Effect of Composition on Stress Corrosion Cracking of Austenitic Stainless Steels in Boiling MgCl<SUB>2</SUB> Solutions of Various Concentrations

Abstract

The effect of composition on SCC of austenitic stainless steel has been investigated in various boiling MgCl2 solutions. The stress applied was a constant load of 25kg/mm2. The relation between the boiling point of MgCl2 solution (concentration of MgCl2) and the time to fracture was determined. The results obtained are as follows:(1) Commercial stainless steels show the maximum susceptibility to SCC over a certain concentration range of boiling MgCl2 solutions.(2) The sensitized stainless steel suffers intergranular stress corrosion cracking in low-concentration boiling MgCl2 solutions.(3) Based on a study of the effect of component elements, it is found that the boiling point of MgCl2 for the minimum time to fracture is shifted to lower temperatures in presence of C and Si and to higher temperatures in presence of Mo, N, P, Cr and Cu, while Ni decreases the susceptibility to SCC over the whole temperature range investigated.(4) The time to fracture consisted of the induction time and the propagation time. The mechanism of SCC is also discussed here. (Received September 30, 1974) Although there have been numerous reports on the effect of composition on the stress corrosion cracking of austenitic stainless steels in concentrated chloride solutions, few data on the relations between the effect of composition on SCC and environmental factors are available and the majority of the studies are made in boiling The present report describes the experimental results of the effect of composition on SCC of austenitic stainless steels in various concentrated boiling MgCl2 solutions and the significance of boiling 42% MgCl2 solution as accelerating test medium. MaterialsMaterials were prepared in a high frequency induction furnace as basic 18Cr-10Ni alloy with varying C, Cu, N, P contents and a low Mo content, basic 17Cr-13Ni alloy with varying Si and Mo contents, basic 18Cr alloy with varying Ni content, and basic 10Ni alloy with varying Cr content. As P enhances the susceptibility to SCC in boiling 42% MgCl2 solution(8), the amount of P was adjusted in order to recognize the effects of alloying elements. Specimens were made through series of such processes as forging and hot rolling to 7mm thick plates and cold rolling to 4.9mm thick ones. They were soluquenched and then shaped to tensile test speci-*

Chloride-Induced Stress Corrosion Cracking of Oxide-Dispersion-Strengthened Austenitic Steels

“…The transgranular stress corrosion cracking (TGSCC) of austenitic stainless steels can be explained by the film-induced cleavage, [36][37] or HE mechanism. 17,38 In this test, the sample was immersed in a saturated MgCl 2 solution at 143°C, which provides a slightly acidic environment by the hydrolysis of MgCl 2 following the electrochemical reaction:…”

“…The cathodic reduction of protons to hydrogen ions on the metal surface will then promote the uptake of hydrogen atoms into the crack tip. 17 It has been found that hydrogen could diffuse and enrich in the crack tips during the rupture of the surface film. 33,37,[39][40] It is suggested that hydrogen can assist the crack propagation during SCC by either the anodic dissolution at the crack tip sustained by the cathodic reduction of hydrogen ions, [41][42] or the martensite phase transformation in unstable austenitic steels resulting from hydrogen absorption.…”

“…14 The crack propagation in austenitic stainless steels involves a combination of electrochemistry and fracture mechanics, which may involve the mechanisms such as slip dissolution, 16 film-induced cleavage, 14 and hydrogen embrittlement (HE). 17 The current research on SCC of ODS steels has been limited to ODS ferritic steels such as 19Cr-ODS steel and 19Cr-4.5Al-ODS steel, which show low SCC susceptibility. 18 This is not surprising as ferritic steels are more resistant to SCC than austenitic steels.…”

Mechanically Assisted Corrosion

“…Various alloys display various modes of crack growth and examples have been compiled by Scully [11]. Figure 11.9 shows an example of intergranular and transgranular crack growth on the same alloy but in different concentrations of the same electrolyte [12]. …”