J Fail. Anal and Preven.(2010)10: 399-407 Conclusion and Suggestion (1) The unqualified selection of the belt matrix material as 301 stainless steel alloy whose corrosion resistance is inferior to 304 and 316 stainless steel coupled with the lack of a protective surface treat Oxide Laver was one of the main causes of the failure Physical Adsorption (2)On the failed steel belt, localized defects as micro cracks, hydrogen blisters, and erosion traces were the Chemical Absorption @② major failure morphologies. These surface/fracture features which resulted from hydrogen uptake during service and ultimately hydrogen embrittlement. The high pressure washing also caused an erosive effect hat contributed to the failure (3) The hydrogen that permeated into the stainless steel ig. 11 Main phenomena of hydrogen embrittlement according to belt was introduced primarily from the aggressive solutions applied in the activation, deoxidation, and CH is the hydrogen concentration in ppm, PH, is the electroplating steps of the tin plating process. hydrogen gas pressure in MPa, R is the gas constant, and T (4) Inappropriate technological parameters in activation is the absolute temperature in K. At room temperature, and deoxidation steps, and especially the high I ppm of dissolved hydrogen can lead to a pressure of pressure washing water in the washing step after 2x 10 MPa [24]. In this case, the concentration of electrolytic deburring, were the two aggravating hydrogen was 17 ppm, so hydrogen embrittlement was factors in the failure. The inappropriate parameters possible. Once the hydrogen pressure is high enough accelerated the rate of hydrogen evolution and break metallic bonds. micro cracks would be formed to consequently aggravated hydrogen embrittlement alleviate the pressure, seen in Fig 5b. After that, newly while the high pressure washing facilitated propaga- generated hydrogen could enter the freshly formed surfaces tion of micro cracks on the steel belts and resulted in and create another region of H2 gas pressure. Under this the ultimate fracture repetitive process, micro cracks propagate and then connect Two suggestions are given to mitigate the observed failure into larger ones, and finally cause macroscopic fracture of process he stainless steel belt. Furthermore. based on the fem results, the high-pressure water washing step will provide (1) Materials with superior corrosion resistance such as the stresses necessary to propagate the micro cracks and 316L stainless steel or duplex stainless steel are cause final fracture suggested as replacements for the 301 and even the To sum up, this failure procedure is briefly described. 304 stainless steel as the belts matrix materials Initially,micro cracks or micropores were engendered by (2) Technological parameters for the tin plating process hydrogen embrittlement, and were gradually connected must be optimized. The current density during into larger ones. Emergence of cracks caused the strength activation and deoxidation steps, and pressure of the to decrease. The cracks then propagated both along the washing water should be appropriately reduced axial direction of the belt primarily because of hydrogen accumulations and across the thickness of the belt under Ack gments The work was supported by both Advance Semiconductor Engineering(ASE) Group and Shanghai Leading the high-pressure washing water. The aggressive acid Academic Discipline Project(Project Number: Bl13) condition in plating technics may deepen these cracks according to reacting with the exposed steel on the fresh surface of cracks. Thus, a long dark smooth strip can be observed on the edge of the cross section of fracture. with References growth of effective thickness trength of the steel belt further reduced deformation L. Shanghai Jiao Tong University, Analysis of Metal Fracture Sur- face. National Defense Industry Press(1979)(in Chinese) ccurred or steel belts under high-pressure water 2.Han, G, He, J. Fukuyama, S, Yokogawa, K: Effect of stain- washing, and dimples were simultaneously generated in the martensite on hydrogen environment embrittlement of mid of the belt along thickness. Eventually, the steel belt ed austenitic stainless steels at low temperatures. Acta 46(13),4559-4570(198) fractured, and a small area of dimples was left in the 3. Ji. G. World Standard Steel Handbook. Standards Press of China middle part of the cross section of fracture (2004)(in Chinese)CH is the hydrogen concentration in ppm, pH2 is the hydrogen gas pressure in MPa, R is the gas constant, and T is the absolute temperature in K. At room temperature, 1 ppm of dissolved hydrogen can lead to a pressure of 2 9 105 MPa [24]. In this case, the concentration of hydrogen was 17 ppm, so hydrogen embrittlement was possible. Once the hydrogen pressure is high enough to break metallic bonds, micro cracks would be formed to alleviate the pressure, seen in Fig. 5b. After that, newly generated hydrogen could enter the freshly formed surfaces and create another region of H2 gas pressure. Under this repetitive process, micro cracks propagate and then connect into larger ones, and finally cause macroscopic fracture of the stainless steel belt. Furthermore, based on the FEM results, the high-pressure water washing step will provide the stresses necessary to propagate the micro cracks and cause final fracture. To sum up, this failure procedure is briefly described. Initially, micro cracks or micropores were engendered by hydrogen embrittlement, and were gradually connected into larger ones. Emergence of cracks caused the strength to decrease. The cracks then propagated both along the axial direction of the belt primarily because of hydrogen accumulations and across the thickness of the belt under the high-pressure washing water. The aggressive acid condition in plating technics may deepen these cracks according to reacting with the exposed steel on the fresh surface of cracks. Thus, a long dark smooth strip can be observed on the edge of the cross section of fracture. With growth of cracks, effective thickness and strength of the steel belt were further reduced. Plastic deformation occurred on the steel belts under high-pressure water washing, and dimples were simultaneously generated in the mid of the belt along thickness. Eventually, the steel belt fractured, and a small area of dimples was left in the middle part of the cross section of fracture. Conclusion and Suggestion (1) The unqualified selection of the belt matrix material as 301 stainless steel, an alloy whose corrosion resistance is inferior to 304 and 316 stainless steel, coupled with the lack of a protective surface treat￾ment, was one of the main causes of the failure. (2) On the failed steel belt, localized defects as micro cracks, hydrogen blisters, and erosion traces were the major failure morphologies. These surface/fracture features which resulted from hydrogen uptake during service and ultimately hydrogen embrittlement. The high pressure washing also caused an erosive effect that contributed to the failure. (3) The hydrogen that permeated into the stainless steel belt was introduced primarily from the aggressive solutions applied in the activation, deoxidation, and electroplating steps of the tin plating process. (4) Inappropriate technological parameters in activation and deoxidation steps, and especially the high￾pressure washing water in the washing step after electrolytic deburring, were the two aggravating factors in the failure. The inappropriate parameters accelerated the rate of hydrogen evolution and consequently aggravated hydrogen embrittlement while the high pressure washing facilitated propaga￾tion of micro cracks on the steel belts and resulted in the ultimate fracture. Two suggestions are given to mitigate the observed failure process: (1) Materials with superior corrosion resistance such as 316L stainless steel or duplex stainless steel are suggested as replacements for the 301 and even the 304 stainless steel as the belt’s matrix materials. (2) Technological parameters for the tin plating process must be optimized. The current density during activation and deoxidation steps, and pressure of the washing water should be appropriately reduced. Acknowledgments The work was supported by both Advanced Semiconductor Engineering (ASE) Group and Shanghai Leading Academic Discipline Project (Project Number: B113). References 1. Shanghai Jiao Tong University, Analysis of Metal Fracture Sur￾face. National Defense Industry Press (1979) (in Chinese) 2. Han, G., He, J., Fukuyama, S., Yokogawa, K.: Effect of stain￾induced martensite on hydrogen environment embrittlement of sensitized austenitic stainless steels at low temperatures. Acta Mater. 46(13), 4559–4570 (1998) 3. Ji, G.: World Standard Steel Handbook. Standards Press of China (2004) (in Chinese) Fig. 11 Main phenomena of hydrogen embrittlement according to Nelson [22] 406 J Fail. Anal. and Preven. (2010) 10:399–407 123