Microstructure development in 24Cr-14Ni-2Mn stainless steel after aging under various nitrogen/air ratios

摘要

The purpose of this study is to investigate the effect of the nitrogen/air ratio on delta-ferrite, sigma- phase and Cr_2N formation in 24Cr-14Ni-2Mn stainless steel, a universal core material for welding wire, under a nitrogen atmosphere. Experimental results showed that a high nitrogen/air ratio accelerated the phase transformation from delta-ferrite in the gamma phase and decreased sigma-ferrite. A critical nitrogen/air ratio (CNR) was found in this study. Above this critical atmosphere, the delta-ferrite content increased with increasing nitrogen/air ratio. The sigma phase content in the test material decreased with increasing nitrogen/air ratio because the sigma phase was transformed from delta-ferrite. The Cr_2N precipitates grew with higher nitrogen/air ratio. Analysis with EPMA & TEM was performed for the microstructure studies. The Cr_2N precipitates became denser and coarser if the nitrogen/air ratio was increased.