Variation of nitrogen solubility and mechanism of pore formation during production of porous Fe–Cr–Mn–Si–C material

Abstract

Experiments regarding the synthesis of porous metallic materials were performed by dissolution of nitrogen into molten hypereutectic 77Fe–8Cr–6Mn–5Si–4C (wt-%) and hypoeutectic 79Fe–8Cr–6Mn–5Si–2C alloys, and water quenching. A uniform pore distribution was obtained only for the hypereutectic alloy. To study the effect of the alloy composition and microstructure on the pore distribution, the variation of nitrogen solubility during primary solidification was calculated for both alloys, taking into account the phase composition changes. A mechanism of pore formation is proposed. In the hypereutectic alloy, an increasing nitrogen supersaturation in the melt during primary carbide growth is believed to fuel the growth of nucleated N2 pores. The primary M7C3 carbides play an essential role in preventing pore coalescence. In the hypoeutectic alloy, a decreasing nitrogen solubility gap between the austenite dendrites and the liquid does not allow extensive pore growth. The absence of primary carbides favours the formation of a single large pore.