Relation between Carbide Precipitation and Toughness in 13Cr-3.8Ni Cast Steels

Abstract

Relation between toughness degradation and carbide precipitation of 13Cr-3.8Ni cast steel has been studied experimentally and theoretically. The results are summarized as follows:
(1) Chromium carbide (M₂₃C₆) precipitated at prior austenite grain boundary in austenite region deteriorates the toughness to give mosaic-like intergranular failure.
(2) Notch toughness, FATT (°C), is a function of both carbon content, C (wt %), and cooling rate from 950°C, R (°C/h), and the following relation is obtained. FATT=3119·C-45 log R-13
(3) The rate-determining stage for the carbide precipitation is considered to be the formation of carbide.
(4) Reducing silicon content and increasing molybdenum content improve toughness as the result of retarding M₂₃C₆ precipitation along grain boundaries.