The Mossbauer spectroscopy studies of epsilon to cementite carbides transformation during isothermal heating from as-quenched state of high carbon tool steel

This work presents results of investigations using the Mossbauer spectroscopy technique and their interpretation concerning transformation of ² to cementite carbides during tempering in relation to the previously conducted dilatometric, microscopic and mechanical investigations. Investigations were performed on 120MnCrMoV8-6-4-2 steel. The in°uence of the tempering time on nucleation and solubility of ² carbides, and on cementite nucleation and growth, was determined. The analysis of phase transformations during various periods of tempering using the Mossbauer spectroscopy technique made possible to reveal ¯ne details connected with the processes

Plasma nitriding of CA-6NM steel: effect of H2 + N2 gas mixtures in nitride layer formation for low N2 contents at 500 ºC

This work aims to characterize the phases, thickness, hardness and hardness profiles of the nitride layers formed on the CA-6NM martensitic stainless steel which was plasma nitrided in gas mixtures containing different nitrogen amounts. Nitriding was performed at 500 ºC temperature, and 532 Pa (4 Torr) pressure, for gas mixtures of 5% N2 + 95% H2, 10% N2 + 90% H2, and 20% N2 + 80% H2, and 2 hours nitriding time. A 6 hours nitriding time condition for gas mixture of 5% N2 + 95% H2 was also studied. Nitrided samples results were compared with non-nitrided condition. Thickness and microstructure of the nitrided layers were characterized by optical microscopy (OM), using Villela and Nital etchants, and the phases were identified by X-ray diffraction. Hardness profiles and hardness measured on surface steel were determined using Vickers hardness and nanoindentation tester, respectively. It was verified that nitrided layer produced in CA-6NM martensitc stainless steel is constituted of compound layer, being that formation of the diffusion zone was not observed for the studied conditions. The higher the nitrogen amounts in gas mixture the higher is the thickness of the nitrided layer and the probability to form different nitride phases, in the case γ'-Fe4N, ε-Fe2-3N and CrN phases. Intrinsic hardness of the nitrided layers produced in the CA-6NM stainless steel is about 12-14 GPa (~1200-1400 HV)