The influence of chromium nitrides precipitation on the fatigue behaviour of duplex stainless steels

S. HEREÑÚ; M. G. MOSCATO; I. ALVAREZ; A. F. ARMAS

Verbania, Lake Maggiore

Encuentro; XVII International Colloquium "mechanical fatigue of metals" (ICMFM-XVII),; 2014

The final mechanical properties of metals are determined by changes in its microstructure caused by different thermal and mechanical treatments. In highly   alloyed duplex stainless steels (DSSs), the proper cooling path to maintain a favorable balance of ferrite and austenite and avoid unwanted secondary phases is difficult to achieve. The risk of formation of sigma phase and other intermetallic phases comes from insufficient cooling from high temperature whereas chromium nitrides (Cr2N) behaves in the opposite way. In order to homogenize the microstructure after fabrication processes, thermal treatments from high temperature followed by rapid cooling are usually carried out. Therefore, the analysis of Cr2N precipitation becomes of a great concern. Although Cr2N precipitation is not an unknown phenomena in DSSs is considered less detrimental that  sigma phase or spinodal decomposition. Moreover, no information is available on the influence of chromium nitrides on their fatigue behaviour.This work attempts to study the influence of thermal treatments, chemical composition and microstructure in the susceptibility of Cr2N precipitation in different DSSs. Special interest is placed on relating this precipitation with the fatigue response. The heat treatment temperature, the nitrogen content and the ferrite grain size affect the amount of Cr2N precipitates producing different degrees of embrittlement in DSSs with subsequent differences in the fatigue life.