The normal working temperature of the heat exchanger is greater than 200 degrees, but sometimes the stainless steel bolts are easy to rust. The reason is that at high temperature, the thermal cycle will lead to some stainless steel models becoming non stainless steel. Therefore, stainless steel fastener materials must be chosen with caution.
Contrary to general cognition, stainless steel will not remain stable forever. For example, the thermal cycle mentioned earlier will lead to chromium content in some stainless steel, which is reduced to rust prone level. Therefore, in the specific application scene, we should choose the stainless steel model which can meet the special needs of the scene.
So, for stainless steel fasteners, what are the types of stainless steel that are suitable for use?
First, the next 300 series of stainless steel, of which 18-8 stainless steel, are the most commonly used materials for fasteners, joints, pipes and pipes. This type of stainless steel has excellent corrosion resistance, but when heated to 200 degrees, the chromium content will be reduced because of the deposition effect of carbon. Chromium and carbon will generate chromium carbide at high temperature, which is not rust free. 304L and 321 stainless steel can alleviate this problem. In the ordinary environment, the above models of stainless steel can be used as fasteners.
Let’s look at the next 400 series stainless steel, while the chromium content of stainless steel in less than 300 series stainless steel, but there is no carbon deposition problem is similar to that of 300 lines, and also used for heat treatment, indicating that the 400 series stainless steel can be used in operating temperature up to 400 degrees Celsius in the environment. However, the chromium content in the stainless steel is only about 12%-14%, and it will still be corroded in a serious chemical atmosphere. The 300 series stainless steel contains chromium elements of 16%-20%, but it will not be corroded. The strength of the 300 – line stainless steel and the 400 – system stainless steel is the same. In general, 410, 416 and 430 stainless steel are suitable for fasteners in 400 series stainless steel.
Here are some special stainless steel, such as A-286 stainless steel, which is the most widely used in aerospace industry. It belongs to iron-based stainless steel. It contains 15% chromium, heat treatment and cold hardening. Basically, all aerospace industry fasteners can provide A-286 fasteners.
There are also MP35N and MPl59, which are two very good materials in high temperature and high corrosive environments, containing 19% chromium. But their prices are high even in the space industry. This material is usually used only when there is no other choice, because the output is not high, except the price is very expensive.
Generally speaking, if the working temperature is not high and the environment corrosion is serious, fasteners made of 300 series stainless steel can be used. If the strength requirement is high, but the environmental corrosion is not serious, the 400 series stainless steel can be used. A-286 stainless steel fasteners can be used if the 300 and 400 series stainless steels are not applicable.
Source: China Stainless Steel Fasteners Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)