1、International Standard INTERNATIONAL ORGANIZATION FOR STANDARDlZATION*MEYHAPOAHAR OPTAHHBAUHR IlO CTAHAAF-TH3AUHH-ORGANlSATlON INTERNATIONALE DE NORMALlSATlON Steel - Determination of total or effective thickness of thin surface-hardened layers Acier - D NOTE - Surface-hardened layers with thickness
2、es of more than 0,3 mm are covered by IS0 2639, Steel - Determination and verifica- tion of the effective depth of carburized and hardened cases; and IS0 3754, Steel - Determination of effective depth of hardening after flame or induction hardening. b) a longitudinal section obtained by machining a
3、1 mm deep flat (this method applies only to round bars - see figure 1); other depths of flat may be specified; 2 Methods of measurement The two methods usually selected are : - the micrographic method; - the microhardness measurement method. The choice of the method and its accuracy depend on the na
4、ture of the thin layer and on its presumed thickness. Since the method used also affects the result obtained, the choice has to be made by prior agreement between the parties concerned. c) an oblique section; the thinner the layer, the more acute the angle u between the plane of the section and the
5、sur- face must be (see figure 2). As it is a difficult operation to determine the angle CY, it is preferable, wherever possible, to use an oblique section with a groove having a depth close to the presumed thickness of the thin layer (see figure 3). It is then possible to calculate the thickness of
6、the thin layer without having to measure the angle CL (see 2.1.2). Small samples (with a section of less than 4 cmz) shall be examined all round their perimeter. Where samples are large, several samples shall be selected to ensure that they are fully representative. Sections taken from the corners o
7、f polygonal products, being special points, shall not be included. 2.1 Micrographic method The number and relative position of the various samplings shall be specified by agreement between the parties concerned. This method consists in examining the structural variations, from the periphery inwards
8、to the centre, brought about by the treatment. The total thickness of the thin surface layer is defined as the distance from the surface examined to the limit beyond which no visible structural variation is detected, as compared with the structure of the unaffected metal. Using the customary methods
9、, micrographic polishing shall be carried out so as to avoid rounding off the sharp edges of the section, thus varying the angle of the oblique section. To en- sure that this does not occur, the sample shall be mounted or shall be held in a clamp. The surface of the product may, if necessary, be pro
10、tected by depositing a metal coating on it electrolytically. The effective thickness is defined as the distance from the surface examined to the limit of a reference structure.) Etching using 2 to 4 % nital (i.e. a 2 to 4 % solution of nitric acid in alcohol) or another appropriate reagent, will sho
11、w up the structure of the steel. I) When, for example, the reference structure is martensitic, the effective thickness is termed martensitic. 1 Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without
12、 license from IHS-,-,-IS0 4970-1979 (El 2.1.2 Measurement The total or effective thickness of the thin layer shall be measured either using a micrometer eyepiece, or directly on the ground glass screen of a projection microscope. In most cases the recommended minimum magnification is 200 x . By a pr
13、eliminary examination at low magnification it will be possible to ensure that there is no significant variation in the thickness of the surface layer along the perimeter examined. Several measurements (at least five) shall be taken on the part where the surface layer shows a uniform thickness, and t
14、hese shall be taken at regularly spaced points. The thickness of the surface layer is taken as the average of these measurements. NOTES 1 In the case of the machined flat (see figure 11, the thickness of the layer, e, is given by the formula e=R-dR2+b2-2bd2Rf-f2 where b is the distance measured on t
15、he flat; f is the depth of the flat; R is the radius of the sample. If the flat is 1 mm deep, this formula is simplified as follows : e=R- R2+b2-26 a is the angle of the oblique section. 3 In the case of a grooved oblique section (see figure 31, the thickness of the layer, e, is given by the formula
16、 I e = e- I where I is the distance measured; I is the length of the groove on the oblique section; e is the depth of the groove. 2.2 Microhardness measurement method This method consists in determining the changes in Vickers microhardnessl) under a 294 N (300 gf) load, measured from the circumferen
17、ce inwards to the centre of the product. Where the thickness of the hardened surface layer is not com- patible with the size of the impression, other loads may be used by prior agreement between the parties concerned. The total thickness of the thin surface layer is defined by the distance from the
18、surface to the limit beyond which the hard- ness of the unaffected metal is reached. The effective thickness is defined by the distance from the sur- face to the limit beyond which the required hardness (reference hardness) is reached. 2.2.1 Selection and preparation of sample The sample may be one
19、of the following types : a) a section perpendicular to the longitudinal axis of the product, or, if the product has no longitudinal axis, a sec- tion perpendicular to the surface at a location to be agreed between the parties concerned (this section is identical to that used in the micrographic exam
20、ination); b) a longitudinal section identical to that used in the micrographic examination; cl a test piece with steps : these steps are precision- ground from the surface of the product to the part where the structure is that of the basis metal, and are 0,05 or 0.10 mm thick (see figure 4); the ste
21、pped test piece is to be used when a limiting value for the thickness of the surface layer is specified; d) a simple or grooved oblique section identical to that used in the micrographic examination. The sample is prepared in exactly the same way as for the micrographic method, although the sample d
22、oes not undergo etching, in order to simplify the measurement of the size of the impression. During the machining of the steps, precautions shall be taken to avoid causing any structural changes as a result of grinding. 1) The Knoop microhardness method may be used. 2 Copyright International Organiz
23、ation for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,-: ,j IS0 4970-1979 (E) 2.2.2 Measurement The hardness impressions shall be situated along one or several parallel lines normal to the surface and inside
24、a 1,5 mm wide interval, W (see figure 5). The first impression shall be situated at a distance from the surface equal to approximately twice the length of its diagonal. The distance between two adjacent impressions, S, shall not be less than 2,5 times the length of the diagonal. The difference betwe
25、en the distances from each impression to the surface (d2 - d, for example) shall not exceed 0,l mm, and the accumulated distance shall be measured to an accuracy of + 25 pm. The diagonals of the impressions shall be measured to an accuracy of f 0,75 urn. The impressions shall be made under a 2,94 N
26、(300 gf) load and measured with the aid of an optical device providing a magnification of about 400 x . These determinations shall be carried out on the surface in two specific areas to be agreed between the parties concerned. For each one of these areas, the results shall provide data for plot- tin
27、g a graph of variations in hardness against the distance to the surface. NOTE - In the case of the machined flat or the oblique section, the thickness of the layer is calculated using the formulae in 2.1.2. 3 Test report The test report shall contain the following information : a) the grade and the
28、treatment of the material; b) the number and locations of samples taken from the piece; cl the method of measuring adopted, and the procedure; d) the type of thickness measured (total or effective); e) the results of measurements enabling the thickness of the surface layer to be defined; f) any abno
29、rmalities observed during measurement; g) any incidents occurring during measurement. Figure 1 - Longitudinal section obtained by machining a fiat Figure 2 - Simple oblique section 3 Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo repro
30、duction or networking permitted without license from IHS-,-,-IS0 4970-1979 (E) Figure 3 - Grooved oblique section Figure 4 - Stepped test piece Figure 5 - Siting of the microhardness impressions 4 Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
