Laser gas‐assisted nitriding of steel: residual stress analysis

Abstract

Purpose

The laser nitriding process is involved with high temperature heating and high cooling rates. This, in turn, results in high levels of thermal stresses in the heated region. Moreover, the residual stress in the heated region remains high after the completion of the heating process, which limits the application of the laser nitriding process. The purpose of this paper is to investigate thermal stresses development and residual stress levels in the nitrided region.

Design/methodology/approach

The microstructural changes and residual stress development in the laser gas‐assisted nitrided zone are examined. Finite element modeling is carried out to predict temperature and stress fields in the laser nitrided layer. The indentation tests and X‐ray diffraction (XRD) technique are used to determine the residual stress levels while previously derived analytical formula is used to predict the residual stress levels in the nitrided region.

Findings

The residual stress predicted attains values within 230 MPa, which remains almost uniform in the nitrided layer, except in the surface region. In this case, residual stress reduces slightly due to the low temperature gradient developed in this region and the unconstrained expansion of the free surface. When comparing the residual stress predicted with the measurement results as obtained from the XRD technique as well as the indentation tests, all the results are in reasonably good agreement. The small discrepancies between the experimental data and predictions are attributed to the assumptions made in the model study and the measurement errors.

Research limitations/implications

The depth of nitrided layer is limited 60 μm. This limits the applicability of the coating for high wearing rates.

Practical implications

The nitrided surface improves the surface properties of steel, which can be used in industry more efficiently.

Originality/value

The paper describes an original model study on stress formation, an experiment for surface characterization and estimation of residual stress formation and contains new findings.

Citation

Yilbas, B., Arif, A.F.M., Karatas, C., Abdul Aleem, B.J. and Tabet, N. (2010), "Laser gas‐assisted nitriding of steel: residual stress analysis", Industrial Lubrication and Tribology, Vol. 62 No. 4, pp. 214-223. https://doi.org/10.1108/00368791011051071