BS ISO 16592-2012 Microbeam analysis Electron probe microanalysis Guidelines for determining the carbon content of steels using a calibration curve method《微光束分析 电子探针显微分析 用校准曲线法测定钢碳.pdf

1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 16592:2012Microbeam analysis Electronprobe microanalysis Guidelines for determining thecarbon content of steels usinga calibration curve methodBS ISO 16592:2012 BRITISH ST

2、ANDARDNational forewordThis British Standard is the UK implementation of ISO 16592:2012. Itsupersedes BS ISO 16592:2006 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee CII/9, Microbeam analysis.A list of organizations represented on this committee can b

3、eobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2012. Published by BSI StandardsLimited 2012ISBN 978 0 580 77198 9ICS 71.040.50Compliance

4、with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 31 August 2012.Amendments issued since publicationDate T e x t a f f e c t e dBS ISO 16592:2012 ISO 2012Microbeam analysis Ele

5、ctron probe microanalysis Guidelines for determining the carbon content of steels using a calibration curve methodAnalyse par microfaisceaux Analyse par microsonde lectronique (microsonde de Castaing) Lignes directrices pour le dosage du carbone dans les aciers par la droite dtalonnageINTERNATIONAL

6、STANDARDISO16592Second edition2012-08-01Reference numberISO 16592:2012(E)BS ISO 16592:2012ISO 16592:2012(E)ii ISO 2012 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2012All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by

7、any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCase postale 56 CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail cop

8、yrightiso.orgWeb www.iso.orgPublished in SwitzerlandBS ISO 16592:2012ISO 16592:2012(E) ISO 2012 All rights reserved iiiContents PageForeword iv1 Scope 12 Procedure 12.1 General . 12.2 Reference materials 12.3 Specimen preparation 12.4 Measurement of carbon K Xray intensity 22.5 Background subtractio

9、n 32.6 Establishment of the calibration curve . 43 Evaluation of uncertainty 64 Test report . 6Annex A (informative) Method of estimating the uncertainty of the calculated value using a calibration curve 8Annex B (informative) A practical example of the determination of the mass fraction of carbon a

10、nd the evaluation of uncertainty in a steel 10Bibliography .12BS ISO 16592:2012ISO 16592:2012(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carri

11、ed out through 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. I

12、SO collaborates 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 Internation

13、al Standards. 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 eleme

14、nts of 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.This second edition cancels and repl

15、aces the first edition (ISO 16592:2006), of which it constitutes a minor revision involving the following changes: instructions concerning the establishment of a conductive path from the specimen to ground to prevent charging and instructions concerning the minimization of outgassing of the specimen

16、-mounting medium have been added to Subclause 2.3.2; in Subclause 2.3.3, the meaning of carbon-free ultrasonic cleaning has been clarified; the second sentence in Subclause 2.4.2 has been reworded to make it clear that the requirements apply to both the reference material and the unknown specimen.iv

17、 ISO 2012 All rights reservedBS ISO 16592:2012INTERNATIONAL STANDARD ISO 16592:2012(E)Microbeam 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 determin

18、ation 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 m

19、easured 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 perfor

20、med using normal beam incidence and wavelength-dispersive X-ray 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. Fo

21、r 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, specimen

22、 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 materialsTo establish the calibration curve to determine the carbon content, a suitable reference material or set of

23、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 concentrations;

24、Fe-C compound Fe3C1.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.2.3 Specimen preparation2.3.1 GeneralThe presence of carbon and/or its compounds as

25、 contamination on the specimen surface as a result of specimen 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 referenc

26、e material and the unknown material. ISO 2012 All rights reserved 1BS ISO 16592:2012ISO 16592:2012(E)2.3.2 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

27、to realize that the mounting material can act as a source of carbon contamination. Various mounting media 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 i

28、s used, areas chosen for analysis should, if possible, be close to the centre of the specimen to avoid 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 specim

29、en-mounting medium should be minimized. Virtual leaks from porosity in the specimen and gaps in the mounting 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 fl

30、at, 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 powder. After polishing, it is important to thoro

31、ughly clean the specimen so as to remove any residue resulting from the preparation, using a carbon-free 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 ionizatio

32、n 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 emitted fra

33、ction 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 energy for many

34、 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 number of X-ra

35、ys, 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 and refe

36、rence specimen. Normalization of the counts is acceptable if the current is measured at frequent intervals.2 ISO 2012 All rights reservedBS ISO 16592:2012ISO 16592:2012(E)KeyX beam energy, keVY measured C K intensity, cps/nAFigure 1 Effect of the beam energy on the measured C K intensity (see Refere

37、nce 2)2.4.2 Counting timeFor 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 contamination. In this case, the procedure should include a fixed time (depending on

38、 the instrument) on each point to stabilize the count rate before starting the measurement for both the reference material and the unknown specimen.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 c

39、ontribution 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 might contaminate the surface of the specimen by the electron irradiation are numerous (the specimen itself, residua

40、l gas inside the specimen chamber, oils associated with the vacuum pumps, lubrication of the spectrometer mechanics, etc.). As mentioned above, 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 specimen

41、2.2.4.3 Pulse height analyser (PHA) settingThe 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 choiceT

42、o 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 inten

43、sity and peak-to-background values are available now.2.5 Background subtractionWhen performing quantitative analyses of heavier elements, care is taken in choosing suitable background positions either side of the peak to be measured. The choice of positions is determined by the avoidance of addition

44、al peaks from other elements that might be present within the specimen. In the case of carbon analysis, however, the measured C K intensity is the sum of five X-ray intensities, as shown in Figure 2. These five ISO 2012 All rights reserved 3BS ISO 16592:2012ISO 16592:2012(E)contributions to the tota

45、l 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 in Figure 2), the intensity from the carbon contamination due to electron irradiation during measurement (curve 3), t

46、he 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 material, these additional intensities should be subtracted from the measured total intensity.KeyX wavelengthY measured C

47、 K intensity1 total measured intensity2 net intensity from carbon in specimen3 intensity from contamination due to electron irradiation during measurement4 intensity from contamination due to specimen preparation5 intensity of overlapped peak6 continuous X-ray intensityFigure 2 Contributions to the

48、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 the net intensity in the specimen because the intensities resulting from contamination (curves 3 and 4) are still in

49、cluded. 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 iron 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 overlapping peaks are present, the