In this study, a new powder metallurgy process using mechanical alloying (MA) treatment is proposed for the fabrication of fine-grained high nitrogen stainless steel. Atomized Fe-Cr Powders are mixed with a Cr2N Powder to control its mean composition (in wt%) to be Fe-23%Cr-1%N. This chemical composition is enough to obtain stable austenite single phase at room temperature. The powder mixture is mechanically milled in argon gas atmosphere up to 360 ks (MA Powder). The MA Powder is packed in a stainless steel tube under vacuum and then consolidated by warm-rolling at 1073 K. The bulk material is finally heated to various temperatures (1173 ∼ 1473 K), and then quenched immediately after attaining the heat treatment temperature. The microstructure of MA powder at the end of milling for 36 ks is fully body-centred cubic (bcc). When the bulk material is heated to the temperature above 1373 K, the microstructure is changed to face-centred cubic (fcc) (Cr2N). With the increase in temperature, the content of nitrogen in solid-solution increased and the crystal growth occured. The grain size of a material heated to a very high temperature of 1473 K is found to be 2.2 μm due to fine oxide particles dispersed in matrix. This steel has an excellent combination of yield strength (1.1GPa) and adequate elongation (30%). Such a high strength of the steel is attributed to the combined effects of soild solution strengthening by nitrogen and refinement of grain size.
|Number of pages
|Transactions of the Indian Institute of Metals
|Published - Oct 2003
All Science Journal Classification (ASJC) codes
- Metals and Alloys