J Fail. Anal and Preven.(2010)10: 399-407 of the belt was set zero as the boundary conditions. steel. This alloy which has higher carbon content(up to According to the calculated results summarized in 0.15%o) and much lower resistance to hydrogen embrittle Fig. 10a, the stress concentrates on the corner of the ment than either 304 or 316L stainless steel. Tama [11] bracket and its maximum value is about 8 x 10 MPa, found that the solubility of carbon was very low in steels at Fig. 10b. This maximum stress value far exceeds the room temperature, and was only 0.006% in austenite. This anticipated yield strength of the stainless steel component means the carbon existing in these steels has the potential and must have contributed to the fracture to form carbides such as M23C6, M7C3, etc. The higher the carbon content steels the more likely carbides are to be Failure Analysis present. Carbides and other inclusions, i.e,manganese sulfide, which are precipitated in the grain boundaries, It has been concluded that two factors were the primary become failure initiation sites, 1. e, the nucleation centers of contributors to the failure process: (1)the use of unquali- microvoid nucleation and the development of hydrogen fied materials in the belt and(2) hydrogen embrittlement induced cracks. Although most of cracks are initiated at the driven by the aggressive process media. Consequently, Mns inclusions, some researches showed that it is not further discussion will be conducted on these two aspects. necessary for HISC to nucleate at such inclusions the observed stepwise crack nucleation sites are typically gra laterals selection and carbide-matrix interphase boundaries [7. The intro- duction of above boundaries in 301 is more than it is in 304 It was determined that the matrix material of the stainless or 316 stainless steels. The selection and use of 301 steel belt that failed after one-month use was 301 stainless stainless steel increased the likelihood of HISCs and therefore the probability of failure. Thus, the conclusion can be put forward that inadequate selection of material was one of the main causes of the failure of stainless steel belt. What's more, according to the above analysis, no surface treatment was given to the belt material and the lack of this treatment increased the possibility of failure Hydrogen Embrittlement Hydrogen generation In order to mitigate the hydrogen embrittlement process, of the hydrogen in this st be confirmed bracket Actually, nearly all the six steps in the tin plating process may bring hydrogen to the stainless steel surfaces. How ever, most of the hydrogen is generated in deoxidation, Fig.9 Meshed FEM model of the stainless steel belt activation, and electroplating steps )) enlarged view of cornerof the belt was set zero as the boundary conditions. According to the calculated results summarized in Fig. 10a, the stress concentrates on the corner of the bracket and its maximum value is about 8 9 104 MPa, Fig. 10b. This maximum stress value far exceeds the anticipated yield strength of the stainless steel component and must have contributed to the fracture. Failure Analysis It has been concluded that two factors were the primary contributors to the failure process: (1) the use of unquali- fied materials in the belt and (2) hydrogen embrittlement driven by the aggressive process media. Consequently, further discussion will be conducted on these two aspects. Materials Selection It was determined that the matrix material of the stainless steel belt that failed after one-month use was 301 stainless steel. This alloy which has higher carbon content (up to 0.15%) and much lower resistance to hydrogen embrittle￾ment than either 304 or 316L stainless steel. Tama [11] found that the solubility of carbon was very low in steels at room temperature, and was only 0.006% in austenite. This means the carbon existing in these steels has the potential to form carbides such as M23C6, M7C3, etc. The higher the carbon content steels the more likely carbides are to be present. Carbides and other inclusions, i.e., manganese sulfide, which are precipitated in the grain boundaries, become failure initiation sites, i.e., the nucleation centers of microvoid nucleation and the development of hydrogen￾induced cracks. Although most of cracks are initiated at the MnS inclusions, some researches showed that it is not necessary for HISC to nucleate at such inclusions the observed stepwise crack nucleation sites are typically grain and carbide-matrix interphase boundaries [7]. The intro￾duction of above boundaries in 301 is more than it is in 304 or 316 stainless steels. The selection and use of 301 stainless steel increased the likelihood of HISCs and therefore the probability of failure. Thus, the conclusion can be put forward that inadequate selection of material was one of the main causes of the failure of stainless steel belt. What’s more, according to the above analysis, no surface treatment was given to the belt material and the lack of this treatment increased the possibility of failure [12–15]. Hydrogen Embrittlement Hydrogen Generation In order to mitigate the hydrogen embrittlement process, sources of the hydrogen in this case must be confirmed. Actually, nearly all the six steps in the tin plating process may bring hydrogen to the stainless steel surfaces. How￾ever, most of the hydrogen is generated in deoxidation, Fig. 9 Meshed FEM model of the stainless steel belt activation, and electroplating steps. Fig. 10 Stress distribution on the stainless steel after water washing: (a) FEM calculated result and (b) enlarged view of the bracket’s corner 404 J Fail. Anal. and Preven. (2010) 10:399–407 123