Cadmium Substitution - garteur

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GARTEUR LIMITED Figure E2; S-N curves for specimens coated with ED zinc-nickel and ED zinc-cobalt-iron N= tested by NLR, S=tested by SAAB Page 84 GARTEUR SM/AG17 TP128
GARTEUR LIMITED ANNEX F Stress corrosion cracking studies F.1 Introduction High strength steels are susceptible to hydrogen embrittlement and stress corrosion cracking. Conventional aqueous electrodeposition processes are less than 100% efficient and during electroplating some hydrogen may diffuse into the steel component. This may lead to failure of the component under tensile loads as a result of hydrogen embrittlement. In order to minimise the risk of failure, components are baked after plating, typically at temperatures of between 190 and 230 o C. The duration of the deembrittlement treatmen is dependent on the ultimate tensile strength of the steel. For steels with maximum tensile strengths in the range 1101 MPa to 1450 MPa the European Standard EN 2133 advises a minimum baking time of 8 hours after cadmium plating [F1]. Steels in the strength range 1451 to 1800 MPa require longer baking treatments usually at least 18 hours whilst for ultra high strength steels, i.e. above 1801 MPa, times in excess of 24 hours must be employed [F2]. Under certain conditions, parts manufactured from high strength steels may fail by stress corrosion cracking. For failure to occur the component must be under tensile stress and be exposed to a corrosive environment. The mechanism of stress corrosion cracking in high strength steels is normally hydrogen embrittlement. Hydrogen may be introduced into steels as a result of corrosion processes occurring on the surface of the component. A damaged coating, for example, may lead to the establishment of a galvanic corrosion cell between the coating and steel substrate. Hydrogen generated as a result of the cathodic reaction may diffuse into the steel, ultimately leading to hydrogen embrittlement failure. In the current programme both aspects of hydrogen embrittlement have been investigated. F.2 Test procedures F.2.1 Hydrogen embrittlement Sustained load testing and slow bend tests were carried on a limited number of coated and heat treated samples to establish whether the recommended de-embrittlement treatments were effective [F3]. Notched tensile specimens were manufactured from AISI 4340 steel heat treated to 1790 - 1930 MPa. The specimens were then electroplated with zinc-nickel and subsequently de-embrittled by heat treating at 190 o C for 3 hours. Two series of 3 test pieces were placed under sustained load for 200 hours at 75% of the notched tensile strength. The tests were conducted at room temperature. A limited number of slow bend tests were conducted by Aerospatiale on a 35NCD16 steel heat treated to 1800MPa. The tests were conducted in accordance with prEN 2831. The initial failure angle, α 0 , and the failure angle after surface treatment, α 1 , were measured. Details are given in reference [F4]. F.2.2 Stress corrosion cracking The risk of stress corrosion cracking occurring as a result of corrosion has been studied using notched tensile specimens. These were loaded to 75% of the notched tensile strength after coating, and are then subjected to alternate immersion in 3.5% sodium chloride solution until failure occurs. The performance of each of the coatings has been GARTEUR SM/AG17 TP128 Page 85
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GARTEUR LIMITED Executive summary B
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GARTEUR LIMITED nickel coatings cou
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GARTEUR LIMITED 11 Tables Coating t
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GARTEUR LIMITED Coating Thickness
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GARTEUR LIMITED As - plated Passiva
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GARTEUR LIMITED As plated Passivate
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GARTEUR LIMITED Coating Potential r
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GARTEUR LIMITED Coating Potential c
Page 48 and 49: GARTEUR LIMITED Properties ED Zn-Co
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Page 64 and 65: GARTEUR LIMITED B.3.3 Coating Adhes
Page 66 and 67: GARTEUR LIMITED Type A Measurements
Page 68 and 69: GARTEUR LIMITED B.7 Figures Hi - Lo
Page 70 and 71: GARTEUR LIMITED ED Cadmium IVD Alum
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Page 82 and 83: GARTEUR LIMITED DBAA DERA NLR NLR B
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Page 116 and 117: GARTEUR LIMITED I.8 Figures Cadmium
Page 118 and 119: GARTEUR LIMITED Cadmium coated bolt
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Page 126 and 127: GARTEUR LIMITED D-28183 Bremen, GER
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