Characterization of the boride layer and wear resistance of the liquid-boronized AISI D2 cold work tool steels

The objective of this study was to improve the wear resistance of an AISI D2 cold work tool steel by liquid-boriding process. The tool steels were liquid-boronized at 850, 900 and 950 ^oC for 2 and 4 hrs. Boriding agent composed of 90 wt.% Na₂B₄O₇.10H₂O and 10 wt.% AI. X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were conducted on the boride layers to characterize the presence of the FeB, Fe₂B, and CrB phases. The hardness of the boriding layer becomes about 2000 HV when the processing at 950 ^oC for 4 hrs. The relationship between volume fraction of the boride phase and case depth was evaluated. Ball on disc tribological testing results show that the coefficient of friction obtained in the FeB phase of the AISl D2 tool steel presented a range of 0.6 to 0.64. While, the boronized tool stee! presents two different phases in the boride layer being the coefficient of friction higher for the test in the FeB phase and the values vary from 0.65 to 0.70. Moreover, the abrasive resistance has improved remarkably.