Contribution of deformation-induced martensite to fracture appearance of austenitic stainless steel

Abstract

Fracture surface commonly carries the evidence of high-energy (ductile/tough) and low-energy (brittle) regions involved in fracture history, the macroscopic appearance of a fracture surface has often been utilised to qualitatively evaluate toughness of materials. For metastable austenitic stainless steels (AISI 304LN), the degree of martensitic transformation affects the fracture appearance and thus depends critically on the strain rate. The two dimensional ductile tearing ridge pattern quantified from many tensile fractographs are observed to predict the nature of disparity in deformation and fracture responses with systematic variation in strain rate of the steel under ambient atmosphere. The spatial distribution of deformation-induced martensite under tension at various stress/strains and strain rates strongly influences void nucleation, growth, coalescence and hence, keeps the impression on the ductile tearing ridge morphologies and dimple geometries on the fracture surface, where the initial inclusion content was constant.

Fractographic correlations with mechanical properties in ferritic martensitic steels

“…This is due to the fact that higher stress triaxiality induced in the centre by the outer shape of the specimen after necking. Similar results have been found by the first author while tensile deformation of AISI 304LN stainless steel by strain rate variation, which has been reported elsewhere [103][104][105][106][107][108][109]215]. The present author experimentally examined that the spatial distribution of micro voids under tension is strongly attributed to the crystallographic variant selection of martensite laths due to applied stress [215,216].…”

“…Lee et al [209] have noticed a decrease in depth and density of micro voids on the fracture surface of AISI 316 stainless steel with increasing strain rate and a corresponding strain rate dependency of the mechanical properties. The first author has already demonstrated the effect of strain rate on the fracture appearances of AISI 304LN stainless steel extensively [103][104][105][106][107][108][109]. The room temperature specimen had the smallest size dimple (i.e.…”

“…Figure 1 schematically illustrates the basic concept of the inter-relationship between the structurefracture-property of materials. The first author has already explained experimentally that there are close interactions between the deformation, fracture, and the corresponding microstructures for different alloys [103][104][105][106][107][108][109][110][111].…”