Characterizing the Mechanical Properties of Steel AISI-SAE 4140 to Apply a Plasma Nitriding Process

Abstract

Surface treatments give physical and chemical properties to the materials, without them showing any change in their
dimensions. Plasma nitriding is a thermochemical treatment, which increases some mechanical properties of metallic
materials. In this article the characterization of the mechanical and micro-structural properties of an AISI-SAE 4140 steel is
presented. To carry out the metallographic characterization, stress, hardness, abrasive wear and X-ray diffraction tests, the
AISI-SAE 4140 steel was mechanized and prepared delivered in a hardened state (quenched and tempered) produced by Shah
Alloys Ltd. making test pieces with their corresponding ASTM standards and nitrifying by plasma half of these at 500ºC for
10 hours. A thickness of 6.78 μm was obtained from the nitride layer that the material acquired. A microstructural constitution
was found formed by martensite and austenite retained in the base material, maintaining the same structure with the
thermochemical process. The nitrided surface showed in its atomic chemical composition (At%) the presence of 8.04% N,
1.69% O and 1.38% Al (element of great importance to achieve great hardness), revealing an increase of 18.55% of surface
hardness and 78.87% of wear resistance. Regarding the tensile properties, there is a 77.65% decrease in its elongation when
subjected to medium and low tensile loads, presenting a deformation of 0.09 mm for the last stress effort of 600 MPa.