Wear Properties of High Nitrogen Austenitic Stainless Steels

STRACT
The main objective of this thesis is to demonstrate the way in which nitrogen alloying improves the sliding wear resistance of austenitic stainless steels, through alteration of their physical, metallurgical and mechanical properties. The effect of nitrogen on cavitation erosion resistance of austenitic stainless and duplex stainless steels is also described.
The resistance of powder metallurgically (P/M) fabricated and cast austenitic stainless steels to sliding wear was measured through pin-on-disc testing. Resistance of some of the materials to cavitation erosion was evaluated with an ultrasonic vibration technique. The experimental work also included measurement of the hardness, lattice parameters, elastic properties and densities of the materials. The effect of nitrogen alloying on hardness in compressive deformation was modeled with the Hollomon equation.
Nitrogen alloying increases the hardness, lattice parameter, Young’s modulus, and shear modulus, but decreases the bulk modulus and Poisson’s ratio. In compressive deformation, nitrogen alloying decreases the strain hardening exponent (n) and increases the strength factor (K) of austenitic stainless steels. Enhanced hardness improves the cavitation erosion resistance of austenitic stainless steels. The resistance to sliding wear is dependent upon the hardness, the amount of plastic deformation on the surface, as well as on the frictional force. The frictional force was found to correlate with the sound velocity in the material.
The results indicate that nitrogen alloying contributes significantly to sliding wear and cavitation erosion resistance of austenitic stainless steels. The effect is enhanced in P/M fabricated materials. Nitrogen alloying does not have a significant effect on friction.