| Recent years, with the gradual increase of domestic logistics costs, the profits of transportation industry in heavy truck area become smaller, which lead to the increasingly serious overloading phenomenon."No more money without heavy load" has gradually become the industry unspoken rules. Chipping wheel spokes and broken roof care are the main form of overloading accidents, which caused by the role of alternating stress fatigue failure after long time high temperature. Recently, light-weight vehicles has become a leading automotive industry, with the rising strength of the wheels-steel, material thickness become smaller and lighter. But in our country, the pressure of wheel manufactures increasingly bigger, which resulted by the serious phenomenon of Spoke chipping and asked top. Based on the current domestic market demand, it’s emergency for wheel manufacturer to develop an ultra-high security card with heavy steel spokes to Heavy Trucks.In order to relief the high scrap rate phenomenon in wheel industry, the subject was carried out with Zhengxing Wheel Group Co.Ltd. Thesis research work and conclusions are as follows:1) Low cost, fatigue resistance, high elongation, high uniformity and high surface quality were studied in low Mn-Nb micro component system, and better used in heavy-gauge steel spokes S500LF.2) The main reason for the failure of the wheel is analyzed of in the issue. Failures mainly occurred in machining and moving process, with point and pit, mixed and uneven performance, Cracking vents by serious segregation in machining process; while the failure in wheels moving process include overloading wheels in reverse, bending and thermal stress reaches the lower limit of fatigue cracking caused by inclusions and cracks caused by excessive.3) In order to ensure the performance requirements of materials, low Mn (0.8%) and micro-Nb (0.015%) was designed to satisfied the elongation of28%; for better uniformity properties, narrow composition and narrow process control were taken in the production process, and elected the critical control points; in order to ensure the surface quality of materials, low Si-contented, low temperature and speed rolling were designediin the process.4) In smelting areas:refining with single-LF process, inclusions A and C is0, B and D is lower1.5. Narrow component smelting furnace98C exceeded only1furnace, furnace2Mn exceeded, but have little effect on performance, the rest are all normal. In Hot-rolled areas: oven temperature (±30℃), the finishing temperature (±20℃) and coiling temperature (±20℃) in the range of coverage was98.24%,97.25%and95.82%.5) S500LF organization is ferrite and pearlite, ferrite mean grain size was6.69μm, the volume fraction was90%; organization of Q345B with the same level was ferrite and pearlite, with ribbon serious, the average ferrite grain size7.04μm, the ferrite volume fraction was62%. Reduce and mitigate S500LF ribbon Wilcoxon bodies are conducived to improved fatigue resistance; S500LF mean yield strength is404MPa; tensile mean is514MPa; extension rate is29.4%; the higher-order energy of S500LF and380CL were about250J, but S500LF the ductile-brittle transition temperature is lower than380CL about6℃; stiffness of S500LF were significantly higher380CL. Welding areas, the spokes base metal, welding and rim base metal ladder decreasing trend, base metal and wire spokes matched with higher degree; the oxide scale decreased from the original28～30μm to10μm by reducing inlet temperature (1000℃to950℃). |
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