Grain refinement and precipitation strengthening in austenitic steels through Cu addition

Abstract

This study investigated the precipitation strengthening of chemically disordered Cu-rich phase and its effect on the mechanical properties of Cu-doped Fe18Cr14Ni3Mo austenitic steels. A high density of Cu-rich nanoprecipitates with fully coherent structure were formed in the austenitic matrix. These nano-sized Cu-rich nanoprecipitates improved the strength of alloys by hindering the movement of grain boundaries, revealing the disordering strengthening effect. Meanwhile, dense precipitates prevented grain growth, thereby improving grain refinement and further increasing the strength. Particularly, samples with Cu alloying exhibited a more pronounced grain refinement effect on grain-refined samples compared to ones without alloying, thus showing a more significant strengthening effect. The findings of this study not only offer guidance for the design of high-strength materials via disordering effects but also provide new insights in fabricating the ultrafine grain materials.

Impact statement

In this study, we successfully prepared forged austenitic steels with Cu-rich phases via a cold rolling process. Dense Cu-rich phases improved alloy strength by hindering dislocation movement and preventing grain growth, leading to grain refinement. The influence of Cu-rich phase precipitation on mechanical properties and microstructures of Fe18Cr14Ni3Mo4Cu austenitic steels, both virgin and grain-refined, was systematically analyzed and compared. Results showed that mechanical property enhancement in Cu-doped samples was mainly due to grain-refinement and precipitation strengthening. Notably, the role of Cu-rich phases in grain refinement became more significant after cold rolling. Compared to the grain-refined undoped Cu samples, the average grain size of the Cu-doped grain-refined samples was reduced by a factor of 3.2, and the yield strength was increased by a factor of 1.4, demonstrating the effect of Cu-rich phases in preventing grain growth and achieving grain refinement.

Graphical abstract