Cooling effects on microstructure and mechanical properties of 27Cr–4Mo–2Ni ferritic stainless steel

Abstract

The effects of cooling manner on the microstructure and mechanical properties of 27Cr–4Mo–2Ni ferritic stainless steel were investigated. It was found that the Laves phase (except for the TiN and Nb(C, N) particles) was distributed both in the grains and at the grain boundaries in the furnace-cooled specimen. The water-quenched and air-cooled specimens showed only TiN and Nb(C, N) particles. After annealing at 1100°C, the furnace-cooled specimen showed significant grain coarsening as compared to the water-quenched and air-cooled specimens. Furthermore, the Vickers hardness of the furnace-cooled specimen increased, while the total elongation decreased because of the formation of the Laves phase. The precipitation of the Laves phase resulted in the brittle fracture of the specimen during the tensile test.

Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

“…At higher temperatures, detrimental embrittling intermetallic phases such as r (FeCr), v (Fe 36 Cr 12 M 10 ), and Laves phase (Mo,Nb,Ti)Fe 2 can precipitate. Due to the high Cr contents, the Cr-rich r phase is the most frequently observed precipitating phase, while the occurrence of Laves phase has only rarely been described [784][785][786][787][788][789][790][791][792][793]. In a typical superferritic alloy of composition 25Cr-(2-3)Mo-4Ni containing 0.3 wt% Nb, Laves phase was found to nucleate as first intermetallic phase during aging at 850°C.…”