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Abstract: An investigation was carried out to analyze and quantify the mechanical property changing mechanism of high speed steel by pulsed magnetic treatment. Specifically, a pulsed magnetic treatment system was designed and applied to the tool material treatment. The micro-hardness and red hardness were measured to quantitatively investigate the influence of magnetic treatment on the mechanical properties. Results showed that high speed steel material possessed better mechanical properties using the proposed pulsed magnetic treatment, of which the maximum increase of micro-hardness was 50HV. Also, the red hardness with low temperature could be improved. Moreover, the influence of magnetic treatment conditions on the micro-hardness change rate was investigated. It was shown that the micro-hardness change rate first increases and then stabilizes with the increase of magnetic field intensity, and it decreases with the increase of magnetization time. Ultimately, the dislocation densities were calculated by XRD data analysis according to the Williamson–Hall method and the interaction between magnetic field and dislocation was discussed in detail. Results revealed that the dislocation density of high speed steel material increased by 24% after pulsed magnetic treatment. The dislocation multiplication and motion induced by magnetic field led to the increase of dislocation density, which was the main reason of the increase in micro-hardness. The dislocation pile-up mechanism was responsible for the treatment effects of different magnetic treatment conditions. The dislocation configuration determined from TEM micrographs was in good agreement with the X-ray results and the discussion of dislocation mechanisms. [Copyright &y& Elsevier]