Rail fastenings made of spring steel 918 127

DB Standard January 2021 Technical specification DBS

Rail fastenings made of spring steel 918 127 Rail clips, tension clips, spring clips *

* Leaf springs, wire form springs Continued on pages 2 to 9

DB Netz AG, I.NAI 412, Theresa Zimmermann, [email protected], Tel.: +49 (0) 89 1308 7636

Supersedes June 2010 issue

Contents

Page FOREWORD ......................................................................................................................... 1 INTRODUCTION ................................................................................................................... 2 1 SCOPE OF APPLICATION ................................................................................................ 2 2 NORMATIVE REFERENCES ............................................................................................. 2 3 TECHNICAL REQUIREMENTS ......................................................................................... 4 3.1 General information ......................................................................................................... 4 3.2 Material ........................................................................................................................... 4 3.3 Surface quality ................................................................................................................. 4 3.4 Decarburization ............................................................................................................... 4 3.5 Vickers hardness ............................................................................................................. 4 3.6 Shape and dimensions .................................................................................................... 4 3.7 Spring characteristic, clamping force ............................................................................... 5 3.8. Fatigue resistance .......................................................................................................... 5 3.9. Corrosion protection ....................................................................................................... 5 3.9.1 Process-related hydrogen embrittlement ...................................................................... 5 3.9.2 Process-related hydrogen embrittlement ...................................................................... 5 3.9.3 UV radiation .................................................................................................................. 5 3.9.4 Salt spray test ............................................................................................................... 5 3.9.5 Salt spray test under changing climatic conditions ........................................................ 6 3.9.6 Clamping force and fatigue resistance .......................................................................... 6 4 QUALIFICATION AND QUALITY ASSURANCE ............................................................... 7 4.1 Qualification of the manufacturer ..................................................................................... 7 4.2 Qualification of the product .............................................................................................. 7

4.2.1.1 Qualification tests ................................................................................................... 7 4.2.1.2 Qualification tests in the context of MPQ renewal .................................................. 8 4.2.2 Field testing .............................................................................................................. 8

4.3 Quality assurance by the manufacturer ........................................................................... 8 5 TEST METHODS ............................................................................................................... 9 5.1 General information ......................................................................................................... 9 5.2 Determining the spring characteristic, theoretical clamping force ..................................... 9 5.2.1 Determining the spring characteristic ............................................................................ 9 5.2.2 Determining the theoretical clamping force ................................................................... 9 5.3 Vertical fatigue resistance...............................................................................................10 5.4 Horizontal fatigue resistance across the longitudinal direction of the rail .........................11 5.5 Horizontal fatigue resistance in the longitudinal direction of the rail ................................11

Foreword

Page 2 DBS 918 127 January 2021

This DB standard was produced by DB Netz AG, Gleistechnik with DB AG Quality Assurance, based on DBS 918 127, June 2010 issue. It represents the interests of Deutsche Bahn AG. The following changes have been made:

• Editorial and structural revision • More extensive test instructions for rail fastenings with corrosion protection • Cathodic dip coating no longer permitted • Assessment of surface quality • Products' vertical vibration displacement, minimum clamping force and distance

between tilting protection and rail base added to DB engineering drawings

Introduction

This DB standard complements the rules on qualification and quality assurance for rail fastening systems contained in DIN EN 13481 and 13146 regarding fastenings made of spring steel. This DBS has been introduced by the Federal Railway Authority as a technical construction regulation and is considered to be a recognized rule of technology within the meaning of Section 2 (1) of the EBO.

1 Scope of application

This DB standard applies to the supply of spring steel rail fastenings for the usage conditions encountered at Deutsche Bahn AG. It is to be applied in connection with the qualification of new spring steel fastenings for the DB AG network (qualification testing) and in the context of quality assurance. In the following text, spring steel fastenings (rail clamps, tension clips, rail clips) are referred to as "products". Where necessary, please refer to the corresponding engineering drawings for product-specific requirements that go beyond the scope of this standard.

2 Normative references

The DB Standard contains specifications from other publications in the form of dated and undated references. These normative references are quoted at the relevant places in the text, and the publications are listed thereafter. In the case of dated references, subsequent amendments or revisions to these publications only belong to this standard if they have been incorporated by means of amendment or revision. In the case of undated references, the last edition of the referenced publication applies (including any amendments). DIN EN 10132-1 Cold-rolled narrow steel strip for heat treatment -

Technical delivery conditions - Part 1: General

DIN EN 10132-4 Cold-rolled narrow steel strip for heat treatment - Technical delivery conditions - Part 4: Spring steels and other applications

DIN EN 10089 Hot rolled steels for quenched and tempered springs - Technical delivery conditions

DIN EN 10204 Metallic products - Types of inspection documents


DIN EN 10221 Surface quality classes for hot-rolled steel round bars and rods –

Technical delivery conditions DIN EN ISO 9712 Non-destructive testing - Qualification and certification of NDT

personnel DIN EN ISO 6507-1 Metallic materials - Vickers hardness test - Part 1: Test method DIN EN ISO 9227 Corrosion tests in artificial atmospheres - Salt spray tests DIN EN 13481 Railway applications - Track Performance requirements for rail fastening systems DIN EN 13146 Railway applications - Track Test methods for fastening systems DIN EN ISO 3887 Steels - Determination of depth of decarburization DIN EN ISO 7500-1 Metallic materials - Calibration and verification of static uniaxial testing

machines - Part 1: Tension/compression testing machines - Calibration and verification of the force-measuring system

DIN EN ISO 9513 Metallic materials - Calibration of extensometer systems used in

uniaxial testing Measuring equipment for testing with uniaxial loading

DBS 918 235 "Technische Lieferbedingungen – Elastische Zwischenlagen und

Zwischenplatten" (Technical specification – Elastic rail pads and intermediate plates)

DIN EN ISO 12944 Paints and varnishes - Corrosion protection of steel structures by

protective paint systems DIN EN ISO 4628 Paints and varnishes - Evaluation of degradation of coatings -

Designation of quantity and size of defects, and of intensity of uniform changes in appearance

DIN EN ISO 4892-2 Plastics - Methods of exposure to laboratory light sources - Part 2:

Xenon-arc lamps VDA 233-102 Cyclic corrosion testing of materials and components in automotive

construction DIN EN ISO 20567-1 Paints and varnishes - Determination of stone-chip resistance of

coatings - Part 1: Multi-impact testing DIN 50969-1 Prevention of hydrogen-induced brittle fracture of high-strength steel

building elements - Part 1: Advice on the prevention DIN 50969-2 Prevention of hydrogen-induced brittle fracture of high-strength steel

building elements - Part 2: Test methods


DIN EN ISO 6270-2 Paints and varnishes - Determination of resistance to humidity - Part 2: Condensation (in-cabinet exposure with heated water reservoir)

3 Technical requirements

3.1 General information

The DIN EN 13481 series of standards specifies the requirements for complete rail fastening systems. The areas of application of the products are defined in guideline 820.2010 "Ausrüstungsstandard Schotteroberbau für Gleise und Weichen" (Ballast track equipment standard for tracks and switches) and in guideline 820.2020 "Ausrüstungsstandard Feste Fahrbahn" (Slab track equipment standard). Sections 3.3 to 3.8 below apply only to uncoated products. 3.2 Material

Spring steel in accordance with DIN EN 10089 or DIN EN 10132-4 is to be used as the material as per the DB engineering drawing. An inspection certificate "3.1." in accordance with DIN EN 10204 shall serve as verification that the material used meets the properties specified in the contract. The purity of the material should be at least K3 ≤30 according to Appendix 2. DIN EN 10247 "Micrographic examination of the non-metallic inclusion content of steels using standard pictures" will not be applied. Macroscopic inclusions (e.g. exogenous slag) are not permissible. The quality of the material shall be verified on a cast-by-cast basis. 3.3 Surface quality

The maximum depth of isolated surface defects (e.g. scoring, scaling, scarring, overrolling, peeling or burrs) on the finished product must not exceed 0.2 mm. Bending marks are permissible as long as they do not impair the functioning of the product. The products must be inspected for cracks by qualified/regularly trained staff using an appropriate method – excluding visual inspection – (see DIN EN 10221). Cracks with a depth of ≤0.2 mm are permissible. For the chosen crack inspection method, the manufacturer must prepare a corresponding test instruction by a certified person belonging to the company (qualification at least level 2 according to DIN EN ISO 9712). 3.4 Decarburization

The permissible decarburization on the finished product is ≤0.2 mm, evidenced by microscopic examination in accordance with DIN EN ISO 3887. 3.5 Vickers hardness

The hardness test on the finished product must be carried out according to Vickers in line with DIN EN ISO 6507-1. In the event of any disputes, the test according to HV 30 shall apply, whereby the surface at the test surface must be ground down by approximately 1 mm. Please see the engineering drawings for the required values for each material type. Alternative test methods (e.g. Rockwell, Brinell) require the approval of the DB AG Quality Assurance department. 3.6 Shape and dimensions

The corresponding DB AG engineering drawings apply to the installation situation, shape and dimensions of the products.


3.7 Spring characteristic, clamping force

The spring characteristic of brand-new products as well as their permanent deformation and theoretical clamping force shall be determined and documented in accordance with Section 5.2. The product must adhere to the theoretical minimum clamping force according to the DB engineering drawing. 3.8. Fatigue resistance

Determining the fatigue resistance helps to assess a product's fitness for purpose throughout its useful life. The fatigue resistance of the products shall be determined as described in Sections 5.3, 5.4 and 5.5. The required vibration displacement for each product can be found in the relevant DB engineering drawing. The products must achieve the required number of cycles to failure without damage. The difference to the theoretical clamping force prior to the fatigue test must not exceed 20%. 3.9. Corrosion protection

Unless otherwise agreed, products should not be supplied with corrosion protection. Any corrosion protection to be applied shall be specified in the order documents. Permitted corrosion protection coatings can be found in the DB engineering drawings. Spring steel products may only be provided with corrosion protection if it is ensured that the requirements for rail fastenings under DBS 918 127 are not impaired when producing the coating and that this is verified as indicated below. The manufacturer must set limit values for coating thickness. The coating thickness of the samples must be documented. 3.9.1 Process-related hydrogen embrittlement

Verification of the prevention of process-related hydrogen embrittlement shall be provided based on DIN 50969-1 and -2. Alternatively, verification can also take the form of the manufacturer/supplier demonstrating that no hydrogen is produced by the chosen coating method or at any point in the coating process (including cleaning). 3.9.2 Process-related hydrogen embrittlement

Verification of the prevention of hydrogen embrittlement due to operating conditions must be maintained in accordance with Annex 1. 3.9.3 UV radiation

The corrosion protection effect must not be impaired by UV radiation. Durability must be verified once by the test in accordance with DIN EN ISO 4892-2 procedure A, table 3, cycle no. 1 (minimum duration 1000 h) and a subsequent salt spray test in accordance with DIN EN ISO 9227 (NSS) over a period of at least 720 h without base metal corrosion. Afterwards, no corrosion (red rust) should be visible on the base material (based on DIN EN ISO 4628, rust grade Ri 0). 3.9.4 Salt spray test

The effectiveness of the corrosion protection method must be demonstrated to DB Netz AG, Technik- und Anlagenmanagement Fahrbahn (Management of Track Technology and Infrastructure) through one-time verification in the form of a neutral salt spray test (NSS test) in line with DIN EN ISO 9227 over a period of at least 720 h (based on corrosion protection category C5 medium in accordance with DIN EN ISO 12944-6). Afterwards, no corrosion (red rust) should be visible on the base material (based on DIN EN ISO 4628, rust grade Ri 0). In


order to take damage to the coating into account (e.g. due to track ballasting), the coated products must be blasted with a chilled-iron abrasive in accordance with DIN EN ISO 20567-1 before the salt spray test. 3.9.5 Salt spray test under changing climatic conditions

A salt spray test under changing climatic conditions in accordance with VDA 233-102 must be conducted over at least four test cycles. In order to take damage to the coating into account (e.g. due to track ballasting), the coated products must be blasted with a chilled-iron abrasive in accordance with DIN EN ISO 20567-1 before the salt spray test. 3.9.6 Clamping force and fatigue resistance

On at least two products with corrosion protection, the clamping force shall be verified according to Section 5.2 and the vertical fatigue strength according to Section 5.3. Table 1: Scope of one-time tests to verify corrosion protection

No. Test Number of test pieces

1 Verification of coating thickness for coated products 10 products 2 Salt spray test in accordance with DIN EN ISO 9227 (NSS)

over at least 720 h on products that have been blasted with a chilled-iron abrasive in accordance with DIN EN ISO 20567-1

10 products

3 Resistance to UV radiation in accordance with DIN EN ISO 4892-2 procedure A, table 3, cycle no. 1 (minimum duration 1000 h) and a subsequent salt spray test in accordance with DIN EN ISO 9227 (NSS) over a period of at least 720 h

10 products

4 Salt spray test under changing climatic conditions in accordance with VDA 233-102 on products that have been blasted with a chilled-iron abrasive in accordance with DIN EN ISO 20567-1

10 products

5 Verification of the prevention of process-related hydrogen embrittlement based on DIN 50969-1 and -2. 10 products

6 Verification of the prevention of hydrogen embrittlement due to operating conditions in accordance with Annex 1 and subsequent determination of clamping force in accordance with Section 5.2

10 products

7 Clamping force in accordance with Section 5.2 and vertical fatigue resistance in accordance with Section 5.3 2 products

3.10 Marking An identification mark should be imprinted on the products. This should consist of: - Product code (e.g. 12, 14, 21) - Manufacturer's identification mark - Last two digits of the year of manufacture - Batch identification (optional) Example of marking: 14 H 18 XY (Skl 14 – Manufacturer – Year manufactured 2018 – Batch identification)


4 Qualification and quality assurance

4.1 Qualification of the manufacturer

Prior to the first delivery to DB AG, the manufacturer's ability to manufacture a product as specified in the contract shall be verified. This applies to every product and shall take the form of a "manufacturer-related product qualification" (MPQ). One component of the MPQ is the qualification testing according to Section 4.2.1 in the context of the initial delivery and, in case of a renewal of the MPQ, the results of the continuous quality assurance according to Table 3. The MPQ is conducted by the DB AG Quality Assurance department. The manufacturer/supplier shall bear the cost of the MPQ (see list of permanent-way products subject to quality inspection).

4.2 Qualification of the product

4.2.1.1 Qualification tests

Prior to the first delivery to DB AG, every product must undergo a qualification test. The qualification test may only be carried out by test centers recognized by DB AG. The vendor shall bear the cost of the qualification test. All requirements described in Section 4 must be verified in this qualification test. See Table 2 for the required number of test pieces. The test results for each single tested product must meet the requirements.

Table 2: Scope of testing

No. Test Number of test pieces

1 Surface quality (see Section 3.3) 40 products

2 Shape and dimensions (see Section 3.6) 30 products from the test pieces in no. 1

3 Chemical analysis and purity of the material (see Section 3.2)

3 products from the test pieces in no. 1

4 Decarburization (finished product) (see Section 3.4) 2 products from the test pieces in no. 1

5 Spring characteristic, clamping force (mean value) (see Section 5.2)


6 Vertical fatigue resistance (see Section 5.3) 10 products from the test pieces in no. 5

7a Horizontal fatigue resistance (lateral) (see Section 5.4) 4 products from the test pieces in no. 2

7b Horizontal fatigue resistance (longitudinal) (see Section 5.5)


8 Vickers hardness (see Section 3.5) 10 products from the test pieces in no. 1 or 5

DB AG may set additional requirements and tests. DB AG also reserves the right to waive tests if, for example, the product properties do not require certain tests or if properties are already well known.


4.2.1.2 Qualification tests in the context of MPQ renewal

According to GL 120.0381V15, an MPQ must be performed at least every six years. After 3 years, a one-time extension is possible if deliveries have been made under a contract and the conditions on the basis of which the MPQ was granted have not changed. The scope of testing can be found in Table 2. DB AG Quality Assurance reserves the waive tests or to coordinate the performance of tests with manufacturers. The performance of tests in the factory's own laboratories requires the approval of DB AG Quality Assurance. The chosen scope of testing shall be documented (justified) in the MPQ report. 4.2.2 Field testing

Before the first series delivery to DB AG, an approval from the Federal Railway Authority (EBA) must be submitted for each new product and field testing on a line specified by DB AG must be carried out

- for a period of at least one year, and - a track load of ≥ 20 million load tonnes (tonnes = metric tons)

For this purpose, an application for approval for field testing must be submitted to the EBA. The competent unit at DB AG may, in consultation with the EBA, waive field testing for minor product changes (e.g. coating, surface painting, etc.) that do not adversely affect the product's aging stability The exact period of field testing will be determined by DB Netz AG's Permanent Way Engineering department and the EBA. 4.3 Quality assurance by the manufacturer

The manufacturer shall ensure the quality of the products by means of an appropriate statistical process control. The tests and scope of testing shown in Table 3 are minimum requirements. Notwithstanding the above, every product shall comply with the technical requirements according to Section 4. The unit responsible for technical aspects at DB AG may set additional tests.

Table 3: Minimum requirements for tests and scope of testing relating to quality assurance

Test Minimum scope of testing Decarburization (see Section 3.4) 1 product per batch

Surface quality (see Section 3.3)

1 product per 1,500 units

Shape and dimensions (functional dimensions) (see Section 3.6)


Vickers hardness (see Section 3.5)


Theoretical clamping force (see Section 5.2.2) 1 product per 1,500 units

Vertical fatigue resistance (see Section 5.3)

2 products per batch

Coating thickness for coated products 6 products per 5,000 units


The minimum requirements for tests and scope of testing may be changed in coordination with the DB AG Quality Assurance department. Compliance with the requirements set out in this DB standard shall be assured by means of test schedules and test plans and presented to DB AG on request.

5 Test methods

5.1 General information

For the tests described below, the measurement accuracy of the displacement transducers must correspond to at least Class 1.0 on the basis of the calibration process according to DIN EN ISO 9513, and the measurement accuracy of the force measuring equipment to at least Class 1.0 on the basis of the calibration process according to DIN EN ISO 7500-1. 5.2 Determining the spring characteristic, theoretical clamping force

5.2.1 Determining the spring characteristic

Ten load cycles consisting of a load from the lower load cycle Fu = 0.5 kN (initial load) to the upper load cycle Fo = 25 kN and subsequent load relaxation shall be performed for each individual product. The test equipment must be designed and set up in such a way as to reproduce the actual loads that will be experienced when the product is installed on the track. In justified exceptional cases and in consultation with DB AG, the spring characteristic may be determined with a lower load cycle Fu = 0.5 kN (initial load) up to an upper load cycle individually determined for each product in relation to the respective design. During qualification testing, the first and tenth load cycles shall be documented as well as the load cycle following the vertical fatigue resistance test according to Section 5.3. The number of load cycles in the manufacturer's quality assurance may be reduced (e.g. from ten to five) in consultation with DB AG's Quality Assurance department 5.2.2 Determining the theoretical clamping force

The theoretical clamping force is determined with the aid of the force-deflection graph recorded during the last load cycle under Section 5.2.1 (example see Fig. 1) and is based on the standard installation situation (e.g. design distance between tilting protection and rail base). The nominal dimensions of the rail fastening components in the regular installation situation are to be taken as a basis. The compression of any elastic components is to be taken into consideration when determining the distance between the product's tilting protection and the rail base in accordance with the DB engineering drawing.


Fig. 1: Example of determining theoretical clamping force from spring characteristic For the purposes of quality assurance in accordance with Table 2, the theoretical clamping force on individual manufactured products should be determined and documented during production. 5.3 Vertical fatigue resistance

Test pieces tested according to Section 5.2.2 shall be used to determine the vertical fatigue resistance. These are to be fastened in accordance with the respective engineering drawings in such a way as to reflect how they will be installed on the track. The areas of the fastening resting on the rail base are to be raised by the design-specific nominal amount for the rail fastening system concerned. The required vibration displacement for each product can be taken from the respective DB engineering drawing and is based on the stiffness class according to DBS 918 235, which has a direct impact on the fastening. Orientation values for vertical vibration displacement: f = 1.4 mm for Cstat. >200 kN/mm f = 1.7 mm for Cstat. ≤200 and >60 kN/mm f = 2.0 mm for Cstat. ≤60 and >40 kN/mm f = 2.5 mm for Cstat. ≤40 and >22.5 kN/mm f = 3.0 mm for Cstat. ≤22.5 kN/mm Taking the respective installation situation as a basis, 10% of the required vibration displacement is to be implemented as fastening loading (taking lifting forces on the track into account) and 90% of the required vibration displacement as load relaxation on the fastening. When testing rail clips, the required vibration displacement results from a load relaxation on the fastening of 1.0 mm and loading on the fastening up to a stopping point specified in the design (e.g. mechanical limitation by means of an overload protection).


The required number of cycles to failure is: n = 5∙106 for the qualification test (frequency: max. 18 Hz) n = 3∙106 for quality assurance Following the fatigue resistance test, the theoretical clamping force of the tested product is to be determined again in accordance with Section 5.2.2. The clamping force is then determined after the first load cycle after the fatigue test during which the force/deflection graph is to be recorded. 5.4 Horizontal fatigue resistance across the longitudinal direction of the rail

The horizontal fatigue resistance is to be determined on unloaded products in the direction of movement across 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. The test shall be conducted at a frequency of 7–9 Hz. The required number of cycles to failure is n = 3∙106. 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. 5.5 Horizontal fatigue resistance in the longitudinal direction of the rail

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.


This is represented by the respective image series (0, 2, 5) to the left of the basic series. 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.


NOTE The image series plate 1 attached to this appendix contains the image series at a 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 5, which should be used as far as possible as the basis for agreements on the evaluation method. 7.2.3 Unless otherwise agreed, the entire ground surface to be evaluated must be examined in each case. The sulfidic and oxidic inclusions are counted separately and written down as shown in the examples in Tables 6 and 7. If only individual, predefined measuring fields or measuring field areas are tested on the ground surface to be evaluated (which will only be useful in exceptional cases), the size and distribution of these measuring fields or measuring field areas must correspond to the conditions of a static test. 7.2.4 Calculation scheme for evaluation with method K The calculation scheme described in this appendix that is used to derive the cumulative characteristic values is based on prerequisites and considerations that assume that, for ease of calculation, the most frequently counted size code 4 receives the factor of 1. The factors


resulting from the geometric series for the other size codes are rounded in such a way that only doubling or halving is required in the calculation (with any necessary shifting of the decimal point). The resulting deviation in the calculation is within the scatter range, which results from the fact that non-metallic inclusions are not uniformly distributed in the steel. The larger inclusions are given a higher degree of criticality. Table 5 shows the factors to be applied in the calculations. For the calculation of the cumulative characteristic values, the following procedure is applied (see also the examples in Tables 6 and 7): the number of non-metallic inclusions observed of each inclusion type (SS, OA, OS, OG) and size code is multiplied by the respective factor

( , see Table 5) and the products are added up, generally separately for the sulfides and the oxides as a whole. The "initial subtotals" of a single ground surface obtained in this way are then added up for all specimens of the test unit, so that a "second subtotal" (in mm²) is obtained for all specimens. This result is converted to a ground surface of 1000 mm² according to the following equation:

The "cumulative characteristic value" calculated separately for sulfides (S) and oxides (O) can, by agreement, be combined into a "total cumulative characteristic value" by addition. The two cumulative characteristic values or the total cumulative characteristic value indicate the degree of purity of the test unit examined. The numerical values obtained in both cases should be whole numbers if possible and must be rounded for this purpose if necessary. The determined characteristic value for the degree of purity must be identified in each case by the letter K and, linked to it, the size code for the smallest inclusions recorded and, if necessary, by the code letters of the inclusion types. This will help avoid confusion and the comparison of results with different contents. The notation is (according to Table 6): K4 = 66 (S:26, O:40) Tables 6 and 7 each show an evaluation example including full details of the evaluation conditions.

Table 5: Factors for evaluation with method K 8 Test report The test report must specify the following, with a reference to this appendix: a) Steel grade and cast identification b) Form and dimensions of the product from which the specimens were taken


c) Method used in accordance with Section 2.4 and, where appropriate, its specific features d) Result of the evaluation, as agreed - For method K The specification of the smallest size code taken into account, either including the intermediate results or, preferably, only the final results (cumulative characteristic values for S and O or total cumulative characteristic value) in the notation as per Section 7.2.4

*) S = sulfides, O = oxides **) Converted to a ground surface of 1000 mm² and rounded to whole numbers. Table 6: Example of an evaluation using method K4 according to Section 7.2 (see Table 4) (case of a 100-mm square stainless-steel billet melted while exposed to air)


Table 7: Example of an evaluation using method K1 as per Section 7.2

*) S = sulfides, O=oxides **) Converted to a ground surface of 1000 mm² ***) Rounded from 1.69 to 1.7


Image series table 1: Diagrams for the examination of non-metallic inclusions of spring steels NOTE The diagrams in image series table 1 are about one-third the original size. The table can therefore only provide a general impression of the image series table in its original size.


Image series table 2: Classification of Image series table 3: Classification of lines of inclusions by their width disconnected inclusions of the OA type Magnification 200:1 (left-hand series) and of multiple inclusions

occurring in one observation field of the types SS, OS and OA under one size code

Magnification 200:1

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Rail fastenings made of spring steel 918 127