高氮奥氏体中温转变过程的研究

Intermediate Temperature Transformation of the High-nitrogen Austenite

研究含氮量在 ( 2 6～ 2 7) %wt范围的过饱和高氮奥氏体 2 2 5℃中温转变过程中发现 ,Fe N中温转变与Fe C系中温贝氏体转变有明显不同。高氮奥氏体在 2 2 5℃等温时首先析出γ′ Fe4 N ,形成γ Fe(N)与γ′ Fe4 N的亚稳定组织 ,等温 1～ 2h后在含氮量降低的奥氏体中形成α Fe ,8～ 10h后分解成 (α Fe +γ′ Fe4 N)的两相稳定组织 ,显微硬度最高可达 110 0HV0 0 2 5。分解后的两相组织晶粒细小 ,使衍射峰宽化 ,扫描电镜观察以及X ray衍射分析表明 :分解产物随等温时间延长粗化不明显。

The intermediate temperature transformation(225℃ tempering,)process of super-saturated Fe-(2.6～2.7) N %wt austenite at 225℃ were studied.It was showed that the characteristics of the intermediate temperature transformation for Fe-N alloy were obviously different from that for Fe-C alloy.The fine nitrides of γ′-Fe 4N were firstly precipitated from high-nitrogen austenite when isothermally treated at 225℃,and then the metastable system,γ′-Fe 4N and nitrogen-depleted γ-Fe,was formed.The α-Fe phase could be identified after the isothermal treatment for 1～2h and for 8～10h,the parent phase γ-Fe(N) could completely transform into two-phase structures (α-Fe+γ′-Fe 4N).The corresponding microhardness of stable decomposed structure could be 1100HV0.025,and the grains were very fine,which resulting in the broaden of diffraction peak.The SEM and X-ray diffraction analysis showed that the coarsening of decomposed structure was not evident even after long time treatment.