Comportamento tribológico de aços ferramenta utilizados em estampagem a quente

Abstract

The use of hot stamping is increasing in the manufacture of automotive parts, therefore the influence of processing and the development of new materials that allow greater productivity have been studied over the years. In this context, the present work aims to study the tribological behavior of tool steels,1.2344 (H13, X40CrMoV5­1), 1.2367 (X38CrMoV5­3), WP7V® and CP2M®. For the study, the tool steels were heat treated in a salt bath, with an austenitization temperature of 1050 °C and triple tempering of 2 hours each. The tempering temperatures were selected só that the hardness ranges of 46­49, 54­55 and 57­58 HRC were reached. The wear tests were conducted using a tribometer configured in two tests: i) in the reciprocating sliding configuration, unlubricated, with a frequency of 5 Hz, applied load of 25 N, time of 60 minutes and temperature of 200 °C in addition to room temperature. Alumina spheres (Al2O3) of 5 mm in diameter and hardness of 1455 HV0.3 were used for the counterbody, and ii) in the linear scratch configuration, with a progressive load of 4 to 40 N at room temperature. Metallographic analyses, hardness, microhardness and nanohardness measurements, X­ray diffraction, impact tests with and without notch, scanning electron microscopy, 3D interferometry and Raman spectrometry analyses were performed. The results showed the formation of a tribolayer of oxides (Fe2O3) in the wear tracks for the four steels studied. In addition to oxidative wear, the predominance of abrasive and adhesive wear, in addition to the presence of debris and plastic deformation, were also observed. Greater wear of the spheres was observed for the tests at room temperature. Material transfer between the tool steels and the ball was also observed. The CP2M® steel presented the best tribological performance when compared according to the COF and wear rate results for the tests at room temperature and 200 °C, but low impact resistance due to the presence of coarse carbides. Carbides with hardness values in the order of 15.75 to 16.76 GPa and 12.13 to 23.54 GPa were found in the nanohardness tests on the WP7V® and CP2M® steels.