Effects Of Cu, Cr And P On Weathering Steel Of355MPa Grade

In recent years, the high-speed railway construction is booming and several passenger dedicated lines (PDL) with design speed of350km/h are under construction with the considerable progress of national economy. However, some of the key technology in high speed train, especially the primary materials and components for the bogie of the CRH3-type high speed vehicle are dependent on imports although the whole vehicle can be manufactured and assembled in China. The frame of the bogie in CRH3is made of355MPa grade low alloy weathering steel (S355J2W) manufactured in Europe. In the present research, the microstructure, mechanical properties and corrosion resistance property of the355MPa grade low alloy weathering steel with different Cu, Cr and P contents were studied to ensure the suitable chemical composition for the domestic production of the steel. The main results of the present research are as follows:1. The import S355J2W mainly contains the elements such as C, Mn, Cu, Cr, S, P, Si, Al, Nb, etc, and metallurgical quality is excellent because of a low S content. The microstructure of S355J2W at room temperature is composed of pearlite and ferrite, and the grain size of the ferrite is about20μm. The yielding strength is375MPa, and the elongation is about35%and the ductile to brittle transition temperature (DBTT) is about-40℃. The1.34g/m2-h weight loss rate indicated that the steel owns excellent corrosion resistance. All the results above could meet the requirements of EN10025-5.2. After normalizing, the yield phenomenon disappeared and the mechanical properties of S355J2W decreased obviously. It is found that the local deprivation of C in ferrite can be considered as the main reason from the results of Electron probe micro-analyzer (EPMA). The yield phenomenon can reappear when the alloy is annealed at lower temperature. It is suggested that the suitable heat treatment temperature range is between550℃and680℃, which can be also used for the testing alloys after hot rolling.3. The microstructure of the testing alloys at room temperature is also composed of pearlite and ferrite. When the content of Cu is low, the yielding strength is less than355MPa, yet with the increase of Cu, Cr and P, the yielding strengths of testing alloys will be higher than355MPa. The testing alloy also possesses good performance in both impacting and bending properties.4. The corrosion resistance of the testing alloys was also examined. When the content Cr or P is separately added, it seems almost no obvious influence on the corrosion resistance. However, when the content of Cu is increased, the weight loss of the ally will be sharply decreased. It is clear that the corrosion resistance of the alloy is improved by the formation of complex oxide layers, which is due to the enrichment of the Cu and Cr on the inner side of the rust.5. Based on the results and the relative standards, the chemical composition range of the355MPa grade domestic-production weathering steel can be suggested as:Cu:0.28-0.33%, Cr:0.40-0.85%, P≤0.03%.