This study has been carried out to the low temperature plasma nitriding treatment on the mechanical properties of stainless steel at temperature range between $400^{circ}C$ and $500^{circ}C$. It was found that there was precipitated to free CrN matrix below $400^{circ}C$ and there was precipitated S-phase of STS 316L, ${varepsilon}$-phase of STS 409L and ${alpha}N$-phase of STS 420J2. STS 316L has formed relatively abundant CrN phase and ${gamma}^{prime}-Fe_4N$ phase at $500^{circ}C$, alternatively STS 409L and STS 420J2 were more deeply nitrided than STS 316L at $500^{circ}C$.