Estimate of Hydrogen Density at Starting Point for Crevice Corrosion and Cracking of Cold Rolled Type 304 Stainless Stee
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1226-II03-02
Estimate of Hydrogen Density at Starting Point for Crevice Corrosion and Cracking of Cold Rolled Type 304 Stainless Steel
S.Kajikawa, Y.Isobe, A.Kuromiya 1 and M.Okido2 1
Material Engineering. R and D Department, DENSO CORPORATION, Kariya, Japan Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya University, Nagoya, Japan 2
ABSTRACT In the past work about cold worked SUS304, cracking from a corrosion pit was observed and it was presumed to be HE-SCC. In this work, to estimate the hydrogen density at starting point of HE-SCC, the amount of hydrogen diffused from the corrosion pit was measured by Thermal Desorption Spectroscopy. Then, assuming that pitting corrosion takes the form of half sphere shape and grows with time, the simulation model was made that hydrogen absorbed and diffused from the pit surface with the development of corrosion. The profile of the hydrogen density in SUS304 from pit initiation till crack initiation was calculated based on this model. And then, compared with the measured hydrogen amount by cyclic corrosion test, the hydrogen density at the starting point was derived 0.3ppm. At this density level, HE-SCC can occur in high strength SUS304.
INTRODUCTION Since high strength stainless steel can contribute to the improvement of corrosion resistance and a reduction in the weight of vehicles, expectations for its application to automotive components have been increasing. We performed an automotive field test by attaching SUS304 pipes highly strengthened by cold working to a vehicle, in a previous study [1]. In the test, we indicated that cracking may be caused from microscopic corrosion pits generated in crevices, and that it is highly possible that this cracking is hydrogen-embrittlement type Stress Corrosion Cracking (HE-SCC). Assuming that the cracking is HE-SCC, it is considered that the cracking was caused because the amount of hydrogen that absorbed in the sample with the development of corrosion exceeded the allowance value of the sample. This study aims to calculate the hydrogen density at the moment when SUS304 highly strengthened by the transformation of strain-induced martensite cracks at the corrosion pit. First, we conducted an experiment focusing on hydrogen caused during corrosion by the bench corrosion test, and then measured the amount of hydrogen absorbed in the sample from the corrosion portions. Next, we created a calculation model to derive the hydrogen density in the sample, which changes with the development of corrosion, and calculated the hydrogen density distribution at the time of the occurrence of cracking. By comparing both densities, we calculated the hydrogen density at the starting point of cracking. EXPERIMENTAL DETAILS
SUS304 plates with the chemical composition indicated in Table 1 were processed into cylindrical pipes by deep drawing and ironing and used for test samples. Table 1. Chemical composition of type304 stainless steel (mass%) C 0. 029 Ni 8. 44
Si 0. 20 Cr 17. 88
Mn 0. 43 Al 0. 005
P 0. 007 N 0.
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