Analysis of the Causes of Flattening and Cracking of High-strength Steel DP780
With the development of automotive lightweighting,the application of advanced high-strength steel materials has become an important way to reduce vehicle weight and improve automotive collision resistance performance.A certain manufacturer used continuous annealing DP780 high-strength steel to process round tubes for seat frames through rolling technology.However,during the inspection of the flattening process performance,cracks appeared in the sample.Physical and chemical inspection and analysis were conducted on the flattened and qualified samples,and no obvious inclusions were found in the scanning electron microscope and metallographic analysis.The metallographic structure of the flattened and cracked samples was larger than that of the qualified samples,and the martensite in the qualified samples was fine and dispersed in the ferrite matrix.After conducting experimental analysis on bending performance and hole expansion performance,it was found that cracking occurred on the flattened cracked sample after being bent 180 °.The hole expansion rate was 20.3％,which was lower than the qualified sample's 24.7％.Based on comprehensive analysis,the differences in composition systems caused the cracking of the product,resulting in coarser grain size,poor coordination between grains during deformation,as well as low bending and expansion performance,which were the main reasons for the cracking of the round tube during flattening.
780DPflattening and crackingalloy elementsorganizationexpansion rate
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