Internal component heat treatment issues

It is best not to subject stainless steel components to post-weld heat treatment along with the equipment, but it depends on the specific circumstances and cannot be generalized.

Is it due to the temperature? Could you explain it in more detail? What happens if a piece is heat-treated after welding? Thank you~~

During heat treatment, the internal components should not be heat-treated together if it’s not necessary; the prefabricated parts can be welded first.

My personal opinion is that it’s not possible. The heat treatment temperature for carbon steel or chromium-molybdenum steel is generally around 700°C (see the screenshot for details); this temperature falls within the sensitization range of austenitic stainless steels, which is 450°C to 850°C. When austenitic stainless steel is heated for a short period at temperatures between 450°C and 850°C (a range commonly referred to as the sensitization temperature), it develops a tendency to suffer from intergranular corrosion. This reduces the corrosion resistance of stainless steel. This is because the solubility of carbon in austenitic stainless steel is highly dependent on temperature; when austenitic stainless steel is exposed to temperatures above its sensitization threshold, high-chromium compounds (Cr23C6) precipitate. When the chromium content in such stainless steel drops below the threshold value required for resistance to corrosion, intergranular areas become deficient in chromium, leading to intergranular corrosion. In severe cases, the material can turn into powder.

This guy is special – I found several questions he answered, and he can truly be called a problem solver. His answers are accurate, comprehensive, and accompanied by illustrations. . . . Isn’t the sensitization range 450~550? Maybe I’m mistaken

Does this requirement have to be met by both stressed and unstressed elements?

This post was last edited by jizhanwei22 on 2018-11-13 15:01. Yes, it has nothing to do with whether it is a stressed component; it depends only on the material and temperature. If the design temperature of a container falls within the sensitization range of austenitic stainless steels (450°C–850°C), care should be taken to select an appropriate stainless steel for corrosion protection: 1. It is recommended to use stainless steels containing Ti or Ni ； 2. It is recommended to choose ultra-low carbon stainless steel ； 3. It is recommended to choose duplex stainless steel.

Thank you for the compliment! The sensitization temperature for austenitic stainless steels is between 450°C and 850°C. You can search on Baidu; basically, it’s these two numbers, or their approximate values.

The compressed components certainly need to be taken into consideration, but the cylinder is made of carbon steel, while the internal components are made of 304L steel; moreover, the temperature only reaches that level during the heat treatment process. Is that not sufficient?

My views have been detailed in the reply; please read it carefully – it should cover most of your questions. Take a close look, read it first before asking, so as to avoid repeating questions.