Recently, we are experiencing problems regarding the corrosion of our metal product. The steel raw material that we use was SAPH 45 / SAPH 440 ( in reference to JIS ). However, corrosion only appeared in a particular area where there is thread. Initially, we thought that the corossion was due to the following reasons: 1. Surface stress applied on the area where corrosion was found ( during threading process, the stress applied on the hole was enormous that smoke was observed during processing ) 2. Heat ( friction between the metal and the tapping bit ) 3. Atmospheric condition ( humidity is high ) Upon laboratory analysis, it was also found out that there were presence of chlorine which somehow affected the rate of corrosion. Is it possible that chlorine is present in the atmosphere and combines with the air that affected the rusting of the metal? Thanks!