both the reference material and the unknown material. 2.3.2 Specimen mounting Although it is often possible to analyse a specimen without the use of a mounting medium, for smal
24、l 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 media are available, such as Bakelite, copper- filled or aluminium-filled and even graphite-filled resins, and it is recom
25、mended that the user evaluates the different types. Where a mounting medium is used, if possible, areas chosen for analysis should be close to the centre of the specimen to avoid smearing effects close to the mounting medium/specimen interface. 2.3.3 Specimen polishing and cleaning The surface finis
26、h of the specimen to be examined should be flat, clean and dry. The specimen should be prepared in the standard metallographic manner, using silicon carbide papers for grinding and diamond- impregnated pads for polishing, etc. Final polishing should be with a carbon-free material such as alumina pow
27、der. After polishing, it is important to thoroughly clean the specimen so as to remove any residue resulting from the preparation using carbon-free ultrasonic cleaning. 2.4 Measurement of carbon K X-ray intensity 2.4.1 Beam energy and beam current The X-ray emission level of carbon is low due to low
28、 ionization probability and also because the absorption of C K radiation is very strong in almost all matrix materials. 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 e
29、mitted fraction of X-rays is strongly decreased compared to the generated intensity because of the high absorption 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 energ
30、y for many types of carbide which commonly occur in steels is in the region of 6 keV 2, in practice a value of 10 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 numb
31、er of X-rays but with an associated increase in beam diameter. Unless the beam diameter is an issue, the beam current 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
32、 and reference specimen. Normalization of the counts is acceptable if the current is measured at frequent intervals. BS ISO 16592:2006 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 05:43:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 3 Key X beam energy, keV Y measured C K intensity, cps/nA
33、Figure 1 Effect of the beam energy on the measured C K intensity (see Reference 2) 2.4.2 Counting time For best results, the EPMA instrument should have an effective anti-contamination device with a liquid nitrogen cooling plate and/or a microleak of air or oxygen on the specimen to limit the contam
34、ination. 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. NOTE 1 For an instrument with high contamination rates, a better strategy may be to collect as many counts in as short a time as p
35、ossible before the contribution of counts due to the contamination becomes unacceptably large. The preferred strategy will be different from instrument to instrument. NOTE 2 The origins of the carbon that may contaminate the surface of the specimen by the electron irradiation are numerous (the speci
36、men itself, residual gas inside the specimen chamber, oils associated with the vacuum pumps, lubrication of the spectrometer mechanics, etc.). The contamination which arises from the electron irradiation may be reduced by a liquid nitrogen cooling plate and a jet of air or oxygen on the specimen 2.
37、2.4.3 Pulse height analyser (PHA) setting The PHA settings should be adjusted to remove all high-order diffraction lines at the wavelength used 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 choice
38、 To obtain good counting statistics, the crystal used should provide a high count rate and a good peak-to-background ratio at the wavelength used 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 int
39、ensity and peak-to-background values are available now. BS ISO 16592:2006 Licensed Copy: sheffieldun sheffieldun, na, Mon Nov 27 05:43:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 4 2.5 Background subtraction When performing quantitative analyses of heavier elements, care is taken in choosing suita
40、ble 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 may be present within the specimen. In the case of carbon analysis, however, the measured C K intensity is the sum of five X-ray intens
41、ities, as shown in Figure 2. These five 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 (A), the intensity from the carbon contamination due to elect
42、ron irradiation during measurement (B), the intensity of continuous X-rays (C) and the intensity of any overlapped peak (D). In order to determine the net C K intensity generated in the unknown and reference material, these additional intensities should be subtracted from the measured total intensit
43、y. Key X wavelength Y measured C K intensity 1 total measured intensity 2 net intensity from carbon in specimen 3 intensity of contamination (B) 4 intensity of contamination (A) 5 intensity of overlapped peak (D) 6 continuous X-ray intensity (C) Figure 2 Contributions to the measured C K intensity T
44、he peak profile method may be used to determine the level of continuous X-ray generation (C). However, the resultant peak height and/or area does not give the net intensity in the specimen because the intensities resulting from contamination (A) and contamination (B) are still included. To estimate
45、the net intensity generated in the specimen without the contributions due to contamination (A and B), it is very useful to measure C K intensity on a pure iron reference specimen under identical conditions to the unknown. This method involves collecting counts on pure iron from the maximum peak inte
46、nsity position for C K, without moving to background positions, to determine the X-ray intensity related to the zero carbon content. Where overlapping peaks are present, the contribution made by the element(s) must be estimated using appropriate reference materials. BS ISO 16592:2006 Licensed Copy:
47、sheffieldun sheffieldun, na, Mon Nov 27 05:43:48 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 5 2.6 Establishment of the calibration curve The calibration curve for the determination of the carbon content of steels should be established from the relationship between the net C K intensity and a number
48、of certified reference materials of differing carbon contents, as shown in Figure 3. As there is a linear relationship between the carbon contents and the C K intensity in the range of 0 % to 1,0 % carbon (by mass), the calibration curve is given by Equation (1): 01ii Ibb C=+ (1) where Ii is the X-r
49、ay intensity measured on the reference material; Ci is the mass fraction of carbon in the reference material; b0 is the intercept on the intensity axis; b1 is the slope of the calibration curve. The coefficients b0, b1 may be calculated by the linear least-square fitting procedure (see Annex A). When using pure iron for background subtraction, the net intensity when the carbon content is zero should theoretically correspond with zero, but will always have a fini