Investigations On The Surface Spalling Mechanism And Performance Improvement Of ZG-Mn13 Railway Frog

ZG-Mn13 cast steel, which is used in the railway frog, forms frequently the pitting spot even spalling on the surface due to the influence of alternate load and the corrosion atmosphere, which leads to the failure of the whole component.Based on the failure mechanism analysis of frog surface spalling, through the research into the surface spalling fracture, chemical composition, microstructure, surface hardness and mechanic properties, a conclusion can be drawn that the railroad frog surface spalling and falling block is attributed to corrosion fatigue failure. Under the combined condition of the intensive impact load and the environment corrosion, fatigue cracks firstly sprout from the material flaw place and the slipping line place where the work hardening forms because there are the casting defects of shrinkage, air hole and inclusion in the material organization. When the superficial and the inferior superficial cracks unceasingly expand and converge, the surface flaking block come into being.In order to have a further study on the effect of the in-service condition of railway frog on its failure, finite element software of ANSYS is used to analyze the complex stress condition of the frog. The result indicates that the maximum stress at the superficial contact point reaches 5300MPa, and the action depth reaches 15mm with the stress 830MPa, which is consistent with the actual hardening depth of high manganese steel frog. In addition, the horizontal stress induced from friction force and impact load is 2400MPa, and the depth reaches 1.5mm with the shearing stress of 700MPa, which accelerate directly the frog surface flaking.By decreasing carbon content, increasing manganese content, adding an niobium, titanium, vanadium, molybdenum and rare-earth elements, and adding a small copper or nickel to improve its corrosive resistance, and by developing new casting and heat treatment techniques, the properties of ZG-Mn13 steel is improved based on the original high manganese steel materials. The results indicate that, materials crystal grain is homogeneous in size, crystal boundary can be purified, and corrosion fatigue life of the new ZG-Mnl3 steel exceeds that of the original high manganese steel by three times, even without lowering of abrasion resistance. Thus extends the useful life of the railway frog.