Flat narrow plates ion-nitrided on one side under various nitriding conditions are studied for the determination of mechanical properties of nitrided layers. The change of elastic modulus is calculated from deflection test of a cantilever set-up and the change of thermal expansion coefficient is obtained from curvature-temperature relation on the assumption that these changes are in proportion to the amount of nitrogen concentration, which is again to follow one-dimensional diffusion equation.
It is found that the thermal expansion coefficient at the nitrided surface has been increased by 2 to 12% over the value of non-nitrided core, and elastic modulus at the nitrided surface has been increased by a maximum of 700%, whose value is dependent on the nitriding conditions. Also, the axial extension due to the diffused nitrogen into Fe lattice is found to be about $0.1×10^{-3}$ to $0.3×10^{-3}$ in terms of strain.
Using the above results, the distribution of residual stress is obtained. At room temperature, the core has a low level of tensile stress having about 2 to 25kg/㎟, while the nitrided surface is in compression with a peak of about 50 to 200kg/㎟.
본 연구의 목적은 이온질화 처리된 탄소강에서의 일차적 기계적 성질들(탄성 계수와 열팽창 계수)의 변화를 구하여 잔류 응력의 분포를 알아 내는데 있다.
기계적 성질의 변화를 질소 이온의 확산농도와 같은 함수들로 가정하였으며, 외팔보의 처짐 시험과 온도변화에 따른 곡률을 측정하여 이들 변화를 계산하였다. 또한 격자 상수의 변화로 인해 생기는 팽창을 계산하였으며, 이들 결과를 이용하여 이온 질화 후에 생기는 상온에서의 잔류 응력 분포를 구하였다.
