Research And Development Of High Weathering S450EW Steel For Railway Freight Wagons

Railway constructions in China are rapidly developing. With the development of high-speed, heavy-haul and quantitative reduction railway, higher requirements have been put forward on the comprehensive practical properties of weathering steel for railway freight wagons. Based on the summary of weathering steel history, a new generation of the high weathering steel for railway freight wagons has been researched and developed. The work would have an important guiding meaning in the development of weathering steel production technology and railway freight wagons technology.The effects and mechanism of the corrosion-resistant alloy elements chromium and nickel in the weathering steel have been systematically studied. The high weathering S450EW steel has been developed through significantly raising the level of chromium content combined with appropriate chemical constituents and rolling technological design. In order to further optimize the chemical constituents and rolling technology, the industrial tests have been performed. The main conclusions obtained from this study are summarized as follows.(1) Under the conditions of cycle infiltration corrosion and salt spray corrosion, with chromium or nickel content increasing, the free corrosion potential and polarization resistance of the weathering steel gradually are improved, the radius of capacitive reactance arc is increased, the compactness of inner rust layer is increased and the crystallinity is reduced, the corrosion rate of weathering steel is decreased. As chromium content increases, the diffraction peak intensity of both α-FeOOH and γ-FeOOH in surface rust layer are enhanced, and the ratio of α-FeOOH/γ-FeOOH is increased, the adhesive ability between inner rust layer and matrix is reinforced, the crack is reduced obviously, and the compactness increases. With regard to improving the corrosion resistance of weathering steel, the effect of chromium is better than nickel. When chromium content is increased from 1.09% to 3.51%, the corrosion rate decreases from 1.45g·m-2h-1 to 0.96g·m-2h-1.(2) With chromium content increasing, the tensile strength and yield strength of weathering steel are gradually increased, the elongation appears to be declined, the impact energy is first raised and then decreased. When chromium content is more than 2.51%, the impact energy are greater than 60J. When nickel content increases, both the tensile strength and yield strength of weathering steel are increased, however the elongation and impact energy have no obvious change. In terms of improving the comprehensive mechanical properties of weathering steel, the effects of chromium are much bigger than nickel.(3) With the increase of chromium content, the tensile strength of weathering steel at welded joint is gradually increased, but the elongation is decreased. The strength of weathering steel at wielded joint is close to parent metal, although the elongation is inferior to parent metal. Compared with parent metal, the weathering steel has better welding performance with higher impact toughness at fusion line area and heat affected zone.(4) Based on Q450NQR1 steel, SE450EW steel is prepared through increasing chromium content substantially, increasing nickel content appropriately, and reducing carbon and manganese content at the same time. An appropriate rolling technology has been developed in order to meet the objectives and requirements of the steel design.(5) Through industrial tests, S450EW steel has been mass produced successfully. Its corrosion resistance is 1.5 times higher than Q450NQR1 steel and comprehensive mechanical properties and welding property are slightly better than Q450NQR1 steel. The parameters of S450EW steel fully meet the requirements of No.[2010]841" Technical conditions of high weathering steel hot-rolled sheet (strip) for railway freight wagons (provisional)".