Effect of boron on microstructure and mechanical properties of PM sinteredand nitrided steels

PM Distaloy and Astaloy alloys have many applications in the automotive ind ustry and are used in structural elements with different wear resistance va lues. Their main features are adequate density, hardness, tensile strength, and good ductility. For the purpose of the experiment presented here, Dist aloy SA and Astaloy Mo powders, alloyed with various amounts of elemental b oron powder, were used. The Distaloy and Astaloy alloys were produced throu gh mixing, compacting, and sintering at t = 1393 and 1473 K, and, after the completed sintering process, they were plasma nitrided at 793 K. Experimen tal results showed that if boron was added, while sintering, the shrinkage phenomena increased ( 1473 K) and some parameters of those alloys (density, hardness, and tensile strength) were improved. Upon the ion nitriding trea tment of the surface of base Astaloy Mo samples, a surface layer was create d composed of the E solution and gamma' nitride, whereas the surface layer on the Distaloy SA base was mainly composed of a gamma' compound. Boron act ivates the sintering process of Distaloy SA and Astaloy Mo samples but it h as no significant impact on the surface layer's thickness of Distaloy SA al loys as opposed to Astaloy Mo alloys in which boron promotes a greater thic kness of surface layers along with a reduced depth of nitrogen diffusion. ( C) 2001 IoM Communications Ltd.