Corrosion Behavior And Mechanism Of Ultra-high Strength Maraging Steel In Acidic Environment

As a typical high alloy ultra-high strength steel, high strength, good toughness and simple process of heat treatment is the performance characteristics of 00Ni18Co12Mo5Ti maraging steel A more accurate understanding on corrosion resistance of this maraging steel has an important practical application value on full play to the ultra-high strength and high toughness of this steel in actual application. By means of chemical immersion, electrochemical measurements, morphology observation and componential analysis. Corrosion behavior and mechanism of ultra-high strength maraging steel in the environment of acid FeCl3 solution was comprehensive studied in this paper. Corrosion difference between pretreatment with strongly oxidizing HNO3 medium and reducing H2S atmosphere were obtained. And corrosion resistance with 15-5PH Stainless Steel and 40Cr low alloy steel was compared. The results of this study to estimate the service life of the steel grade has reference value. For iron and steel enterprises energy conservation and emissions reduction also has important practical significance.Compare corrosion rate, macroscopic and microscopic surface morphology features pretreated with HNO3 acid and H2S atmosphere by using immersion corrosion weight loss. Results show that 00Ni18Co12Mo5Ti maraging steel macroscopic features is rivers shape. Microscopic features is honeycomb with cavernous.15-5PH stainless steel presents the typical pitting corrosion morphology, The size of corrosion pits pretreated with H2S atmosphere reached 752.6μm, it is 10 times of pretreated with HNO3 acid.40Cr low alloy steel shows severe spalling corrosion morphology in two atmosphere. Corrosion rates of 00Ni18Co12Mo5Ti maraging steel is 9g/m2-h. It is 9 fold of stainless steel and 40 percent of low-alloy steel by nitric acid passivation; while the rates achieve 9.5g/m2·h by hydro sulfuric acid passivation.lt is slightly lower than stainless steel and 20 percent of low-alloy steel. The corrosion rate of both sample before 36h is quick than after 36h, show that prophase of corrosion is the key point. According to Tafel polarization curve, there is an obvious passivation layer after pretreatment. Corrosion potential and corrosion current density change trend is match with corrosion rate.Compare polarization curve, EIS and microscopic features by using electrochemical measurements, morphology observation and componential analysis. This article shows that the stable passivation layer pretreated with HNO3 acid is better than pretreated with H2S atmosphere. Metallography shows intergranular corrosion is there during the initial corrosion. SEM shows pore diameter on the surface of sample is 40μm. Before 36h is rivers shape with no microporous. Microporous begin grow up from 36h. New microporous appear in the internal of corrosion hole during the later corrosion. EDS shows Fe2O3 is main corrosion products.Heat treatment refined lath martensite and microstructure of 00Ni18Co12Mo5Ti maraging steel, precipitate get well dispersion. Heat treatment test result shows with temperature increases, corrosion rate increases, corrosion potential decreases, Tafel cathode area decreases, corrosion resistance decreases.The corrosion potential increased over extension of the time, the passivation effect after short aging time is better. Compared corrosion potential, corrosion current density and hardness, we find corrosion resistance decreased while hardness and corrosion current density increase. Both passivation and electro less plating can improve the corrosion resistance of sample.