Influence of Clad Metal Chemistry on Stress Corrosion Cracking Behaviour of Stainless Steels Claddings in Chloride Solution

Edmilson O Correa,Reginaldo P Barbosa,Augusto J A Buschinelli,Eduardo M Silva

doi:10.4236/eng.2010.25051

Abstract

The effect of clad metal composition on stress corrosion cracking (SCC) behavior of three types of SMAW filler metals (E308L-16, E309-16 and E316L-16), used for cladding components subjected to highly corrosive conditions, was investigated in boiling 43% MgCl2 solution. In order to evaluate the stress corrosion cracking susceptibility of the top layer, constant load tests and metallographic examinations in tested SCC specimens were conducted. The susceptibility to stress corrosion cracking was evaluated in terms of the time-to-fracture. Results showed that the E309-16 clad metal presented the best SCC resistance. This may be attributed to the presence of a discontinuous delta-ferrite network in the austenitic matrix, which acted as a barrier to cracks propagation. Concerning to E308-16 and E316L-16 clad metals, results showed that these presented a similar SCC test performance. Their higher SCC susceptibility may be attributed to the presence of continuous vermicular delta-ferrite in their microstructure.

Highlights

It is well established that sensitization-induced intergranular stress corrosion cracking of similar austenitic stainless steels weldments occurs predominantly in the heat affected zone (HAZ)
In applications where the austenitic stainless steels are used for cladding components subjected to highly corrosive conditions, the evaluation of the susceptibility to stress corrosion cracking (SCC) of the weld metal turns more relevant [5]
The NACE standard does not mention the maximum hardness required to the as-welded austenitic stainless steels to avoid stress corrosion cracking when exposed to environments containing chlorides, it is believed that the maximum hardness value of 250 HV may be adopted in this condition

Summary

Introduction

It is well established that sensitization-induced intergranular stress corrosion cracking of similar austenitic stainless steels weldments occurs predominantly in the heat affected zone (HAZ). Because that, traditionally, these steels are joined each other with weld metals containing 5% to ~10% residual delta ferrite in the interdendritic boundaries with the unique objective of reducing the occurrence of hot cracking and microfissuring in the weld metal. In applications where the austenitic stainless steels are used for cladding components subjected to highly corrosive conditions, the evaluation of the susceptibility to SCC of the weld metal turns more relevant [5]. The formed delta ferrite undergoes a solidstate transformation to austenite. Previous work has shown that the ferritic phase is more active electrochemically than the austenite phase, resulting in the preferential corrosion of the ferrite on exposure to aggressive environments [6]

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Conclusion