In situ synthesis of a porous high-Mn and high-Al steel by a novel two-step pore-forming technique in vacuum sintering

Abstract

In this work, a novel in-situ two-step pore-forming process in vacuum sintering (ITPVS) technique combining low-temperature processing to produce open pores through the interdiffusion among the intrinsic components in the base steel, and subsequent high-temperature processing to further improve the porosities by the sublimation of Mn via previously formed open pores, was proposed to produce a lab-scale porous FeMnAl steel. For the first time, a high-Mn and high-Al steel with open and overall porosities of ∼59.6 vol.% and ∼63.7 vol.% (percent in volume, vol.%) was synthesized by isothermal holding of the quaternary elemental Fe/Mn/Al/C powder mixture at 640 °C for 1 h and the subsequent sintering at 1200 °C for 1 h. Elemental Al partly incorporated into/reacted with α-Fe and α-Mn after sintering at 640 °C for 1 h, leading to the overall and open porosities promoting by ∼26.6 vol.% and ∼25.6 vol.%. After sintering at 1200 °C, FeMnAl steel with increased porosities mainly comprising of austenite and α-Fe obtained. The compression strength and corresponding strain of the 1200 °C-sintered porous specimen without crack on the surface was ∼75 MPa and ∼25%. The ITPVS technique takes advantage of using the intrinsic components like Al, Mn and Fe in steels to produce porous structure. This is beneficial to avoiding the contamination of the FeMnAl steel matrix caused by the employment of the foreign pore-forming agents.