**5. Conclusion**

Hercules™ alloy was developed with an aim to reduce cost of austenitic stainless steel and for use as an alternative to 304SS with target applications

## *The Evaluation of the Comparative Corrosion Behaviour of Conventional and Low-Nickel… DOI: http://dx.doi.org/10.5772/intechopen.102381*

being reinforcement bars and fasteners, taking advantage of higher strength of Hercules™. In order to fast forward acceptability for this alloy, additional applications were proposed where corrosion resistance is of importance such as rolled sheets for manufacturing of water tanks and other corrosion resistant products.

The general corrosion behaviour of Hercules™ alloy and 304SS have been evaluated using cyclic polarisation technique and immersion tests. Polarisation curves of NaCl tests showed that in higher chloride content of 3.56 wt. %, all test alloys corroded severely. When the concentration was reduced to 1 wt. %, the passive region of Hercules™ B was significantly extended, making this alloy more resistant to initiation of localised corrosion. However, once pitting initiated, it propagated faster, which was observed by the size of hysteresis loop and confirmed by visual examination of corroded coupons. This nullifies the anticipated effects of Mo and this has been explained using thermodynamics of corrosion. Immersion tests in FeCl3 also proved to be extremely aggressive making these alloys not suitable for use in aggressive chloride environments such as swimming pools and sea water. Additional polarisation and immersion tests in H2SO4 showed that all test alloys had an ability to spontaneously passivate in this environment, thus making Hercules™ useful in such reducing environments at room temperatures.

It is however, arguable whether or not Hercules™ alloy (with 0.5% Mo) can be used as a substitute for 304SS for when Ni prices are high because the tests conducted here did not provide sufficient rigour to validate the corrosion resistance of Hercules™ against 304SS. Thus, this leaves a gap for further work to be conducted. The work presented here simply outlines the comparative behaviour of Hercules™ to 304SS and more corrosion tests via in-situ environments should be performed in order to qualify Hercules™ alloy. Temperature, composition and test parameters are other factors that can be investigated further in order to perform application-based tests. Evidently, the solutions outlined by the corrosion test standards are too aggressive for these alloys. Building from this work, a more suitable test procedure can be developed and thus, providing newly developed LNASSs a chance to demonstrate their corrosion resistant strengths, as already observed with 1 wt. % NaCl and H2SO4 tests.
