Piotr Kula

Investigating Fatigue Strength of Vacuum Carburized 17CrNi6-6 Steel Using a Resonance High Frequency Method

The bending fatigue strength of 17CrNi6-6 steel subjected to vacuum carburizing with high pressure gas hardening has been measured using a novel high-frequency technique. The test records the changes in resonance and consists of observing resonance frequency changes in a vibrating system with a single degree of freedom as a result of the forming of a fatigue crack. Moreover, a mechanism of fatigue nucleation and propagation in steel hardened by vacuum carburizing is presented.

Method of determining the strain hardening of carburized elements in Ansys environment

The paper presents a method based on FEM analysis of determining the strain hardening of elements after the thermochemical treatment. A computational algorithm, which takes into account two factors, has been suggested. Firstly, the gradient of material properties resulting from the changes in the carbon content in the surface layer after the carburizing process. Secondly, the phase transformations occurring during the hardening of the material. The proposed flowchart did not include the flow effect, which greatly reduced the computation time by eliminating tedious CFD calculations. Thanks to an original program Converter coupled with a commercial softwares SimHard, SimCarb J Math Pro and Ansys the carburizing process followed by quenching in gases was modeled. In parallel to the numerical calculations the results were verified experimentally. The results of FEM analysis for the tube made of stainless EN 16CrMn5 subjected to three processes of thermochemical treatment have also been presented in the paper. The experimental results were compared with the numerical simulations and a satisfactory convergence has been achieved.

The Role of Carbides in Formation of Surface Layer on Steel X153CrMoV12 Due to Low-Pressure Nitriding (Vacuum Nitriding)

The mechanism of formation of surface layer on steel X153CrMoV12 in the process of vacuum nitriding (low-pressure nitriding) in a universal vacuum furnace in an atmosphere of dissociated ammonia at a pressure of 30 × 102 Pa (30 mbar) is studied by the methods of light microscopy and measurement of microhardness. The chemical composition of the nitrided layers is determined.

Effect of the Content of Retained Austenite and Grain Size on the Fatigue Bending Strength of Steels Carburized in a Low-Pressure Atmosphere

The effect of the content of retained austenite and of the initial austenite grain size on high-cycle fatigue of two low-alloy steels 16MnCr5 and 17CrNi6-6 after carburizing in a low-pressure atmosphere (acetylene, ethylene and hydrogen) and subsequent high-pressure gas quenching is investigated.