Effect of Nb/Ti/Zr/W on precipitation behavior and mechanical property of 310S austenitic stainless steels

Abstract

In order to improve the high-temperature (HT) microstructural stability of 310S-type austenitic stainless steels (ASSs), the effects of minor-alloying elements (Nb, Ti, Zr, and W) on the precipitation behaviors and mechanical properties of 310S ASSs were systematically investigated. The designed alloy ingots were hot-rolled at 1423K, solid-solutioned at 1423K for 0.5h, stabilized at 1173K for 0.5h, and then aged at 973K for different hours. The microstructure and precipitated phases at different heat-treatment states were characterized by XRD, OM, SEM-EDS and TEM, respectively. It is found that the addition of Ti or Zr can refine the matrix grains remarkably, but Ti can deteriorate the HT microstructure stability of alloy sharply, i.e., a large amount of coarse Cr23C6 and σ particles are precipitated both on GBs and in the matrix after long-term aging. In addition, the impurity of Si should be controlled strictly for the inhibition of G-Ni16Si7Zr6 phase precipitation in Zr-containing ASSs. Mo accelerates the phase transformation of Cr23C6 to (during aging, while W plays an active contribution to the HT microstructure stability. The designed Fe-25Cr-22Ni-0.73Mo-0.35Nb-0.046C (mass fraction/%) alloy exhibits excellent mechanical properties (σYS=237MPa,σUTS=545MPa, δ=39%) due to its higher microstructural stability at 973K, which is expected to be applied as fuel claddings.

Keywords

• fuel cladding
• austenitic stainless steels
• 310s
• minor-alloying
• precipitation behavior
• mech-anical property