Development Of 500CX High Strength Steel Plate For Dump Truck Carriage

With the development of economy in China, the basic construction engineering and long-distance-transport carrying capacity increased greatly and dump truck demands in recent years soared. Dump trucks become indispensable vehicles in engineering construction, demand for steel plate of truck box rise greatly. Truck-manufacturing industry generally use Q235 or Q345 steel to manufacture carriage. Such steel plate is of low strength, poor wear resistance. Therefore, steel plate with high strength wear-resistant for truch boxes is the development trend of material demand in truck- manufacturing industry.Tonghua Iron and Steel Limited Company developed 500CX high strength steel plate for dump truck carriage, used in the dump truck carriage bottom and side plates whch bear a larger force as important structural parts through the advanced FTSR (Flexible Thin Slab Rolling) short flow production line for the production of high strength 500CX truck boxes.Process parameters for the production of 500CX high strength steel in steelmaking, refining, continuous casting, and rolling for the carriage board were studied in this work and combining with the production technology and production equipment in the company, in-depth analysis of the production for truck boxes of 500CX high strength steel from practical process.C-Mn composition design has formed through experimental study. Through the pretreatment of hot metal desulfurization, the sulfur content should be reduced to a low level ([S]≤0.01%). LF refining process should apply basic white slag (w(FeO+MnO)≤1%), submerged arc heating and argon-blowing stirring to molten steel to achieve [S]≤0.010%, [P]≤0.020%, [N]≤0.006%, and ∑[S]+[N]+[O]<150ppm in order to improve the purity of molten steel for better steel welding performance. The addition amount of various kinds of alloys should be rigidly controlled. In calcium treatment procee, the Ca/Al should be controlled in the range of 0.08～0.12, Als content should be of 150-250ppm, and the inclusion shapes should be changed to increase the plasticity and machinability of the steel. Reasonable continuous-casting process parameters should be controled, such as, reducing the superheat of molten steel (15-20 ℃), decreasing secondary cooling water flowrate by 20%, using secondary cooling water with 30～40℃, reducing oscilation amplitude of mould from ± 3mm to ± 2.5mm, applying electromagnetic stirring and the rapid cooling solidification in continuous casting to prevent the center segregation of slabs. Rapid cooling after rolling continuous casting slab can reduce banded structure of steel. Large reduction is applied in rough rolling, reduction ratio>50% in rough rolling R2, to crush casting microstructure of thin slab. The strength of steel is increaseb from "chilling" control in and after rolling. Uniform cooling with controlling laminar flow cooling water can reduce the plate buckling. Residual water cleaning device is used to achieve precise temperature control so that the uniformity and stability of coiled strength are ensured.The performance of 500CX high strength truck boxes shows that yield strength ReL≥ 500MPa, tensile strength Rm=550～700 MPa, cold bending (sample widness b=35mm, bending diameter d=3.0a(sample thickness)) qualifies, room temperature impact work AK is between 90～140 J. Composition and performance of 500CX high strength carriage board produced can meet the requirement of the steel plate.