Plasma nitriding is an effective surface treatment to improve unsatisfactory wear properties of machine elements. Such machine elements may also subject to magnetic fields in many industrial applications. Therefore, AISI 4140 ferromagnetic steel samples were plasma nitrided. Then, the samples were quenched in water and then post-aged at a temperature of 400 degrees C for 30 and 120 min in plasma environment. Reciprocating wear tests were performed under different oriented DC magnetic field to determine wear behavior of the samples. It was obtained that the magnetic field and its orientation during wear test were the most effective parameters on wear behavior. It was observed that post-aged samples showed better wear resistance and lower friction coefficient values than the merely nitrided samples. Hard Fe16N2 precipitations were formed in the nitrided layer after post-aging treatment and their amount increased with magnetic field. This gave rise to improvement the wear resistance. (C) 2015 Elsevier B.V. All rights reserved.