Experimental Research On Cold Extrusion Deformation Performance Of Medium Carbon Steel After Quenching And Tempering

As the rapid development of automobile and equipment manufacture in China, the market demand of auto parts grow up. Among all kinds of auto parts, the quenched and tempered medium carbon steel parts, such as gears, axial parts, connectors, are produced by the process of cold extrusion followed by quenching and tempering, which with low efficiency and high fraction defective. Combined with plastic mechanics, materials science and computer aided analysis technology, take 40Cr as a subject, the forming behavior and plastic deformation rule are investigated, and the feasibility of cold extrusion process for medium carbon steel after quenching and tempering is also discussed in the study.Through experimental work and numerical simulation, the allowable deformation degree of medium carbon steel in different quenched and tempered states are found; the contribution of deformation degree, die angle and ratio of the height to diameter are discussed for the deformation performance.There is not any crack defect including center crack during the forward extrusion process. However,“double-peak”phenomenon, which will be disappeared by increasing deformation degree, occurs on the top side of the part. Based on the analysis of the hardness test and metallographic observation, mechanical property of the parts after cold extrusion and the development of microstructure are discussed. According to experimental analysis results of forward extrusion parts and splines, a new process route“medium carbon steel work piece�'quenching and tempering�'cold extrusion�'stress relief annealing�'finishing�'part”, which is different from the traditional process route“medium carbon steel work piece�'softening annealing�'cold extrusion�'quenching and tempering�'finishing�'part”, is put forward.