In China, the development of weathering steel began in 1960s. In 1965, 09MnCuPTi weathering steel was successfully produced in our country. In early 1980s, after weathering steel was included in the national key project of science and technology, has been developing rapidly, and our country have developed weathering steel with 09CuPTiRE and 09CuPCrNi as the representative, and began mass production. However, weathering bridge steel has not been widely applied.
The performance of weather resistant steel is continuously improved
By the end of 1989, three steel produced weathering Baoji bridge factory, steel NH35q, set up in the original section of the Beijing Guangzhou line Wuhan branch Xun Si river. This is the first weathering steel bridge in china. As a test of bridge bridge, a bridge will be located in the central hole is exposed, coating on the remaining two hole. In 1992 October, the weathering steel bridge was successfully set up and successfully opened to traffic. In the long term service in the process of bridge girder bridge has conducted a number of observations, found that the rust layer steel top cover plate, two side plates form the appearance of dark brown, very dense, hard scratch no peeling; bottom due to evaporation of water vapor directly river erosion, for many years in the wet state, failed to form a dense the rust layer and stable layer of loose rust, prone to peeling. Later changed to painting.
The weathering steel has not been widely used after its successful development. The reason has the following points: one is due to weathering of bridge steel bridge did not cause the manufacturing sector at the time; two is the relevant units failed to carry out the strong promotion of NH35q; three is the steel development have not been able to form a series, can not meet the many needs of the bridge development.
With the continuous development of China's economy, the use of weather resistant steel in bridge construction has aroused the attention of bridge steel researchers. In China, iron and steel enterprises represented by Wugang, Anshan Iron and steel company and Baosteel have begun to try and develop. Relevant research and experiments show that weathering steel has good mechanical properties, weldability and environmental corrosion resistance. The use of weathering steel bridge, compared with the use of ordinary carbon steel, its project cost is basically the same or little increase, while the cost of life cycle is greatly reduced. Therefore, weathering steel is worth popularizing energetically on steel structure bridge.
The performance of weathering steel is increasing with the domestic steel has introduced, in chemical composition, carbon content decreased, carbon equivalent and welding cold crack numerical sensitivity decreases, welding performance has been continuously improved; the production process is developed by quenching and tempering to TMCP, not only reduces the production cost, and shorten the production cycle by the organization; tempered martensite and traditional ferrite + pearlite to bainite and acicular ferrite, the steel toughness, weldability and weather resistance and processing performance are greatly improved.
The high performance of weathering steel bridge development way
With the development of metallurgical technology, modern high performance weathering steel bridge will usually carbon content below 0.08%, in order to improve the toughness of the steel and welding performance; adding Cu, Ni, Cr and a small amount of Mo and other weather elements, in order to improve the weathering steel toughness and corrosion resistance.
There are 3 ways to develop high-performance weathering bridge steel in our country:
One is the traditional process of quenching and tempering. Such as the United States bridge structural steel standard (ASTMA709/A709M-95) in 70W (carbon content greater than 0.12%), it has higher requirements to the welding process, preheating before welding, therefore, long production cycle, high cost.
Two is the low carbon TMCP process route. The carbon content of this steel is generally 0.07%~0.11%, although there is no need for quenching and tempering treatment, but due to the relatively high carbon content, there are still some problems in the application. For example, the thicker the steel plate is, the higher the sensitivity coefficient of welding is, and the preheating is needed during welding. Therefore, the problem of reduction of toughness occurs when welding with large line energy is adopted.
Three is the ultra low carbon bainitic steel line. The carbon content of ultra low carbon bainitic steel is strictly controlled less than 0.05%. Therefore, because of its high strength, high toughness and good weldability, the corrosion resistance of the micro section electrode is better because of the good uniformity of the microstructure and the smaller electrode potential difference in the micro interval.  Moreover, this kind of steel needs no quenching and tempering treatment, reduces production cost and shortens production period. It is the development trend of high strength weather resistant bridge steel.
In addition, WNQ570 steel Wuhan Research (Q420qE) design of corrosion resistance with the ultra low carbon (less than 0.02%) complemented by appropriate Cu, Cr, Ni and other weather resistance element ratio, the high purity purification treatment, and through appropriate casting rolling and heat treatment process, to make steel plate microstructure of acicular ferrite is better in ferrite organization, the atmospheric corrosion resistance is significantly enhanced.
Due to the design of low carbon, micro alloying and TMCP or TMCP+T process, the domestic high performance weather resistant bridge steel has more obvious microstructure uniformity and excellent impact toughness.
Micro alloying, so that weathering bridge steel worthy of the name
The high performance weather resistant bridge beams developed at home are designed to improve their mechanical properties by adding micro alloying elements, especially niobium. From the result of adding niobium in stainless steel, niobium has obvious effect on pitting corrosion. The corrosion behavior of Nb steel in seawater has been studied by AC impedance method. The results show that corrosion potential of Nb containing steel increases gradually with the increase of corrosion time. The corrosion potential of Nb free carbon steel remains unchanged, which shows that the corrosion resistance of niobium steel is better than that of carbon steel. The corrosion product of Nb steel is more dense than that of carbon steel, and its action is equivalent to forming protective film on the surface of Nb steel. Therefore, niobium can be used as a barrier to corrosion, and Nb microalloying helps to resist weathering of bridge steels