Potentiodynamic measurements, Slow Strain Rate Tests (SSRT) and Constant Load Tests (CLT) were executed on austenitic stainless steels to investigate chloride induced stress corrosion cracking (CISCC). Tests were conducted in boiling 43 wt% calcium chloride (CaCl2) and 45 wt% magnesium chloride (MgCl2) solutions. For the tests one CrNiMo and five CrMnN were chosen. To get mechanical reference values glycerin was used at SSR test as inert medium. Additionally influences of chloride concentration and temperature were investigated in potentiodynamic measurements and slow strain rate tests on the highly alloyed CrNiMo steel. All tests were conducted under atmosphere conditions. The variation of nickel content among the CrMnN steels showed no influence in time to failure. The comparison between manganese and nickel austenitic steels in time to failure showed, that Ni-stabilized austenitic steels do have a 10 to 100 times higher time to failure than Mn-stabilized steels if CISCC is induced.
Nonmagnetic austenitic stainless steels are used in many applications where CISCC plays a major role. The aim of this investigation is to study comparative material resistance against Chloride Induced Stress Corrosion Cracking (CISCC) on highly alloyed austenitic stainless steels, in this case chromiummanganese- nitrogen (CrMnN) and chromium-nickel-molybdenum (CrNiMo) steels, under atmosphere conditions. To gain results in appropriate times without additional acidification or applied pressure hot or even boiling, concentrated salt solutions in connection with Slow Strain Rate Tests (SSRT) or Constant Load Tests (CLT) are used due to their high boiling points and high chloride contents. Critical chloride concentration and temperature raise with the alloying content of steels1. Boiling MgCl2 solutions with different chloride content are one of the most popular media in which CISCC on highly alloyed austenitic stainless steels is investigated2-7. Ambient conditions as chloride concentration, temperature, pH-value, cation species, pressure and time are strongly influencing CISCC8. Alloying and metallurgical factors have an enormous influence on CISCC susceptibility as well3-5. The major prediction one can make out of these tests is whether the material is resistant to CISCC in this kind of solution or not. Streicher2 and Speidel3 et al. interpret this conditions as dry out situations, when water is evaporated and a high concentrated salt solution remains.
Our testing was established under controlled variation of electrolyte parameters like chloride content and temperature to show their influences on electrochemical and CISCC behavior of the tested stainless steels. The pH value has not been changed due to difficulties in measuring pH in such hot and high concentrated salt solutions.
An approach has been proved, to what extent electrochemical measurements can give a first indication whether the tested steel is susceptible to stress corrosion cracking in a defined medium. CISCC initiation and propagation are linked closely to the shape of the potentiodynamically measured i- E plots. These are basically influenced by temperature, chloride concentration and pH value of the solution. Temperature plays a major role, resulting first in accelerated reactions and second in a decrease of mechanical properties of the tested materials.
MATERIALS
Six highly alloyed stainless steels have been investigated. Material W1 to W5 are CrMnN steels and material W6 is a superaustenitic CrNiMo steel.
