Microstructure thermostability of high nitrogen austenitic stainless steel.pdf

Microstructure thermostability of high nitrogen austenitic stainless steel1 2 Zhizhong Yuan , Qixun Dai, Xiaonong Cheng, Kangmin Chen, Jing Wu School of Materials Science and Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, PR China Abstract: High nitrogen austenitic stainless steel, Fe24Mn18Cr3Ni0.62N, was isothermal annealed from 750 to 900 for different time to investigate the thermostability of its microstructures. Results show that precipitations were Cr2N and firstly formed along the grain boundary. The time-temperature-precipitation diagram was established, according to which the critical cooling rate of this material with less than 0.1~0.5 vol. % of precipitated Cr2N was specified as 30 /min. The microhardness of the matrix in samples annealed at different temperatures decreased with the diffusion of nitrogen from the matrix to grain boundaries. Key words: Austenitic stainless steels, Nitrogen, Thermostability, Nitride 1. Introduction Basically, there are three categories of thermostability during the manufacture and heat treatment of austenitic stainless steels (ASS): formation of δ ferrite at high temperature; martensite transformation at cryogenic temperature; carbide, nitride and other intermetallics precipitate under certain heating conditions. The third one is very important for ASS with nitrogen content, which is very important for cryogenic application and attracts great attention [1-5]. Nitrogen alloyed ASS are easy to precipitated Cr N at temperatures ranging from 500 to 105, which will result in 2 1 Supported by Specialized Res