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Original title: Manufacturer of hot-dip galvanized bolts explains the features of duplex stainless steel bolts. Carbon steel bolts come in various strengths depending on their intended use, while stainless steel bolts are designed to resist rust. What if one needs bolts that possess both sufficient strength and excellent corrosion resistance? http://p1-tt.byteimg.com/large/dfic-imagehandler/d38c90d6-4c3e-42e4-80e8-6e8bf1b067be?from=pc Many people would say that the surface of carbon steel bolts can be galvanized; indeed, this is one solution. However, galvanizing is merely a superficial treatment, and compared to the inherent corrosion resistance of stainless steel, no amount of galvanizing can make its corrosion resistance better than that of stainless steel bolts. Moreover, even after galvanizing the bolts, they cannot be used indefinitely in all environments; in extreme conditions such as those found in airplanes and ships, galvanized bolts are simply not suitable. To give the bolt both the corrosion-resistant properties of stainless steel and the strength of carbon steel bolts, the only perfect solution is to combine these two requirements into one. Thus, duplex stainless steel bolts were created. Dual-phase stainless steel bolts are based on 304 stainless steel bolts; their chromium content is increased, and other iron elements are added, enabling these bolts to possess the properties of both austenitic and ferritic stainless steels. This is why they are called dual-phase stainless steel bolts. Through the processing of the base material and by controlling its elemental composition, heat treatment enables these duplex stainless steel bolts to achieve a strength level of 8.8 or higher, without any impact on their original corrosion resistance. As a result of the combination of various elements, their corrosion resistance is improved compared to that of conventional austenitic 304 stainless steel. http://p6-tt.byteimg.com/large/dfic-imagehandler/591d224d-77c5-4bf5-a9f2-91dd00522a51?from=pc The material code for bipolar stainless steel bolts can be represented by the number 2205. Practical tests have shown that its strength level can reach grade 10, and its corrosion resistance even exceeds that of SUS316 stainless steel bolts. However, the application areas of duplex stainless steel bolts are quite specific; they are only used in special industries such as shipbuilding equipment and high-pressure vessels. Due to their high cost, duplex stainless steel bolts are generally not chosen in ordinary industrial applications, as cost considerations play a role in such decisions. The plasticity of duplex stainless steel bolts is not as good as that of ordinary stainless steel bolts. With the same level of production capacity, it is possible to manufacture 304 stainless steel bolts, but not duplex stainless steel bolts; moreover, during cold heading, the equipment required to produce these bolts must have a greater pressing force. Dual-phase stainless steel bolts are also divided into four different types. The first type is the low-alloy dual-phase stainless steel bolt, which is characterized by the absence of molybdenum in its composition. The second category consists of medium-alloy duplex stainless steel bolts, which have higher corrosion resistance than those in the first category. The third category consists of high-alloy duplex stainless steel bolts; experiments have shown that their corrosion resistance is more than 25% higher than that of low-alloy duplex stainless steel. The last type is super duplex stainless steel bolts, whose elemental composition includes high levels of molybdenum and nitrogen, as well as amounts of tungsten and copper. These super duplex stainless steel bolts are primarily used in the aerospace industry. http://p3-tt.byteimg.com/large/dfic-imagehandler/db565ff9-7f13-4caa-941e-8e832fac026c?from=pc Generally speaking, if the requirements of the usage environment are high and ordinary bolts are not sufficient, then dual-phase stainless steel bolts can be considered as an alternative. In environments containing chlorides, corrosion of steel is very severe; therefore, duplex stainless steel bolts can be used. In acidic oil and gas environments, even ordinary steel cannot withstand corrosion over long periods of time; therefore, duplex stainless steel bolts are also commonly used in oil drilling facilities. Seawater is highly corrosive to steel, which is why dual-phase stainless steel bolts are also used on ships. When materials move at high speeds in air, they generate heat, which can affect their performance; therefore, dual-phase stainless steel bolts are also utilized in aircraft.