Effect of aging on the structure and mechanical properties of austenite stainless steel N50 alloyed with nitrogen, niobium and vanadium

Abstract

In this study, the austenitic, corrosion-resistant N50 steel alloyed with different nitrogen, niobium and vanadium content was investigated. This steel is used in the production of high-strength, cryogenic pipes. The production process for these pipes involves aging at 650 °C–665 °C for 50–100 h. Therefore, steels were examined in their as-delivered state, after aging at 650 °C, 100 h and after solid solution heat treatment. The structure of the steel was analyzed using optical and scanning microscopy, tensile and impact strength tests were conducted at room temperature and at −196 °C. It was found that the total volume fraction of the precipitated phase after aging is more dependent on the total concentration of nitride-forming elements—Nb and V, than on nitrogen. Aging does not affect the basic operational properties at room temperature, but it can significantly affect toughness at −196 °C.