Usually the heat exchanger can be normal working temperature to 283 ℃, but the temperature is easy to rust stainless steel bolts. The reason is that, in the high temperature environment, the heat cycle can cause some stainless steel tissue to be non – stainless steel. Therefore, when selecting stainless steel fasteners, the requirements must be met to prevent later loss. The following will introduce the optional materials for the stainless steel fasteners.
300 series stainless steel fasteners
300 – line stainless steel is the most commonly used material for the manufacture of fasteners, joints, pipes and pipes. Among them, 304 stainless steel fasteners are the most. 18 – 8 steel is the nominal content of 300 series stainless steel chromium and nickel. The surface of such materials has excellent corrosion resistance, but if the 304 stainless steel is heated to 199 degrees, the carbon content will decrease the content of chromium. This is due to the formation of chromium carbide in the combination of chromium and carbon at high temperature, and the chromium carbide is not antirust.
If 304L stainless steel can be used to alleviate this problem, the carbon content of 304L stainless steel is only about 1 / 3 of the 304 stainless steel. The use of 321 stainless steel or 347 stainless steel can avoid the formation of chromium carbide. 321 stainless steel and 347 stainless steel are titanium and niobium respectively, and their chemical properties are very stable. Since titanium and niobium have a larger affinity for carbon than chromium, they are formed at high temperatures with carbon and niobium, respectively, so that chromium can be retained. So 304, 321, and 347 stainless steel are used to make bolts for 300 series stainless steel.
In addition, because the strength of 300 series stainless steel can only be strengthened in cold forming, so when the temperature reaches 283 degrees, the thermal cycle will reduce the strength of fastener to the annealing state. If the degree of intensity is not acceptable, even 321 or 347 should be reconsidered, and in this case, the other materials are selected.
400 series stainless steel
The chromium content of the 400 series stainless steel is lower than that of the 300 series stainless steel, but there is no carbon deposition problem, and it can be heat treated. It can be used in the working environment with a temperature of 393 degrees. But because the chromium content is only 12%-14%, it will be corroded in a serious chemical atmosphere. However, the chromium content of the 300 system reaches 16%-20%, and it will not corrode. The other 400 series of stainless steel has magnetic properties. The 410, 416, and 430 series of 400 series of stainless steel are used for fasteners.
The use of 304 stainless steel is not suitable for 283 degrees in the operating environment, if the decline in strength of materials close to the annealed state can accept, can choose a stable material 321 or 347 stainless steel and the like, and if the strength requirement is high, and the surrounding environment corrosion is not serious, can use 400 series stainless steel can meet the requirements.
Source: China Stainless Steel Fasteners Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)