Experimental Study On Micro-alloying Steel For Heavy Haul Railway Freight Car Axle

The working condition of axles becomes worse with increase of train speed and axle load in our country.According to this situation,the research direction and performance indexes of micro-alloying steel for heavy haul railway freight car axle are brought forward,and some systematic reseach work are done for the first time,including laboratory study,industrial trial-manufacture,real properties study and fatigue strength research in this paper.By experimental study in laboratory,chemical components of micro-alloying axle steel have been confirmed,the CCT curve has been determined,and process test of heat treatment has been carried out.Meanwhile,mechanical property and metallographic structure of test steel have been studied,fine structure and precipitation phase distribution of the axle steel have been observed under TEM,atom spatial distribution and segregation of each element composition have been analysed by 3DAP,precipitate structure and size distribution have been researched by physicochemical phase analysis method,and then the strengthening-toughening effect and mechanism of micro-alloying element in steel have been discussed.Combined with laboratory experimental study,the production process and physical performance of industrial trial-manufactured micro-alloying axle steel and axle have been tested and analysed.The study results show,the metallographic structure of trial-manufactured LZ45Cr V axle is fine uniform,the grain size can reach above 9,the tensile strength R_m≥670MPa,the yield strength R_el≥375MPa,the elongation after fracture A≥20%,the reduction of area Z≥37%,and the impact performance at room temperature A_KU2≥40J in transverse,A_KU2≥50J in longitude,the ductile-brittle transition temperature is about-50℃,the corrosion resistance is obviously improved compared with carbon axle steel.All the performance indicators reach the operation requirements of heavy-load railway wagon axle.The fatigue limit of small sample and full-scale LZ45Cr V axle are studied,and the fatigue strength of heavy-load wagon axle designed with LZ45Cr V has been calculated and evaluated.The results show that the fatigue limit of the smooth small sample LZ45Cr V axle is 336.6MPa and which of the notched small sample is231.7MPa,and then the notch sensitive coefficient q is 1.42;The full-scale fatigue limit of axle body is 226.3 MPa,position of wheel seat is 120.8 MPa.The maximum permissible stress of LZ45Cr V micro-alloying axle steel used in solid axle has been determined according to TB/T 2705-2010.Compared with common carbon steel,the fatigue reliability of heavy-load railway wagon axle RF₂ that designed and manufactured with LZ45Cr V,has obviously improved.The micro-alloying steel heavy-load railway wagon axle studied in this paper has reached the design objective,which fills in the blank of the research in micro-alloying steel axle and provides new material and idea in improving the carrying capacity and service life of railway wagon axle in our country.