1、June 2009 English price group 6No part of this translation may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).ICS 77.140.01!%M(n“2420575www.din.deDIN
2、50969-1Prevention of hydrogeninduced brittle fracture of highstrength steel building elements Part 1: Advice on the prevention,English translation of DIN 50969-1:2009-06Vermeidung fertigungsbedingter wasserstoffinduzierter Sprdbrche bei hochfesten Bauteilen aus Stahl Teil 1: Vorbeugende Manahmen,Eng
3、lische bersetzung von DIN 50969-1:2009-06Prvention dacier de construction rsistance lve afin dviter les ruptures fragiles hydrognes induits Partie 1: Mesures prventives,Traduction anglaise de DIN 50969-1:2009-06SupersedesDIN 50969:199012www.beuth.deDocument comprises 8 pagesDTranslation by DIN-Sprac
4、hendienst.In case of doubt, the German-language original shall be considered authoritative.03.16 DIN 50969-1:2009-06 2 A comma is used as the decimal marker. Contents Page Foreword . 3 Introduction 4 1 Scope 5 2 General 5 3 Measures to be taken at the design and manufacturing stages 5 3.1 Design mea
5、sures 5 3.2 Material-related measures . 5 3.3 Manufacture-related measures 6 3.4 Minimizing residual tensile stresses 6 4 Coating process 6 4.1 General 6 4.2 Pretreatment for activation of the surface for subsequent coatings 7 4.3 Coating . 7 4.4 Heat treatment after coating . 7 Bibliography . 8 DIN
6、 50969-1:2009-06 3 Foreword This standard has been prepared by the Expert Group Wasserstoffinduzierter Sprdbruch of Working Committee NA 062-01-76 AA Galvanische berzge of Normenausschuss Materialprfung (Materials Testing Standards Committee). Amendments This standard differs from DIN 50969:1990-12
7、as follows: a) an Introduction has been included; b) Clauses “Normative references” and “Terms and definitions” have been dropped and a Bibliography has been included; c) the former Clause 3 dealing with the loading test has been included in DIN 50969-2. Previous editions DIN 50969: 1990-12 DIN 5096
8、9-1:2009-06 4 Introduction For the purposes of this standard, hydrogen-induced cracking or brittle fracture resulting from the manufacturing process is damage to the material caused by the diffusion of atomic hydrogen into the material. Such damage can be initiated by a critical combination of diffe
9、rent influencing factors: a) material-related factors: structure/structural imperfections (lattice defects, impurities, grain boundaries); strength/strain hardening; ductility/toughness; degree of purity (inclusions, segregation, impurities); the presence of elements such as phosphor and sulfur; mec
10、hanical stress; b) manufacture-related factors: geometric boundary conditions (notches, burrs, abrupt transitions between forms); degree of forming/cold forming/hardening; heat treatment (case) hardening, tempering, annealing); residual tensile stresses; c) factors related to the coating process; pr
11、etreatment (pickling, cathodic degreasing, etc.); electrolytic deposition of metal coatings. Principles Steel building elements can absorb hydrogen as a result of the tendency atomic hydrogen to diffuse through the metal lattice to energetically favourable positions. If tensile stresses are also pre
12、sent, this can lead to critical material conditions, resulting in pre-cracking. Pre-cracking implies fractures occurring at stresses below the yield stress of the base material. When the material is subjected to mechanical stresses, brittle fracture generally occurs in a delayed manner (i.e. some ti
13、me after the start of loading), since hydrogen atoms gradually diffuse to the location of maximum tensile stress, where they accumulate and thereby reduce the cohesiveness of iron atoms. Therefore, the crack tip with its high concentration of tensile stresses is an energetically favourable position.
14、 As a result, the hydrogen moves to the crack tip, exerts its deleterious effects on the steel and thus facilitates the growth of cracks. Hydrogen-induced cracking or even fracture can occur in all high-strength steel parts. There is no tensile strength limit beyond which steel within the meaning of
15、 this standard is to be considered a high-strength steel, since this phenomenon is a system property the key of which is the critical interaction of the influencing factors material condition, mechanical stresses and hydrogen content. For all steel parts having a tensile strength 1 000 N/mm (even if
16、 localized as in case hardened or cold formed structures or in the vicinity of welds), the problem of hydrogen-induced embrittlement shall be particularly taken into account. DIN 50969-1:2009-06 5 1 Scope This standard specifies methods of preventing hydrogen-induced brittle fracture resulting from
17、the manufacturing process. It also advises on the relationship between material choice, manufacture and coating. This standard does not apply to building elements made of high-strength steel strip material produced in a strip coating process. 2 General Already at the early stages of production, when
18、 designing components and choosing the material, care shall be taken to minimize the risk of delayed hydrogen-induced brittle fractures. The person applying the coating shall be provided by the purchaser with detailed information on the tensile strength of the component and on areas with a particula
19、rly high risk of brittle fractures. Manufacturing, joining and surface treatment processes shall be carried out in such a way that any damage resulting from delayed hydrogen-induced brittle fracture is precluded with the necessary certainty. The necessary measures and tests in compliance with the st
20、ate of the art such as, for example, the minimization of component stress, the choice, composition and control of the chemicals used, physical and chemical process limits, type of tests, testing frequency, number of specimens, etc., shall be defined in the process and test schedules. The tests carri
21、ed out shall be documented. 3 Measures to be taken at the design and manufacturing stages 3.1 Design measures The building elements shall be designed to prevent critical local peak stresses (sharp-edged notches, punched edges, burrs, holes in radii, bend radii, etc.). Thin-walled building elements w
22、ith sheet thicknesses or diameters 1 mm are particularly susceptible to brittle fracture. Wherever possible, the material strength specified shall be the minimum acceptable value for the given application. 3.2 Material-related measures The decisive material parameters are tensile strength and toughn
23、ess. The susceptibility of a steel to hydrogen-induced embrittlement increases in direct proportion to the material strength and in inverse proportion to its toughness. In order to achieve the required material condition, the material exhibiting the greater toughness shall be selected. The measures
24、taken to prevent hydrogen-induced fractures shall be verified by the building element manufacturer on the basis of intensive tests, and compliance with these measures shall be specially checked and documented during the sampling and manufacturing processes. Mechanically and thermo-chemically surface
25、-hardened building elements as well as building elements where hardening occurs in the heat-affected zones of welds are particularly susceptible to brittle fractures. The extent of the susceptibility is a function of the material cross section and the core hardness, as well as of the thickness and h
26、ardness of the high-strength surface. The person applying the coating shall be provided by the purchaser with detailed information on the tensile strength of the component and on areas with a particularly high risk of brittle fractures. DIN 50969-1:2009-06 6 3.3 Manufacture-related measures In cases
27、 where the tensile strength Rm 1 000 N/mm2, special measures shall be taken to prevent hydrogen-induced embrittlement. Owing to the risk of -ferrite formation on the surface, building elements shall be subjected to dephosphating prior to heat treatment. 3.4 Minimizing residual tensile stresses For b
28、uilding elements in which critical residual tensile stresses are induced, e.g. by thermal action (heat treatment, welding, thermal cutting), cold working or machining (including grinding), the following shall be observed on completion of such processes: the building elements shall be heat-treated at
29、 as high a temperature as possible without exceeding the temperature of any earlier heat treatment; the heat treatment procedure and the parameters applied (temperature, time) shall be defined and specified. All traces of grease, oil and lubricant shall be removed from the elements to prevent their
30、being “baked in” and thereby extending the pickling time. For the element manufacturing process it shall be checked, verified and documented that the design and material-related measures taken actually minimize the risk of hydrogen-induced embrittlement. 4 Coating process 4.1 General Pickling and an
31、y electrolytic, cathodic treatment (e.g. degreasing or deposition of metal coatings) generally involve the risk of hydrogen absorption. The extent of this risk depends on the amount of hydrogen absorbed by the material (see also “Principles”). The person applying the coating is required to evaluate
32、each step of the treatment processes at which hydrogen can penetrate into the material structure. The process development and evaluation shall be verified by tests and documented. The measures and tests necessary to determine the treatment steps such as, for example, the choice, composition and cont
33、rol of the chemicals used, physical and chemical process limits, type of tests, testing frequency, number of specimens, etc., complying with the state of the art, shall be defined in the process and test schedules. For building elements potentially subject to hydrogen damage, the safe and uncritical
34、 proceeding during the production phase shall, in addition to the measures described above, be verified by additional loading tests. DIN 50969-1:2009-06 7 4.2 Pretreatment for activation of the surface for subsequent coatings The chemical and/or electrochemical pretreatment (e.g. pickling) to be per
35、formed immediately before coating shall be carried out in such a way that the amount of hydrogen absorbed by the building elements is kept to a minimum. The following parameters shall be adhered to: no cathodic degreasing; pickling together with suitable inhibitors; pickling for as short a time as p
36、ossible. The time required for pickling heat-treated building elements can only be kept short if, for example, heat treatment was carried out in a protective gas or in a vacuum, with all organic residues having been previously removed; if necessary, heat treatment may be preceded by a mechanical cle
37、aning process such as abrasive blasting or vibratory grinding. The maximum pickling time shall be laid down and care shall be taken to ensure that this time is not exceeded. The person applying the coating is required to determine the effective inhibitor in the pickling process and to ensure that no
38、 other inhibitors are used. This includes tests to determine the lifetime/effectiveness of the pickling inhibitor as a function of the degree of exhaustion and impurity of the pickle, and to check whether it is necessary to replenish the pickling inhibitor during the pickling process. These tests sh
39、all be agreed with the manufacturer of the pickling inhibitor. Proof of suitability of the inhibitor as an additive for pickling high-strength steels shall be provided by the manufacturer of the inhibitor and certified by the person applying the coating. NOTE A method of testing the effectiveness of
40、 inhibitors is described in Part 2 of this standard. 4.3 Coating Coating shall be controlled so that the hydrogen absorbed by the base material is kept to a minimum. 4.4 Heat treatment after coating In cases where hydrogen absorption during the coating process (e.g. resulting from aprotic electrolyt
41、es and an aprotic pretreatment) cannot be precluded, the hydrogen absorbed shall be reduced to an uncritical amount by subsequent heat treatment or ageing. The conditions for ageing shall be specified on the basis of the coating process used (see the relevant technology standards). When selecting th
42、e ageing temperature, it is to be taken into account that the properties of the base material and those of the coating material shall not be adversely modified. In this connection, the person applying the coating shall be informed of the material properties of the building element by the manufacture
43、r. NOTE A method of testing the effectiveness of the heat treatment after coating is described in Part 2 of this standard. DIN 50969-1:2009-06 8 Bibliography DIN EN 10020, Definition and classification of grades of steel DIN EN ISO 4042, Fasteners Electroplated coatings DIN EN ISO 15330, Fasteners Preloading test for the detection of hydrogen embrittlement Parallel bearing surface method
