Why is sensitization treatment required for 316L during the crystal corrosion test?
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I would like to ask everyone: why is sensitization treatment required first when conducting the \"stainless steel sulfuric acid-copper sulfate corrosion test\" on ultra-low carbon steels or stabilized steel grades (with Nb and Ti added)? This post was last edited by wuyumin on 2009-2-17 09:02]
If the test passes after sensitization, it can replace the un-sensitized test. It mainly depends on whether sensitization treatment is required before testing as per the design requirements
Could you explain the principle and necessity of sensitization treatment before conducting a crystal corrosion test on 316L?
Austenitic stainless steels tend to develop intergranular corrosion susceptibility within the sensitization temperature range; without undergoing sensitization treatment, their intergranular corrosion susceptibility cannot be manifested, and it is therefore not possible to determine whether intergranular corrosion will occur. Principle: Austenitic stainless steel is subjected to solution treatment upon leaving the factory, resulting in supersaturated carbon levels in the steel. In the sensitization temperature range, the supersaturated C precipitates and forms carbides with the Cr near the grain boundaries. The C within the grains does not have time to diffuse to the grain boundaries to combine with that C, and as a result, the Cr that is consumed comes primarily from the area near the grain boundaries, reducing the Cr content there to below 12%. The electrode potential and corrosion resistance in this area are lower than those of the grains themselves, leading to microcellular corrosion in the medium – this is what is known as intergranular corrosion. This post was last edited by ljfdd2002 on 2009-2-17 10:14.]
I am extremely grateful for the guidance and assistance of all my teachers.
When austenitic stainless steel is cooled slowly within the range of 400 to 850 degrees, carbonized compounds such as Cr23C6 with a high carbon content have time to precipitate and accumulate at the grain boundaries, resulting in areas adjacent to these compounds having a lower carbon content. In corrosive environments, this leads to a tendency for intergranular corrosion; this temperature range is known as the sensitization range. The sensitization treatment carried out before the intergranular corrosion test, as mentioned by the original poster, is primarily intended to evaluate the intergranular corrosion sensitivity of austenitic stainless steels. There are three methods to prevent intergranular corrosion: 1. Solution treatment, 2. Reducing the carbon content in the steel to no more than 0.03%, 3. Adding stabilizing elements such as Ti and Nb.
All of those who commented upstairs are correct; you can also refer to ASME Sec II Part D, edition 2004, Appendix A, which is not mandatory but provides more detailed explanations.