Prediction of steel resistance to stress corrosion cracking in seawater based on accelerated tests and structural studies

S Yu Mushnikova ,O A Khar’kov

doi:10.1051/e3sconf/201912104009

Abstract

The paper presents the tests results of resistance of various structural steel classes to SCC in chloride solutions. The experiments were performed using cantilever bending tests developed by NRC “Kurchatov Institute” – CRISM “Prometey” with stepwise increasing load of Charpy-type precracking specimens. The criterion estimation of resistance to SCC when β = σSCC/σC > 0.85 was confirmed by the laboratory test results compared with the case studies of corrosion-mechanical fracture of shipbuilding structures in real life service conditions. A new approach of SCC susceptibility of austenitic stainless steels in marine conditions is proposed. It is based on estimation of the critical temperature of SCC when testing for SSRT in a concentrated solution of calcium chloride at temperatures from 20°C to 100°C. Specific features of the structural-phase composition of steels that detrimentally affect the resistance to SCC were discovered during the complex testing.

Highlights

In recent years, austenitic stainless steels, hardened through the use of various methods of thermal and thermo-deformational treatments, are beginning to be used in shipbuilding together with low- and mediumalloyed steels
Common methods of hardening stainless steels are: solid-solution hardening; dislocation hardening due to cold plastic deformation; dispersion hardening during the formation of particles of carbide, nitride or intermetallic phases from a supersaturated γ-solid solution; grain boundary hardening; substructural hardening during high-temperature thermomechanical processing (HTMP) [1,2,3,4]
slow strain rate tests (SSRT) were carried out according to standards ISO 7539-7 and ASTM G129 [14,15] under some conditions: - the rate of deformation was 2·10-7 s-1 and 2·10-6 s-1; - used smooth cylindrical specimens; - tested in air to characterize the material and to use it as reference; - tested in 3.5% NaCl at a free corrosion potential and at room temperature; - tested in 25% CaCl2 at temperatures 20-100°C

Summary

Introduction

Austenitic stainless steels, hardened through the use of various methods of thermal and thermo-deformational treatments, are beginning to be used in shipbuilding together with low- and mediumalloyed steels. In order to successfully introduce high-strength steels of any structural classes for the manufacture of high-loaded marine structures, it is necessary to determine their resistance to stress corrosion cracking (SCC). Stress corrosion cracking remains one of the most dangerous fracture types of medium and high alloy steels in seawater, despite significant achievements in identifying and explaining the nature of SCC [10,11,12,13]. The results of comparative studies of resistance to SCC of low- and medium-alloyed steels and austenitic stainless steels, which were prepared with application of various strengthening mechanisms, are given

Materials and methods of investigations

Test results of low and medium alloyed steels

Findings

Conclusion