The longitudinal fatigue resistance is to be determined on unloaded products in the direction of movement in the longitudinal direction of the rail. The products are to be fastened in accordance with the DB engineering drawing in such a way as to reflect how they will be installed on the track.
The required vibration displacement is f = ±0.4 mm and is to be initiated above the rail base with normal roughness.
In the case of products whose design cannot absorb the required vibration displacement (e.g. rail clips), the vibration displacement is absorbed by the rail. At the end of the test, the wear on the product must be documented.
The test shall be conducted at a frequency of 7–9 Hz. The required number of cycles to failure is 3∙105.
Appendix 1:
Verification of the prevention of hydrogen embrittlement due to operating conditions 1. Test preparation
The products must be submitted to the corrosion test in a fastened condition. For this purpose, the products should be fastened using a suitable fastening device that simulates the load during use. The fastening device itself (including bolt and washer) must be constructed from a material that does not participate in the corrosion reaction. Coated steel is recommended. The coating should consist of a galvanic zinc-nickel layer, transparently passivated (with sufficient coating thickness of >6 µm on the main surfaces) or a cathodic corrosion protection. If a section of a rail is used for the test, this section should not be coated. It is recommended that the fastening device should use the design shown in Fig. 2.
Designs that deviate from the fastening device suggested in Fig. 2 should be discussed with the end customer and adjusted if necessary. Once the clamp force has been applied, the fastening device should be placed in the corrosion chamber in such a way as to reflect how the product will be installed on the track.
Fig. 2: Example of a fastening device
2. Test procedure
The corrosion test should take place under changing climatic conditions as follows:
• 4 h salt spray test, NSS test method based on DIN EN ISO 9227
• 4 h cooling phase at room temperature 18–28 °C and 30–80% relative humidity
• 16 h warm, humid storage, test climate CH in accordance with DIN EN ISO 6270-2 Test duration is 25 cycles.
The test cycle for the salt spray test is based on DIN EN ISO 9227 but deviates from the normative specification for the test solution to be used.
A brine mixture should be used as the test solution. This solution should be prepared from sodium chloride (purity level according to DAB 7) and calcium chloride (anhydrous, medium-fine grain size, pure) and deionized or distilled water (conductivity <2 mS/m). The specified concentration of the solution is 40 ± 2 g/l NaCl and 10 ± 1 g/l CaCl2.
The pH of the solution should be adjusted to 3.5 ± 0.2 using hydrochloric acid. The measurement should be conducted by an electrometric method.
To achieve the maximum corrosion effect, it is important that dry, anhydrous air be introduced into the chamber during the 4 h cooling phase. It must be ensured that the compressed air used is free of oil and water. It is recommended that the compressed air be produced by oil-free compressors (e.g. dental compressors).
The minimum requirement for documentation is the recording of the time and temperature in the test chamber as well as images of the changes in the products. For this purpose, photos must be taken before and after the test.
At the end of the cycles and after the clamping force has been determined in accordance with Section 5.2, the specimens should be evaluated by visual inspection (naked eye) for corrosion, cracks or breakages of the products. Cracks or breakages in the products are not acceptable. To improve the visibility of cracks, the product should be cleaned with water and a soft brush before inspection.
Appendix 21:
Microscopic examination of special steels using standard diagrams to assess the content of non-metallic inclusions
1 DIN 50602:1985 (withdrawn): Metallographic examination; microscopic examination of special steels using standard diagrams to assess the content of non-metallic inclusions
1 Scope and purpose
1.1 This appendix describes the testing of spring steels for non-metallic inclusions in the form of sulfides and oxides. Macroscopic and microscopic methods are used for this purpose.
Microscopic testing can be performed on the metal microscope and with automatic equipment. This appendix establishes a method for microscopic testing on a metal microscope using an image series table of systematic structure and generating a description in terms of the inclusion type, inclusion size (in length and width or diameter) and prevalence (image series table 1). A characteristic value, which is proportional to the content of inclusions larger than a defined limit size, can be calculated separately for oxide and sulfide contents or as a total value. The determination of maximum sizes is also provided for.
1.2 The appendix applies to the formed profile products listed in Table 1 and Figure 1. For flat products in the form of sheets and strips and other products of low thickness, special aspects must be observed and sampling and evaluation arrangements must be made.
1.3 For steels affected by the sulfide form, the steel-iron test sheet 1575* is in preparation, which takes into account the length:width ratio of the sulfides.
* To be obtained from Verlag Stahleisen mbH, P.O. Box 8229, 4000 Düsseldorf, Germany
2 Terms
2.1 Degree of purity
The degree of purity (characteristic value K3) is an indication of the content of non-metallic inclusions in the form of sulfides and oxides in a product. The characteristic value K3 is a value that reflects the content of such sulfides and oxides by determining the percentage area of non-metallic inclusions (beginning at a specified inclusion size) in the microstructure as the cumulative value of the area-proportional count, based on an area of 1000 mm².
2.2 Image series table
The image series table 1 is an image table organized according to the geometric number series and showing the area content of non-metallic inclusions per line. It shows typical steel inclusion shapes with the area doubling from image to image in the series (vertically).
Variations by length x width or prevalence are shown for equal areas within a line (horizontal) next to the main series for the inclusion types as examples for evaluation.
Figure 1: Sampling from products of different dimensions
Table 1: Position of the ground surface for different dimensions 3 Scope of testing
3.1 The degree of purity of a cast or a delivery lot is not represented by individual specimens and must therefore be determined on several specimens. In general, the degree of purity is tested on at least 6 specimens.
3.2 For each order, it must be checked whether the circumstances permit a reduction in the number of specimens to less than six, taking into account the size of the consignment, the preceding forming processes, if any, and the position of the specimen in relation to the starting material. If the scope of testing is to deviate from "at least 6 specimens”, this can be agreed upon in the delivery specifications.
3.3 If the quantity of material submitted for testing has special features, e.g. if the pieces do not originate from the same cast or if the dimensions of the individual pieces differ
significantly, these special features must be taken into account when agreeing upon the scope of testing (see Section 3.2).
4 Sampling and sample preparation
4.1 The specimens must be taken in such a way that the ground surface to be evaluated is, as closely as possible, parallel to the principal direction of elongation and, in the case of rotationally symmetrical cross-sections, in the plane through the axis of the product. This creates optimal conditions for the comparison of the non-metallic inclusions in terms of their linear expansion.
4.2 Table 1 in conjunction with Figure 1 contains rules for the arrangement (sampling points) of specimens in round and square steel tubes and wide flat steel with a smaller width:thickness ratio.
4.3 When grinding the specimens, the inclusions must not be torn out or altered in shape, and no particles of the grinding or polishing medium may be forced into the ground surface. If necessary, the grinding must be hardened. The specimens should therefore be ground carefully and polished as briefly as possible.
5 Structure and application of the image series table 5.1 Image series table 1
5.1.1 The basis of the image series table 1 is 4 image series (vertical) of the most frequently observed forms of inclusions with the type codes 1, 3, 6 and 8 (basic series) of 9 images each with the size codes 0 to 8. The image scale of the image series table 1 is 100:1. The following inclusion types are distinguished:
Inclusion type SS - sulfidic inclusions in line form;
Inclusion type OA - oxidic inclusions in dissolved form (aluminum oxides);
Inclusion type OS - oxidic inclusions in line form (silicates);
Inclusion type OG - oxidic inclusions in globular form.
The derived image series 0, 2, 4, 5, 7 and 9 are described in Sections 5.1.2 and 5.1.3.
The nine images of an image series with the size codes 0 to 8 show, under the size code 0, the smallest microscopic inclusion evaluable at magnifications of 100:1 and, under the size code 8, inclusions that are partially in the macroscopic range of the respective inclusion type.
The area of the inclusions shown doubles from image to image according to the geometric series , where n is the size code.
The length of the relevant inclusion increases from image to image by a factor of 1.5 with a simultaneous increase in the average width of the lines, so that the basic formula for increasing the area is maintained. The length and, in row 6 also the width, are noted on the images of image series table 1 to facilitate measurement. The length of an oxide is greater for the resolved form OA than for the closed line form OS for the same width, since the area would otherwise be different for the same size code.
The size code 9 is reserved for macroscopic inclusions that are not shown in the image because they extend beyond the image field boundary.
5.1.2 If a single inclusion of the same length is half as wide as in the comparative image of the basic series 1, 3 or 6, the area has only half the value, i.e. the size code is reduced by 1.
Similarly, this procedure also applies to the evaluation of thicker inclusions with an area that is twice as large. Then the size code is increased by 1.
5.1.3 If further non-metallic inclusions are visible in the field of view which are smaller by up to 2 size codes, their area in the pitch circle is also increased and the size code is increased by 1, as shown in image series 4 and 7 to the right of the respective basic series. Sulfides usually occur in the form of nests, so that it was possible to dispense with the presentation of individual sulfides. If sulfides occur in isolation, the length or area estimates are based on the dimensions of the longest inclusion in the SS image series and the size code is reduced by 1.
5.2 Image series tables 2 and 3
5.2.1 The principle of equal size codes for equal areas of inclusions also applies to thinner, more elongated inclusions and those with a higher degree of resolution than shown in image series table 1. Since the linear expansion of these inclusions usually exceeds the image field boundary (pitch circle) in the microscope, they are described numerically in Tables 2 and 3, with the specification of the respective size code for different combinations of length and width.
The image series tables 2 and 3, which supplement image series table 1, are intended to provide assistance in assigning a size code when the size code needs to be reduced or increased for thinner, more highly resolved or more strongly clustered inclusion forms than those that correspond to the images of the basic series. The principle of adjusting the size code according to the area of the inclusions also applies when thicker inclusions occur, the length of which was initially assigned according to one of the basic series in image series table 1.
When using the image series tables 2 and 3, the scale (200:1) must be noted when making associations with the basic series of the image series table 1 in (100:1).
Table 2: Scheme for the assignment of narrow elongated non-metallic inclusions to the lines of the image series table 1 (i.e. to the size codes) according to their width and length
Table 3: Ranges of the mean lengths of non-metallic inclusions given in Table 2
5.2.2 The two series (OA, and OS and SS) of image series table 2 provide a visual aid for determining the width of such inclusions. The respective length is not expressed here and must therefore be measured and assigned to a size code according to the information in Tables 2 and 3 or Figure 2.
5.2.3 Image series table 3 shows OA type inclusions in the left-hand series at varying resolutions. The associated numbers indicate the amount by which the size code assigned to the total length is to be reduced corresponding to a greater degree of disconnectedness (see Section 6.2.3 and note Section 6.2.4). The line width is to be evaluated according to image series table 2.
The right-hand series of the image series table 3 is used to classify clustered inclusions, for which not only the quantity and the mutual spacing, but also the area of all non-metallic inclusions, i.e. also their total linear expansion, must be taken into account for a classification in comparison with a single inclusion of the basic series. The associated numbers indicate the amount by which the size code is to be increased as the prevalence increases.
5.2.4 When classifying globular inclusions, insofar as they are not shown in image series table 1, i.e. in the case of very small, very large or highly clustered inclusions, the principle of classification according to the total area of the inclusions is also applied.
5.3
For better clarity and more efficiency, it is possible, with sufficient practice, to use only the basic series 1, 3, 6 and 8 of the image series table 1 along with the image series tables 2 and 3 for a smaller inclusion thickness, higher degree of resolution and greater prevalence during the test, or to limit oneself to their image. This is because the derived image series 0, 2, 4, 5, 7 and 9 only show evaluation examples with a deviation from "one" size code, e.g.
with the same linear expansion of the inclusion.
6 Performing the tests
6.1 The ground specimens are viewed with a microscope at a magnification of 100:1. This magnification is equal to the image scale of the image series plate 1.
reduced scale of approximately 1:3 compared to the original table. It can therefore only give an overview of the structure.
For the actual evaluation, the image series table on a scale of 1:1 should be used, which can be obtained from Beuth Verlag GmbH, D-10772 Berlin.
Observation can be made either at the eyepiece or at the ground surface projected onto a ground-glass screen. The observation field must have the same size as the comparison images of the image series table 1 (preferably 80 mm in diameter; however, fields with a diameter between 75 and 80 mm are permissible). It is useful to limit the observation field to this dimension by means of a pitch circle in the eyepiece or on the ground-glass screen. For the observation of very thin inclusions, it is advisable to work at a magnification of 200:1. This magnification is equal to the magnification of the image series tables 2 and 3.
6.2 When classifying the non-metallic inclusions in an observation field, one identifies the image in the image series table 1, possibly supplemented by the applicable image in the image series tables 2 and 3, that corresponds to the observed one. For this purpose, it is expedient to start from the length measurement or length estimation of the most significant inclusion.
6.2.1 In the evaluation, special attention must be paid to the fact that the image series table 1 shows individual fields of view for the size codes 6, 7 and 8 of image series 0 to 6, in which the relevant length of the characteristic non-metallic inclusion extends more or less far beyond the diameter of the field of view circle. In these cases, the classification of observed non-metallic inclusions is carried out according to the numerical data for the length given below the images. Unless otherwise agreed, inclusions of even greater length (with the same and greater thickness) are uniformly assigned the code 9.
6.2.2 If, within one observation field, inclusions of different types and shapes corresponding to the image series can be clearly distinguished from each other, they should be treated as if they occurred separately in different fields of observation.
6.2.3 Inclusions of types SS, OS and, in the case of a low degree of resolution, also OA, that lie one after the other in a line are to be regarded as contiguous if the distance between two inclusions is smaller than the length of the smaller of the two inclusions. The distances are also measured. Point-shaped inclusions are not taken into account for the formation of such a total length.
6.2.4 For inclusion type OA, the image series table 3 (left-hand series) provides rules for evaluating the degree of resolution for the formation of the area-related size code. If the average spacing of the particles of such an inclusion line is greater than the spacing of the point-shaped inclusions shown in the upper left image of image series table 1, the inclusions are categorized as inclusion type OG. This description is intended to show that, in principle, disconnected lines, which correspond to the situation for oxides, must receive lower size codes. These usually fall back into ranges that are no longer registered with the K4 value, for example, but can still be observed with the K1 value.
6.3 In general, the entire ground surface on the specimens that is to be evaluated is examined. Exceptions to this, which can only be considered for method K, must, if necessary, be specifically agreed upon and laid down in the relevant delivery terms.
7 Evaluation
7.1 Basic information
7.1.1 The non-metallic inclusions observed are identified in the following order, separated by a period, in terms of the type code for the image series concerned (inclusion type and form) and the size code of image series table 1 determined in accordance with Sections 6 and 7, e.g. 1.2, 5.3, 6.5
It is not permissible to use fractional numbers to indicate the size allocation (e.g. 2,5; 4½).
7.1.2 Forms are used for convenience to enter the test results and their evaluation.
7.2 Method K
7.2.1 In certain cases, it may be appropriate to record all non-metallic inclusions above a specified inclusion size and to indicate the degree of purity of a cast or batch by means of a cumulative characteristic value K that characterizes the area of the inclusions. For such an evaluation, the size of the ground surfaces of the specimens to be evaluated must be at least 100 . For the sampling points of the specimens and the size of the ground surface, the instructions in Sections 4.2. apply
Table 4: Evaluation guidelines for method K
7.2.2 For the evaluation, it must be decided at which size code the non-metallic inclusions will begin to be recorded. This (lowest) code depends mainly on the manufacturing process (casting in particular), as well as on the intended use of the material in question and its dimensions.
On the basis of experience and practice, it is possible to indicate the rules contained in Table
On the basis of experience and practice, it is possible to indicate the rules contained in Table