Microstructural characterization of grade 300 and grade 350 maraging steels and electrochemical study in hydrofluoric solution

Abstract

The electrochemical behavior of solution-annealed grade 300 and grade 350 maraging steels subjected to two different aging temperatures in an aqueous hydrofluoric acid (HF) medium was evaluated. The microstructural and hardness studies showed the effects of the chemical composition and heat treatments on the material properties. Although it is not possible to observe them, the fine intermetallic composites deposited during aging allow a significant increase in the hardness of materials, which was reduced when aged at 560 ◦C, where there was formation of reverted austenite. The results showed that, in both steels, solution-annealed samples that were not aged showed a better corrosion behavior than the aged samples. The reversion of austenite during aging at temperatures above 560 ◦C increases the phase limits and its susceptibility to corrosion. The greater amount of cobalt and titanium in grade 350 maraging steel increases the amount of fine intermetallic precipitate rich in molybdenum and titanium during aging, therefore improving its mechanical properties, but also reducing its corrosion resistance.