Nitriding of AISI 1020 steel: comparison between conventional nitriding and nitriding with cathodic cage

Abstract

Cylindrical samples of AISI 1020 steel were nitrided, using the techniques of conventional plasma nitriding and cathodic cage. In the latter, the samples are kept at floating potential, inside of a cage that works as a cathode and to shield the samples from the cathodic potential. A systematic study was conducted in order to evaluate the efficiency of this technique in the elimination of edge effect, in comparison with conventional plasma nitriding. In addition, another comparative study of the phases obtained using the conventional plasma nitriding and nitriding with cathodic cage was performed. Two metallic cages were used, one made of austenitic stainless AISI 316 and other one made of AISI 1020 steel, to prove the effect of deposition in nitriding with cathodic cage. The samples which were nitrided by this new technique had shown nitriding rates, crystalline phases, and microhardness, similar to those samples which were nitrided conventionally. However, it was possible to confirm the elimination of edge effect through the characterization by optical microscopy and by microhardness test along the samples surfaces. The samples were characterized by optical microscopy, microhardness tests and X-ray diffraction.

Changing the characteristics of the nitrided layer using three different plasma configurations

“…No microhardness variations between edge and center were detected in the sample treated by CCPN. This result agrees with previous studies in other steels [1,10,11]. The CCPN sample had a lower microhardness compared with the DCPN and PPN treatments, probably due to the lower thickness of the composite layer.…”

“…When piece of complex geometry is nitrided by plasma produced by direct current (DCPN), effects such as overheating, electric arcs and irregular layer occur, making the process impracticable. In order to avoid this undesirable effect, solutions such as pulsed voltage source (PPN) and cathodic cage discharge (CCPN) are being presented as alternatives [1][2][3]. With the voltage source pulsed, effects are avoided by controlling pulse width (ton) and pulse repetition time (toff).…”

“…In the discharge by cathodic cage the control is realized by the electrical shielding of the sample, thus avoiding the direct bombardment of the ions on its surface [4]. However, by modifying these sources, it will also modify the plasma species, which interfere with the kinetics of nitriding [1]. The population intensity of the plasma species in the PPN configuration will depend on ton and toff because each species has its own population growth.…”

Caracterização Estrutural De Aços Interstitial Free Nitretados a Plasma

“…As principais vantagens apresentadas no processo de nitretação a plasma estão na economia do tratamento, pois o consumo de gases e de energia é menor comparado aos processos de nitretação a gás ou banho de sais [1], maior controle dos parâmetros de processo e ainda no aumento da quantidade de íons nitrogênio de alta energia na superfície do material, que contribuem tanto para o processo de nitretação quanto para a manutenção do plasma [2]. Na nitretação a plasma, enquanto o material é tratado em altas temperaturas acontece a difusão do nitrogênio em sua estrutura.…”

Improving the Abrasive Wear Resistance of a Microalloyed Steel by Plasma Nitriding

“…Basically, two distinct zones are formed on the steel surface after the thermochemical treatment of plasma nitriding: (i) the diffusion layer that appears darker after a chemical etching, and (ii) an upper bright layer referred to as compound layer (or white layer). The latter can be constituted of a mono-phase structure, with the presence of only one type of nitride (γ'-Fe 4 N or ε-Fe 2-3 N or alloying nitride), as much as a two-phase or poly-phase structure, comprising of a mixture of different nitrides [10][11][12][13][14] . Mahboubi and co-workers 8 verified a reduction in the core hardness (softening) when the microalloyed steels are treated at higher temperatures, making them less suitable for nitriding at high temperatures.…”