1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS 7926:1998 ICS 77.080.2
2、0 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Quantitative micrographic methods to determine the percentage content of non-metallic inclusions in cast steelThis British Standard, having been prepared under the direction of the Engineering Sector Board, was published under
3、the authority of the Standards Board and comes into effect on 15 August 1998 BSI 1998 The following BSI references relate to the work on this standard: Committee reference ISE/6 Draft for comment 97/709854 DC ISBN 0 580 29531 1 BS 7926:1998 Amendments issued since publication Amd. No. Date Text affe
4、cted Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee ISE/6, Steel castings, upon which the following bodies were represented: BEAMA Ltd. British Pump Manufacturers Association British Valve and Actuator Manufacturers Asso
5、ciation Castings Development Centre Hopkinsons Limited Institute of British Foundrymen Lloyds Register of Shipping Ministry of Defence Railway Industry AssociationBS 7926:1998 BSI 1998 i Contents Page Committees responsible Inside front cover Foreword ii Introduction 1 1 Scope 1 2 Normative referenc
6、es 1 3 Definitions 1 4 Information and items to be agreed and to be documented 1 5 Sampling 1 6 Preparation of specimens 2 7 Determination of the percentage inclusion content 2 8 Test report 2 Annex A (normative) 3 Figure 1 Test block 2 Table 1 Non-metallic inclusion content ranges from a variety of
7、 melting and refining processes 2ii BSI 1998 BS 7926:1998 Foreword This British Standard has been prepared by Technical Committee ISE/6. Annex A is normative. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for the
8、ir correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 3 and a back cover. BSI 1998 1 BS 7926:1998 Introduction Non-metallic inclus
9、ions are present in all metals and alloys and, for the most part, their presence is detrimental. One of the few beneficial effects is the enhancement of machinability. Not all non-metallic inclusions, however, are beneficial to machinability, notably hard oxides such as alumina which are present in
10、cast steels. Non-metallic inclusions can be divided into two discrete categories. Exogenous inclusions which originate from refractory materials used to contain molten metal during casting and/or entrapped slag, and indigenous inclusions which are natural products of melting and refining processes.
11、The oxide composition of both types of non-metallic inclusion can vary widely and is generally very complex. For this reason, this standard concentrates on determining the quantity of non-metallic inclusions contained in cast steel rather than discriminating between the various discrete oxide and/or
12、 sulfide phases that might be present. In most cases it is the quantity and shape of non-metallic inclusions that has the greatest effect on the mechanical properties of the cast steel and also the machinability. 1 Scope This British Standard specifies two micrographic methods for determining the no
13、n-metallic inclusion content of cast steels. Numerical values of the area fraction of non-metallic inclusions present in samples of cast steels is specified. The percentage content ranges of non-metallic inclusions are specified for four melting and refining methods in use in steel foundries through
14、out the UK. In addition to the definitive requirements, this standard also requires the items detailed in clause 4 to be documented. For compliance with this standard, both the definitive requirements and the documented items have to be satisfied. 2 Normative references The following normative docum
15、ents contain provisions which, through reference in this text, constitute provisions of this British Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. For undated references, the latest edition of the publication referred to applies. B
16、S EN 1559-1, Founding Technical conditions of delivery Part 1: General. BS EN 1559-2, Founding Technical conditions of delivery Part 2: Additional requirements for steel castings. ISO 4990:1986, Steel Castings General technical delivery requirements. 3 Definitions For the purposes of this standard,
17、the following definitions apply. 3.1 inclusions non-metallic material, generally oxides and sulfides, present in cast steels 3.2 area fraction of inclusions surface area covered by inclusions as a percentage of total sample area under examination 4 Information and items to be agreed and to be docume
18、nted The following information to be supplied by the purchaser shall be fully documented. Both the definitive requirements specified throughout the standard and the following documented items shall be satisfied before a claim of compliance with the standard can be made and verified. a) The melting a
19、nd refining processes to be employed, see Table 1. b) The sampling technique and number of specimens to be examined, see clause 5. c) The number of counts per specimen, see clause 5. d) The acceptance category (see Table 1). 5 Sampling At least two specimens, from two different locations in the test
20、 block shall be taken and several counts shall be conducted on each. The degree of sampling and counting shall be agreed between the casting producer and purchaser, see clause 4. Specimens shall be at least 400 mm 2 (20 mm3 20 mm) and shall be cold-sawn from the bottom of a test block, after 20 mm o
21、f metal has been discarded (see Figure 1).2 BSI 1998 BS 7926:1998 Figure 1 Test block 6 Preparation of specimens The specimen shall be cut from the test block, ground and metallographically polished so as to obtain a smooth surface for examination. When polishing specimens, tearing-out or deformatio
22、n of the inclusions present, scratching and contamination of the polished surface shall be avoided. The surface shall be clean and the shape of the inclusions shall not be affected by polishing. 7 Determination of the percentage inclusion content 7.1 General 7.1.1 Determination of the percentage inc
23、lusion content shall be carried out in accordance with A.1 or A.2. NOTE Method 1 involves a simple manual count using a calibrated reference grid which facilitates the calculation of the area fraction of non-metallic inclusions. Method 2 utilizes a computer with appropriate software. 7.1.2 Method 1
24、Following preparation and examination in accordance with A.1 the area fraction of non-metallic inclusions shall conform to Table 1. 7.1.3 Method 2 Following preparation and examination in accordance with A.2 the area fraction of non-metallic inclusions shall conform to Table 1. 8 Test report The tes
25、t report shall contain the following information: a) the number and year of this British Standard, i.e. BS 7926:1998; b) melting and refining process and the cast number; c) location of specimen surface within test block; d) results of the examination; e) report number and date. Table 1 Non-metallic
26、 inclusion content ranges from a variety of melting and refining processes Category Melting and refining processes Area fraction, Area fraction, minimum maximum % 1 Induction or arc melting and argon oxygen decarburizing (AOD) or vacuum arc degassing (VAD) 0.01 0.08 2 Induction or arc melting and ga
27、s stirring in ladle 0.04 0.15 3 Induction melting 0.04 0.24 4 Arc melting 0.07 0.38 Wrought steel (for comparison only) 0.01 0.03BS 7926:1998 BSI 1998 3 Annex A (normative) A.1 Method 1 procedure A.1.1 Prepare the specimen in accordance with clause 6. A.1.2 View using an optical microscope at a magn
28、ification which enables the non-metallic inclusions to be readily identified and at a size approximately half that of the grid point spacing. NOTE In most cases the chosen magnification is3 100. A.1.3 Fix a test grid, 65 mm3 65 mm, with major squares at 10 mm intervals and minor grid markings in 1 m
29、m squares of clear plastic, to the microscope projection screen in a position which corresponds to the centre of the screen area. A.1.4 Choose the selected area randomly and mark with ink on the clear screen each of the non-metallic inclusions. Continue until a direct representation of the 65 mm3 65
30、 mm area has been made and a full replica of the non-metallic inclusion area is marked on the transparent screen. Take at least 10 readings see 4c) for each specimen and calculate the average reading. A.1.5 Remove the transparent screen and count the squares covered by the non-metallic inclusion are
31、a and determine the area fraction using the following equation. Area fraction (%) of inclusions = number of squares covered by inclusions3 100 4 225 NOTE The transparent screen may be retained as a permanent record for re-checking as necessary. A.2 Method 2 procedure A.2.1 Prepare the specimen in ac
32、cordance with clause 6. A.2.2 View the specimen using an optical microscope with lens configuration to facilitate a maximum magnification of3 100. A.2.3 Fit a black and white video camera to the microscope for the purpose of capturing a clear image of the field of view on a video monitor. Connect th
33、e monitor, in turn, to a computer loaded with software capable of point counting. A.2.4 Take at least 10 readings see 4c) for each specimen and calculate the average reading. A.2.5 Calculate the area fraction of inclusion as a percentage (%) from the following equation. Area fraction of inclusions3
34、100 Area of field of view NOTE The computer files may be retained as a permanent record for re-checking as necessary.BSI 389 Chiswick High Road London W4 4AL | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
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