Structural characterization of fluidized bed nitrided steels

Abstract

The nitriding behaviour of 34CrAlNi7, 42CrMo4 and 40CrMnMoS86 steels was investigated nitrided in the fluidized bed processes. The nitriding processes were carried out at a temperature of 575 degrees C for treatment times of 6, 12 and 18 h. The nitrided samples were fully characterized using metallographic, microhardness and XRD techniques. Test results indicated that thickness of the compound layer on the steel surface changed in the range from 10 to 18 mu m depending on steel type and treatment time, and gamma'-Fe4N and epsilon-Fe2-3N formed in the compound layer. The hardness of the diffusion layer was over 1000 HV. Depending on the chemical composition of steels, the case depth ranged from 155 to 525 mu m. Kinetics studies showed that the effective diffusion coefficients are 298 x 10(-14) 525 x 10(-14) and 68.8 x 10(-14) m(2)s(-1), for 34CrAlNi7, 42CrMo4 and 40CrMnMoS86 steels, respectively. The fluidized bed process realizes the highest hardness of the case layer, 1095 HV, with fairly high growth rates, 27 mu m/h. (c) 2005 Elsevier Ltd. All rights reserved.