Abstract
Two distinct AISI type 316 stainless steels, of Brazilian and Swedish origins, were compared regarding their creep fracture mechanisms at 600, 700 and 800°C. The possible mechanisms associated with the creep fracture strength were identified by means of fracture maps proposed either by Ashby and collaborators or by Miller and Langdon. Experimental creep results were consistent with the general Ashby and collaborators map for face centered cubic alloys. By contrast, the two different 316 steel displayed significant differences in the model-based map of Miller and Langdon. In the present work, changes in the maps frontier are proposed as well as the introduction of a new field in the map related to grain boundary precipitation. These propositions allowed the Miller and Langdon map to be coherent with the experimental creep fracture results of both 316 stainless steels.
Highlights
Structural applications of AISI type 316 austenitic stainless steel (316 steel for short) at high temperatures in nuclear reactors[1,2,3,4], normally involve constant load conditions
For long time SS1 creep tested at 800°C, Fig. 1, which displays intergranular fracture, the value of n was around 3
The evidences from experimental data both in Ashby et al.[7] map, Fig. 8, and in the results shown in the present paper, indicate that the inclination of the boundary line between the fields of transgranular fracture and wedge cracking fracture must be in a way that the stress will vary reversely with the temperature
Summary
Structural applications of AISI type 316 austenitic stainless steel (316 steel for short) at high temperatures in nuclear reactors[1,2,3,4], normally involve constant load conditions Under such conditions, plastic strains are continuously being accumulated in the well-known creep process[5]. Creep fracture is the result of a rupture process involving mechanisms of nucleation, growth and interconnection of cavities and pores followed by crack formation and propagation[6] These are the typical fracture mechanisms before final failure in ductile materials like the 316 steel subjected to long time high temperature conditions. In long time creep, which is the usual situation for industrial applications, both w and r cavities predominate in association with intergranular fracture Each of these initial processes of creep fracture in ductile alloys become the controlling mechanism depending on the stress, temperature and strain rate. If one can predict the total time to fracture of a component operating under creep conditions, it is possible to promote preventive maintenance with the purpose of replacing the component
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