FORMATION OF RESIDUAL STRESSES IN COMPOUND lAYER DURING GAS NITRIDING MEASURED BY IN SITU TECHNIQUE

Abstract

Residual stresses have a strong influence on the properties of nitrided parts. Therefore knowledge of their origin and magnitude is of great interest and aprerequisite if changes in the stresses are intended. From the relevant theories of residual stresses in gas nitrided materials it can be concluded that stresses which are generated during nitriding can be reduced by plastic deformation and increased during cooling from nitriding temperature to room temperature. The increase in residual stresses should be a result of the volume misfit generated by different thermal expansion coefficients of the compound layer and the steel matrix. The theories mentioned have not thus far been confirmed by experimental work. Therefore one aim of the investigations was to clarify the origin of residual stresses as well as the different influences on the formation of residual stresses, especially during cooling from nitriding temperature to room temperature. Previously, residual stresses of nitrided parts could only be measured after nitriding. In the present work it will be shown, for the first time, that residual stresses cansuccessfully be determined in situ during the gas nitriding process by a special nitriding device installed in an X-ray diffractometer.