Abstract
The influence of the nitrogen compression plasma flow impact on the phase and element composition and tribological properties of AISI M2 and AISI T1 high-speed steels was investigated in this work. The bank capacitor initial voltage, the number of pulses and nitrogen pressure in the vacuum chamber varied during experiments, providing the change of energy deposited in the surface layer within the limits of 5–13 J/cm 2 per pulse. X-ray diffraction analysis, Auger electron spectroscopy, Rutherford backscattering analysis, scanning electron microscopy, optical microscopy, friction coefficient and microhardness measurements were used for the characterization of the treated samples. It was found that the treatment of both types of steel resulted in austenite formation in the surface layer and carbide partial dissolution. The growth of energy deposited in the surface layer leads to the increase of thickness of the affected by treatment layer up to 24 μm and to the decrease of MC and M 6C carbides volume fraction in the analyzed layer. Treatment leads to nitrogen penetration into the steel up to the depth of 400 nm and the redistribution of the alloying elements in the surface layer. The decrease of hardness due to dissolution of carbides was observed almost in all range of treatment parameters, thus making unsuitable the usage of the compression plasma flow treatment for high-speed steels tribological properties improvement as a stand-alone technique.
Highlights
Different types of ion-plasma nitriding techniques are used for modification of steels mechanical properties [1,2,3,4,5,6,7,8,9]
At the same time high temperature, high cooling speed in the surface layer of steel during compression plasma flow (CPF) treatment can result in the change of carbide morphology, concentration of residual austenite, the microstructure of martensine grains causing a possible worsening of tribological properties
MC carbide is considered insoluble in high-speed steels, while in steels containing only vanadium it dissolves at the temperature of 1373 K
Summary
Different types of ion-plasma nitriding techniques are used for modification of steels mechanical properties [1,2,3,4,5,6,7,8,9]. At the same time high temperature, high cooling speed in the surface layer of steel during CPF treatment can result in the change of carbide morphology, concentration of residual austenite, the microstructure of martensine grains causing a possible worsening of tribological properties (while nitrides formation improves it). It means that CPF treatment of a high-speed steel could cause tribological properties improvement in a narrow range of treatment parameters only. That is why it is necessary to study the influence of CPF treatment parameters (the energy of a discharge capacitor, nitrogen pressure in a vacuum chamber, the number of pulses) on the phase and elemental composition, microstructure and tribological properties of high-speed steels
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