The effect of long-term isothermal aging on dynamic fracture toughness of type 17-4 PH SS at 350°C

Abstract

The change of impact performance with the extension of aging time on the type 17-4 PH stainless steel at service temperature (350°C) is studied in this paper, the alternation of dynamic fracture toughness and fractography of the type stainless steel for various holding time at this temperature are also researched by instrumental impact test and scanning electron microscope. All results indicate that the plastic deformation energy (EPL), tearing energy (ETE). absorbed-in-fracture energy (Et) and dynamic fracture toughness (KId) of this type alloy are all monotonically decreased with the continuation of time at 350°C,the characteristic of the decline is the KId fall is fast at the forepart of aging test and then descend is slowness, it says the toughness of the alloy is degraded and the degradation was mainly taken place at the early stage of aging test. The fracture mode of this alloy changes from dimple fracture into cleavage fracture and intergranular rapture with the extension of aging time. Those illuminate that the fracture toughness of this alloy has degraded with the extension of aging time at 350°C. ©2005 The Japan Institute of Metals.