Development of high strength atmospheric corrosion

Progress of high-strength atmospheric corrosion-resistant steel for railway vehicles

in order to speed up the construction of railway modernization and build a well-off society in an all-round way, at the same time, in order to adapt to the fierce competition in the passenger and freight market and meet the requirements of fast, heavy-duty, safe, reliable, high-quality and environmental protection of railway freight, with the development of national economy and technological progress, the variety, grade and quality of railway vehicles will be greatly improved

the strategic focus of the development of railway industry is to increase speed and heavy load, which requires railway vehicles, especially freight cars, to reduce the dead weight of vehicles. In addition to reasonable selection of design parameters and optimized structural design, the most important way to reduce the dead weight of vehicles is the variety, performance and quality of steel

due to China's vast territory and great differences in climatic conditions, we should also pay enough attention to the corrosion of materials. The scrap metal materials and equipment caused by corrosion is equivalent to% of the annual output of metal. The annual loss of metal due to corrosion failure in the world is more than 100 million tons, and the resulting economic losses account for 5％GNP。 Due to corrosion, 10-20% of steel structures in China have become waste

therefore, it is necessary to jointly tackle key problems from the aspects of selecting reasonable design parameters, optimizing structural design and improving the service performance (variety and specification, mechanical properties, corrosion resistance) of railway steel (plates and profiles)

1 current situation of railway vehicles and requirements under the new situation

1.1 current situation of railway vehicles

for a long time, the technical standards of railway vehicles in China have been derived from the standards of the Soviet Union in the 1950s and 1960s. The technical progress of railway vehicles depends on the variety, performance and quality of steel products in China to a certain extent. Before the 1980s, steel structures basically used plain carbon steel, 09Mn2, etc., while atmospheric corrosion-resistant steel has always been dominated by 09CuPTiRE with a yield strength of 295mpa and 09CuPCrNi with a yield strength of 345mpa, while the strength level of weathering steel in the United States and other countries has reached 550MPa. The scientific and application tests of this copper phosphorus series weathering steel show that its corrosion resistance is generally equivalent to about twice that of ordinary carbon steel and times that of ordinary carbon steel in harsh environments. Up to 2001, this kind of weather resistant steel has been used on the main railway freight cars and boxcars. With the formulation of major technical policies for heavy-duty and speed-up railways, the selection of high-strength and weather resistant structural steel to reduce vehicle weight and improve vehicle performance is particularly prominent and urgent

1.2 speed up and heavy load put forward new requirements for the technical equipment of railway vehicles

China's railways now have 38000 passenger cars and 560000 freight cars. The company's current pet wire is a translucent white plastic car, with about 2000 new passenger cars and 25000 freight cars every year. New vehicles should be designed and produced according to the requirements of high-speed, fast, fast and heavy load. For a large number of existing passenger and freight vehicles, the task of transformation is also very arduous to make them meet the above technical policies. Due to the large number of trucks and large amount of steel, the paper mainly talks about the problem of trucks

in the future, freight cars should mainly develop new general and special freight cars with light weight, high strength and corrosion resistance, express freight cars with a running speed of 120km/h, and large four axle freight cars with 25t axle weight and low dynamic action

increasing axle load is the way to generally improve freight capacity and economic benefits, and it is the common development trend of railway freight transportation in mainland countries of the world. The freight cars with a load of 60t or more in China have reached more than 95% of the total number of freight cars. Under the condition that the length of the station line is difficult to continue to extend and the axle load of 21t remains unchanged, the potential to continue to increase the weight of trains is very small. To further improve the weight of trains and operate heavy-duty trains, we must speed up the development of freight cars with a low power effect with a 25t axle load

it is imperative to develop special purpose trucks. With the deepening of China's reform and opening up, railway freight has entered the buyer's market. Traditional bulk transportation goods, such as coal and oil products, will gradually decrease with the establishment of pithead power station and the laying of oil pipeline. For high value-added goods, due to the lack of suitable transportation vehicles, slow speed, long transportation cycle, or door-to-door transportation, the share of railway transportation in various transportation modes is also decreasing. In order to cope with this situation, we should improve the competitiveness of the railway in the transportation market. Railway vehicles should no longer be dominated by open, flat, shed and tank general-purpose vehicles. We should develop special vehicles and develop new types of vehicles that meet the needs of the market. At present, China's railway special-purpose trucks account for only 5% of the total number of trucks, while the special-purpose trucks in the United States account for more than 60% of the total number of trucks, and Russia accounts for 32%. It should be said that the gap between China's special-purpose trucks is large. The development of special-purpose trucks is a promising new topic for vehicle design and manufacturing departments and Steel Research and production departments with new materials and new shapes. It is hoped that the high-strength steel (yield strength 600MPa or above) required for the manufacture of special vehicles (special trucks and special passenger cars) can also be supplied at home, so as to reduce and eliminate the gap with foreign vehicle steel technology

2 development of high-strength atmospheric corrosion-resistant steel

2.1 steel gold new material is a technological progress of an iron enterprise with a partnership entrepreneurship platform as the carrier

during the Tenth Five Year Plan period, China's iron and steel industry has been developing continuously and rapidly. In 2002, the output of crude steel was nearly 181 million tons, the steel was 192 million tons, and the imported steel was nearly 25million tons. China is not only the world's largest steel producer, but also the world's largest steel importer. After joining the WTO, in the fierce domestic and international competition, it has brought opportunities and new hopes to China's iron and steel industry. At present, remarkable achievements have been made in the structural adjustment of the iron and steel industry, especially in recent years, the iron and steel industry has expanded the investment scale by about 137billion yuan by using the technological transformation of national debt. The renewal of metallurgical equipment and technological progress have created conditions for the production of high-tech steels urgently needed by the country, such as high-strength weathering steel, pipeline steel, automotive steel, etc. Both rolling mill capacity and smelting level have been greatly improved

in the past 20 years, the improvement of steel quality has benefited from the promotion of full continuous casting technology and the development of out of furnace refining technology, and the cleanliness of steel is constantly improving. Domestic iron and steel enterprises regard the establishment of clean steel production series as the first task of technological transformation. At least LF and other ladle refining furnaces are set up, and Rh or VD furnaces are added in the second or third phase of transformation projects. Baosteel, WISCO, Angang and Wugang have improved the production process of s ＋ P ＋ n ＋ h ＋ t.o ≤ 50ppm

in the study of microalloying of steel and ultra-fine grain steel, it is confirmed that impurity elements have some beneficial effects, such as dragging grain boundary movement, grain boundary pinning, inhibiting recrystallization and so on

it is well known that the improvement of cleanliness greatly improves the performance of steel, especially the impact toughness and corrosion resistance. The typical converter smelting clean steel production process (hot metal pretreatment, top and bottom combined blowing of converter, LF refining) can produce molten steel with C ≤ 0.03%, s ≤ 0.005%, P ≤ 0.005%, n ≤ 0.003%, t.o ≤ 0.002%. The effect of adding RH refining, decarbonization and deep desulfurization is remarkable. It can produce clean molten steel with C ≤ 0.002%, s ≤ 0.001%, P ≤ 0.003%, n ≤ 0.003%, t.o ≤ 0.0015%. The control level of ultra clean in the contemporary world is (s + P + N + H + t.o) ≤ 50ppm

at present, China has put into production a total of 15 sets of strip mills, including 9 sets of continuous and semi continuous mills, 5 sets of thin slab continuous casting and rolling mills, and 1 set of Steckel mill. There are 9 hot-rolled wide strip mills under construction and continued construction, including 3 hot strip mills, 5 thin slab continuous casting mills and 1 Steckel mill. It is estimated that by 2005, the production capacity of hot rolled wide strip steel in China will exceed 50million tons, and the production quality will be greatly improved

2.2 production and trial production of high-strength atmospheric corrosion resistant steel

as we all know, the main mechanisms to improve the strength of steel include: solid solution strengthening, precipitation strengthening or precipitation strengthening, dislocation and substructure strengthening, fine grain strengthening, etc. Among these strengthening mechanisms, only fine grain strengthening is the only effective way to improve both strength and toughness. Relying on reasonable and effective alloy design and optimized TMCP process, without changing the current composition system of atmospheric corrosion-resistant steel, add a small amount of Microalloying Elements Nb, V, Ti, and adopt controlled rolling process to obtain fine grain structure, and improve strength and toughness by fine grain strengthening

the two most commonly used weathering steels 09CuPCrNi and 09CuPTiRE are selected, the microalloying element NB is added, and the deformation induced ferrite transformation (DIFT) principle is adopted to obtain the fine-grained structure, which greatly improves the strength. At the same time, the toughness, weldability and corrosion are equivalent to or improved with the original weathering steels 09CuPCrNi and 09CuPTiRE. In this regard, the general iron and Steel Research Institute has made great progress in theoretical basic research and industrial trial production under the situation of a large number of redundant ordinary membranes. At the same time, Baosteel, WISCO, Benxi Iron and steel, Panzhihua Iron and steel, Masteel and other steel plants have also accumulated more experience in the development and production of weathering steel

2.2.1 laboratory research

in the national 973 "major basic research on new generation steel materials" project, grain refinement was used as the main means to improve the properties of steel. In the research process, it was found that the DIFT mechanism had an obvious effect on Microstructure and grain refinement. This refinement method and principle have been produced and supplied in several steel plants in China, and the main varieties are ordinary carbon steel and microalloyed steel, At present, it has been applied in automobile and other industries. However, there are not many previous studies on the mechanism of deformation induced ferrite transformation and the effect of microalloying element Nb on the grain refinement of weathering steel, especially the weathering steel of copper phosphorus system. This paper tries to summarize the recent research results

two kinds of weathering steels produced by Benxi Steel and widely used in the railway vehicle and container industry are selected for the test, namely 09CuPCrNi and 09CuPTiRE, which are produced in large scale. At the same time, microalloyed element NB is added to the steel respectively, and the added Nb content is (wt%): 09cupcrninb steel - 0.021~0.03%, 09cuptirenb steel - 0.017~0.03%

the DIFT mechanism is applied, and the low temperature and large reduction process is adopted. The start rolling temperature of finish rolling is 850 ℃ - 820 ℃, and the crimping temperature is 400 ℃ - 600 ℃, which is rolled from the blank thickness of 40mm to 3mm. The test results of 09CuPCrNi and 09CuPTiRE without Nb and 09CuPCrNi and 09CuPTiRE with Nb are as follows

mechanical properties of 09CuPCrNi and 09CuPTiRE without NB

the yield strength of 09CuPCrNi and 09CuPTiRE is about 400MPa and 345mpa respectively for weathering steel routinely produced by steel mills. Although the process conditions adopted in the current test are relatively harsh, and the general large-scale industrial production cannot be achieved, compared with the mechanical properties and ferrite grain size of the rolled steel plate, the strength and ferrite grain size of the steel plate are not significantly improved compared with the large-scale production of weathering steel. From the perspective of ferrite grain size, the ferrite grain size after low temperature and high pressure is 6.8-10.2 μ m. The grain size of weathering steel produced by conventional industry (8-10 μ m) In contrast, the effect of thinning is not obvious; After rolling, the yield strength of 09CuPCrNi steel is 430 MPa and that of 09CuPTiRE steel is 350 MPa, which is not much higher than that of normal production weathering steel. It can be seen that if the composition design of weathering steel is not changed and micro alloying elements are not added, the mechanical properties of weathering steel cannot be greatly improved even under such harsh process conditions as low temperature and high pressure

mechanical properties of 09cupcrninb and 09cuptirenb containing Nb

after adding a small amount of microalloying element Nb, the refining effect is very obvious, the structure of steel is significantly refined, and the grain size of ferrite is basically 3-5 μ m. Steel plate