Technical requirements for austenitic stainless steel cladded tube sheets
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There are two questions: 1. Under what circumstances is there a requirement for a ferrite content in the surfacing layer of austenitic stainless steel? If there is a request, how should it be handled? 2. Under what circumstances is it necessary to perform stress-relief heat treatment on the tube sheet?
Generally, there are requirements regarding the ferrite content. It is measured after the corrosion-resistant layer is applied, and it is generally between 3-8%. There are also ones that go up to 10. Stress-relief heat treatment is carried out after the transition layer has been built up.
Why are there requirements for the ferrite content, and why is stress relief treatment necessary?
Ferrite is very important for preventing intergranular corrosion in austenitic stainless steels; its amount must be just right – neither too much nor too little. The range of 3-8 mentioned earlier has been tried by us, but it’s difficult to achieve that range, and it’s easy to exceed the desired level. A range of 3-10 works better, and the amount of ferrite is measured using a specialized instrument.