Kurzzeitprüfmethoden zur Untersuchung des Einflusses von Wärmebehandlung und chemischer Zusammensetzung auf die Korrosionsbeständigkeit martensitischer Chrom-Nickel-(Molybdän)-Stähle mit tiefem Kohlenstoff-Gehalt

Short-duration test for evaluating the influence of heat-treatment and chemical composition on the corrosion resistance of low carbon martensitic chromium nickel (molybdenum) steels The following procedures were examined and compared for their suitability as rapid corrosion tests in comparative investigations on the influence of heat treatment and other production parameters on martensitic chromium-nickel-(molybdenum) steels of low carbon content:

• –Measurement of the mass loss in boiling 20% acetic acid, and in some cases 5% nitric or 1% hydrochloric acid.
• –Immersion in sulphuric acid/copper sulphate solution (modified Strauss test).
• –Current density/voltage curves in 1 N sulphuric acid.
• –Measurement of pitting potential und activation pH in 3% sodium chloride solution (on limited scale).

The test materials employed contained 0.032–0.082% carbon, 11.6–16.4% chromium, 3.8–5.9% nickel and 0.31–1.6% molybdenum. The most suitable testing procedures were selected according to the steel type. Up to a mass loss rate of ≥ 0.05 mg · cm^?2 · h^?1 (materials with resistance inferior to steel type 13-6-1) the acetic acid test provides an excellent basis for comparison. Provided the optimal testing temperature is adopted, current density/voltage curves and immersion in sulphuric acid/copper sulphate solution yield usable results with all steel types investigated. The value of the information yielded by the test procedures is generally enhanced by metallographic characterization of the corroded surfaces; in particular the localization of chromium-depleted structure zones is made possible by this.