ROLE OF C AND N IN THE BRITTLE-FRACTURE OF FE-26 CR

A study of the role of C and N in the brittle fracture of Fe-26 wt pct Cr has been under-taken on alloys containing combined C and N levels of 67 and 570 ppm. Mechanical and microstructural characterization has been performed on structures involving C and N in the states of solute, grain boundary precipitate, and intragranular precipitate (with emphasis on plate-like intragranular nitrides). Fracture mechanisms have been elucidated through microscopic evaluation of electropolished strips pulled in the ductile to brittle transition temperature (DBTT) range. DBTT variations larger than 200°C were observed. The alloys are embrittled by grain boundary carbonitrides and intragranular nitrides. Quenching to suppress precipitation was beneficial to the low C and N alloy but led to severe embrittlement at the higher C and N level. Roles of carbides, nitrides, and twins in microcrack formation were revealed. A relationship between precipitation annealing temperature, embrittlement mode, and DBTT was established. © 1979 The Metallurgical of Society of AIME.