A new method for predicting susceptibility of austenitic stainless steels to intergranular stress corrosion cracking

S Rahimi,T.J Marrow

doi:10.1016/j.matdes.2019.108368

Abstract

Microstructures of type 304 austenitic stainless steel, produced through thermo-mechanical processing, were analysed with large area EBSD and optical image analysis assessments of the attacked grain boundary cluster after DL-EPR testing. The thermo-mechanically processed microstructures were exposed to acidified potassium tetrathionate (K2S4O6) solution under tensile stress and the lengths and distributions of the initiated intergranular crack nuclei were assessed. The crack populations were quantified by fitting a Gumbel extreme value statistics distribution to evaluate their characteristic crack length. A factor (susceptibility parameter) is introduced to rank the degree of susceptibility to intergranular stress corrosion cracking of thermo-mechanically processed microstructures. This accounts for the network connectivity of the sensitised grain boundaries, the grain size and the degree of sensitisation. Similar rankings are obtained for this susceptibility parameter and characteristic crack lengths of the assessed microstructures, in which the thermo-mechanical treatments increased the population of grain boundaries with resistance to stress corrosion cracking.

Highlights

Marrow / Materials and Design 187 (2020) 108368 mechanical strengths, superior corrosion resistance, and good weldability. If sensitised, they become susceptible to intergranular stress corrosion cracking (IGSCC), a mode of environmentally assisted degradation, which is the progressive initiation and propagation of cracks along the network of susceptible grain boundaries when exposed to corrosive media in the presence of sufficient mechanical driving force [1,2,3,4]
This study aims to unify these parameters in an IGSCC susceptibility factor
The interfacial energy of high energy boundaries can be reduced through different microstructural evolutionary mechanisms such as: (i) reorientation of grain boundary plane into lower energy status [62]; (ii) formation of low energy boundaries by multiple twinning and grain boundary dissociation [63]; and (iii) reduction in grain boundary area by grain growth [64]

Summary

Introduction

Marrow / Materials and Design 187 (2020) 108368 mechanical strengths, superior corrosion resistance, and good weldability If sensitised, they become susceptible to intergranular stress corrosion cracking (IGSCC), a mode of environmentally assisted degradation, which is the progressive initiation and propagation of cracks along the network of susceptible grain boundaries when exposed to corrosive media in the presence of sufficient mechanical driving force (i.e. stress) [1,2,3,4]. Intergranular carbide precipitation leads to local chromium depletion and a loss of corrosion resistance in the vicinity of the carbides (i.e. grain boundary) [1,9] These sensitised boundaries make stainless steels susceptible to intergranular corrosion (IGC) and IGSCC in corrosive environments [10]. A form of sensitisation may occur in stainless steels exposed to irradiation by fast neutrons or protons [5,6], and with precipitation of grain boundary intermetallics [1,11,12]

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